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Basengreen DIY 48V battery with 2A active balancing seems odd, min cell not rising

 
Batteries
Last Post by DougL 2 days ago
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Posts: 22
 DougL
Topic starter
January 6, 2025 9:11 pm
(@dougl)
Eminent Member
Joined: 6 days ago

I just watched my Basengreen batteries hit full-charge and stop charging and I looked with the BMS software at the battery cells and saw lots of balancing going on with each battery having a Vdiff of over .100V . I saw the balancing indicators moving around all the max V cells but the problem was the min V battery voltage was not rising. Charging had stopped because the max cell hit a threshold OV alarm value but I would have expected to see the min V of 3.455 on the low cell to start climbing as power was dumped into it from the max cells.. But instead I saw the min V cell voltage gently dropping as nothing was charging it.

My JK BMSs dump the charge into the min cell but it seems the Basengreen balancer is maybe just bleeding off power from the max cells. Therefore it will take a long time before the low/min cell(s) balance up with the max cells.

Does this sound like what others are observing?

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Posts: 84
 JLankford
January 6, 2025 11:45 pm
(@jlankford)
Estimable Member
Joined: 2 months ago

@DougL

Which charging control method are you using on the 18K? SOC control or Volt control?

I have found that when using SOC control the 18K will stop charging immediately upon seeing 100%. So there is never a top balance opportunity. Worse, if the SOC reference hasn't been reset recently then the system may still be very far from full when the charging is stopped. When the 18K is set for Volt control, it is doing a much better job of approaching a full charge - I see battery voltages approaching the 56V charging voltage (a value that's controlled from the BMS).

This post was modified 2 days ago 2 times by JLankford
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 DougL
(@dougl)
Joined: 6 days ago

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Posts: 22
January 7, 2025 1:36 am
Reply toJLankford

@jlankford 

I switched to Volt with a set high voltage of 59V since the BMS is set for 58.4(3.65 per cell). What happens is when one cell in each of the 3 battery packs hits 3.65V then the BMS "cell OV" alarm is triggered and charging is stopped. Once the battery cells are below 3.50V(56V) then the "cell OV" alarm is cleared and charging can happen again.

What I don't like is that at this top level charging, I see my low cells in all 3 battery packs are at around 3.45V while the high cells are at 3.65V.  So there is a decent amount of SoC missing from those low cells and since the balancer looks like it only burns off energy from the high cells, as opposed to moving energy from high cells to the low cell, it'll take a long time to bleed/waste lots of SoC from those high cells to get them to match the low cell.

BTW, this large .1xx Volt difference only shows up above 3.4x volts and at the nominal pack voltage I observe > 10 mV Vdiff.

I will likely move my top charge peak voltage down from 3.65 once I get everything balanced and 58V(3.5V) is a pretty good level.

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