If you think a 16v DC direct shorted li-ion battery is more safe than a 120v ac spot welder with safety measures in places (breakers, fuses) then I don’t think you need to be doing this.
Take it from a dummy that worked for many years with industrial batteries and now is an electrician, DC can be way more dangerous than AC. People seem to think batteries are safe because they are small and not many volts. Truth is something as small as 48 volts dc can kill you, and dc when it gets a hold of you hurts way worse (first hand experience).
I try to base my decisions on facts and feedback. I did my research on chinese spot welders, didn’t like it too much, and after that I started doing research & gathering feedback on LiIon as power source, since I have plenty of experience with them, but only up to some 50A.
All facts and friendly feedback is welcome and appreciated. Some of the comments though are perhaps stepping into authoritative and pure criticism area. Just my feeling, can be wrong.
Based on sony vtc5a specifications the cells are rated for 100A / 3 seconds, I need up to 20ms. 10 of them in parallel might be sufficient for this purpose. The safety is an unknow because I can’t find research on their behaviour after thousands of high current pulses. So my stochastic math is something like this
Pa=probability that a single 50ms 100A pulse will cause internal damage
Np=number of pulses in a year
Nb=number of batteries in the pack
Pt=total chance that after Np pulses there would be no issues
If Pa=0.999 999 (assumption)
Np=2000 (pulses in 2 years)
Nb=10 (batteries in the pack, paralleled)
0.999999 to the power of (2000x10) is some 98% chance that there would be no serious problems.
This assumed probability of 0.999999 is the lowest one acceptable, below it the odds of having no problems after 2000 welds drop rapidly to unacceptable levels
for example
for Pa=0.99999 total Pt=82%
for Pa=0.9999 total Pt=13%
Since I have no idea if chance of a serious problem is better or worse than 1 pulse in a million (0.999999) I will not pursue this path.
You will still need to connect each of the cells to that cable. Maybe some 12 stranded, one for each cell, stripped and twisted together with a copper/brass bolt to connect two cable clamps then re wrapped or sleeved.
i used to work in an auto repair shop, i’ve seen my share of blown up lead acid cells. true, not all swell up, but all heat up, and some smell like rotten eggs, the thing is they are under the hood, and you do not really have a way to notice that change until it is too late. it could be boiling under the hood and you would not know, until you lose power, than you open the hood, than “boom” and if you’re unlucky, you got acid burns, on your face, and hands. or if you lucky, it blows up in the car spilling acid all over engine bay.
they do not only blow up due to shorts, i’ve seen swollen\boiling batteries due to bad charger.
I do have 2 VTC5A that cost me nothing, and also have easy access to a thermal cam, but I am not going to do this test. The outcome is predictable and toxic.
in the open behind a shield down the wind it should be fine. It’s probably too much energy and battery won’t survive, but how it fails would be quite interesting to see. I’m sorry that you are not interested in trying it. My offer still stands.
BTW some RC lipos are rated to more than 60C often meaning more than 200A. They get a bit spongy and warm during that.
Seriously? You are offering us $10 to produce a movie for you. In this movie you want to see one of our expensive batteries destroyed. And filmed on an expensive camera that may or may not get struck with flying debris. Then repeat the whole process if the battery survives. And then we have to clean up the mess and dispose of it properly. And if you are fully satisfied we get $10.
That’s insulting even on a budget forum.
I think the flaw in your probability calculations (aheeem assumption) is that it assumes a brand new battery for each pulse ¶. When in reality the second time you short a battery/cell the probability is NOT the same as the first time. And this is true for the third time thru all proceeding times.
The point being the more you pulse it the more each pulse has a chance of a catastrophic (defined as potentially inflicting permanent damage to anyone in the vicinity).
Tell us how you quantify the additional increasing risk for each short. And if you cant, then admit that you don’t understand the risk.
OK, there is really nothing to add here in terms of “don’t do it”.
But I get a ribbing for not using a DMM, and this fella (?) wants to pretty much make a bomb ?
I’m not entirely convinced he’s serious but if he is, he should be banned - as was insinuated I should, when I bought up my lack of DMM ownership.
Edit - banned from using liion - not from the forum.
I just realised that could have been misconstrued.
I’m sorry if you feel it is insulting, it was not my intention, nor was I trying to be unfriendly, and I’m a bit sad with the unfriendliness between the lines of some of the replies.
The borders of our knowledge and experience are often broadened by experiments. That was my motivation. VTC5A is around $6. Disposing of it properly, at least for me, involves dropping into the proper battery recycling garbage bin. $10 was not a reward but a compensation for expenses of ruined VTC5A. If you are not interested and find it personally insulting I apologize.
