NEVER Build a sealed building to house batteries

[Korishan]

View: https://www.youtube.com/watch?v=6LbBryib8yY


The owner built everything to higher standards and tried to do everything right. Heavy duty plywood, double insulation, climate condtioned, BMS's, built away from the main home.
But yet, because he built it too good and sealed, he created a potential explosive force, which ended up happening. The details as to why the cell(s) failed is unknown.

The biggest take away here is, Do NOT build a SEALED container for your battery storages. Always provide a ventilation path to the outside atmosphere. It's better to waste some extra energy trying to maintain temps, cooling/heating, than it is to potentially have to replace the whole structure and anything else damaged in the process.

Be careful folks!

 

[Fukuokian]

Korishan, thank you for posting this! I definitely was heading towards a similarly over-sealed setup! I'm currently looking at adding a H2 sensor that will trigger my ventillation fans.​

 

[Korishan]

I wouldn't rely on a sensor that could possibly fail. Cold air sinks and H2 rises. Have top vents on both sides of the room and an exhaust fan always blowing out. Doesn't have to be much flow. Being at the top allows heat to escape as well. Any heating needed to could be localized to the cells directly.
This would allow for good ventilation and almost zero risk of pressurization

 

[OffGridInTheCity]

Very interesting.

Air flow - The powerwall under my house which is 'open to outside air' via typical crawl space vents around the perimeter. The heat/cool of the house above keeps this area within 55F/13C in winter and 75F/24C summer... which I believe is reasonably 'gentle' on the 18650 cells temperature wise.

BMS can fail - Absolutely! I'm in my office most every day - so I rely on the Batrium Toolkit Blue-Bar app and a custom web page (with bold, red alerts) on a 3rd monitor 24/7 for peace/confidence as to what's happening. Would not be as comfortable relying on BMS with no monitoring of the BMS itself.

I have a stand-alone, purchased, LifePo4 48v battery powering my APC 3000 - and I occasionally check the attached monitor, but it makes me more nervous that then powerall because I don't see it daily.

My camp trailer battery (27kwh) I monitor on my desktop as well.... it get's charged up to 4.15v/cell for trips, so I really depend the Batrium Toolkit to track what's happening as that's only 50mv margin to overcharge.

Operating voltage range - Powerwall charging to 4.0v max leaves a 200mv buffer on the upper end for some messiness / to avoid overcharge. Discharge to 3.5v leaves plenty of room on the bottom end for messiness.
**I wonder if things overcharged in the youtube?

Operating current range - 50ma/cell (overall average) to a max of 250ma/cell - pretty low stress.
**I wonder the 'stress level' of the powerwall in the youtube?

Linked Fire Alarm - right over the powerwall.

Cell level fusing - each cell has 28awg wire to buss... hopefully, a big short will tend to tamp itself down.
Note: LifePo4 cells of larger size don't lend themselves as easily to cell level fusing - and perhaps there's a larger potential here than with smaller a 18650 cells? I'm not sure - no one does cell level fusing that I've read, only battery level fusing for LifePo4.

Conclusions for my situation:
With these operating circumstances, and 8 years under my belt, I'm not thinking the powerall will fail catastrophically within 'hours' for no reason - I'm thinking weeks and a trend (sagging pack or voltage irregularities) will be manifest in plenty of time (weeks) for an intervention.

However, fire could erupt per cell? or electronic equipment! But that's true of the oven in the kitchen as well. I did go ETL equipment.

Nothing is 100%.

 

[Fukuokian]

I wouldn't rely on a sensor that could possibly fail.

Yep, I agree! My original plan was to have the vents sealable for the winter to keep the heat. (I've quickly rethunk that idea ).

I'm pretty sure I'll have enough natural convection from my vent placements (two 15cm openings high & low at opposite corners of the box) during the winter, but I still like the idea of venting out very quickly in the case of a thermal runaway. In reality, this is not very likely to happen; but, it still is a possibility. There's a way to use an arduino and cheap sensors to trigger the fans. The sensors have a typical 3-5 year lifespan, so I was already thinking to have several in operation at once, and replace them at regular intervals.

 

[Korishan]

What I would recommend for controller the fans is to use solid state controls, not software. However, software can override and/or monitor what's going on.
Transistors, thermistors, and diodes works really well at controlling switching without the need of programming. Then use the arduino/mcu to monitor what's going on, or use another transistor switching to bypass the solid state devices to force the fan early

 

[Fukuokian]

What I would recommend for controller the fans is to use solid state controls, not software. However, software can override and/or monitor what's going on.
Transistors, thermistors, and diodes works really well at controlling switching without the need of programming. Then use the arduino/mcu to monitor what's going on, or use another transistor switching to bypass the solid state devices to force the fan early

This is definitely the better solution, but in my case I don't have the expertise to put it together. I'll try to build in extra redundancy to alleviate the extra risk with my approach.

 

[Korishan]

but in my case I don't have the expertise to put it together

ChatGPT to get the schematics, get a few components (which you probably already have), and solder together All the sensor is just a glorified resistor in most situations. So you use it as a voltage divider to the switch, the transistor (FET), so that when the biased voltage moves higher it triggers the FET which then turns on which then turns on the fan(s).
And for those sensors that output a set voltage, such as those that will pull the signal line high to 3V3 or 5V, just use it directly to turn on the FET.

 

[Korishan]

Will does a good coverage on the topic.

View: https://www.youtube.com/watch?v=zvZlTMgEU6s


One thing I hadn't thought about is that the safety system Needs to have its own power source. If the batteries are failing and venting is required, there goes the power source to run the equipment. So it's good to have a secondary battery to run the safety equipment.
This would be a good case for having the low capacity cells, the <50Ah cells ones. Even if they are still running at 48V. Which, just a quick thought would be really easy to set up charging. Use some beefy diodes so that the safety battery can keep charged, but if something happens to the main, it can't discharge that way. Maybe even have a solid state relay that would fully disconnect if the main battery goes bad.

 

[Fukuokian]

Needs to have its own power source

I was planning to have a two power sources for redundancy. (I had thought about what will happen if the main battery fails and there's no power available to spin the fans.)

I had thought of using something like an YX850, but didn't want the onboard charging to the second power source. (Some people cut the charging diode, but I want to find a solution that isolates the power sources.)

Found I could use a Mini 5V DPDT signal Relay, but I'd have to connect a capacitor to handle the switchover so the Arduino doesn't reboot. That's as far as I got researching... kinda got distracted as parts started coming in.

I've got a few options for the backup power source... it doesn't need much power... I'll have an extra deep cycle AGM when I decommission my old solar setup; but the bulk of the old system will go into a camper so I'd hafta invest in a AGM compatible charger/maintainer. Also have an unused PWM, 100w solar panel and a car battery. (That's probably what I'll use, but I haven't committed to it.)

 

[Fukuokian]

Oh, another thing I picked up from watching the original video you posted is that I want the doors of my battery box to be able to blow open. It's kinda a last ditch effort to minimize damage in the event of an explosion. He talks about garage doors being a somewhat giving way for an explosion to be directed/released.

Some other things I thought about are posting warnings on/near the box so firefighters/people are aware of the contents. I already have high voltage warning signs ready, but realized it'll be good to add a "Lithium-ion Battery Storage Equipment" sign. (in Japanese)