# Batteries in Series and Parallel



## Hollie Maea (Dec 9, 2009)

There really are just two simple rules to follow when figuring out series and parallel connections (This is assuming you are not mixing chemistries).

1. Do the cells (or strings) have the same number of amp hours? If yes, you can connect them in series. If not, you shouldn't.

2. Do the cells (or strings) have the same voltage? If yes, you can connect them in parallel. If not, you shouldn't.

Every "entry" has to match voltage for parallel and capacity for series. So if you have, for instance, a bunch of 3.2V 60ah cells, you can string two of them in parallel to get 120ah. But you have to double up all of them before you string them in series so that the ah matches. Likewise, if you have a 120V pack you want to parallel to increase capacity, you have to make the other pack be 120V before you connect them in parallel.


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## major (Apr 4, 2008)

Johnny_5 said:


> I saw other threads that had the discussion on connecting these together, but my question wasn't answered there.
> 
> I am in need of a 24v system to provide power for 4x A40-300 Ampflow Brushed DC Motors. And I am slightly unsure how to decide how many amp hours I need in my battery system. I have attached a link to the performance charts at the bottom of the post, I plan on running the motors at peak efficiency all of the time.
> 
> ...


Hi J_5,

Taking this at face value, let's call peak efficiency from the motor plot at 50A. 4 motors at 50A each is 200A. So 200A from a 24V battery: Using 1C, go for 200Ah cells. If you use 2V/c (like PbAcid), use (12) 200Ah cells in series. If you use 3.2V/c (like LiFePO4), the use (8) 200Ah cells in series.

In a perfect world 200Ah at 50A per motor would get you an hour of run time per charge. Reality says that will be more like 20 to 30 minutes with Pb and maybe 40 to 50 minutes with Li, depending on the DoD you choose to live with. If you need longer run time, increase the Ah. Get larger cells (first choice) or parallel cells. When paralleling cells, use all the same Ah cells.

Should you need less run time, get smaller cells, but beware of the C-rating to make sure they can deliver the required power.

Regards,

major


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## major (Apr 4, 2008)

Johnny_5 said:


> I am in need of a 24v system to provide power for 4x A40-300 Ampflow Brushed DC Motors.


I took a google at the motor http://www.ampflow.com/ampflow_motors.htm. Strange they don't mention a power rating for the motor. It does look like a nice little guy. You don't say your intent, but this is a DIYelectriccar forum, so I warn you, these motors, even 4, won't be suitable for a car


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