SOK Troubles (user error)

[Alkaline]

OP is your BMS still working?

 

[corn18]

What would happen if a 100/50 MPPT failed and sent 100/50 to an FLA battery?

 

[mrzed001]

What would happen if a 100/50 MPPT failed and sent 100/50 to an FLA battery?

It will charge and charge ... and boil the battery.

Best case scenario:

Worse case scenario: FLA battery explodes.
Not like NMC cells, no fire. But sprays strong acid everywhere.

Worst case scenario: if lot of battery or small not vented room then Hydrogen (HHO) explosion :

 

[jharrell]

Nope it should burn up and no longer allow power to go in our out of the unit. But if burns up and allows power to flow in/out then its a badly designed unit.

Why do these BMS have a 4 series limit? Given enough voltage anything will conduct, its just a matter of how much it can withstand. 17v was after they noticed the problem, once current flows voltage would be pulled down from VOC of 93v.

Relion, Battelborn and SOK all list over charge protection and every one has the same over charge exclusion in their warranty. To over charge the battery such that they expanded enough to split a metal case is an extreme condition, the primary component at fault is the solar controller not the BMS, the BMS attempts to protect but it is not warrantied to do so on any brand.

It would be great if Will purposely tried to destroy one of these batteries to see what the BMS limits are as far as over voltage.

 

[12VoltInstalls]

would be great if Will purposely tried to destroy one of these batteries to see what the BMS limits are as far as over voltage

To do a nice, scientific destructive test on the (?five?) commonly purchased batteries could run over $5000 never mind a protected open area and paying fire support to limit liability.
I’d actually prefer to know what component or how to otherwise protect against a SCC failing closed and dumping unregulated charge down the throats of whatever batteries one might use.
While it seems that it’s unlikely or uncommon for this kind of failure of an SCC, in my case my solar is generally unmonitored as many as 14-16hrs/day while I’m at work. The situations described appear highly likely to start a fire if not ‘caught’ in the midst of it happening.

 

[jharrell]

To do a nice, scientific destructive test on the (?five?) commonly purchased batteries could run over $5000 never mind a protected open area and paying fire support to limit liability.

I think Will has the funds to do it and the video would easily recoup the costs, he's destroyed much more than 5k in teardowns.

Over voltage and over current test are sorely needed to get a grip on BMS quality, at this point LFP's all seem limited by the BMS capabilities.

This is an uncommon failure for an SCC, again if this happened to a lead battery it could have been worse. Who knows what the SCC did, maybe it didn't conduct a full 93v from the panels but instead went into 24v charge mode (it autodetects according to manual) and the SOK BMS could not handle 20+v for some reason.

I know I would not skimp on a solar controller in general, but especially at that kind of voltage, it is the primary voltage protection device (the only one with traditional batteries).

 

[Will Prowse]

Yikes, quite a lot of bad information in this thread. Where should I start. First off, the sok is not special, even UL listed batteries for medical/military application will still be destroyed by high voltage. There is a limit to any OVD circuit. I don't think sok or any company should be responsible for this. There is over voltage protection within the working voltage range of the battery, and a fet based BMS accomplishes this well.

In marine application, alternator regulator failure leading to high voltage has destroyed any battery on the market. Battleborn, valence, sok etc.

Even if you use a fortress battery, simpliphi or discover battery (top of the line lifepo4), they will all be destroyed by high voltage, and I personally don't think it's fair to honor these warranty claims.

The individual should be responsible for these types of failures. I've had over voltage from transformer based chargers and I've destroyed BMS in the process. Did I blame the company? Absolutely not. It was MY fault, and no one else. Using these batteries can only be done in the way they are designed to be used. If you use cheap mppt and it fails, that's on the user. Not the company.

 

[Will Prowse]

@HighTechLab anything else you want to add to this? Or disagree with?

 

[HighTechLab]

@HighTechLab anything else you want to add to this? Or disagree with?

I think you hit the nail on the head. Everything has a point of failure. If you exceed the limits, it will break.

Rock climbers use ropes in case they fall, a rope properly rated for the climbers weight will properly protect them. If you use dental floss, it's going to snap and you're going to hit the ground and get hurt. If you have a BMS with an 85v MOS rating, and hit it with a voltage exceeding that from the solar controller, it's not the BMSs fault for failing...Just like it's not the rope's fault for snapping.

Use high quality components, and think of what happens if they fail. Just like skydivers carry a backup parachute.

 

[TorC]

Yikes, quite a lot of bad information in this thread. Where should I start. First off, the sok is not special, even UL listed batteries for medical/military application will still be destroyed by high voltage. There is a limit to any OVD circuit. I don't think sok or any company should be responsible for this. There is over voltage protection within the working voltage range of the battery, and a fet based BMS accomplishes this well.

In marine application, alternator regulator failure leading to high voltage has destroyed any battery on the market. Battleborn, valence, sok etc.

Even if you use a fortress battery, simpliphi or discover battery (top of the line lifepo4), they will all be destroyed by high voltage, and I personally don't think it's fair to honor these warranty claims.

The individual should be responsible for these types of failures. I've had over voltage from transformer based chargers and I've destroyed BMS in the process. Did I blame the company? Absolutely not. It was MY fault, and no one else. Using these batteries can only be done in the way they are designed to be used. If you use cheap mppt and it fails, that's on the user. Not the company.

Thanks, Will. I agree with this.

With your influence, I think the first thing that would help is if you might be able to help get BMS makers to include an overvoltage protect limit. At least then both sides would have a reference to point to as to who is responsible for a failure. It would also be helpful for the below:

Yes, this problem rests in large part with cheaper parts, but isn't exclusively there. There are some of use out there who, even with Tier-1 equipment and taking care to run it within spec, would like to have some way to know that what may be one of several SCCs in a bank at least has a layer of defense against one of those SCCs failing and putting PVoc on the battery bus. That's what this thread has been going on about for most of its eight pages thus far. If you or anyone else has further thoughts on circuit design I at least would welcome it.

 

[HighTechLab]

I just recorded, and need to edit the video...

I just tested the overcharge protection by applying voltage to a fully charged 12v battery. I was at 50v when the battery could no longer protect itself. The BMS failed closed because one of the FETs broke down internally and short circuited. My shop now smells awful.

Any engineer designing a product needs to determine a limit of what is a reasonable amount of margin. In this case, a 12v battery can't help you if you feed it somehow manage to feed it 50v...Reasonably high enough. You would never have 50v on a single battery even in a 48v system...for 48v, you would need over 100v on the main terminals which is usually impossible. The caps in an inverter would blow long before this.

You could argue 50v is too low, but where is the limit? 50v is obviously high enough that of the thousands of batteries sold, this is the first case that the BMS was pushed past its limit and allowed the battery to overcharge.

While improvement is always good, and I am urging SOK to make their BMS fail in a safe manner instead of unsafe, I can't fault them for the issue at hand, because it took very severe abuse and didn't burn the OP's rig to the ground. The cells within the SOK battery meet UN 38.3 T7, which means if they are overcharged they don't catch fire.

 

[jharrell]

While improvement is always good, and I am urging SOK to make their BMS fail in a safe manner instead of unsafe, I can't fault them for the issue at hand, because it took very severe abuse and didn't burn the OP's rig to the ground.

Not sure what else they could do, FETs tend fail short there is no way to guarantee they fail open, there are two in series so both have to fail however you have many in parallel and any set of two can fail and cause current to pass.

Only way to make it safer is to add more switches in series, which means a secondary BMS with perhaps a contactor or you really want fail safe then a pyro disconnect like a Tesla.

 

[mmtech]

If you are looking for a automatic halon system go to your local boat dealer. Most sport cruisers use them. And NO they are not dangerous to humans.

 

[12VoltInstalls]

the only one with traditional batteries)

There is some bms use with lead acid but I know basically nothing.
A simple voltage regulator device would do it- use the output to trigger a higher voltage/amp relay

 

[jharrell]

There is some bms use with lead acid but I know basically nothing.
A simple voltage regulator device would do it- use the output to trigger a higher voltage/amp relay

Nothing stopping someone from using a BMS with lead acid, I have never seen it, most rely on their solar controller to not accidentally pass high voltage to battery.

I am sure there are voltage sensitive relays out there that could be used as a OV protection device for any battery and might not be bad idea on a high voltage solar system, again though never seen one used.

 

[TorC]

Part of the challenge in designing a safety disconnect is we don't even have a reliable characterization of rate of voltage rise when SCC shorts PV to battery. I'm not sure it even can be reliably described. I believe the current best theory is SCC shorts PV to battery through working BMS. Battery sinks current to hold PV voltage to battery, until voltage rises to BMS cutoff. Battery lineDC bus voltage than quickly spikes to PV Voc, fries BMS, which brings the unprotected battery online again, which goes back to holding PV voltage to battery, rising slowly or not so slowly until the cells overpressure and vent.

 

[HighTechLab]

 

[HighTechLab]

Part of the challenge in designing a safety disconnect is we don't even have a reliable characterization of rate of voltage rise when SCC shorts PV to battery. I'm not sure it even can be reliably described. I believe the current best theory is SCC shorts PV to battery through working BMS. Battery sinks current to hold PV voltage to battery, until voltage rises to BMS cutoff. Battery line voltage than quickly spikes to PV Voc, fries BMS, which brings the unprotected battery online again, which goes back to holding PV voltage to battery, rising slowly or not so slowly until the cells overpressure and vent.

A great way to put it!

 

[jharrell]

Excellent video, this is the kind of tests I want to see, would love to see an over current one as well .

 

[HighTechLab]

Excellent video, this is the kind of tests I want to see, would love to see an over current one as well .

I'm not sure how to pull this one off. I have 2* 8v / 225A power supplies, I could put them in series but I think 225a is not enough. In parallel @ 450a is much better, but with only 8v to work with, it gets tricky trying to push 14v @ 450a (6.3kw)