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150A Daly Smart BMS - Shutting off with incorrect readings

treetrnk

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Joined
Jul 20, 2021
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Location
Pennsylvania
I have a 8s 24v 280AH lifepo4 battery made with eve cells. As far as I can tell it is working great, but I can never get the BMS to work correctly. I'm already on my second.

The first had a loose connection which I'm pretty sure fried the BMS. It worked, but would shut off when the inverter was pulling more than 4 amps from it. I fixed that loose connection (and tightened all of the other connections to make sure) and I got another 150A Daly smart BMS.

The new one worked for maybe a month, but it started randomly complaining that the cell voltage was too high and would shut off. When it does this, it is usually cell 5 or 6 that are too high, and it will say one of the cells is over 4v. However, if I unplug the BMS and plug in my cell balancer instead, it says that all of the cells are at normal voltages, somewhere in the 3-3.6v range. Then, when I plug the BMS back in, all of the warnings are gone, and it gives the same cell voltages that the cell balancer did. I have also checked with a voltmeter when the BMS is plugged in, and the BMS is wrong.

This would happen once or twice a week, and I thought maybe it was humidity causing the issue. I live in a converted school bus, so humidity is a problem, especially where I live in Pennsylvania, USA. Recently, the problem has gotten worse. It will complain that cell six is over 4.2v and cell five is under 2v. And it's happening multiple times a day, especially in the middle of the night. Last night I think it happened 5 times.

So my question is, did I just get another bad BMS or is it possible that this is being caused by humidity? Is there anything else that might be causing the issue? Thanks for the help!
 
Folks complain about the Daly, especially the Bluetooth models. Rightly or wrongly I’d consider another brand based on the consistent problems you report.

Do of course double check to make sure there is not user error.

The overkill bms comes with great instructions.
 
So my question is, did I just get another bad BMS or is it possible that this is being caused by humidity? Is there anything else that might be causing the issue? Thanks for the help!
Have you checked cell voltage at the balance wire connector on the BMS end?
Pin 1 is negative so voltage at pin 2 should be ~3.2V. Pin 3 ~6.4V… and pin 9 your battery voltage (~3.2 x 8). This represents what the BMS is seeing.

Dielectric grease at this and other connections will help with humidity.

It would seem odd to get 2 BMSs with that same issue. My money would be on bad connection(s) somewhere. If the pin 5 (cell 4 positive, 4x 3.2V = 12.8) reads 0V, then the BMS sees the voltage at pin 6 as 6.4V higher than pin 4 (5x 3.2 = 16V). This type of connection issue, perhaps with pin 5 showing ~2V would explain why pin 6 might read high 3.2V + 1.2V undercount from pin 5).

The balance wire NEEDS to tell the BMS the correct cell voltages, or the BMS may act as you describe. Hopefully this makes sense.
 
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Have you checked cell voltage at the balance wire connector on the BMS end?
Pin 1 is negative so voltage at pin 2 should be ~3.2V. Pin 3 ~6.4V… and pin 9 your battery voltage (~3.2 x 8). This represents what the BMS is seeing.

Dielectric grease at this and other connections will help with humidity.

It would seem odd to get 2 BMSs with that same issue. My money would be on bad connection(s) somewhere. If the pin 5 (cell 4 positive, 4x 3.2V = 12.8) reads 0V, then the BMS sees the voltage at pin 6 as 6.4V higher than pin 4 (5x 3.2 = 16V). This type of connection issue, perhaps with pin 5 showing ~2V would explain why pin 6 might read high 3.2V + 1.2V undercount from pin 5).

The balance wire NEEDS to tell the BMS what it needs or the BMS may act as you describe. Hopefully this makes sense.

I see a lot of people just crimp on eyelets on their sense leads. I always crimp and solder mine just for this reason. I never rely on just a crimp on this size wire.
 
I see a lot of people just crimp on eyelets on their sense leads. I always crimp and solder mine just for this reason. I never rely on just a crimp on this size wire.
I am guilty of this but I test the heck out of every wire and connector.
 
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