Top Balancing woes.

LVLAaron

Solar Enthusiast
I've got 16x 100ah cells. Initially tried to parallel all of them and get them up to 3.6.

I only had a dinky 5amp CCCV gadget and at 3.3v it was pushing ~2 amps. I imagine it would have taken a year to top balance at that rate. It ran for 48 hours and the voltage didn't move at all.

So I broke them into packs of 4p. I also ordered the bench top supply that Will recommends.

Got the bench supply today. Read the book. Hooked it up to a small 12v pack I have to test it. Had it set on 13v and no current. Clipped it onto the pack, the leads got red hot, heard some popcorn, and released the magic smoke. :eek: (pictures attached)



Plan B.

I have some "20 amp" CCCV chinese gadgets. Tuned one to 3.6 volts and cranked up the current. Battery voltage is 3.31 - Only pushing 2 amps.

Are my expectations wrong?
 

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smoothJoey

Ooga Booga!
Cells fresh off the boat usually come ~50% charged.

100 amp hours * .5 state of charge * 16 cells = 800 amp hours
800 amp hours / 5 amps = 160 hours

That is assuming that your wires are sufficiently sized for purpose.

This link will help

If you have any questions after you have read the doco just holler.
 

LVLAaron

Solar Enthusiast
Were you assuming that the black terminal was negative? Those cells have black as positive and tan is the negative. Its a good thing to test them for polarity and put something big and red on the + end.

It's a pack I built. I'm sure the polarity is correct.
 

LVLAaron

Solar Enthusiast
Cells fresh off the boat usually come ~50% charged.

100 amp hours * .5 state of charge * 16 cells = 800 amp hours
800 amp hours / 5 amps = 160 hours

That is assuming that your wires are sufficiently sized for purpose.

This link will help

If you have any questions after you have read the doco just holler.

Yeah. I've been through that. I ordered that bench power supply.. it immediately exploded :)


I have a 75 amp AIMS charger coming, as well as the overkill solar BMS. I should probably pack up the project until those arrive and I can get some bulk charge into these things before messing with a 5 amp top charge.
 

Bob B

Photon Sorcerer
How were you connecting the power supplies to the cells ..... do you have a picture of the leads and connection points?
Most of the time when the power supply isn't achieving it's rated output ... the problem is with the connection to the pack.
 

LVLAaron

Solar Enthusiast
How were you connecting the power supplies to the cells ..... do you have a picture of the leads and connection points?
Most of the time when the power supply isn't achieving it's rated output ... the problem is with the connection to the pack.

It's wired well. All 14ga copper, crimped and soldered.
 

LVLAaron

Solar Enthusiast
I'm impatient, so I wired it up in 12v to get some amps going in. No BMS but I'm monitoring it while I'm in the shop. I'll check voltage drops and report back if anything seems out of place.
 

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DerpsyDoodler

Photon Sorcerer
I'm impatient, so I wired it up in 12v to get some amps going in. No BMS but I'm monitoring it while I'm in the shop. I'll check voltage drops and report back if anything seems out of place.
if you're not familiar with lfp, highly suggest you actively monitor (preferably with a BMS) a series-built pack you're charging. especially near the end of the charge where the voltage begins to rise quite fast. this is where your outliers or slightly different charge states will matter, because some cell voltages will rise and exceed max faster than others.
 

LVLAaron

Solar Enthusiast
if you're not familiar with lfp, highly suggest you actively monitor (preferably with a BMS) a series-built pack you're charging. especially near the end of the charge where the voltage begins to rise quite fast. this is where your outliers or slightly different charge states will matter, because some cell voltages will rise and exceed max faster than others.

Yep. I'm watching it very closely. Once they get up to 3.5 I'll charge the individual parallel strings with a hobby RC charger to get the last few amps in.
 

Bob B

Photon Sorcerer
I'm impatient, so I wired it up in 12v to get some amps going in. No BMS but I'm monitoring it while I'm in the shop. I'll check voltage drops and report back if anything seems out of place.
You have now increased the possibility of damaged cells by a LOT. The final ramp to full will happen so fast it will make your head spin.
 

LVLAaron

Solar Enthusiast
I'm two feet from it, and looking right at the meter. When I get above 3.4 I'm going to switch to my RC balance charger.
 

LVLAaron

Solar Enthusiast
Back in Parallel. Slowly creeping up the voltage. 8.2amps going in with a hobby charger.
 

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