BMS performance

[Daham]

How do I determine if the BMS is doing its job?

 

[John Frum]

The BMS has more than one job.
Broadly speaking the 2 main jobs are cell balancing and protecting the battery.
If the BMS is configurable you can change the configuration so that you can test some of the protection features.
What BMS are we talking about?

 

[berksrunner]

Checking to see whether it is balancing should be relatively simple - just check out your cell voltages. If your BMS does not have any sort of display or bluetooth app, you might want to consider leaving a digital cell balancer attached to your battery (or at least have leave the leads attached) so that manual checking can be easily done at a glance.

Checking to see if the BMS will effectively prevent over and under voltage would be a bit more complicated, again assuming your BMS does not have its own display or bluetooth interface.

Which BMS is it?

 

[Pierre]

The best is to discharge your battery pack and note at what voltage the BMS disconnects the load. Record overall and individual cell voltages and you may find an individual cell that caused the disconnect. Repeat this for a charge cycle.

 

[John Frum]

The best is to discharge your battery pack and note at what voltage the BMS disconnects the load. Record individual cell voltages and you may find an individual cell that caused the disconnect. Repeat this for a charge cycle.

If the BMS is not doing its job this test will damage the battery.

 

[Pierre]

If the BMS is not doing its job this test will damage the battery.

Obviously overseeing this process is mandatory.

 

[Daham]

Checking to see whether it is balancing should be relatively simple - just check out your cell voltages. If your BMS does not have any sort of display or bluetooth app, you might want to consider leaving a digital cell balancer attached to your battery (or at least have leave the leads attached) so that manual checking can be easily done at a glance.

Checking to see if the BMS will effectively prevent over and under voltage would be a bit more complicated, again assuming your BMS does not have its own display or bluetooth interface.

Which BMS is it?

 

[Daham]

Im using DALY 8S BMS 24 volts 100A on 24 volts Lithium 16 X 150 AH battery

 

[John Frum]

Im using DALY 8S BMS 24 volts 100A on 24 volts Lithium 16 X 150 AH battery

Is it configurable or hard coded?
If its hard coded look up the values and create test cases based on the values.
If its configurable, configure these values to safer values then test.
For instance set the per cell low cutoff of to 3.1 volts so that you can safely run a discharge and see if the protection circuit triggers at the expected value.

 

[Daham]

Is it configurable or hard coded?
If its hard coded look up the values and create test cases based on the values.
If its configurable, configure these values to safer values then test.
For instance set the per cell low cutoff of to 3.1 volts so that you can safely run a discharge and see if the protection circuit triggers at the expected value.

It is hard coded and not configurable

 

[John Frum]

It is hard coded and not configurable

Cool look up the specs and devise tests.
Cell undervolt is easy but slightly dangerous
pack undervolt is easy but slightly dangerous
Cell overvolt is easy and slightly less dangerous if you are careful
Pack overvolt is easy and slightly less dangerous if you careful
Personally I wouldn't recommend you test over current.
If the fets disconnect on some of the safer tests above I would take it as read that it will work in the overcurrent case.
As far as balancing.... thats harder to test.
First you need to unbalance the cells and then observe the balance lead bringing the high cell down.
Since the Daly balance current is about 30milliamp this is hard to observe.

 

[berksrunner]

You definitely need one of these if you don’t already have one. I would just leave it connected and use it to periodically monitor the cells and confirm that the bms is working.
ISDT BattGo BG-8S Battery Meter, LCD Display Digital Battery Capacity Checker Battery Balancer Battery Tester for LiPo/Life/Li-ion/NiMH/Nicd https://www.amazon.com/dp/B07797N9BG/ref=cm_sw_r_cp_apip_TgMB6T3eAhT9d

 

[Pierre]

Im using DALY 8S BMS 24 volts 100A on 24 volts Lithium 16 X 150 AH battery

It is hard coded and not configurable

2P8S config with 1x 8s BMS — you have some testing to do ! Maybe test one string at a time.

 

[berksrunner]

Also, just FYI: I recently installed three of the Overkill Solar BMS units which have bluetooth configuration and monitoring. It's an excellent product and totally worth the small premium over the daly, in my opinion. I love being able to see precisely what the BMS is doing in real time on my iphone.

 

[John Frum]

I forgot to warn you.
Not all the Daly BMSs have the same settings.
At least some of the lifepo4 versions have the cell low cutoff factory hard coded to <2.5 volts per cell.
Which is disastrously low.
From memory its 2.2 volts per.
Not sure what they were thinking.

 

[Pierre]

8S2P config with 1x 8s BMS — you have some testing to do !

Also, just FYI: I recently installed three of the Overkill Solar BMS units which have bluetooth configuration and monitoring. It's an excellent product and totally worth the small premium over the daly, in my opinion. I love being able to see precisely what the BMS is doing in real time on my iphone.

Agreed. This is my ‘go to’ BMS for now.

 

[Gazoo]

Also, just FYI: I recently installed three of the Overkill Solar BMS units which have bluetooth configuration and monitoring. It's an excellent product and totally worth the small premium over the daly, in my opinion. I love being able to see precisely what the BMS is doing in real time on my iphone.

Also for the support and warranty. I am planning on this one as well...the 24 volt version.

 

[berksrunner]

Also for the support and warranty. I am planning on this one as well...the 24 volt version.

I have 3 of the 24v in parallel. I switched to this arrangement (8s3p) from my original 3p8s which had a 123smartbms. The new arrangement is sooo much better. My water heater used to cause like 2 volts of voltage sag and now it barely moves the needle.

 

[Archetype-IS]

I have 3 of the 24v in parallel. I switched to this arrangement (8s3p) from my original 3p8s which had a 123smartbms. The new arrangement is sooo much better. My water heater used to cause like 2 volts of voltage sag and now it barely moves the needle.

Are you using three Overkill BMSs for the 8s3P? That could explained the no voltage dip.

Or was just one 123smartbms 3p8s not enough amperage?

 

[Pierre]

I have 3 of the 24v in parallel. I switched to this arrangement (8s3p) from my original 3p8s which had a 123smartbms. The new arrangement is sooo much better. My water heater used to cause like 2 volts of voltage sag and now it barely moves the needle.

I much prefer your new configuration - better cell / pack management overall.