series and parallel

[Bill M.]

I need 24 volts DC. I have 2, 12 volt batteries connected in parallel. Can I hook up a separate circuit at the same time with the batteries connected in series for that circuit to make 24 volts?

[wulfraat]

No, not at the same time. One or the other - series or parallel.

Want to see 2 lead acid batteries melt down and catch fire? Try hooking them up in series and parallel at the same time

[kb0zke]

Correct. One or the other.


That said, IF you were to include some heavy-duty switching devices, you could have it. No, you wouldn't have both 12 and 24 volts at the same time, but you could have one or the other without having to move cables around. Is that what you need, or do you need both at the same time?


If you need both 12v and 24v at the same time you will need separate battery banks for each. If you only need one or the other at any given time you could either move cables around (cheapest option, but more overall work) or you could install switches that would do it for you at a higher cost.

[wulfraat]

Or just use a victron Orion DC-to-DC converter to supply 24v from 12v or vice versa...

https://www.victronenergy.com/dc-dc-converters

[Bill M.]

Thanks for good answers to a dumb question. The Orion says it is 88 percent efficient. I think that is better than the Res-med converter I am running now. And better than having a melted puddle of lead and acid.

[Paprika]

You mentioned ResMed, Bill. If you're using a ResMed CPAP (as I am), you can get a 12V adapter for it. Try a Google search for 'resmed 12v adapter".

[Bill M.]

Yeah, I have a 12 volt adaptor for it. The adaptor is a 12 to 24 volt DC converter. 13.5 amps at 12 volts in, 3.75 at 24 volts out rated. I do not know if it is more or less efficient at lower power with the tube heat and humidifier off. I was trying to find a way to run it more efficiently to extend my battery life. With my lead/acid batteries I am basically only good for one night when charging with the generator since I never get charged all the way and wish to not go below 12.2. So I am working between 12.2 and 12.5 or maybe 12.6 with a very long generator run.

[gator.bigfoot]

Of course if you hook them up in series to get 24 volts you can still pull out 12 volts if you tap off the middle. Not a great approach though, since the the one battery will have more draw unequellizing the bank.

[uncle_bob]

Hi

Trying to get both 12 and 24 from a stack of batteries is indeed not a good idea. You will draw down the "12V" battery a bit more than the other one. Imbalanced batteries do not share loads well. Getting them charged back up can also be a bit interesting (since one gets more wear than the other).

Regardless of how you do it, going from 80% to 100% efficiency isn't going to make that big a difference. If you make it 10 hours as it is that will get you to 12 hours. Fiddling the charger parameters (like with a temperature probe) can get that much or more if it's cold out.

Indeed the only real answer is to double (or triple or quadruple) your battery capacity. That gets you to 2,3 or 4 nights and a lot less wear and tear on the batteries. (Full discharge and full recharge are far more wearing than partial charge / discharge).

Bob