Monitoring pack pressure for safety

curiouscarbon

Science Penguin
due to a number of factors, availability and ease of engineering mainly, i have decided to go with an S type strain gauge 200kgf, four units.

it has one M12 attachment on each side. instead of using a threaded rod to compress pack, using four of these with threaded rod on each side.
that way, it's as if there's just four threaded rods holding the pack together between two metal plates (and some insulation..)
but each threaded rod can report the tension on itself.
read by load cell amplifier

for assembly i would observe the four readings and tighten until readings match calibrated target.
like airplane orientation readout.

14282-03.jpg
14282-02.jpg



so there'd be four total. upper left, upper right, lower left, lower right.

each one has 200kgf full scale capacity. due to the geometry splitting the load and 150% load capacity rating i feel pretty decent about it being able to hold.

got four 300Ah cells with threaded studs pre-laser welded. planning on relying on oshcut to get some stainless steel sheets laser cut and maybe bent to create the battery case.

it's gotta happen! for science.

adding this diagnostic feature will increase the BOM by about 300usd for four load cells and four load cell amplifiers. this is for research and data collection. however.. it absolutely will be able to detect a very clear signal if the cells were to swell in a failure mode.

edit: this is the work in progress CAD model
1635100089324.png
 
Last edited:

Roswell Bob

Solar Addict
I like the strategy of putting cells in an outside bunker with inverter. I had a safe room installed in corner of basement when we built house so that is probably good for now. All concrete 6'x16' that I put a 2" vent pipe onto. Maybe phase II we put the batteries in a concrete outhouse with the inverter

In the event of a shorted cell I don't know what can be done to prevent fire. I think that parallel arrays of cells should be fused with a fast acting fuse. A fuse in each string would prevent the whole pack from delivering energy to the one failed cell. This might go a long way towards preventing a fire. In any case, I wouldn't put multiple strings together without fusing each string. I worked at secureplane which burnt to the ground when a battery went critical. Google secureplane fire.

Yes, some of these chemistries have electrolytes that produce oxygen. My boss told me to design a battery pack for a MK48 torpedo. Pack is in a can pressurized for very high pressure as it travels underwater at some secret depth :) He told me to look at the cells the RC airplane guys are using because they pack a lot of energy. I found the cobalt technology produces oxygen while burning. I told boss we couldn't use them. Would be putting a bomb inside a torpedo inside of a submarine. Went with an alternate chemistry.
 

Roswell Bob

Solar Addict
wow.. you are overdoing it. Totally waste of money. It is your money tho. W/e makes you happy go for it
Yea, expensive. If the spring constant is known a fairly good measure of pressure should be had by just measuring spring height. I would probably go the load cell direction if I wasn't retired and poor.
 

curiouscarbon

Science Penguin
i do feel a bit silly doing this; it’s to collect data 🤷‍♂️ no other way to satisfy my curiosity.

planning on posting the data for free anyways because i wanna keep the knowledge accumulation ball rolling 🤞
 
Top