wiring batteries in series and parallel at the same time

[darksheep85]

This is something I've been thinking about for a while and the Internet doesn't seem to have an answer. So I'm hoping someone here might be able to shine some light on the subject.

2x12v batteries in series gives us our 24v (doubles the voltage, amps stay the same)

2x12v batteries in parallel would give 12v (voltage stays the same, but doubles the amps)

IS IT POSSIBLE to connect 2 batteries in series AND parallel to give 24v and double the amps?

I know this is done with large battery banks such as electric forklifts. But I can't find any information as to whether you can do this with just 2 batteries.

My other point for asking this question is in theory, you could have 24v for the starting/charging system. Also, you could tap the parallel connections to get 12v from both batteries equally, preventing unequal charges.

Does this sound like it could work, or am I barking up the wrong tree? Is there some principle of battery physics that says you need more than 2 batteries for a series/parallel configuration?

Let's find out who the electrical engineers are!

 

[rhurey]

No, not possible.

The series requires one batteries negative (0V reference) to be connected to the other batteries 12V output.

Parallel requires both negatives and both positives to be connected.

So mutually exclusive. Cause actually doing both would result in connecting the positive and negative of one battery to each other.

 

[gimpyrobb]

you can only do series/parallel with 4 batterys.

 

[tim292stro]

No it can't be done without fireworks. Take a moment to think about how electrons flow: the path of least resistance, just like water in a stream.

If you hooked batteries up as both series (green path) and parallel (blue path):


You can see you are providing a red path of flow - which is a dead short for each battery. If you did this with 4/0 battery cable I'd guess you'd have about 30-45 seconds to run before it exploded, but when you hooked it up for the first time the electrical gods would send down their arc fault of doom to tell you it was about to go from bad to worse...
https://www.youtube.com/watch?v=P35HRYHFz7c

Gimpyrobb is exactly right, this is a valid series parallel that is most often talked about in the world of batteries:

 

[darksheep85]

Thank you for the responses. I wanted to ask someone who knew before I tried an experiment and ended up looking like Two-Face from Batman.

I was just thinking about if there was another way to find 12v without a converter or equalizer or 2nd alternator. Not to say that any of those is a bad option.

 

[The King Machine]

I think it depends on how much your expecting to draw from the 12 volt side. If your going to run just a CB radio, then I would consider just tapping a line from the ground battery to a 12 volt fuse box. If you going to run a full stereo system with amps and subs then you will need to go another route.

 

[tim292stro]

We just talked about 12/24v loads in a system in another thread and how some of the issues are created/resolved - the problem with some of this electrical stuff is that it ends up spread out all over hte place - there is an electrical subforum under the restorations group, but often this stuff is more akin to a "hot rod or modification" so it gets scattered.

Thank you for the responses. I wanted to ask someone who knew before I tried an experiment and ended up looking like Two-Face from Batman...

I was just thinking about if there was another way to find 12v without a converter or equalizer or 2nd alternator. Not to say that any of those is a bad option.

The issue is how you do it. If you're looking for just a little bit of power, a DC-DC step-down or "buck" regulator will get you there with fairly little complexity. If you're looking for more than 30Amps of 12V continuously, I'd recommend either using a Vanner and a separate 12V battery, or just going and installing a separate 12V system (alternator, battery, loads). It'll save you a bunch of headache later.

If you tap a 24V series string with even a few milliamp (0.001Amp) load, it'll create a charge imbalance in the battery string over time and your batteries won't last long. After the first or second early cycle of battery replacements it will have been cheaper to go through the expense of either DC-DC-regulators or a Vanner...

 

[gimpyrobb]

Yeah, a low cost 24-12v converter($20) will save tons of headaches.

 

[M37M35]

I'm using one of these.

Just make sure you wire it so it switches off with everything else. The circuitry draws some power even when nothing is hooked to it. I'll add a 12v alternator and battery in the future, but this works good for now.

 

[tim292stro]

Those would be the "cheap" DC-DC step down regulators we talk about - they are available up to 25Amps, then things start getting expensive ($100+).

 

[Redcedarme]

I was wanting to do this as well, and may have thought of a solution. I have a 48v golf cart. 4 - 12v in series. I want to use my 12v desulfurization charger/maintainer on it. It works fine if I go from one battery to the next individually. I know I'd create a dead short if I wired them all together in parallel while they are wired in series, but... What if I used diodes inline with the 12v parallel charging circuit to only let the 12v flow in? The 48v wouldn't be able to make a circuit, correct??

 

[DavidWymore]

So...if you didn't have two big batts, but you had 4 small ones and you wanted to fire off a deuce...series into parallel or...? How are the 5ers with 4 batts wired?

 

[montaillou]

Unless it's been converted, the truck runs off of 24v. You can certainly make a bigger 24v battery, and this could be useful for long starts in the winter maybe, if you have the space for it.
I'm in the process of building a LiFePo powerwall for my camper, it'll be 25.6v, 600 amp battery - figure if I need to, I can always jump the truck off it

 

[VPed]

The 5ers have two pairs of batteries wired in series, and the series pairs are paralleled.