Daly BMS (250A 4s 12V) reading wrong cell voltage for first cell

[Oarheiljer]

I just built my first LifePo system following Will's youtube videos and buying from his links. I have two 12V 270Ah banks in parallel with two 250Ah Daly BMS's on each bank. One of the BMS's works perfectly. The other shows the first cell voltage 0.1V lower (see screen shot below) than the other 3. When I measure with my volt meter all cells are perfectly balanced at 3.3V. I swapped out the 2 BMS's and I'm getting the same error on the other battery bank with the other balancing harness.

So my question is: can this happen? Will it correct itself eventually or is this something to worry about (e.g. is there something wrong with the BMS)? Is there anything else I should do/check? I disconnected the second bank for now as to not damage anything.

Thanks for your help!
Peter

 

[snoobler]

Welcome to the forum:

To clarify, you have two 12V and two BMS.

One BMS works on both batteries with that battery's harness.

The other BMS shows a discrepancy with your voltmeter even with the other BMS' harness.

If I have it correct, sounds like a defective BMS.

Might be a calibration issue, but I don't know if that's a thing or how it might be accomplished.

 

[Pete7]

I would start by cleaning the contacts and ensuring they are a good fit.

 

[Oarheiljer]

Thanks for your replies @snoobler and @Pete7! I'm attaching a quick diagram of the system. I hope that clears things up. And to @Pete7 's point, it's a brand new install with clean contacts. I even swapped out the ring connectors of cell 2.1 just to be 110% sure. It didn't make any difference. Also, as I mentioned above, I swapped the 2 BMS's and BMS2 shows the same problem on either battery bank/balancing cable.

So am I dealing with a bad BMS or is this still within tolerance?

 

[snoobler]

Did BMS1 work on battery2?

I would not regard a full 0.1V discrepant voltage measurement acceptable.

You indicated 3.3V measured. Was that 3.3, 3.30 or 3.300 when you measured on your meter?

 

[Oarheiljer]

@snoobler Yes, BMS1 works perfectly on battery2 (also using the balancing leads from battery 2). For cells 2-4 my measurements match what I see on the BMS down to the 2nd digit. e.g. 3.34xV where x means the measurement was different. My volt meter measurement of cell 1 also matched the measurements of the cells 3-4 down to the second digit. It also measured 3.34xV, so perfectly balanced.

 

[Oarheiljer]

This just in from Daly customer support. Should I believe them?

 

[snoobler]

No.

.1V is an 8.7% error over the operational range of the cell.

 

[Pete7]

Certainly you could have a duff cell. However, rather than disconnect the battery with it, can I suggest you use it. Mine came with one cell out of sink, one cell charging higher than the others. I spoke to Sterling and they said no problem use it, so I did boiling a kettle regularly whilst I was doing other stuff on the boat and then charging back up over a period of a month. The result is they all are now pretty much balanced and stay that way. I can't find the screen shot unfortunately but the over voltage warning was triggered for one cell which spooked me enough to make a call. Once discharged and charged up again the warning cleared.

That's not to say yours will also sort themselves out, but you have nothing to loose by running it through a few cycles. If its duff then its duff and it would be better to find out now rather than down the road.

The only thing I have noticed is the cycle count on the Daly doesn't work and is always Zero. I have followed Rod Collins advice and chosen a quite conservative charging profile, so 14v for bulk/absorption and 13.3 for float but only when we are on board the boat.

Photo taken during one of the early charges.

 

[snoobler]

There's

Certainly you could have a duff cell. However, rather than disconnect the battery with it, can I suggest you use it. Mine came with one cell out of sink, one cell charging higher than the others. I spoke to Sterling and they said no problem use it, so I did boiling a kettle regularly whilst I was doing other stuff on the boat and then charging back up over a period of a month. The result is they all are now pretty much balanced and stay that way. I can't find the screen shot unfortunately but the over voltage warning was triggered for one cell which spooked me enough to make a call. Once discharged and charged up again the warning cleared.

That's not to say yours will also sort themselves out, but you have nothing to loose by running it through a few cycles. If its duff then its duff and it would be better to find out now rather than down the road.

The only thing I have noticed is the cycle count on the Daly doesn't work and is always Zero. I have followed Rod Collins advice and chosen a quite conservative charging profile, so 14v for bulk/absorption and 13.3 for float but only when we are on board the boat.

Photo taken during one of the early charges.

He doesn't have a cell problem. He has a BMS problem. He measures 3.34V on all 4 cells with a voltmeter. Daly reports cells 2-4 at 3.34 and cell 1 at 3.2.

He has a second BMS that he put on the battery using the same harness, and that BMS reads the cell correctly.

BMS issue.

 

[Oarheiljer]

Thanks again for both of your thoughtful responses! I think I'll move ahead with both your suggestions:
1. Try to run the battery through a few cycles monitoring closely with my volt meter to make sure I don't fry cell 2.1.
2. Push to get Daly to replace the BMS. From reading the forum it doesn't sound like this is going to be easy. Any suggestions on dealing with them?

 

[snoobler]

If you use it, disable balancing.

Another argument for replacement is having a 0.1V error in voltage reading means the balancing function of the BMS can't work properly at all. If you enable balancing, it will constantly be trying to balance the higher cells and bleed them down, lowering them 0.1V lower than cell 1.

 

[Creatura_n]

i have the same problem, how did you solved?

 

[PA1PDR]

Same here: exactly the same problem on a SH39F003 DALY 300A BMS HW version 2.10, SH Version 6.29
Have you solved it?

 

[Goldvogel85]

Same problem here:

Cell	Displayed voltage	Measured voltage
1	3.156	3.30
2	3.314	3.31
3	3.314	3.30
4	3.312	3.31

Strange thing is, that the BMS has worked fine for several month. The problem suddenly occured from one moment to the other. Connections are all ok.

Daly BMS 4S 40A
HW version: BMS-ST030-303E
SW version: 20210712-1001T

 

[PA1PDR]

Same here: exactly the same problem on a SH39F003 DALY 300A BMS HW version 2.10, SH Version 6.29
Have you solved it?

I solved the problem from my end, but don't know if this would work for you. The problem is that the DALY BMS has tied its 5V negative to the negative of the battery. If you now connect a PC or laptop to the USB serial, then when and if the BMS cuts out, or you otherwise uncouple the negative, all the current tries to flow via the negative and the USB negative, via the PC to the negative of other consumers.
This is not a sustainable situation of course, so something (e-fuse, semiconductor etc) inside the BMS blows up.
If you then restore the situation, I suspect there will still be a small current flowing via the 5V negative, causing that .1V difference.

I was successful by wiring the battery side of the BMS to one of the negative pins of one of the ports (NTC or UART, pick one that has 0 Ohms with the USB ground). Of course I now never leave the USB tied to anything when in operation, as one of the MOSFETS shutting off will then cause all the current to again flow to my measly wire, PC, or other component that will never be able to withstand 300A. (I have the 300A Daly on a 4S2P LifePo4 bank)

Hope this helps!

 

[PA1PDR]

Note: before trying, you have to have exactly the situation of the OP: all cells are perfect balanced, when using a volt meter however on the BMS there is a clear difference on the 1st Cell AND you have created a situation where by one of the negative sides of any of the ports was tied to the negative side of the consumers AND you had one of the (CHARGE/DISCHARGE) MOSFETS trip.

Caveat lector

 

[brawr]

Sorry to ressurect this, I have exactly the same problem from a very similar setup to OP. 2x 4s 280AH batteries, each with a DALY 150AH smart BMS, placed in parallel for a 560Ah 13.8v bank. This is freshly assembled from new cells.
The below screenshots are using the same cells and wires, only the BMS is different. All cells measure at 3.50V with my multimeter.

The other thing I'm having trouble with is the battery with the dodgy BMS is not accepting charge when in parallel with the good one. If I charge the battery with the bad BMS seperately, it will accept charge, but only at about 50% of the rate of the battery with the good BMS.
Not sure if it makes any difference, but the B- to P- resistance of the bad BMS has varied between 7.5-28ohms, the good one is consistently 0.5ohms.

Unlike PA1PDR's scenario above, this is not connected to anything other than the cells and the small DALY bluetooth module.

I've reached out to DALY store on AliExpress, but have so far only received a reply saying that it is probably due to incorrectly tightened or corroded terminals, which is not the case. I'll continue to chase them, but would appreciate any suggestions on where to go from here. @Oarheiljer and @Creatura_n did you resolve this? Did your bad BMS also not charge in parallel?
Thanks all!

'good' BMS:

'Bad' BMS:

 

[Tim Tim]

Try doing a factory reset on the BMS. I had a major issue once with one of two 250A BMS’s set up on two 12v batteries in parallel and that is what corrected it. Mind you I still have one that indicates a negative current when charging but I can live with that.

 

[brawr]

Try doing a factory reset on the BMS. I had a major issue once with one of two 250A BMS’s set up on two 12v batteries in parallel and that is what corrected it. Mind you I still have one that indicates a negative current when charging but I can live with that.

Thanks Tim Tim, I tried the software reset options in the app and it didn't make any difference. I also tried disconnecting it from everything for a few minutes and reconnecting it, ditto. Is there another reset method I've missed?