Slower charge with BMS vs without

[ericfx1984]

So I have been in the process of bringing the voltage up on a 4p4s, 304 amp hour battery

Started out at 3.3 volts when the cells were delivered and I'm really only getting between 13 and 18 amps when the BMS is hooked up

Since I purchased two bms's I thought maybe it was a limitation of the BMS and I figured I could work around that by attaching the second BMS despite the load.. but it's still only charged at about 16 amps

So then I thought for entertainment I would connect directly to the battery, bypassing the BMS for a few minutes and sure enough it shot up to about 28 amps of charge curre



I'm not really sure I understand why it would do this.. it doesn't make a whole lot of sense to me.. anyway I've reattached the BMS and I'm charging through the BMS.. but I still have absolutely no idea what is going on

Update:. (also added picture)

This is one of these little cheap jobs maybe 3 in by two and a half inch got it on Amazon for $15 I just needed some type of battery management system for the initial charge to get it close so that I could then reconfigure to parallel and do proper top balance afterward

 

[BentleyJ]

Is the BMS getting hot? Seems like the only way for the BMS to cause the problem is due to high internal resistance which makes heat. Normally a BMS has no way to modulate charge or discharge current.

 

[RCinFLA]

Make sure you don't have discharge disabled on BMS although the setting should be overridden at 13 amps of charge current. It adds a diode voltage drop to charging path when engaged.

 

[ericfx1984]

I updated an attitude information as well as a picture of the battery management system found on Amazon... I want to clarify I don't intend to actually use this Bms

 

[RCinFLA]

You have a cheapo that uses fixed supervisor I.C.'s. Some of these do not have very good tolerance on low cell and cell overvoltage sensing. Some often have LiPO supervisor chips even though they say they are for LFP cells so their trip voltages are not correct for LFP cells.

If it thinks cells are below low cell cutoff voltage, because they are LiPO supervisor chips, it will disable discharge and limit charging rate.
You can check the voltage drop across the BMS. If it is operating properly it should not have more than about 0.1v drop across BMS.

Don't expect to pull 100 amps through it, for more than a few minutes, before it gets very hot.

 

[ericfx1984]

You have a cheapo that uses fixed supervisor I.C.'s. Some of these do not have very good tolerance on low cell and cell overvoltage sensing. Some often have LiPO supervisor chips even though they say they are for LFP cells so their trip voltages are not correct for LFP cells.

If it thinks cells are below low cell cutoff voltage, because they are LiPO supervisor chips, it will disable discharge and limit charging rate.
You can check the voltage drop across the BMS. If it is operating properly it should not have more than about 0.1v drop across BMS.

Don't expect to pull 100 amps through it, for more than a few minutes, before it gets very hot.

How do you determine if it has the lipo supervisor ICS?

And even if it does, shouldn't it still allow twice as much current to go through if I hook up two battery management systems?

 

[ericfx1984]

Well mystery solved... Max charge current is 10a... Yet I could do nearly twice that... Who knows

 

[ericfx1984]

So I noticed that if I attach the battery management load (p-) to the charge port (c-) at the current increases from 18a up to 26a

I have just been leaving the load disconnected since I'm only charging

Could this be because there is nothing on the load side? I know in the past when I've used computer power supplies if I did not load up one of the rails (5v?) That the 12v rail would not output full amperage

Well mystery solved... Max charge current is 10a... Yet I could do nearly twice that... Who knowsView attachment 104114