Charging 12v SLA Batteries connected in S3P2 1

[DERCANDYMANN]

I'm building an electric-assist bicycle and I'm trying to find a way to charge the 12 volt Sealed Lead Acid batteries I'll be using. There are six batteries in all, four 12v/12Ah and two 12v/17Ah arranged in a serries/parallel curcuit as shown in the picture below. Is it possible to charge them as "one big" battery? I have found an inexpensive 24V/5Amp charger made for SLA batteries; can I use that charger on this configuration? If not, what is the safest, most inexpensive way to charge these batteries (practicality would be helpful too)? Thank you.
*Note that if you cannot see the image below, download the file attached to this thread and open it in Windows Picture and Fax Viewer.

-DERCANDYMANN
"I can do all things through Christ who strengthens me." Philippians 4:13

 

[itsmoked]

You are using one of the 17Ah bats in each group right?

Yes, you can hook them up that way.

There is always an issue with hooking batteries in parallel. A common failure mode is a shorted cell. This reduces the battery's total voltage. The other batteries promptly rush to discharge into that battery, sometimes with explosive results.

The conservative thing to do in that case is to fuse the batteries individually. So if one shorts you don't get 150A rushing into it, the fuse blows instead.

Yes, your charger should be fine. You can use it in that configuration.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Alternative would be to have three strings in parallel. Each string should be comprised of similar capacity cells, so don't mix 12AH and 17AH in one string. Keith's idea of fusing cells or strings of cells is very sensible.


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If we learn from our mistakes I'm getting a great education!

 

[DERCANDYMANN]

Yes, there is one 17Ah battery in each group of three. How would I go about fusing them together? How many amps would the fuses need to be?

-DERCANDYMANN
"I can do all things through Christ who strengthens me." Philippians 4:13

 

[itsmoked]

What is the normal operating current of the system?

You'd want the fuses to be around that value.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DERCANDYMANN]

The operating current is 24 volts @ 41Ah as explained in the download on the original post.

-DERCANDYMANN
"I can do all things through Christ who strengthens me." Philippians 4:13

 

[itsmoked]

I'd probably go with 30A fuses.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DERCANDYMANN]

Ok, so how many do I need? Between which batteries should I put them? I just want to be sure. I try to save the fireworks for the 4th of July...

-DERCANDYMANN
"I can do all things through Christ who strengthens me." Philippians 4:13

 

[itsmoked]

At the positive terminal of each battery.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DERCANDYMANN]

Thank you all. This was very helpful.

-DERCANDYMANN
"I can do all things through Christ who strengthens me." Philippians 4:13