# Mixed parallel and series batteries

Hey Guys

I know if you want more amps(range) your run batteries in parallel and more volts(speed) in series. Now lets say I wanted 192v and I was using 12v batteries. That gives me 16 batteries. Now lets say that I have room for 20 batteries and want more range. I could bump my voltage up to 240v and be done, but according to the web calculators I only need 192v and 240v does not buy me any extra range (only top end). I could drop my voltage down to 120v but then I could not get the speed I want. Is there any problem with mixing parallel and series in one pack? Ie using 20 batteries but maintaining 192V. What happens when one goes to recharge the pack (suspected problem)?

Thanks
Lazlow

[QUOTE=Lazlow;393]Hey Guys

I know if you want more amps(range) your run batteries in parallel and more volts(speed) in series. Now lets say I wanted 192v and I was using 12v batteries. That gives me 16 batteries. Now lets say that I have room for 20 batteries and want more range. I could bump my voltage up to 240v and be done, but according to the web calculators I only need 192v and 240v does not buy me any extra range (only top end). I could drop my voltage down to 120v but then I could not get the speed I want. Is there any problem with mixing parallel and series in one pack? Ie using 20 batteries but maintaining 192V. What happens when one goes to recharge the pack (suspected problem)?

Thanks
Lazlow[/QUOTE]

You would only need a circuit that is able to switch between the battery packs in order to achieve this. I’m not too sure if there would be any problems with charging but I’m sure someone else can explain that part of it. In theory, it’s achievable.

problems. when you wire a pack in parallel you are esentially doubling the size of the batteries. instead of 20 batts you have 10 batts at twice the size. just like you stated. the problem occurs in mixing because you will then have batts at X ah rating and batts at 2X (twice as much) ah rating. this will cause an over discharge and then over charge conditon for the X rated batts. Throw in the amp draw during acceleration and you now have different voltage drops. the bigger batts (2X) will sustain a higher voltage and the smaller batts (X) will dip farther. now you have a pack that has batts of dissimilar amperage AND voltage. It’s a majorly unmatched pack that is subjecting each batt to different rates of usage (or wear). In short. no. not a good idea. Consider using batts of 1/2 the capacity and running a 3 parallel (3P) string for 48 batts total. That would give you the same voltage and 50% more capacity.

Cheers.

[QUOTE=inSANe DIEGO;398]problems. when you wire a pack in parallel you are esentially doubling the size of the batteries. instead of 20 batts you have 10 batts at twice the size. just like you stated. the problem occurs in mixing because you will then have batts at X ah rating and batts at 2X (twice as much) ah rating. this will cause an over discharge and then over charge conditon for the X rated batts. Throw in the amp draw during acceleration and you now have different voltage drops. the bigger batts (2X) will sustain a higher voltage and the smaller batts (X) will dip farther. now you have a pack that has batts of dissimilar amperage AND voltage. It’s a majorly unmatched pack that is subjecting each batt to different rates of usage (or wear). In short. no. not a good idea. Consider using batts of 1/2 the capacity and running a 3 parallel (3P) string for 48 batts total. That would give you the same voltage and 50% more capacity.

Cheers.[/QUOTE]

Interesting angle on this that I did not consider. I keep forgetting that not every batter comes with a regulating circuit, so, with that in mind, this is absolutely correct. Believe it or not, these discussions are helping me with the R&D phase of my project.

[QUOTE=lstockman;397]You would only need a circuit that is able to switch between the battery packs in order to achieve this. I’m not too sure if there would be any problems with charging but I’m sure someone else can explain that part of it. In theory, it’s achievable.[/QUOTE]

The circuit would be ok to switch the pack for charging, but the usage problems will still be there.

One could make a pack of 32 or 64:eek: (2P) 6 volt batts and have a ciruit to switch between series (during HARD acceleration) and parallel (cruising), but a controller designed to handle it would be cost prohibitive. Not to mention the nominal voltage would go to 96 when in parallel and that would probably be ok only for street- not high way driving.

Basically you have to stick to designing your pack to batt numbers divided by 2.

Cheers

[QUOTE=lstockman;400]Interesting angle on this that I did not consider. I keep forgetting that not every batter comes with a regulating circuit, so, with that in mind, this is absolutely correct. Believe it or not, these discussions are helping me with the R&D phase of my project.[/QUOTE]

No worries. That’s what makes “open source” so great. Two minds better than one. Several minds sets records.

Cheers

I have been considering doing this on my car splitting the battery pack and wiring both halfs to the secondary contactor, the reason is that I have to split the pack for my regen circut anayway and maybe this would eliminate a expensive contactor. I have to do more thinking on this though. Maybe it won’t work. I would have to wire to the primary contactor too. What would I gain? anything or would it be a waste of time and materal?

there would be no advantage to changing the wiring. You will still have the same KW/H rating. If you wire for more volts, you can program your controller to use only 144 Volts so you will have less voltage sag while retaining the AH. For example: you have 20 12v 100 AH packs. If you wire them in parallel you will have 120 V at 200 AH, now if you wire all of them in series you will have 240 V at 100 AH. Take the 120 V and multiply it by the 200 AH and you get 24000 W hrs divide that by your other scinario of 240 v, and you get 100 AH. Just wire the pack to the highest voltage and program the controller to the max motor voltage. You will get so much more speed from your motor, and you will have the same range as parallel. The result is you wont be stressing the batteries as much to put out their entire voltage.