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Looking for advice on building a battery for my application.

ericj205

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Sep 24, 2019
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Need 12V, 50Ah or less. I have been using a MK Battery M22NF Gel for a couple years. I would like to move to something more compact and lighter weight with a form factor that is specific to my application. I would like the battery pack to be flat, like a brownie baking pan, it can be approximately 20” x 20” x 2”.

I have not built a battery before so this would be my first foray. I would re-use my Renogy Wanderer 10A controller and 100W HQST-100P solar panel. I have a mechanical engineering degree and love tinkering so I believe I am capable. Just looking for some direction and assistance collecting parts.

I want to make this as low cost as possible but still meet my footprint goal. I could definitely reduce the Ah capacity if necessary but would like to get 50 as my starting point.
Thanks in advance for your help. Ask away if you have any questions before responding.
 
I would like the battery pack to be flat, like a brownie baking pan, it can be approximately 20” x 20” x 2”.

Lifepo4 is the safe and popular chemistry.
With those dimensions you will need to make your battery out of cylindrical cells.
38120s is a popular form factor for lifpo4 cells.
There are others but its the nicest to work with imho.
 
Thx. Suggestions on a reliable online supplier for that product and a battery management board for this application?

I guess I will search for threads or videos for a battery build with that type cell.
 
ok, what if i use headway 31820s cells, stack 4 in series in a springloaded pvc tube capped at both ends to get 12V nominal, then create 3 more tubes just like it for a total of 4 tubes. Then lay the 4 tubes flat, next to each other with all the positives on 1 end and all the negatives on the other end. Then connect all positives with custom bus bar and all negatives with custom bus bar.

Wouldn't that give me a 4S4P battery configuration with 12V and 40aH?

If so, what should i use for BMS? Will my Renogy Wanderer 10A work with this battery?
 
ok, what if i use headway 31820s cells, stack 4 in series in a springloaded pvc tube capped at both ends to get 12V nominal, then create 3 more tubes just like it for a total of 4 tubes. Then lay the 4 tubes flat, next to each other with all the positives on 1 end and all the negatives on the other end. Then connect all positives with custom bus bar and all negatives with custom bus bar.

Wouldn't that give me a 4S4P battery configuration with 12V and 40aH?
I can't visualise what you are describing.
I do know that they make plastic holders and busbar kits for the 38120s, that would probably be ideal.

If so, what should i use for BMS?

A cheap commodity 4s bms from aliexpress or similar.
Depends how much charge and discharge amperage you require.
Be warned that the low voltage disconnect is too low on the ones I have seen.
If your amperage requirements are low you could use the load ports on the renogy charge controller.
My cheap little solar charge controller does low voltage disconnect.

Will my Renogy Wanderer 10A work with this battery?

If you provide a link to the manual I may be able to give you a better answer.
 
low voltage disconnect on the solar charge controller is 10.8 volts for lifepo4.
That's too low for me.
 
Am I correct in calling the configuration in my photo a “4s4p” pack? Is this an acceptable configuration (versus 4p4s)? If so, do I need to shop for a BMS for 4s4p?
 
Am I correct in calling the configuration in my photo a “4s4p” pack? Is this an acceptable configuration (versus 4p4s)? If so, do I need to shop for a BMS for 4s4p?

BMSs are just concerned with the serial part.

For a 12.8 volt lifepo4 battery you want 4s.
For a 25.6 volt lifepo4 battery you want 8s.
For a 25.2 volt lifepo4 battery you want 16s.
 
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