Why did my Daly BMS fail and should I replace it?

[Matty-Lee]

I have had my battery up and running for less than a year now. It's connected to the solar charging system in my van which I use for occasional for weekend trips away.
When the van isn't being used which is most of the time the whole of the charging system is disconnected and the battery is just left to keep a tracker powered via USB.

I was out in the van at the weekend and on the final day the power failed completely. Fortunately I was able to get it all working by taking the BMS out.

I'm surprised that it has failed as the demand on the system is small so I'm wondering why it decided to fail and whether it is actually worth me replacing with another?

There doesn't seem to be any obvious damage on the outside of the unit.





Do you think it is worth me undoing those screws and taking a look inside?

Admittedly the BMS was never mounted with great airflow but there is a charge controller temperature sensor in there and it never gets that hot in the box.
It was a mild winter's day here in the UK when it broke and the temperature in the box was about 8 degrees Celsius.
That's it, squeezed in at the bottom (disconnected).




Any ideas? I know some people don't bother with a BMS so it it worth me spending out on another?

Thanks,

Matt

 

[Steve_S]

You ultimately wrapped & insulated that BMS and over time it cooked itself. BMS' NEED Free Air circulation for cooling, the vast majority of these use the actual casing as a heat sink. Quite a few people do not realize this and do not allow for enough airflow and suffer the same consequences. Of course they will not openly admit to it until pressed, which of course does not help to Educate others.

 

[labeeman]

I have had my battery up and running for less than a year now. It's connected to the solar charging system in my van which I use for occasional for weekend trips away.
When the van isn't being used which is most of the time the whole of the charging system is disconnected and the battery is just left to keep a tracker powered via USB.

I was out in the van at the weekend and on the final day the power failed completely. Fortunately I was able to get it all working by taking the BMS out.

I'm surprised that it has failed as the demand on the system is small so I'm wondering why it decided to fail and whether it is actually worth me replacing with another?

There doesn't seem to be any obvious damage on the outside of the unit.

View attachment 84695

View attachment 84696

Do you think it is worth me undoing those screws and taking a look inside?

Admittedly the BMS was never mounted with great airflow but there is a charge controller temperature sensor in there and it never gets that hot in the box.
It was a mild winter's day here in the UK when it broke and the temperature in the box was about 8 degrees Celsius.
That's it, squeezed in at the bottom (disconnected).

View attachment 84697


Any ideas? I know some people don't bother with a BMS so it it worth me spending out on another?

Thanks,

Matt

How do you know it failed and did not disconnect protecting the batteries? If you over-discharge the batteries or overcharge the batteries it could cost you a van or have to buy new batteries.

 

[MisterSandals]

I know some people don't bother with a BMS

I wouldn't take advice from these people.

I wouldn't buy a BMS that had "Lifepo4" printed on it either.

 

[Matty-Lee]

How do you know it failed and did not disconnect protecting the batteries? If you over-discharge the batteries or overcharge the batteries it could cost you a van or have to buy new batteries.

Good question.
I don't think it would overcharge, the solar charger is set to charge the battery to 80%.

When I got it going again the solar charger reported 40% battery left.

I have no interface to this BMS so no way to see what is going on.

Do you think if I reconnect the BMS it may have reset and start working again?

 

[MisterSandals]

I don't think it would overcharge, the solar charger is set to charge the battery to 80%.

Just out of curiosity, how does one do this? By voltage? If so, what charger and voltage?

 

[Matty-Lee]

Just out of curiosity, how does one do this? By voltage? If so, what charger and voltage?

The charger is made by Epever, I'm unable to check the exact model.

I asked how to do it here https://diysolarforum.com/threads/help-keeping-my-cells-healthy.23367/#post-279200

 

[MisterSandals]

I asked how to do it here

Some good advice from smart people in that thread. What voltage are you charging to for 80%?

 

[Matty-Lee]

Some good advice from smart people in that thread. What voltage are you charging to for 80%?

Unfortunately I don't have the system to hand but I'm pretty sure that I set it up as per this suggestion.

"You want boost and float to be 13.6 if it won’t let you make them the same, have boost be 13.8 and float be 13.6"

 

[MisterSandals]

I am a very conservative charger and settled around there (13.8V bulk but float just below where they settle in an hour).
13.8V will be more like 100% charge but its a good gentle, barely 100%. I tried dozens of charge cycles and that's what i found best for my batteries.

 

[Steve_S]

I'll chime in and simplify things a bit... worn path trodden too many times.
There really is NO Point in charging production cells above 3.425V per cell or 13.7V for a "12V pack". Once fully charged and taking less than 0.05C amps the battery IS fully saturated to that voltage. This will still settle (normal for LFP) once charge stops and if Grade-A Cells should level out around 3.400 +/- 0.100 This is also the TOP of the Working Voltage Range.

NOTE, Voltage read at BATTERY TERMINALS ! There is ALWAYS line loss between gear & battery terminals, every connector, fuse/breaker, even Battery Terminal Lugs can and DO introduce resistance and add to the losses. Cheap Chrome Plated Brass battery terminals are Notorious and can drop as much as 0.5V and I have seen worse (very rarely).




SOURCE Downloable Resource PDF: Luyuan Tech Basic Lifepo4 Assembly Guide

 

[labeeman]

Good question.
I don't think it would overcharge, the solar charger is set to charge the battery to 80%.

When I got it going again the solar charger reported 40% battery left.

I have no interface to this BMS so no way to see what is going on.

Do you think if I reconnect the BMS it may have reset and start working again?

Measure the voltage on each cell and see what voltage they are if any is below 2.5 VDC the BMS may have disconnected due to cell under voltage to protect the battery.

 

[Matty-Lee]

Measure the voltage on each cell and see what voltage they are if any is below 2.5 VDC the BMS may have disconnected due to cell under voltage to protect the battery.

Good idea. Thanks I will do that.

 

[Matty-Lee]

I measured the voltage of each cell, 3.25, 3.26, 3.25 & 3.23 so no problem there considering that they have been charging without a BMS for a few days.

I'm confused though because I have just reconnected the BMS to see if it would work and it did.

So now I'm wondering why it cut off the power in the first place.
If it happens again it is a pain as it's all under the driver seat and not easy to work on.

Could it have just over heated?

 

[labeeman]

It could have overheated but it has been charging for a few days and is not valid for the reason for the BMS to disconnect as the cells are back up to voltage need to check the voltage when the BMS has disconnected not several days after the fact.

 

[Matty-Lee]

It could have overheated but it has been charging for a few days and is not valid for the reason for the BMS to disconnect as the cells are back up to voltage need to check the voltage when the BMS has disconnected not several days after the fact.

Thanks, that will be tricky in the field. I'll see if I can replicate it by running it down on purpose at home.

 

[Pim57]

If the BMS disconnected because of overheating, it would have switched on again as soon as the temperature dropped.

If the BMS disconnected because of low voltage, it stays disconnected until the voltage rises above a certain hysteresis.

 

[Matty-Lee]

If the BMS disconnected because of overheating, it would have switched on again as soon as the temperature dropped.

If the BMS disconnected because of low voltage, it stays disconnected until the voltage rises above a certain hysteresis.

Ah OK, it was night time when the power failed so the solar charger was completely dead too.

So what you are saying is that if I had waited until daylight the solar charge controller would have happily started charging the battery again through the BMS?

 

[OffGridInTheCity]

I wouldn't take advice from these people.

Strongly agree with @MisterSandals - operating BMS is always recommended. Without one, things can go south very quickly leading to damaged cells and worse and you won't even realize it.

 

[Pim57]

Ah OK, it was night time when the power failed so the solar charger was completely dead too.

So what you are saying is that if I had waited until daylight the solar charge controller would have happily started charging the battery again through the BMS?

Yes, that’s most likely that the battery just died during the night. The solar would have recharged the battery as soon as the sun comes out.