JBD BMS: only 1 cell won't balance

[JumpyGuy]

I have a small 4 cell, 12v pack with a JBD BMS. It operates fine, but the #2 cell is always out of balance. I have balancing enabled, start voltage at 3000mv and delta to balance at 10mv. I can see the BALANCING indicators intermittently on the other 3 cells, and they are kept close to each other, but I don't ever see the BALANCING indicator on the #2 cell. It seems to me that the BMS should be trying to balance that cell, but isn't. Am I missing something?

 

[Partimewages]

You should not start balancing before 3.400 per cell. Try that and charge to 13.7-14 volts. Your cells don't look bad.

 

[Bob B]

If you start balancing at 3 volts you could cause the pack to become unbalance.

 

[JumpyGuy]

You should not start balancing before 3.400 per cell. Try that and charge to 13.7-14 volts. Your cells don't look bad.

Thank you! I'll adjust the start voltage to 3.4v.

To adjust the charge voltage to 13.7-14, do I change the battery over voltage protection?

 

[Partimewages]

OVP should be 3.65 set in the BMS.
Charge voltage should be set in your charger. What charger are you using? A link might help if you aren't sure.

 

[JumpyGuy]

OVP should be 3.65 set in the BMS.
Charge voltage should be set in your charger. What charger are you using? A link might help if you aren't sure.

OK, thanks. The cell OVP is set at 3.65, and battery OVP is 14.6. I'm just charging it from a basic wall charger. I don't think it's configurable. Here's a link: https://www.amazon.com/gp/product/B0B3CV4S2Y

 

[Partimewages]

I would be very careful with that charger. I have no personal experience with this type but reading here some have bad experiences. They tend to over charge.
I don't know your usage or system but if this is a regular use then I would recommend a Victron IP 22 or 65. Configurable and bluetooth.

 

[mikefitz]

don't ever see the BALANCING indicator on the #2 cell.

You only have passive balancing, thus only high cells are 'pulled down' to low cell values. It's probable you have set 'balance only when charging', hence no balance activity in the capture pic.
Set voltage to start balance at 3.4 volts with a delta of 15mV.
Your pic shows a fully charged battery with good balance, so don't worry, things will improve slowly.
With a 66Ah battery charging up to 20 amps seems about right, the battery maximum of 14.48 volts under charge and a minimum of 11.07 volts under load is OK. My preference would be charge to 14.2 volts and discharge to 12 volts.
As suggested the 'smart automotive chargers' are not ideal, perhaps OK short term, but a configurable charger with ideal charge profile is prefered.

Mike

 

[Lt.Dan]

The JBD BMS is a passive balancer, so it pulls down high cells, but will not bring up low cells. You don't see "BALANCING" on cell number 2, because there is nothing to do with it. It must bring the other 3 down to meet it.

The BMS is acting as intended.

 

[Ampster]

The JBD BMS is a passive balancer......

Which is why I added an active balancer to my system. I have an Orion BMS which traces its heritage to EVs but is still would have a hard time with my 3P16S 42 kWh pack when one or two buddy pairs were low. That is a lot of Watthours to pull down to get to the level of the low cells. My cells are not matched so I turn off the passive balancing on the Orion and let the active balancer shift the Watthours to the lower voltage group of parallel cells.

 

[Alkaline]

Your cells are balanced, around 3.4v they are full.