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Cheap equipment!

Lt.Dan

Lt.Dan

Solar Wizard
Joined
Dec 25, 2020
Messages
3,886
Location
Tulare, Ca
Hey guys, my dad just sent me these photos of some cheap 50ah cells and a cheap $10 BMS that I had rolling around in a box in the garage, that we slapped together and has been in his enclosed trailer for a couple years now, just for the lights inside, and they are topped up with a 100w solar panel on the roof.

Nothing damaged really, just 2 cells swelled up and let the magic smoke loose. I'm betting BMS died and full PV voltage (18v) went to the cells. Wiring isn't even really discolored from heat or anything, just electrolyte inside the box.

Just a reminder for everyone to use quality equipment and dont cheap out like we did for this project!

IMG_4784[1].jpg

IMG_4786[1].jpg
 
How can 18volt from the pv go in that battery?
A mppt or pwm will not sent more than 14.6v
Or have you set the solarpanels direct to the battery?
I hope not ,its than more a surprise that it hold that long
 
Brucey said:
Enclosed trailer, prob got super hot in there in the summer?
Click to expand...
Yes I'm sure. Especially out in the desert of AZ.

Suijkerbuijk said:
How can 18volt from the pv go in that battery?
A mppt or pwm will not sent more than 14.6v
Or have you set the solarpanels direct to the battery?
I hope not ,its than more a surprise that it hold that long
Click to expand...
My mistake, he is using an MPPT, I wasn't thinking when making the post lol.

Must have just been severe imbalance
 
Based on the environment the cells were subject to I am not sure that you can lay the blame on cheap equipment. Good thing it was simply a blow out and not a fire. One comment though. I do not see any separators used.
 
Taking a closer look, is the charger hooked directly to the cell terminals? I can't tell if the charger is being run through the BMS.
If not, BMS would not be able to cutoff the charge and bms may not be balancing adequately. The charger only knows to go to total pack V (assuming 14.4V) also.

If charger is run through bms, bms is for LFP chem right?

Input is likely close to 6A@ 14V (.1c)

The vents usually only open when cell is severely overcharged.

Would be curious to know charger and bms make to see specs.
 
fnnwizard said:
Taking a closer look, is the charger hooked directly to the cell terminals? I can't tell if the charger is being run through the BMS.
If not, BMS would not be able to cutoff the charge and bms may not be balancing adequately. The charger only knows to go to total pack V (assuming 14.4V) also.

If charger is run through bms, bms is for LFP chem right?

Input is likely close to 6A@ 14V (.1c)

The vents usually only open when cell is severely overcharged.

Would be curious to know charger and bms make to see specs.
Click to expand...
Wow I think you caught something! I originally installed this battery with just the MPPT. My father added the loads himself and I didn't double check his work.

It looks like he added loads directly to the battery terminals itself, bypassing the BMS. And if he ever disconnected the MPPT to move the battery or anything, im willing to bet he put the negative back directly onto the terminals instead of onto the BMS like he should have!

Good catch!!!
 
Suijkerbuijk said:
How can 18volt from the pv go in that battery?
A mppt or pwm will not sent more than 14.6v
Or have you set the solarpanels direct to the battery?
I hope not ,its than more a surprise that it hold that long
Click to expand...

There are documented instances where PMM and MPPT failed and shorted full PV to battery.

BMS engages OVP, then BMS gets hit with full array voltage and pops. BMS dead. No charge protection anymore.
 
Lucky there wasn't a spark when the vent happened or it could have been a lot worse.
 
robbob2112 said:
Lucky there wasn't a spark when the vent happened or it could have been a lot worse.
Click to expand...
It's still a non-propagating chemistry. And the gases released burn at a lower temp (~350*F to my understanding) than the plastic box it was in, melts. I don't think it would have caused a problem.
 
Lt.Dan said:
Wow I think you caught something! I originally installed this battery with just the MPPT. My father added the loads himself and I didn't double check his work.

It looks like he added loads directly to the battery terminals itself, bypassing the BMS. And if he ever disconnected the MPPT to move the battery or anything, im willing to bet he put the negative back directly onto the terminals instead of onto the BMS like he should have!

Good catch!!!
Click to expand...
Tell him to limit contact with the dielectric fluid
 
Hydrogen is about 50 percent of the gas released. Around 20 percent oxygen and the rest is just stuff you don't want to breath. The oxygen depends on if there was a short that caused very high temps or if it just vented from overcharge.

Add a spark and you have a fireball.
 
robbob2112 said:
Hydrogen is about 50 percent of the gas released. Around 20 percent oxygen and the rest is just stuff you don't want to breath. The oxygen depends on if there was a short that caused very high temps or if it just vented from overcharge.

Add a spark and you have a fireball.
Click to expand...
Found this article, doesn't cover the bigger prismatics I don't think.


I'm not sure what they mean by void space. Is that the empty space within the battery enclosure? It almost seems like a constant light extraction/circulation system would be best, to avoid hydrogen concentration ever getting to dangerous levels, versus detecting hydrogen and then turning on extraction fans.
 
Yeah, we have talked about things before, a burst disc and fan to vent to outside tied to a hydrogen detector.

Burst disc's are expensive so just plain foil with an X embossed into it and a tiny pinhole to start. Cell vents it opens the burst disc and starts the fan which has to be a type that doesn't spark.

Running one constantly means a lot of moving air and keeping the batteries the same temp as the outside air
 
robbob2112 said:
Cell vents it opens the burst disc and starts the fan which has to be a type that doesn't spark.
Click to expand...
Brushless computer fans would do it. Easy and cheap. 4x high velocity fans in series would be perfect for 48v and cost what. 30 bucks?
 
SparkyJJO said:
Brushless computer fans would do it. Easy and cheap. 4x high velocity fans in series would be perfect for 48v and cost what. 30 bucks?
Click to expand...
We use these in commercial 48V rack equipment. we have also added a resistor in series to reduce the voltage from 56 to 48V. It stopped premature failures. They move some air and not to loud like the little fans.
 
Lt.Dan said:
Hey guys, my dad just sent me these photos of some cheap 50ah cells and a cheap $10 BMS that I had rolling around in a box in the garage, that we slapped together and has been in his enclosed trailer for a couple years now, just for the lights inside, and they are topped up with a 100w solar panel on the roof.

Nothing damaged really, just 2 cells swelled up and let the magic smoke loose. I'm betting BMS died and full PV voltage (18v) went to the cells. Wiring isn't even really discolored from heat or anything, just electrolyte inside the box.

Just a reminder for everyone to use quality equipment and dont cheap out like we did for this project!

View attachment 246723

View attachment 246724
Click to expand...

Thank you for posting this @Lt.Dan

In my life’s journey, I have learned far more from my failures than my successes. Any time a Forum Member is willing to post a safety item such as this thread I very much appreciate it. These posts can be priceless to help other avoid such events. None of us are infallible, nor know it all.

Glad it turned out ok for your Dad & other than the bit of equipment damage nothing went up in flames.

It is hard to understand exactly the issue, without investigation, analysis, & report. IMO, one of the greatest values of this forum is to analyze & consider such events in order to design & build our DIY systems better / safer. That being said, I appreciate what you have posted here, & would really appreciate your opinion on what happened. From looking thru the photos & posts it seemingly looks like some circuits were directly attached to the pos / neg terminals for the cells bypassing the BMS ?

Your report here after you analyze could be instrumental in helping your fellow DIYer.
 
Suijkerbuijk said:
A good bms shutdown.
Cheap junk not.

For the rest only thing i can thing of is capacitor by the battery systeem.
So if the volts go high that it go to that point.
Click to expand...
There are 48V DC o/u protection mcb.

Use it as control to a proper contactor (Tyco Kilovac) and you have reliable make and break connections. The Kilovac would need a pre-charge circuit.

Of course, it may be less expensive to get a quality BMS and SCC.

www.ato.com

DC Voltage Monitoring Relay, Under/Over Voltage, 12V/24V/48V DC

DC voltage monitoring relay with 2 C/O contacts (2 Form C or DPDT) provide protection for the equipment from undervoltage and overvoltage in DC circuit 12V, 24V, 36V or 48V, adjustable trip delay time, LED indicator for working state, DIN rail mounting, compact design, good quality and low price.
www.ato.com www.ato.com

Same Unit at < 1/5 the price through various Amazon and Aliexpress dealers.
 
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