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Moochdocking for initial charge?

ThatGreenBronco

ThatGreenBronco

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Jan 21, 2021
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I have four 280ah cells and the Overkill BMS on their way and will assemble & top balance when they arrive. However, I only own a 1.25amp battery tender/charger... anything wrong with moochdocking (plugging battery into camper and camper into my house) to charge it up? Thx!
 
ThatGreenBronco said:
plugging battery into camper
Click to expand...
What exactly does this entail? Using the camper's 12v charger?

With your limited charging capabilities, you can charge them in series (VERY watchfully and with BMS) up to 13.8v or thereabouts. Then to top balance, connect the cells in parallel to top balance to 3.65v. I do not see the capability to perform the top balance in what you listed.
 
It would entail 110v extension cord from an exterior outlet at my house, through an adapter to the 30 amp cable plugged into my camper. Then whatever it is that my camper uses to charge the led acid battery. Sounds like I should go ahead and get a lifepo4 charger in my camper.


I was watching this video above and Will connected a set of cells in parallel to a charger. I was thinking I might could do the same thing with my camper.
 
ThatGreenBronco said:
Will connected a set of cells in parallel to a charger. I was thinking I might could do the same thing with my camper.
Click to expand...
Its HIGHLY unlikely you will have a charger in your camper that can be set to 3.65v for a top balance.

The idea is to get them most of the way charged in series with a big charger. Then use a bench top charger to do the finishing top balance (a big bench top charger can be spendy).
 
ThatGreenBronco said:
I have four 280ah cells and the Overkill BMS on their way and will assemble & top balance when they arrive. However, I only own a 1.25amp battery tender/charger... anything wrong with moochdocking (plugging battery into camper and camper into my house) to charge it up? Thx!
Click to expand...
I did mine just using a Battery Tender, 1.25A It had a lithium setting, but no documentation as to what voltage that produced. Based on experimentation it stops at ~14.3 V and turns off. Since you haven't top balanced yet, be Extremely careful. It will take several days (140 ah (50% SOC?) = 1.25 A * 112 hrs) to get close. Once the pack gets to ~13.5 V it will take off like a rocket and at least one cell will already be near 3.65V. Don't leave it alone. You can then cycle the charge on /off and let the BMS bring the cells into balance. Very tedious and tricky. But it can be done. The one benefit - it lets you learn first hand about the balancing capabilities (and limitations) of your BMS. But what will you charge with the next time? Shouldn't you just get that now?
 
codfish said:
I did mine just using a Battery Tender, 1.25A It had a lithium setting, but no documentation as to what voltage that produced. Based on experimentation it stops at ~14.3 V and turns off. Since you haven't top balanced yet, be Extremely careful. It will take several days (140 ah (50% SOC?) = 1.25 A * 112 hrs) to get close. Once the pack gets to ~13.5 V it will take off like a rocket and at least one cell will already be near 3.65V. Don't leave it alone. You can then cycle the charge on /off and let the BMS bring the cells into balance. Very tedious and tricky. But it can be done. The one benefit - it lets you learn first hand about the balancing capabilities (and limitations) of your BMS. But what will you charge with the next time? Shouldn't you just get that now?
Click to expand...
Edit: I found that my charger isn't made to charge just one cell. Here we go with the long and tedious process, but at least I get to play with my new toys!

Batteries are "out for delivery" and I'll start this process today. At that ~13.5V mark (which I believe I can set an alarm on my overkill bms) what do you think about charging each cell individually up to 3.65V? Or would that be too much current for one cell to handle? :unsure: Thanks SO much!
 
Last edited:
MisterSandals said:
I looked above but could not tell how much current you are talking about. Each 280ah cell should
take .5C (140a) without problem.
Click to expand...
Oh wow! So my measly little 1.25a battery tender would be perfectly fine to hook up to an individual cell. That way I wouldn't have to let my bms handle that super slowly over time... instead I can do it super slowly with a charger lol *facepalm
 
ThatGreenBronco said:
Oh wow! So my measly little 1.25a battery tender would be perfectly fine to hook up to an individual cell. That way I wouldn't have to let my bms handle that super slowly over time... instead I can do it super slowly with a charger lol *facepalm
Click to expand...
Please only use the battery tender with 4 cells in series.
And remember it Will take the pack to ~14.3 volts, that pretty well guarantees that one cell will be over 3.65v.
Use the BMS and check the settings carefully.
 
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