Another Battery Question

Ok, first off thanks for the responses on my last battery question thread. I think we've got that figured out. I do have a follow up question though and maybe this was kind of answered in the last thread but I'm too, let's say, uneducated on the subject to see it. Anyway, I made a little illustration to hopefully clarify my question.

If I have the two 12-volt batteries wired in series to make 24-volts can I wire a small 12-volt accessory to one of the two batteries and get 12-volts off it or will I blow up the 12-volt accessory with 24-volts? If I can get 12-volts off one of the batteries does it matter which one? Will the second battery in the series give me 24-volts and the first 12-volts or will both give me 12-volts. Check the attached illustration to hopefully get what I mean. Thanks again.

Don't ask me. Electricity is magic. I still can't figure out how AC current doesn't get all stopped up in the wires!

YES you can wire a 12 volt accessory to just one battery and get 12 volts.
Either battery will give only 12 volts, as long as you connect the the positive and negative terminals on THE SAME BATTERY.
The only issue you might run into is if you run down that one battery, your 24 volt system will also be affected.

In your diagram, the answer is 12 across EACH battery.

Tenbore said:

Don't ask me. Electricity is magic. I still can't figure out how AC current doesn't get all stopped up in the wires!

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Or how they put the smoke in.

Ride1949 said:

Or how they put the smoke in.

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Yeah, that's what I want to prevent. I've heard it's bad to let the blue smoke out.

redhawker said:

Yeah, that's what I want to prevent. I've heard it's bad to let the blue smoke out.

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That's a different kind of smoke.
The electrical wizards all use a standard black smoke for a base and sometimes
with white tracer smoke if you're deserving enough and they're feeling special that day.

Once you smell the copper smoke, you never forget it.

MHtractorguy said:

Once you smell the copper smoke, you never forget it.

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I've tig welded a bunch of .250 to .500 copper together for some kind of high amperage electrical
stuff. Was years ago and remember a bit of greenish smoke ( hard to tell color under the helmet ) or fumes coming off at
melting temps, maybe 1800- 2000 degree range. Don't recall any special smell, but try pretty hard not to suck
down weld fumes.
Never got any hot enough to actually burn.

when you solder copper pipe it is best to do it in low light and when the flame crossing over the copper turns green you know it's hot enough. And never ever try to use the water based flux.... only the nasty green stuff works. I have another battery question too... but this is getting ridiculous....

So, the two 12 volt car batteries I thought I had killed... did not seem to want to take a charge... I've run both through a reconditioned and now they are both at 12.5 volts... how can I find out how much actual strength... (amp hours?) they now have?

Either buy an expensive load tester or go to any parts store that offers free battery testing.

Most offer free charging, too, if they need more charge.

blume357 - If you have an accurate multi-meter - 12.5V is too low to load test a lead acid battery. If you use several 12V batteries, a simple 12V battery tester might be nice to have. I have had this one for 35 or so years and it has helped me several times. Nice visual indication...

Thanks Richard C... but what do you mean by 12.5 Volts is too low to test? Is that not what the batter is supposed to be when fully charged?

I doubt I can find that tester and if I did I suspect it will cost more than it did when you bought it.

I was thinking I could hook some thing that runs off of 12 volts to the battery... read what the amps are being used and see how long it takes to run the batter down to ... what voltage?

For the OP: Yes you can draw 12V form either battery. I prefer to use the first one in the series to prevent the OOPS of going from + to ground by mistake when hooking up the 12V connection.
Over the years, I've had numerous pieces of farm equipment that used 2x 6V to make 12V. 2X 12 volts hooked in parallel to make more cranking power. 2X 12 volt hooked in series for 24V starting.
I even worked out a system to use a 12V alternator to charge a system that used 24V for starting but ran on 12V during use(that one looked like an octopus with battery cable arms).

Yes, take from half of the 24V system and get 12V. Current is a different matter and is measured in series, not parallel. The 12V circuits in your diagram are parallel to the two 12V batteries wired in series to make 24V.

blume357 - Well good news on battery load testers! Ebay and Amazon have brand new 100 Amp analog testers for less than $30. These are probably Chinese built, but since they are simple testers - they should work fine. No batteries or electronics - uses the battery under test!

The reason I say 12.5V is low is that it should be a minimum of 12.6V after a rest. The voltage will be quite high (13.8 - 14.2 or so) right after a full charge, and then it will slowly drop to 12.6 after an hour or so.

Thanks Richard C... I'll see what I can find.... I think the two are shot and not worth trying to fix but will get a tester to see. I also need to get another AAA, AA, C & D battery tester, Realized I need one in my work van... a lot of gas logs and fireplaces run off batteries now. I often get paid to go out and just replace the batteries on the receiver unit.

Yes, those little battery testers will save replacing a lot of small batteries. Also, get one that will test the 1.5 and 3 volt lithium cells that we use in many everyday devices. I have had watch cells that would die in the package before I ever got around to using them!

The 100 Amp tester has that nice meter that will show you the start voltage and then how much it drops in 10 sec. The scale is calibrated in amp-hours so you can tell about what the remaining capacity of any battery is. I have had several batteries down thru the years that drop to zero V as soon as you switch the tester on. Some will have a cell that will boil and spit out of the filler cap.

I always get automotive and garden tractor batteries that I can check and add distilled water to when needed.

I remember the days of 'topping off' a battery... did not know you could still get them.... but then we never used distilled water ... just the water from the well.

Most lead acid batteries can be topped off. They might have a flat plastic cover with a sticker over it, but you can still get in there (after the warranty expires.)

I only buy Walmart batteries now, and they still have the two caps that are easily removed to top up. You should never let the electrolyte solution drop below the top on the plates. Here in the South, I top up all my batteries every year.