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Old August 12th 03, 01:41 AM
bruce
 
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Default It's another question on batteries & wiring circuits

I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce

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Old August 12th 03, 02:21 AM
Larry
 
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Default It's another question on batteries & wiring circuits

Bruce,
There is not a reliable way to charge the batteries together without using
a battery isolator. Batteries ALWAYS charge at different rates and an
isolator will allow for this.

For the few times you need the extra power, just set the battery switch to
"both", then run off battery number "one" or battery number "two" as you see
fit.

Larry


"bruce" wrote in message
m...
I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce



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Old August 12th 03, 07:38 AM
Meindert Sprang
 
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Default It's another question on batteries & wiring circuits

"bruce" wrote in message
m...
I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.


Well, it works a little different: the relay connects both batteries in
parallel *after* starting, when the generator starts charging. Thus, the
engine always starts from one and the same battery.

Meindert


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Old August 12th 03, 07:44 AM
bruce
 
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Default It's another question on batteries & wiring circuits

Larry

That's ok as long as you don't forget to change the switch from "both"
back to "1" or "2" or you will end up with two flat batteries.

Bruce
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Old August 12th 03, 02:14 PM
Donald Phillips
 
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Default It's another question on batteries & wiring circuits

bruce wrote:
I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce


The way batteries are charged in the factory where they are made is in
series string. This way all batteries receive the same amount of
current and thus the same amount of amp hours. The chargers vary the
voltage to keep the current in spec.

I don't think charging in parallel is the best idea, IMHO.

Donald

--
I'm building a Steel Robert's 434. You can sneak a peek if you wish by
clicking on me link below.
http://bellsouthpwp.net/d/o/donrayp/
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politicians money can buy'




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Old August 12th 03, 06:49 PM
B Walker
 
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Default It's another question on batteries & wiring circuits

Donald Phillips wrote:
bruce wrote:

I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce



The way batteries are charged in the factory where they are made is in
series string. This way all batteries receive the same amount of
current and thus the same amount of amp hours. The chargers vary the
voltage to keep the current in spec.

I don't think charging in parallel is the best idea, IMHO.


Most (if not all) charging circuits rely on the voltage to indicate a
full charge, if I remember correctly roughly 14.7v means a fully charged
lead acid batter. Now if you connect them in parallel the voltage seen
at the regulator is going to likely be wrong for both batteries, leading
to slower charging or overcharging.

And don't connect them in series, cause they you've got 24v ;-)

I'd suggest a switch for 1 - both - 2 batteries, and put a seriously
bright red light on the dash to indicate when you're in 'both' mode...
or a buzzer, or something.. Two seperate meters for the batteries, and
you can switch over to one that needs charging the most...

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Old August 14th 03, 04:02 PM
MIDEMETZ
 
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Default It's another question on batteries & wiring circuits

You don't want to convect both batteries together during starting. The house
battery will draw from the starting battery ( just like jump starting a car,
only the good battery is in the running car ). If you are separating the
batteries separate the load also. All engin related loads on the starting
battery all house loads on the house battery. Ether get a battery combiner or
a battery isolator ( each has its good and bad points ).

Have a dedicated starting battery with the ability to select the house battery
if needed.

Mike D.
************************

I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce


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Old August 17th 03, 06:12 PM
Rich Mechaber
 
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Default It's another question on batteries & wiring circuits

I would echo what others have contributed about not routinely drawing
from the house battery for starting if you set up as you describe. What
surprises me is that almost no one selects a setup I prefer: a
large-ish bank of house/starting batteries, without switches, relays, or
problems. "What if you drain the batteries down?" For this purpose,
and for this purpose _only_, I bought a cheap starting battery.
Unconnected to anything. Once a month, I would affix heavy gauge jumper
cables from it to the main bank during a 6-hour motor to re-charge the
self-dischaged capacity. Left the cover off the battery compartment
while under way so there was no way to forget to remove the cables
later. ("Gee, why are the batteries visible from the saloon?") Cables
served for the emergency start, if needed, connected directly to the
starter solenoid.

HTH,
Rich Mechaber

bruce wrote:

I am redoing the wiring on a small powerboat (6.2 meters). As part of
this I intend to use a dual battery system, I have seen a number of
different circuits that would work. The circuit I prefer users a
latching relay, which is activated by the ignition switch, this places
the batteries in parallel when starting and allows the charging of
both batteries at the same time. When the ignition is off the
batteries are separated allowing one be the house battery without
flattening the other.
At long last comes the question; if the house battery is flat what
effect will this have on the other battery during starting, charging
and the circuit in general.

Thanks in advance
Bruce

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Old August 17th 03, 11:47 PM
MIDEMETZ
 
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Default It's another question on batteries & wiring circuits

The only possible problem with your idea is if you run down the main battery it
will over load the small extra battery. There is lot of loss with jumper
cables plus if you can't disconcert the dead batteries they pull a lot out of
the good battery.

Not to mention the probably sparking during hook up. Problem never happen in
good conditions. At least for me anyway.

Mike
***********

I would echo what others have contributed about not routinely drawing
from the house battery for starting if you set up as you describe. What
surprises me is that almost no one selects a setup I prefer: a
large-ish bank of house/starting batteries, without switches, relays, or
problems. "What if you drain the batteries down?" For this purpose,
and for this purpose _only_, I bought a cheap starting battery.
Unconnected to anything. Once a month, I would affix heavy gauge jumper
cables from it to the main bank during a 6-hour motor to re-charge the
self-dischaged capacity. Left the cover off the battery compartment
while under way so there was no way to forget to remove the cables
later. ("Gee, why are the batteries visible from the saloon?") Cables
served for the emergency start, if needed, connected directly to the
starter solenoid.

HTH,
Rich Mechaber




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