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12v supply from a 24v system
I have a 24v electrical set up on my boat, but need a 12v supply for my VHF
(amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
"Nigel" wrote in message
... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. You need a converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally No, because the other one is connected in series, not in parallel. So one battery gets drained faster that the other and that is the success-formula for wrecking that battery. Meindert |
Hello Nigel,
Seems you have an interesting situation to begin with. If you are charging two 12 volt batteries in series, (with a 24 volt alternator or charger) then unless the two batteries are identical (in age, internal characteristics, etc), they will be charged to two different voltages. Not really the best situation. Now if you connect a load to just one of the batteries, that will upset the equal distribution of charge voltage across each battery, as Meindert has suggested. Of course, it could actually improve the balance, as you can imagine. Just out of curiosity, have you ever measured the voltage across each battery while charging? It would be interesting to see what differences you found, if any. Ignoring all of that, it is really a matter of degree. If you run a VHF from just one of the batteries, that would do a lot less potential harm than if you ran, say, a watermaker. You might get away with just the VHF. If you had a lot of time to play with this, you could arrange to put the same load on each battery. Say a VHF on one and something that mimicked the VHF's load on the other. That would require special wiring, or course, for the battery that didn't have its negative terminal connected to the boat ground. Has this been confusing enough? Good luck. Chuck Meindert Sprang wrote: "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. You need a converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally No, because the other one is connected in series, not in parallel. So one battery gets drained faster that the other and that is the success-formula for wrecking that battery. Meindert |
"Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks Yes, you're correct. It will work. CN |
"Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks INteresting replies. If the batteries are reasonable large, I doubt if the meager load of a VHF would make much difference. Make sure the battery you use for the VHF is the one that has its ground referenced to the boats ground. DOug |
If you use a DC to DC converter, then you know you will be getting a
regulated 12 Volts (or maybe 13.8 for the VHF???) ... just get one with an appropriate power output ... i.e., no need to spend big bucks for more power than you need. I myself would go with a converter ... that way the VHF is guaranteed to work. "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
A VHF doesn't need regulated DC. They are designed to work off of
any reasonable voltage between 11 and 16. "bowgus" wrote in message ... If you use a DC to DC converter, then you know you will be getting a regulated 12 Volts (or maybe 13.8 for the VHF???) ... just get one with an appropriate power output ... i.e., no need to spend big bucks for more power than you need. I myself would go with a converter ... that way the VHF is guaranteed to work. "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
No question that a DC to DC converter completely removes the
problem. Whether it is economical depends on what "amongst other things" Nigel wants to connect at 12 volts. FWIW, Ample Power for one makes 24 volt chargers that are really two independent 12 volt chargers, one across each battery. That ensures the proper charging voltage for each. Chuck bowgus wrote: If you use a DC to DC converter, then you know you will be getting a regulated 12 Volts (or maybe 13.8 for the VHF???) ... just get one with an appropriate power output ... i.e., no need to spend big bucks for more power than you need. I myself would go with a converter ... that way the VHF is guaranteed to work. "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
"Nigel" wrote in
: I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks How about a nice switching (99% efficient) converter, instead of some jackleg series regulator draining power off the 24V system as lots of heat? http://www.samlexamerica.com/product...yID=5&packaget ype=1&title=Stand%20Alone%20DC%20Power%20Converter Figure 10A of each VHF radio and SMALL radar, Add up all the instruction book 12V amperages, then buy the next higher model. This is but one company producing what you need. Search Google for "24VDC to 12VDC converter" with the quotation marks so it doesn't find every converter on the planet. You'll get a whole list of them. This guy's SD-350B-12 at 350W output generates 27A at 12V regulated solid as a rock from ANY dc input voltage between 19 and 36V.....saving the 12V electronics from any nasty spikes on your 24V system....$215? Who's gonna believe that when a 10A battery charger at Waste Marine is double that!! 2:1 input range 1500VAC I/O isolation 100% full load burn-in test Short circuit protection Over load/voltage protection Over temperature protection Forced air cooling by built-in DC fan Low cost, high reliability 2 year warranty Looks like you'd play hell trying to destroy it, too! |
Don't pay any attention to replies that talk about converters. Just run a
pair of leads from the two terminals of the 12v battery. You are simply creating a new 12v distribution system. It is very common for boats and aircraft to install different voltage distribution systems, and you do not need converters to do it. If this was just a single isolated device then you could use either battery. But if the 12v devices involve ANY electrical connection to anything in the 24v system then be sure that the new 12v system uses the battery that is also the battery connected to ground in the 24v system. You could help balance the load between batteries (although I doubt that it's necessary) by using the 12v+ and 24v+ as another 12v circuit, but only for fully isolated items (such as lighting). -- "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
"James Hahn" wrote in message
... Don't pay any attention to replies that talk about converters. Obviously you don't know what you are talking about. With such a setup you achieve two things: 1) one battery will always be drainen slightly more than the other. 2) that same battery will alway be charged a little less than the other because the charger measures the voltage across both batteries in series. So eventually that battery will be in a continuous state of being empty. Imagine what happens when you start the enginge or put another heavy load on a series of batteries where one of them is empty: the empty one will be charged by the full one, but with reverse polarity. Have you ever disassembled a broken battery pack of some device? In 99% of the cases you will find all cells in perfect condition (charged and all) except one, which was obviously the weakest in the chain, showing a reversed voltage. Meindert |
"Meindert Sprang" wrote in message
... snip Obviously you don't know what you are talking about. With such a setup you achieve two things: 1) one battery will always be drainen slightly more than the other. Correct (although it obviously depends on usage). 2) that same battery will alway be charged a little less than the other because the charger measures the voltage across both batteries in series. Incorrect. The charger measures the voltage across both batteries in series. The voltage it sees is the result of both batteries being there, not the one with the highest or lowest charge. The charger will charge until the voltage across the two batteries reaches the correct level. Whether individual cells (and being in the same case or in different cases makes no difference) took a longer time to get up to par simply doesn't matter. So eventually that battery will be in a continuous state of being empty. Imagine what happens when you start the enginge or put another heavy load on a series of batteries where one of them is empty: the empty one will be charged by the full one, but with reverse polarity. This is not what happens, and I cannot imagine what scenario you have in mind that could create this situation. Have you ever replaced one battery in a two-battery 24v system with a brand new battery? What happened when you started the engine? I have and I can tell you the answer - the uncharged battery gradually charged, as you would expect. Have you ever disassembled a broken battery pack of some device? In 99% of the cases you will find all cells in perfect condition (charged and all) except one, which was obviously the weakest in the chain, showing a reversed voltage. You have demolished our own argument. All cells were treated identically, yet one has collapsed! You can't use that evidence to support a claim that cells treated differently are more liable to collapse (which I assume is what you are trying to say). Collapse of one cell is the most common mode of failure for wet cell batteries, but it is not associated with differential discharge rates. For years battery manuafacturers have provided a 12v tap across the first eight cells of high voltage industrial batteries. There has never been any evidence that using the tap shortens the battery life, and it has never been the experience of the users. |
"James Hahn" wrote in message
... 2) that same battery will alway be charged a little less than the other because the charger measures the voltage across both batteries in series. Incorrect. The charger measures the voltage across both batteries in series. The voltage it sees is the result of both batteries being there, not the one with the highest or lowest charge. The charger will charge until the voltage across the two batteries reaches the correct level. There are two possible scenarios: one battery wears more quickly than the other, eventually reaching a state where the cell voltages reach higher values due to increasing internal resistance. Thus the charges shuts off too early, leaving the better battery not topped up. The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Have you ever disassembled a broken battery pack of some device? In 99% of the cases you will find all cells in perfect condition (charged and all) except one, which was obviously the weakest in the chain, showing a reversed voltage. You have demolished our own argument. All cells were treated identically, yet one has collapsed! You can't use that evidence to support a claim that cells treated differently are more liable to collapse (which I assume is what you are trying to say). There is always one cell that collapses first (the weakesrt), due to tolerances in materials, production, etc. By introducing an extra load (wear) on part of the cells in a string, they are more likely to collapse first. Collapse of one cell is the most common mode of failure for wet cell batteries, but it is not associated with differential discharge rates. We all know that a lead-acid battery suffers from deep discharge. And in this setup, it is a plain fact that the battery "below" the tap is discharged sooner then the one "above" the tap. And if the charger is on "the outside" terminals, it can only see the charge state of the entire string, which is in this case, wrong information. For years battery manuafacturers have provided a 12v tap across the first eight cells of high voltage industrial batteries. There has never been any evidence that using the tap shortens the battery life, and it has never been the experience of the users. Uhm, 12V across 8 cells? You are talking about non-rechargable batteries here? Meindert |
"Meindert Sprang" wrote in message ...
No, because the other one is connected in series, not in parallel. So one battery gets drained faster that the other and that is the success-formula for wrecking that battery. No worse, surely, than it would be if there was only that battery and a 12V system. It has no way of knowing that some of its output is being boosted by another 12V. I wouldn't have expected there to be any problem at all with the OP's idea - but if he was worried, he could always swap the batteries every season so they get roughly equal use as the 12V supply. Ian |
Ian Johnston wrote:
"Meindert Sprang" wrote in message ... No, because the other one is connected in series, not in parallel. So one battery gets drained faster that the other and that is the success-formula for wrecking that battery. No worse, surely, than it would be if there was only that battery and a 12V system. It has no way of knowing that some of its output is being boosted by another 12V. I wouldn't have expected there to be any problem at all with the OP's idea - but if he was worried, he could always swap the batteries every season so they get roughly equal use as the 12V supply. mm, the installation and maintenance of most boat batteries is so sub-optimal that pulling a few watts off one battery probably won't make any discernible difference, if done within reason. -- Lithium ion internal and external batteries. Internal from £30 External from £75 (trade) All batteries factory new and guaranteed. http://www.surfbaud.co.uk/ e-mail (www.rot13.com) |
In article , chuck
wrote: Hello Nigel, Seems you have an interesting situation to begin with. If you are charging two 12 volt batteries in series, (with a 24 volt alternator or charger) then unless the two batteries are identical (in age, internal characteristics, etc), they will be charged to two different voltages. Not really the best situation. Now if you connect a load to just one of the batteries, that will upset the equal distribution of charge voltage across each battery, as Meindert has suggested. Of course, it could actually improve the balance, as you can imagine. Just out of curiosity, have you ever measured the voltage across each battery while charging? It would be interesting to see what differences you found, if any. Ignoring all of that, it is really a matter of degree. If you run a VHF from just one of the batteries, that would do a lot less potential harm than if you ran, say, a watermaker. You might get away with just the VHF. If you had a lot of time to play with this, you could arrange to put the same load on each battery. Say a VHF on one and something that mimicked the VHF's load on the other. That would require special wiring, or course, for the battery that didn't have its negative terminal connected to the boat ground. Has this been confusing enough? Good luck. Chuck Ok, now listen up folks. There is no difference between, one 24Vdc battery made with 12 cells in series and two 12Vdc batteries in series, or four 6 Vdc batteries in series, as long as the interconnection links between cells are of similar low resistance. Tapping ANY battery system, in the middle IS BAD. The more power you draw off the tap as a percentage of total power available, the more damage you will do over time to the battery system. A single Vhf Radio will draw say 1 amp Standby, 2 amps Receive, and near 7 amps Transmit. Since most useage figures say 75% Standby, 15% Receive, and 10% Transmit, this would not be a significant load differential across, a battery system of like 8D's in series. That said, tapping a battery system, is a BAD IDEA. If you are running a radar, couple vhf's, GPS or two, Plotter, ECT, then your ASKING FOR TROUBLE, and it WILL find you. Best Idea is to get a Switching DC to DC Converter, like a Numar 32-12-X where X is the total operational load. One could very easily put a Group 12 12Vdc onboard, and use the DC to DC converter to keep the Group 12 battery charged. This is a typical system, that would meet the USCG Fishing Vessel Safety Act, Radio Power Requirement. I have no idea where the first replyer got his information, or training in Marine Electronics, but if he paid any money for it, he should go back and ask for a refund. Bruce in alaska -- add a 2 before @ |
What was it Tolkien said
"Go not to the Elves for advice, for they will say both No and Yes" Well the Elves of the newsgroup seem to have spoken. Actually Nigel I think you've answered your own question - if you are installing a 12V circuit to supply a VHF radio and "other things" then you are going to want to install a switch panel, fuses on the circuits to the radio (+other things etc). In other words you will be crawling over the boat, cutting holes for the switch panel and the radio (+other things), poking wires behind the furniture. Generally makeing a mess and getting bad tempered and irritated - so you may as well do a complete job and put the converter in. Chances are once you have a 12V circuit - you are going to want to connect more bits and bobs to it. Just thought I'd throw my tuppence hapenth in. "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
Well ok ... let's apply a testing paradigm or "if you could choose only one
voltage, what would it be" to arrive at an answer ... how about 16 -11 = 5, divided by 2 gets you 2.5, and adding that to 11 gets you 13.5 ... only 13.8 +/- a tad is more like a real world DC to DC output :-) "Doug Dotson" dougdotson@NOSPAMcablespeedNOSPAMcom wrote in message ... A VHF doesn't need regulated DC. They are designed to work off of any reasonable voltage between 11 and 16. "bowgus" wrote in message ... If you use a DC to DC converter, then you know you will be getting a regulated 12 Volts (or maybe 13.8 for the VHF???) ... just get one with an appropriate power output ... i.e., no need to spend big bucks for more power than you need. I myself would go with a converter ... that way the VHF is guaranteed to work. "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
I've read this thread carefully, and although I'm no sort of expert here, I
think that only Meindert is getting at the truth. Most of the rest of you are getting confused between voltage and current. Because both batteries are connected in series, IRRESPECTIVE of the charging mechanism (eg alternator or smart charger), then both receive an identical charge. If charging starts from a state where one battery is more discharged than the other, then the fuller battery will replenish its charge before the other one, and towards the end of that charging regime its terminal voltage will rise fairly suddenly from around 13V to around 14.5. Now, depending on the precise characteristics of the charging source (different for smart chargers and alternators), the ONLY way that the undercharged battery can continue to receive charge is to overcharge the now fully charged one. This implies applying more than 14.5 volts across the full battery, and this will, of necessity, cause to battery to gas, perhaps even boil in extreme circumstances. Enough said? Guy is probably right in saying that small additional current drain from one of the two batteries is lost in the noise, as it were. But as a concept, asymmetric current from series-connected batteries is bad news. Interestingly, one could get round the problem described above by putting a 14.5V zenner diode around the battery which is not being drained by your 12V circuit, but this isn't without problems either - the diode would have to be capable of handling the maximum charge current, lets say 30 amps. 30A x 14.5V = 420watts - thats a pretty big zenner on a pretty big heatsink!!!! HTH |
"Meindert Sprang" wrote in message
... snip There are two possible scenarios: one battery wears more quickly than the other, eventually reaching a state where the cell voltages reach higher values due to increasing internal resistance. Thus the charges shuts off too early, leaving the better battery not topped up. The charger does not monitor cell voltages. It monitors the voltage across all the cells in series. I don't know what you mean by 'wears', but the initial charge state of individual cells does not affect the voltage level at which the charger shuts off. The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Have you ever disassembled a broken battery pack of some device? In 99% of the cases you will find all cells in perfect condition (charged and all) except one, which was obviously the weakest in the chain, showing a reversed voltage. You have demolished our own argument. All cells were treated identically, yet one has collapsed! You can't use that evidence to support a claim that cells treated differently are more liable to collapse (which I assume is what you are trying to say). There is always one cell that collapses first (the weakesrt), due to tolerances in materials, production, etc. By introducing an extra load (wear) on part of the cells in a string, they are more likely to collapse first. It's not the extra load that causes cell collapse. Mistreatment of the batteries (either, or both) will shorten their life. If they are operated as they are designed to be operated then manufacturing differences between cells are more significant than the fact that some cells have been discharged to a lower level than others. If you do a proper study of those dissambled batteries you will find that the collapsed cell is not random - it has a strong bias towards the poitive terminal. Collapse of one cell is the most common mode of failure for wet cell batteries, but it is not associated with differential discharge rates. We all know that a lead-acid battery suffers from deep discharge. Who is talking about deep discharge? And in this setup, it is a plain fact that the battery "below" the tap is discharged sooner then the one "above" the tap. And if the charger is on "the outside" terminals, it can only see the charge state of the entire string, which is in this case, wrong information. It is not "discharged sooner". It is discharged to a level slightly below the other. The charge state of the 'entire string' is not 'wrong' information. It will indicate the amout of charge required, and any differential between individual cells, or sets of cells, is not relevant. For years battery manuafacturers have provided a 12v tap across the first eight cells of high voltage industrial batteries. There has never been any evidence that using the tap shortens the battery life, and it has never been the experience of the users. Uhm, 12V across 8 cells? You are talking about non-rechargable batteries here? No. I am talking about standard industrial lead acid wet cells, so I guess the number is 10. If you need to know it exactly you can take yourself down to any nearby warehouse and look at the batteries used in a forklift battery system, and count the number of cells set aside for the 12v tap. |
"James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Go and read my last post again. The charge doesn't magically share itself according to need between the two batteries connected in series. Instead, the charging current supplies equal charge to both batteries. If one becomes fully charged before the other, then the only way that the partially charged battery can get more charge is by overcharging the other. That overcharge is "energy" which cannot be stored in the battery, but has to go somewhere, and that somewhere is either/or elctrolysing the battery water to oxygen and hydrogen, and heat. If the discrepancy is small, it probably doesn't matter, but if not, then it certainly does. |
Forget for a moment the issue of connecting a 12 volt load
to a 24 volt system. Consider only the problem of properly charging two 12 volt batteries in series with a single 24 volt charger. My understanding is that unless the two batteries are identical (goes way beyond same make or capacity) they will not be charged to the same voltage. Two electrically non-identical batteries will have different internal resistances (by assumption)and thus charge to different voltages. As I mentioned in an earlier post, Ample Power shares this understanding and offers a 24 volt charger that is in reality two 12 volt chargers, one connected to each of the two 12 volt batteries (which are in series, of course). If my understanding is incorrect, that would mean that a 12 volt marine battery and 8 AAA's in series would all be properly charged by a 24 volt charger (with current limited so as not to destroy the AAA's). An attempted reductio ad absurdum. My point is simply that with a real-world installation of two 12 volt batteries in series, the two batteries will probably measure different voltages. The greater the differences between the batteries, the greater the potential problem (no pun). Without knowing the internal resistances, etc. of the two batteries, it is not possible to know the precise effect of placing a different load on one of the batteries. Doing so would effectively place the added load resistance in parallel with the internal resistance of the affected battery. That could make the two batteries either more or less alike, depending on the values involved. All of this is hand-waving, of course, because a battery's internal resistance is really not a constant, but a function of the battery's chemistry, state-of-charge, etc. It is a non-linear resistance, in that it varies with current. I don't believe we miss the mark here by ignoring these factors, however. Regards, Chuck Pete Styles wrote: "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Go and read my last post again. The charge doesn't magically share itself according to need between the two batteries connected in series. Instead, the charging current supplies equal charge to both batteries. If one becomes fully charged before the other, then the only way that the partially charged battery can get more charge is by overcharging the other. That overcharge is "energy" which cannot be stored in the battery, but has to go somewhere, and that somewhere is either/or elctrolysing the battery water to oxygen and hydrogen, and heat. If the discrepancy is small, it probably doesn't matter, but if not, then it certainly does. |
On Sat, 16 Apr 2005 10:12:46 GMT, "Pete Styles"
wrote: "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Go and read my last post again. The charge doesn't magically share itself according to need between the two batteries connected in series. Instead, the charging current supplies equal charge to both batteries. If one becomes fully charged before the other, then the only way that the partially charged battery can get more charge is by overcharging the other. That overcharge is "energy" which cannot be stored in the battery, but has to go somewhere, and that somewhere is either/or elctrolysing the battery water to oxygen and hydrogen, and heat. If the discrepancy is small, it probably doesn't matter, but if not, then it certainly does. Pete is right on the mark. Reread his prior post. Also go back and read Bruce's post on the subject. It is bad news to tap a battery bank. You can get away with it for a time but it will shorten battery life because the two batteries do not get charged equally. As Pete says, "in order to get the battery that is used the most charged fully you must overcharge the other". There is no way around that. Overcharging a battery not only cause water loss but it can warp the plates in the battery among other things. Overcharging is the biggest killer of batteries. Just ask anyone that still uses a feroresonant charger. They will tell you batteries last only a couple of years. Do it properly and use the inverter. regards Gary |
"Gary Schafer" wrote in message ... On Sat, 16 Apr 2005 10:12:46 GMT, "Pete Styles" wrote: "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Go and read my last post again. The charge doesn't magically share itself according to need between the two batteries connected in series. Instead, the charging current supplies equal charge to both batteries. If one becomes fully charged before the other, then the only way that the partially charged battery can get more charge is by overcharging the other. That overcharge is "energy" which cannot be stored in the battery, but has to go somewhere, and that somewhere is either/or elctrolysing the battery water to oxygen and hydrogen, and heat. If the discrepancy is small, it probably doesn't matter, but if not, then it certainly does. Pete is right on the mark. Reread his prior post. Also go back and read Bruce's post on the subject. It is bad news to tap a battery bank. You can get away with it for a time but it will shorten battery life because the two batteries do not get charged equally. As Pete says, "in order to get the battery that is used the most charged fully you must overcharge the other". There is no way around that. Overcharging a battery not only cause water loss but it can warp the plates in the battery among other things. Overcharging is the biggest killer of batteries. Just ask anyone that still uses a feroresonant charger. They will tell you batteries last only a couple of years. Do it properly and use the inverter. regards Gary I disagree. Two 12v batteries in series to make a 24v battery will self-level with respect to charge. They will self level even if one is tapped to run a VHF. No harm will come to either battery. Voltage can be likened to pressure. I hope this helps. CN |
"Capt. Neal®" wrote in message ... "Gary Schafer" wrote in message ... On Sat, 16 Apr 2005 10:12:46 GMT, "Pete Styles" wrote: "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip The other possibility is that due to a deeper discharge of one battery, it takes longer for the total voltage to reach the point where the charger goes from bulk to float. So while for the more empty battery the charge is still ok (bulk), the other one still gets the full bulk current too while it should receive a float charge. Deeper discharge of some cells in the string will not, of itself, mean that the charge takes longer. The _difference_ doesn't matter. The amount of charge required controls the charge time. Whether OP is running his radio off one battery or both makes no difference to the ah used, and therfore no difference to the charge time (except, of course, that if he uses a converter he will be consuming more ah for a given usage than if he uses just one battery). Go and read my last post again. The charge doesn't magically share itself according to need between the two batteries connected in series. Instead, the charging current supplies equal charge to both batteries. If one becomes fully charged before the other, then the only way that the partially charged battery can get more charge is by overcharging the other. That overcharge is "energy" which cannot be stored in the battery, but has to go somewhere, and that somewhere is either/or elctrolysing the battery water to oxygen and hydrogen, and heat. If the discrepancy is small, it probably doesn't matter, but if not, then it certainly does. Pete is right on the mark. Reread his prior post. Also go back and read Bruce's post on the subject. It is bad news to tap a battery bank. You can get away with it for a time but it will shorten battery life because the two batteries do not get charged equally. As Pete says, "in order to get the battery that is used the most charged fully you must overcharge the other". There is no way around that. Overcharging a battery not only cause water loss but it can warp the plates in the battery among other things. Overcharging is the biggest killer of batteries. Just ask anyone that still uses a feroresonant charger. They will tell you batteries last only a couple of years. Do it properly and use the inverter. regards Gary I disagree. Two 12v batteries in series to make a 24v battery will self-level with respect to charge. They will self level even if one is tapped to run a VHF. No harm will come to either battery. Voltage can be likened to pressure. I hope this helps. CN Capt. Neal thinks I'm wrong. I rest my case! :-) P. |
"James Hahn" wrote in message
... "Meindert Sprang" wrote in message ... snip There are two possible scenarios: one battery wears more quickly than the other, eventually reaching a state where the cell voltages reach higher values due to increasing internal resistance. Thus the charges shuts off too early, leaving the better battery not topped up. The charger does not monitor cell voltages. It monitors the voltage across all the cells in series. That is exactly what I meant and exactly the reason why it can go wrong. So I would like to invite you to shoot holes in my following argument: The charge of a battery is the product of current x time. Both batteries are in series and one load is connected to the set, operating at 24V. Another load is connected across only one battery, operating at 12V. So it is evident that one battery is discharged more than the other. I start to charge the set in series, so the current through both batteries is exactly the same. Since one battery is discharged more than the other and the current throug both is the same, one battery must be charged longer that the other. Exactly how am I going to achive that with the same current through both batteries? One battery will reach the full state before the other but is still being charged with full current because the other battery hasn't reached the voltage that corresponds with full charge. Now, if you can come up with an valid argument why this shouldn't damage one battery, I bow and take my hat off. Meindert |
Hello Meindert,
I agree with your analysis and go a step beyond: even if there is no differential load across one of the batteries, uneven charging is possible (or likely) because of differences in the batteries themselves. Regards, Chuck Meindert Sprang wrote: "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip There are two possible scenarios: one battery wears more quickly than the other, eventually reaching a state where the cell voltages reach higher values due to increasing internal resistance. Thus the charges shuts off too early, leaving the better battery not topped up. The charger does not monitor cell voltages. It monitors the voltage across all the cells in series. That is exactly what I meant and exactly the reason why it can go wrong. So I would like to invite you to shoot holes in my following argument: The charge of a battery is the product of current x time. Both batteries are in series and one load is connected to the set, operating at 24V. Another load is connected across only one battery, operating at 12V. So it is evident that one battery is discharged more than the other. I start to charge the set in series, so the current through both batteries is exactly the same. Since one battery is discharged more than the other and the current throug both is the same, one battery must be charged longer that the other. Exactly how am I going to achive that with the same current through both batteries? One battery will reach the full state before the other but is still being charged with full current because the other battery hasn't reached the voltage that corresponds with full charge. Now, if you can come up with an valid argument why this shouldn't damage one battery, I bow and take my hat off. Meindert |
"Meindert Sprang" wrote in message ... "James Hahn" wrote in message ... "Meindert Sprang" wrote in message ... snip There are two possible scenarios: one battery wears more quickly than the other, eventually reaching a state where the cell voltages reach higher values due to increasing internal resistance. Thus the charges shuts off too early, leaving the better battery not topped up. The charger does not monitor cell voltages. It monitors the voltage across all the cells in series. That is exactly what I meant and exactly the reason why it can go wrong. So I would like to invite you to shoot holes in my following argument: The charge of a battery is the product of current x time. Both batteries are in series and one load is connected to the set, operating at 24V. Another load is connected across only one battery, operating at 12V. So it is evident that one battery is discharged more than the other. I start to charge the set in series, so the current through both batteries is exactly the same. Since one battery is discharged more than the other and the current throug both is the same, one battery must be charged longer that the other. Exactly how am I going to achive that with the same current through both batteries? One battery will reach the full state before the other but is still being charged with full current because the other battery hasn't reached the voltage that corresponds with full charge. Now, if you can come up with an valid argument why this shouldn't damage one battery, I bow and take my hat off. Meindert Duh! the two batteries are in series. The one with the 12v tap cannot become more discharged than the one without because the battery without the tap will charge the one with. Or the one with will discharge the one without until they are both the same. This is the same thing that happens with individual cells in a 12v battery. With two 12v batteries in a series one simply has more cells in a series. CN |
Why all this ranting over a proven fact that drawing 12V off of one battery
of a 24V bank is not a good idea? A 40 amp 24/12 DC/DC converter capable of running all the electronics on the boat can be bought for the price of a couple of golf cart batteries. This is nonsense! -- Glenn Ashmore I'm building a 45' cutter in strip/composite. Watch my progress (or lack there of) at: http://www.rutuonline.com Shameless Commercial Division: http://www.spade-anchor-us.com "Nigel" wrote in message ... I have a 24v electrical set up on my boat, but need a 12v supply for my VHF (amongst other things). Is there any reason why I can't just run a 12v supply from just one of a pair of batteries, or do I need to use a 24v/12v converter. I release this will draw charge from just one battery , but won't the other just top it up and there by drain them both equally Thanks |
In article ,
"Meindert Sprang" wrote: That is exactly what I meant and exactly the reason why it can go wrong. So I would like to invite you to shoot holes in my following argument: The charge of a battery is the product of current x time. Both batteries are in series and one load is connected to the set, operating at 24V. Another load is connected across only one battery, operating at 12V. So it is evident that one battery is discharged more than the other. I start to charge the set in series, so the current through both batteries is exactly the same. Since one battery is discharged more than the other and the current throug both is the same, one battery must be charged longer that the other. Exactly how am I going to achive that with the same current through both batteries? One battery will reach the full state before the other but is still being charged with full current because the other battery hasn't reached the voltage that corresponds with full charge. Now, if you can come up with an valid argument why this shouldn't damage one battery, I bow and take my hat off. Meindert One thing you left out, Meindert, is the fact that the 12Vdc load is still there, and consuming part of the charging current across that battery, which only makes the problem worse..... bruce in alaska -- add a 2 before @ |
"Capt. Neal®" wrote in message
... Duh! the two batteries are in series. The one with the 12v tap cannot become more discharged than the one without because the battery without the tap will charge the one with. Or the one with will discharge the one without until they are both the same. This is the same thing that happens with individual cells in a 12v battery. With two 12v batteries in a series one simply has more cells in a series. If you became familiar with the concept of batteries in series and batteries in parallel, then come back and review your own reply. Meindert |
"Glenn Ashmore" wrote in message
news:cbu8e.7195$Z73.4465@lakeread04... Why all this ranting over a proven fact that drawing 12V off of one battery of a 24V bank is not a good idea? A 40 amp 24/12 DC/DC converter capable of running all the electronics on the boat can be bought for the price of a couple of golf cart batteries. This is nonsense! I agree with you completely, Glenn. It's just that I cannot stand those people who claim to be in the know, are misinforming people who aren't. Meindert |
In article ,
Capt. Neal® wrote: Duh! the two batteries are in series. The one with the 12v tap cannot become more discharged than the one without because the battery without the tap will charge the one with. Or the one with will discharge the one without until they are both the same. This is the same thing that happens with individual cells in a 12v battery. With two 12v batteries in a series one simply has more cells in a series. CN Duhhh, Hay Capt. Neal...... Son, you better go back to your Basic Electrical School, and ask for a refund of your tuition. You didn't learn a thing, about DC Systems. The above is total nonsense, and has to basis in FACT. The current in a series string is the SAME, anywhere in the series string, and limited by the highest resistance element in that string. No charge will flow from one cell in a series string to another cell, in that same series string, and they will NEVER balance themselves out during discharge. That is what and Equilizing Charge does, and that is deterimental to the battery cells that have lower internal resistance, as the Equilizing Charge brings those cells with Higher Resistance up to full charge. The only reason for doing an Equilizing Charge, is that it is less detrimental to the total battery to overcharge the good cells, then it would be to allow the weaker cells to continue to be undercharged. Best you stick to navigation, and leave the Blackgang Stuff to the engineers...... Me |
In article ,
Capt. Neal® wrote: I disagree. Two 12v batteries in series to make a 24v battery will self-level with respect to charge. They will self level even if one is tapped to run a VHF. No harm will come to either battery. Voltage can be likened to pressure. I hope this helps. CN bullcrap.... Better to leave the Blackgang stuff to the engineers that know what they are talking about...... Me |
"Meindert Sprang" wrote in message ... "Capt. Neal®" wrote in message ... Duh! the two batteries are in series. The one with the 12v tap cannot become more discharged than the one without because the battery without the tap will charge the one with. Or the one with will discharge the one without until they are both the same. This is the same thing that happens with individual cells in a 12v battery. With two 12v batteries in a series one simply has more cells in a series. If you became familiar with the concept of batteries in series and batteries in parallel, then come back and review your own reply. Wrong, wrong, wrong, wrong, wrong, wrong and incorrect! How can some people's minds be so ineffective at thinking? Just what the hell do you think a 12v lead acid battery is, anyway? One giant 12v cell? NOT! A twelve-volt, flooded, lead/acid battery consists of six cells of approx 2.2v each. These cells are in a series. When the battery is charged, electrons move through all the cells or the battery will not be charged. Open one cell and the whole battery will show dead because no current can move though the collection of cells in a series but the cells that are not open will show approx. 2.2 volts each. As long as the cells are all connected and none of them are open (or shorted) the battery works as a unit. Perhaps you ******s would understand it better using flashlight D cells as an example. Take one D cell that is half charged (Ni-Cad) and put it into a two-cell flashlight in the company of another NI-Cad) D cell that is fully charged and turn on the switch. The bulb will light and current will pass through the circuit. As well as working to light the bulb, the fully-charged cell will discharge into the half charge cell until the voltage in both cells equalizes. There is no difference between two 12v batteries in a series. As long as the two batteries are are part of a circuit, which is the case in any yacht (unless an isloation switch is turned off so the circuit is no more) then, as is the case in the flashlight example, the two batteries will equalize and they will do so even if one battery has more of a load on it than the other because of a 12v tap to run a VHF. Anytime the two 12v batteries in series are not part of a circuit then the battery with the 12v tap will have its voltage lowered and the battery without the tap will remain unaffected. Two 12v batteries connected in series but not part of a circuit remain, for all practical purposes, two separate batteries. You need to learn how circuits work before you spew your nonsense, Mr. Sprang. It seems to me you're confused when it comes to knowing the difference between volts (pressure) and amps (flow). Batteries always have voltage unless discharged but they only have amperage if they are part of a circuit. Since the batteries, connected as part of a circuit in Nigel's yacht, are in series in the circuit they will both have equal voltage as long as they remain part of said circuit. I hope this helps. CN |
Capt. Neal® wrote:
You need to learn how circuits work before you spew your nonsense, Mr. Sprang. Hmm. Perhaps he should stop being a professional electronics engineer too, eh? Pete |
"Me" wrote in message ... In article , Capt. Neal® wrote: I disagree. Two 12v batteries in series to make a 24v battery will self-level with respect to charge. They will self level even if one is tapped to run a VHF. No harm will come to either battery. Voltage can be likened to pressure. I hope this helps. CN bullcrap.... Better to leave the Blackgang stuff to the engineers that know what they are talking about...... Me I'm an electrician. Don't insult me with this engineer crap. I know how batteries work and I know circuits - particularly DC circuits. You idiots are only correct provided there is no circuit to which the two 12v batteries in series are connected. In any yacht I've ever been on the batteries are part of a circuit of there would be no use to have them aboard other than as ballast. In Nigel's case, tapping off one of two batteries connected in series in a circuit to run his VHF will not cause only the tapped battery to discharge as the voltage in the circuit will be lowered and not just the voltage in the tapped battery. Only if the two batteries were disconnected from the circuit would the tapped battery discharge more than the untapped battery. C'mon, folks, it doesn't take a rocket scientist to figure something this basic out. CN |
"Meindert Sprang" wrote in message ... "Glenn Ashmore" wrote in message news:cbu8e.7195$Z73.4465@lakeread04... Why all this ranting over a proven fact that drawing 12V off of one battery of a 24V bank is not a good idea? A 40 amp 24/12 DC/DC converter capable of running all the electronics on the boat can be bought for the price of a couple of golf cart batteries. This is nonsense! I agree with you completely, Glenn. It's just that I cannot stand those people who claim to be in the know, are misinforming people who aren't. Meindert You don't know squat about batteries in a circuit, Mr. Sprang. You are the one doing the misinforming. Read my other posts and do something about your ignorance. Read this one, too. Perhaps if you read the truth three or four times it just might sink in. Nigel doesn't need anything but a couple of wires tapped off one of the batteries in his series circuit and as long as a circuit is maintained the two batteries will take and maintain an equal charge, irregardless of the tap. It's only when the two batteries are isolated from the circuit by a switch of some sort that the tapped battery will discharge and the untapped battery will not be affected. Unless there is a circuit there is no such thing as batteries connected in series. Connected in a series implies or necessitates a circuit. You can line up 20 flashlight D cells end to end and say they are connected in series but until you complete a circuit they remain separate and distinct cells. If you tap off the one in the center it will discharge and all the others will not be affected but as soon as you connect them to a circuit the discharged battery (ni-cad in this case) will become charged up at the expense of the others until its voltage is raised and the others 'voltage is lowered proportionally. I hope this simple example will reduce your fogged thinking. CN |
"Meindert Sprang" wrote in message ... "Glenn Ashmore" wrote in message news:cbu8e.7195$Z73.4465@lakeread04... Why all this ranting over a proven fact that drawing 12V off of one battery of a 24V bank is not a good idea? A 40 amp 24/12 DC/DC converter capable of running all the electronics on the boat can be bought for the price of a couple of golf cart batteries. This is nonsense! I agree with you completely, Glenn. It's just that I cannot stand those people who claim to be in the know, are misinforming people who aren't. Meindert You don't know squat about batteries in a circuit, Mr. Sprang. You are the one doing the misinforming. Read my other posts and do something about your ignorance. Read this one, too. Perhaps if you read the truth three or four times it just might sink in. Nigel doesn't need anything but a couple of wires tapped off one of the batteries in his series circuit and as long as a circuit is maintained the two batteries will take and maintain an equal charge, irregardless of the tap. It's only when the two batteries are isolated from the circuit by a switch of some sort that the tapped battery will discharge and the untapped battery will not be affected. Unless there is a circuit there is no such thing as batteries connected in series. Connected in a series implies or necessitates a circuit. You can line up 20 flashlight D cells end to end and say they are connected in series but until you complete a circuit they remain separate and distinct cells. If you tap off the one in the center it will discharge and all the others will not be affected but as soon as you connect them to a circuit the discharged battery (ni-cad in this case) will become charged up at the expense of the others until its voltage is raised and the others 'voltage is lowered proportionally. I hope this simple example will reduce your fogged thinking. CN |
"Pete Verdon" d wrote in message ... Capt. Neal® wrote: You need to learn how circuits work before you spew your nonsense, Mr. Sprang. Hmm. Perhaps he should stop being a professional electronics engineer too, eh? Pete He needs to go back to school! CN |
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