Hi all......Newbie here from UK. Looking for help on bms problem.

[johnmac]

After seeing Will's video on diy Lithium batt, build($555 one), I took the plunge and built one for my campervan.

In lockdown for past 3 months, so just tested using my 12v compressor fridge and everything was working A1.

Battery charged fine using my Victron mppt and 160w solar. Then last week went to run the fridge again and nothing.

Fridge light just flashed on and off. Checked voltage on batt. terminals and only showed 1.9v.

Took batt. out of case and tested on the bench. Reading 13.6v on batt. Batt. positive to c- on bms reading 12.6v
but when I put a load on it goes to zero !! bms is jbdspo4so2o 4s 100amp. Hoping someone can throw some light on this for me.

Thanks

 

[Fred S]

Does sound like a bad bms. How many amp-hrs is the battery rated, and how many amps is the test load drawing?
To test the fridge, do you have another 12v battery (eg a car battery) you can use to connect to the fridge, and check its startup amperage draw?

If you can connect the lifepo4 battery directly to the fridge, bypassing the bms, you can run the fridge and check the amps and voltage on the battery to verify it's ok.

 

[johnmac]

Does sound like a bad bms. How many amp-hrs is the battery rated, and how many amps is the test load drawing?
To test the fridge, do you have another 12v battery (eg a car battery) you can use to connect to the fridge, and check its startup amperage draw?

If you can connect the lifepo4 battery directly to the fridge, bypassing the bms, you can run the fridge and check the amps and voltage on the battery to verify it's ok.

Thanks for quick reply. I have connected a 12v lead acid batt. directly to fridge and it works fine. I've also connected the lifepo4 direct and it works also. Battery is fine. Seems to be as soon as you apply a load the bms cuts out. The loads I'm talking about is the fridge itself which I wouln't think
to be any more than 6-8amps on startup. I also tried a tiny 12v drill.

 

[Fred S]

Yes, sounds bad for the bms. It's either broken, or there is a small possibly that some current settings got changed. Any chance on support from the manufacturer, or vendor? Are you able to access it, eg over bluetooth? If there is support, perhaps they can provide a procedure to reset it. (That is not likely.)

If there is no access to it and no support -- you can continue using the battery while awaiting a replacement bms, if:
- you spot-check the 4 cell voltages for balance occasionally.
- ensure that the battery max charging voltage is not exceeded, and also ensure that it can't discharge too low in voltage, say below 12v.

Definitely frustrating. Good luck!

 

[johnmac]

Yes, sounds bad for the bms. It's either broken, or there is a small possibly that some current settings got changed. Any chance on support from the manufacturer, or vendor? Are you able to access it, eg over bluetooth? If there is support, perhaps they can provide a procedure to reset it. (That is not likely.)

If there is no access to it and no support -- you can continue using the battery while awaiting a replacement bms, if:
- you spot-check the 4 cell voltages for balance occasionally.
- ensure that the battery max charging voltage is not exceeded, and also ensure that it can't discharge too low in voltage, say below 12v.

Definitely frustrating. Good luck!

Thanks for your feedback. I'm able to access it over bluetooth, but everything looks normal. Cell voltages are 1: 3.3. 2 3 &4 3.4 Batt. total 13.6.

It's only charged by solar..........will the victron control the max charging voltage. I don't expecting any support.......I'm prepared to buy a replacement, but where i bought it from (Aliexpress) states that this product is no longer available.

 

[Pierre]

Have you checked all the parameter settings of the BMS e.g. LVD/HVD trigger and reset values ? Work through all of them and check for an odd one out. Also check the state of the charge/discharge FET's and if BMS is in 'alarm' mode.

 

[Fred S]

Since you can access it, while looking, check the max charge and discharge trigger settings (amps).

 

[johnmac]

Have you checked all the parameter settings of the BMS e.g. LVD/HVD trigger and reset values ? Work through all of them and check for an odd one out. Also check the state of the charge/discharge FET's and if BMS is in 'alarm' mode.

Thanks for your help. I've checked through the parameters, most of them refer to temperatures, which look ok.

Others that might be relevant:- Charge overcurrent 110A Discharge overcurrent -80a Over vo 3.65v Under voltage 2.5vltage

After sitting idle for a few days cells are now :- 1: 3.342 2: 3.422 3: 3.328 4: 3.420

I'm afraid talking about FET's is going beyond my technical knowledge. I think they act as switches but that's my limit.

 

[johnmac]

Since you can access it, while looking, check the max charge and discharge trigger settings (amps).

Only settings I can see referring to these:- charge overcurrent 110A discharge overcurrent -80A

 

[Fred S]

Those seem wrong, but I doubt they are causing your problem. Probably best to swap the bms and move on.
While waiting, I suppose you could try changing the -80 to 100. Does it actually show as a negative # in the settings?

 

[johnmac]

Those seem wrong, but I doubt they are causing your problem. Probably best to swap the bms and move on.
While waiting, I suppose you could try changing the -80 to 100. Does it actually show as a negative # in the settings?

Yes. It does show -80. Anyway, as you say best to replace and move on. Unfortunately there are none available at the moment.

Do those cell voltages look ok to you ? Am I right in thinking the Victron mppt will prevent the battery overcharging ?

 

[Fred S]

Yes the cell voltages are fine. I'm not familiar with Victrons, but if you limit its boost and equilization voltages to 14.4 (I would just use 14.0), and "float" to something less than that, you'll be fine. You can double-check the cells occasionally for comfort's sake!

 

[Fred S]

Opinions will vary, but here's what I'd set my controller for, when temporarily depending on it to regulate the battery:
Equalization V: 14.0v or disable it
Boost (or Absorb) Voltage: 14.0v
Float Voltage : 13.5v or disable it
Low Voltage Disconnect: 11.5v
Low Voltage Reconnect : 12.5v

Boost Reconnect: 13.2v
Charge limit: 14.1v
Discharge Limit: 12v

You'll have to rely on your inverter, or manual control, or another add-on device to disconnect your battery from the load if the battery voltage gets too low.

 

[johnmac]

Thanks for taking the time to help . If anyone knows where I can get a replacement bms delivered to the UK please me know. Thanks.