Help wiring 4 12volt batteries to make 24 volts

Hi all,

I cant quite wrap my head around how to wire 4 12volt batteries together to make a 24 volt system, but I found this wiring diagram online and want to see if anyone for sure knows if this is correct!

Im almost finished with this solar system!

thanks so much!

It seems correct for my limited knowledge.

Connecting negative to positive combines the voltage to 24. Looks like two groups of those,  connected together.

Well, I found more guidelines about wiring in series/parallel and Im seeing this come up a lot:

Wire the series first, then wire the series sets in parallel.

The leads to inverter are attached to opposite corners of the bank. Make cables the same length.  

When you draw it, put a dotted line around the series segments, this will help you visualize it.

So the original image I attached doesnt follow those guidelines quite right.

This new attachment does, but uses 6 volt batteries.  substitute 12 volt batteries and it would show how to get 4 12 volts batteries wired into a 24volt bank

Yeah, thank you, I have an old background in electronics and I knew the rough outline but I couldn’t visualize it ( too long ago) but I do know that your set up is correct now that I’ve seen it

here's my 4, 6volt, batteries connected to make 24volts

will a  100amp controlier  handle 4  12volt  -100amp batterys connected  in a  parell  do damage  to  batterys  or inverter  t-y

norman launier wrote:will a  100amp controlier  handle 4  12volt  -100amp batterys connected  in a  parell  do damage  to  batterys  or inverter  t-y

It depends on the controller. The better ones allow you to program in the size of the battery bank. Too much current too fast on lead acids won't make ideal charging but too small an array and you get too little in total... It's a trade off...

norman launier wrote:will a  100amp controlier  handle 4  12volt  -100amp batterys connected  in a  parell  do damage  to  batterys  or inverter  t-y

It's not so much the controller itself as the number of amps passing through it.  As David alludes to above, too few, or too many amps is problematic.  Here are general rules of thumb for different battery chemistries, where "C" is capacity in Amphours (Ah), measured over a 20 hour period.  Battery makers will call this the "20 hour rate".  That means the TOTAL number of Amphours you get draining the battery slowly over a 20 hour time period.

Flooded lead-acid : charge at 1/20th of C minimum, 1/10C good, 1/8th of C max
AGM:  charge at 1/20th of C minimum, 1/8C good, 1/5th of C max
LiFeP:  no real minimum rate, 1/10C OK, 1/4th of C max

What is the size of your batteries, 100Ah?  Should be pasted right on the label if it is an off-grid battery.  If instead of Ah it is instead listed as "cranking amps", then you have selected the WRONG kind of battery for solar.  Let's do the math for a 100Ah battery.  Remember that in series volts add, while amps stays the same.  In parallel, amps add while volts stay the same.

If you take two 100Ah batteries and wire them in series, you get 100Ah of capacity at 24V.  If you take the second two 100Ah batteries and wire that pair in series, you also have 100Ah at 24V.  When you parallel the two 100Ah strings, you get a total of 200Ah at 24V.

The final bit of math you need to digest is how many amps you need to properly feed that battery bank without overdoing it.  Let's say you have 100Ah flooded lead-acid batteries.  The math is....

(200Ah/  X 25Vcharging X 1.175fudgefactor = 25 X 25 X 1.175 = 734W max.

Now, it you wanted to charge at an OK rate instead of a maximal rate, the math would be....

(200Ah/10) X 25Vcharging X 1.175fudgefactor = 20 X 25 X 1.175 = 588W.

If you try to squeek by with just bare minimum (NOT recommended) the math would be....

(200Ah/20) X 25Vcharging X 1.175fudgefactor = 10 X 25 X 1.175 = 294W.

The math will of course change as the type of battery changes.  Just plug in the Ah value of your battery with the capacity fraction for your battery chemistry, and you can figure it out yourself.

When you are ready to hook up everything, just tell us what controller you have, and what solar panels you got, and we can help you with the most optimal wiring scheme.  If your controller is MPPT, you need to keep your solar strings at least 40V, and the maximal Voc less than the limit of your controller.

There seems to be some weird bug in the software of this website.  The string for the first formula should be...

200amphours divided by 8

200/8

Can't get rid of the smilely face.