JBD bms cell overcharge issue.

[Watch Me Build]

Ok so one of my cells in a diy 280ah LifePo4 will hit 3.6v while another is at 3.55 and 2 others are in the upper 3.4s.

I realize I need to top balance these cells again, but am living off grid and this is my only power source, so that's not an option at the moment.


I am hooked into an MPPSOLAR pip1012lv-mk. And normally it would charge until the bms reaches cell overvoltage (set at 3.6). And then it stops the charge and when it drifts back to 3.55 it restarts. It will do this a few times, and then the MPP unit decides it has been charged and stops trying to bulk charge it.

However today the bms registered the overvoltage but didn't limit the charge.

I flipped the breaker on the panels coming in to stop it. And when the cell drifted down below 3.5 I restarted the charge and it happened again. Rinse and repeat.

The cell had gotten to 3.7x at one point before I stopped the incoming charge.

What can I do to get this bms doing what it's supposed to do again?

 

[Watch Me Build]

As a little test I set the pack voltage to 13.8 to see if that would get it to stop charging, and it did nothing either.

It did register the pack over voltage. But that's it. It did nothing to limit the charge.

 

[snoobler]

It's not uncommon for the "dumb" BMS to trip as high as 3.75-3.80V. I would push a little higher and see if they cut off. If it doesn't cut off, it has likely failed.

Since top balancing isn't practical, ensure your balance parameters are optimal.

Balancing should only be enabled during charge.
Balance should only occur if voltages are at or above 3.4V.

I would lower your pack charge voltage to a level that it stops occurring. Leave it there for a week. Bump it up .05. See if it changes, rinse and repeat.

You can get cells charged to 95% full at 3.4V

 

[Watch Me Build]

It always cut off at 3.6 though. Always. I watched it because of the out of balance situation I've had since I installed it (even though I thought I had it top balanced well before I moved offgrid)


So you're saying set the whole pack cutoff to something like 13.5 and see if it stops charging?

 

[Watch Me Build]

I tried it. It did nothing.

Is there some sort of reset on these units that I could try before having to buy something else?

 

[John Frum]

Please link to your bms.

 

[Bob Steel]

Have you established that equalisation is turned off in the settings yet? If its not, its maybe trying to put 15+ volts into your battery.

If you check out a charge /discharge graph for your cells or similar size cells you will find that taking the cell voltage above 3.4v is pointless and dangerous in the long term . Compounds as yet unknown clog the interface and are never cleared slowing ion flow and reducing the number of available ions.

So for a start try to make 13.6 volts your maximum.

 

[snoobler]

Assuming the JBD 120A version - like Overkillsolar.

Sounds like you have a failed BMS and significantly imbalanced cells if they're going wonky at 13.5V.

Is it possible you've missed multiple failures to cut-off?

Was BMS cut-off common? They essentially shouldn't happen if the pack is properly functioning and not having an issue.

 

[Watch Me Build]

No they're not going wonky at 13.5. I'm saying I lowered the pack shutoff in settings to 13.5 as a test and it never stopped the charge.

The cells are only unbalanced right at the end. Between 3.45 and 3.6 is the gap between cells.

I always had the bms to limit charge to 3.6 ... And it would. Basically every time it charged the bms would cut it off, and it would do that a few times until the mppsolar unit realized the battery was charged, and stop trying to bulk charge.

 

[John Frum]

Does the log show an event?
If it logged an event but didn't open the charge circuit I suspect the fets failed closed.
Have you independently verified the cell voltages with a dvom?

 

[Bob Steel]

No they're not going wonky at 13.5. I'm saying I lowered the pack shutoff in settings to 13.5 as a test and it never stopped the charge.

Did you switch the unit off and back on after you changed the settings ? This is necessary on some I have noticed . I guess the new settings are loaded at boot up.
If you have an led strip or bulb or big resistor handy you could put it across the high cell to use some voltage up

 

[Watch Me Build]

Does the log show an event?
If it logged an event but didn't open the charge circuit I suspect the fets failed closed.
Have you independently verified the cell voltages with a dvom?

Yes it logs the events every time. Just doesn't do anything about it.

 

[Watch Me Build]

Did you switch the unit off and back on after you changed the settings ? This is necessary on some I have noticed . I guess the new settings are loaded at boot up.

How do you switch this unit on or off?

 

[John Frum]

How do you switch this unit on or off?

There is a 2 pin jst header with a pc style short across the pins.
removing and replacing that short will turn the unit on and off.
Should disable both charge and discharge.
Possibly balancing and voltage sense.
Curious to know what happens.

 

[Watch Me Build]

There is a 2 pin jst header with a pc style short across the pins.
removing and replacing that short will turn the unit on and off.
Should disable both charge and discharge.
Possibly balancing and voltage sense.
Curious to know what happens.

Should I disconnect the battery first? Can I turn the bms off and power will still flow through it?

Got a picture of where on the bms it's located?

 

[John Frum]

Should I disconnect the battery first?

If there is more than a few amps going in or out probably.

Can I turn the bms off and power will still flow through it?

With a properly functioning unit I think it would stop all flow in and out.
As I said in the previous message I'm not sure.
Since I suspect your fets are welded closed I don't think it will stop the current flow which is a bad thing.
Are you still getting current flow stats?

 

[Bob Steel]

Isn't there normally an on/off button on the display panel?
Or disconnect one wire on the PV input first then one wire on the battery input ,wait 10 secs then reconnect the battery and then the PV wire. Don't short anything. Watch out for the capacitors filling up again. A resistor works best before the battery connection.

 

[Watch Me Build]

If there is more than a few amps going in or out probably.

With a properly functioning unit I think it would stop all flow in and out.
As I said in the previous message I'm not sure.
Since I suspect your fets are welded closed I don't think it will stop the current flow which is a bad thing.
Are you still getting current flow stats?

Yes. Everything seems fine except for it just not stopping the charge.

 

[Bob Steel]

I have a charge controller from SMK . On the add it said "Lithium Ready" (Yehr ...joke) I set it to battery type user and all the right settings and when the battery is full it just still jumps into equalisation mode and tries to shove 15+ volts through the cells. The BMS catches it and switches off so the charger stops trying . The BMS switches back on (all within a second or so ) and 10 seconds later the charger tries to do it again. Ad infinitum . So the thing cost me $170 and will not work . In addition it tries to keep the cells at the top all day and I want them to cycle down to 12.5v before the charger turns back on .
I got around this with a $13 voltage controlled relay driving a truck relay with a 20 amp rating connected in the PV line so it could not get any PV input until the battery dropped to 12.5v and it turned off when the battery got to 13.4v. Seems to be working well and cycling the battery about once a week in my situation.

 

[Gazoo]

Yes. Everything seems fine except for it just not stopping the charge.

Try unplugging the header from the BMS and plug it back in. Remove all loads first.

If the BMS still doesn't work then I believe it's defective. I have the 24 volt version of the jbd I bought from Overkill and so far it hasn't failed me.