"DSK" wrote in message
.. .
Gary Warner wrote:
The electrical setup I've created calls for two
12 volt batteries. They are on an A/B/ALL
switch with a battery-combiner (BC) between them.

It would be simpler, cheaper, and more foolproof to simply have each
battery on a key switch. The A/B/Both/Off switches create all sorts of
problems from dead batteries to fried alternators.


Normally I plan to run with the switch in
just the "A" or "B" position. So when the engine
is running the BC will combine the batteries and
both will be charged. When the engine stops and
we are drawing current for light & such, only one
battery will be supplying power. If that one got
drained we could switch to the other to restart
the boat.

Exactly!


QUESTIONS:

TYPE OF BATTERY: I know that Gel or Absorbent Glass Matt
(AGM) are supposed to be better. But for this application
where these is not much vibration, no need to mount the
batteries in any position except "normal" and where the
battery may not get 100% proper storage (ie no trickle
charger all winter) I'm thinking the extra cost is not
worth it. I'm thinking just use regular flooded batteries.

Agree. I don't see enough advantage in your usage to get AGMs, unless
the boatteries are in an inaccessible place and will be difficult to
service.

Also, you don't mention it but are you putting in a hard wired charger?
Definitely get & use a 3-stage smart charger no matter how you rig it.



SIZE will be group 24. I believe the space that I have
for the batteries (under the passenger seat) will take
two Group 24 batteries.

Might be too small. If you're using 2 dual purpose instead a starting &
a deep cycle, then you're getting less cranking amps and less amp-hours
capacity.

http://www.cs.ucf.edu/~matt/leadacid/guide.html


CCA/MCA: I really don't know what size Cold Cranking Amps
or Marine Cranking Amps is necessary/good to turn over the
engine I have. I'm guessing that anything in around about 550
is fine. If I can get more for not much more $$ than that's what
I'll do.

Agreed. This is one case where more is better.


RESERVE CAPACITY: I really don't have much draw on these batteries
so pretty much whatever the RC rating is will be fine for my use.

TYPE: I'm thinking that Dual-Purpose is the way to go. It is possible
that I'd draw a batter down when occasionally sleeping on the boat
overnight and Starting batteries don't like that very much.

neither do dual purpose, for that matter deep cycle batteries get rather
upset if you discharge them past 50%


TWO OF THE SAME: Since they will be charging in tandem (together)
it's best to have two of the same. Also, I'll sometimes have the switch
on "A" and sometimes on "B" so both get approximately the same
useage pattern.

If you were oversizing the batteries so that there wasn't risk of
damaging or hard sulfating them starting the engine, I'd say fine. But
since you're limited in size I'd suggest getting a starting battery and
a deep cycle and marking the switches as such. You might also consider
getting two dual purpose batteries and then finding a place for two golf
cart batteries somewhere else for house loads.



BUYING:
+ Check the date manufactured on the battery and try to get ones that
are
less than 3 months old.
+ Try to get them with a longer free-replacement period as this is a
good
sign of quality
+ Watch out because replacement are sometimes pro-rated and based on the
LIST price, not retail.

Good. I bought two Exide Gr-31 batteries that were approx 6 months on
the slef and they are not really satisfactory. If you can buy dry
batteries and have the vendor fill & charge them, that'd be better too.
Only a battery store will do this though.

Fair Skies
Doug King


Hard to get a nice setup with just the key switches. And my alternator has
survived since 1991 with a Guest 1/2/off switch. 351W Ford motor. I run 2
batteries and use a starting battery in #1 and a dual purpose in #2. Run
the electronics off #2 with a key switch to shut off power to the
electronics and a battery combiner from West Marine to charge the #2
battery. Then I just run the dual battery switch to #1 and turn on the
other switch to run the electronics. If #1 is bad, I can then switch to #2
for starting. Just did this 2 weeks ago, as #2 battery was bad, and only
had $2.69 of warranty left. Running the electronics off their own battery
prevents a couple of problems. Running down the starting battery, the
electronics do not cycle from low power when starting, and the EMF kickback
from the starter / solenoid is isolated from the the electronics, and saves
them.
Bill

And my alternator has
survived since 1991 with a Guest 1/2/off switch.

My understanding is that what can kill an alternator is if the Alt
is putting out power and you switch from, say, #1 to #2. At that
moment when you switch there is no battery connected to the
charging system to take the power thus creating a momentary
surge in power. Some switches are "make-before-break" so
they make the connection to the #2 battery BEFORE breaking
the connections to the #1. (or whichever way you are switching).

But these better type switches can look exactly like the cheaper
type. You have to check the part number (or study it's design
and operation) to determine which type you have.

Gary Warner wrote:
And my alternator has
survived since 1991 with a Guest 1/2/off switch.


My understanding is that what can kill an alternator is if the Alt
is putting out power and you switch from, say, #1 to #2. At that
moment when you switch there is no battery connected to the
charging system to take the power thus creating a momentary
surge in power.

It's not a "momentary surge," it's a voltage spike attempting to reach
infinite! From a Buddhist point of view this might be Nirvana but for
the alternator regulating circuit it is a guaranteed trip to the
afterlife


... Some switches are "make-before-break" so
they make the connection to the #2 battery BEFORE breaking
the connections to the #1. (or whichever way you are switching).

But these better type switches can look exactly like the cheaper
type. You have to check the part number (or study it's design
and operation) to determine which type you have.

Yes exactly. Bill's point about using one battery to buffer his
electronics is also worth noting. We have a somewhat similar set-up but
it's accomplished in the breaker panel.




Doug King wrote
Also, you don't mention it but are you putting in a hard wired charger?
Definitely get & use a 3-stage smart charger no matter how you rig it.


Gary Warner wrote:
On such a smally boat with such low electrical draw and only weekend
use do I really need/want a charger? Won't my generator take care of
charging up the batteries?

Depends on how you use the boat & generator... you've got a genset in a
22 footer? If true then you can skimp on the house banks, fer sure.


Other question: I do have a good home based battery charger. It has
both a full charge & trickle charge setting. But I see that trickly charging
all winter is going to kill the battery.

Yes, whereas a smart charger which has a third stage which "floats" the
battery at a full-charge but less-than-charging voltage will greatly
extend a battery's life; usually they also have a desulfating function.

... So are my choices are basically as
follows ??

A: Charge it when taking it out, then leave it all winter
B: Go to the shop every 2 or 4 weeks and charge it for a while
C: Buy a "smart" or "float" charger and leave that running

A trailer boat can be plugged in at home, whether the charger is wired
in or kept on a shelf is a matter of convenience... I'd go for option
"C" since that will pay for itself by extending the batteries working
life and getting you underway with batteries at peak charge every time.



And is it really OK to leave a smart charger running and connected to
a battery for weeks at a time without checking on it? The thought
of that just makes me a little nervous.

It shouldn't. Of course it is a good idea to check the cells every
couple weeks, but a smart charger will not boil them like a taper
charger or trickle charger (which is basically a taper charger with very
low amperage) will... I go several months without having to top mine up.

Our boat had a large & expensive ferro-resonant taper charger (80 amps
according to it's nameplate!!) wired in when we bought it... top of the
line 1970's technology! But it consistently boiled off the batteries
according to the previous owners maintenance log, and the previous
owners were in the habit of buying new batteries every 18 ~ 24 months.
Expensive! One of the first upgrades was a Xantrex smart charger, which
we used to desulfate (or "condition") the old batteries... gave them a
last hurrah...

Fair Skies
Doug King

"DSK" wrote:

It's not a "momentary surge," it's a voltage spike attempting to reach
infinite!

I think you're mincing words there. It IS a surge and it doesn't last
very long. And I'm not sure what you mean by "attempting to reach infinite"
but there is no way it comes close to "infinite". It it were that easy to
generate
huge (infinite) amounts of power we wouldn't need much oil. And it is
momentary - that is lasting a fairly short amount of time.




Depends on how you use the boat & generator... you've got a genset in a
22 footer? If true then you can skimp on the house banks, fer sure.


What I have is an engine and a generator. The generator is a device bolted
to the engine and runs off the engine via a belt. As in the type of power
generating device that was popular on cars and boats before alternators
took over. The generator connects to a voltage-regulator and "sends" power
to run the boat. Excess power will charge the batteries.



And is it really OK to leave a smart charger running and connected to
a battery for weeks at a time without checking on it? The thought
of that just makes me a little nervous.

It shouldn't. Of course it is a good idea to check the cells every
couple weeks, but a smart charger will not boil them like a taper
charger or trickle charger (which is basically a taper charger with very
low amperage) will... I go several months without having to top mine up.

OK, thanks.

And thanks for the tip about connecting my electronics via a seperate
battery so they they are more protected from spikes when starting
the engine, etc. I'll consider how I might do that in my system.

Again, thanks.

Gary Warner wrote:
I think you're mincing words there.

Yeah, I was trying to be funny.


What I have is an engine and a generator. The generator is a device bolted
to the engine and runs off the engine via a belt. As in the type of power
generating device that was popular on cars and boats before alternators
took over.

D'oh! I am old enough to remember these thingies, it's just been a long
time. IIRC they are not sensitive to open circuit damage anyway, so the
above comments are even more fruitless.



Again, thanks.

Very welcome... I don't claim to have any great expertise but am glad to
relate my experiences & observations.

BTW last year when we were shopping for batteries, I drew up a
spreadsheet to compare battery capacities & prices. It helps make a good
pick, the ones that seemed to offer best performance for the price were
Trojan and Exide. The best performance, and highest price, where the
Rolls/Surrette batteries, which have approximately twice as much power,
weight noticeably more for the same group size, and cost about 3X. The
West Marine batteries are Exides with a different label and a big
mark-up. Did I already say this?

Fair Skies
Doug King

"Gary Warner" wrote in message
...


And my alternator has
survived since 1991 with a Guest 1/2/off switch.

My understanding is that what can kill an alternator is if the Alt
is putting out power and you switch from, say, #1 to #2. At that
moment when you switch there is no battery connected to the
charging system to take the power thus creating a momentary
surge in power. Some switches are "make-before-break" so
they make the connection to the #2 battery BEFORE breaking
the connections to the #1. (or whichever way you are switching).

But these better type switches can look exactly like the cheaper
type. You have to check the part number (or study it's design
and operation) to determine which type you have.





I think all the Guest switches are make before break, At least the newer
ones.