Maxwell D-size 2.7V/350 farad. Six in series will start my car.
Any of maxwells caps are impressive.
As for the Li-ion, if you are really determined to use cylindrical cells you could use some of A123 systems’ 26650s. They are rated for 70 amps continuous, and just get a massive sub ohm power resistor to keep the current under the 100 amp pulse maximum.
Remember that supercaps aren’t your grandad’s caps. They will behave as a dead short for a shockingly long while when you start to charge them so plan your charging circuit appropriately.
“Callies Kustoms ” ” did that test, with Panasonic cells it is on their website.
i don’t think he will (or should be) be “spot-welding” in a house in the first place. Common sense should be in play here, also its unlikely that one is going to make the spot welder “on” the battery, cables would be used with the battery many feet away. Welding along side ANY battery with a plastic shell sealed or not would be just stupid.
Why not just use the transformer out of a microwave oven like the rest of us nutjobs that build a spot welder? Granted I only use mine to weld (mostly) vehicle body panels but some tinkering can get you to the amps you need for battery tabs.
It makes no real sense to use batteries, but I wonder about all the fear…?
The approach seems to be ok(short burst+high current+a lot parallel cell) so everything in spec and safe.
Like others said the transformer from an old microwave would cost next to nothing and works, so this seems to be the best lowcost variant.
just to be sure we are on the same page what spot welding is: it is a process where typically you let big current in range of 1000A run through two thin sheets of metal to weld them together. The pulses are typically between 2ms and 20ms. There can be some smaller sparks but the spot welding itself does not generate lethal voltages or sparks.
this it how it looks typically
My other option is to buy a spot welder from china (cca 200:money_mouth_face: but I have safety concerns there because that thing connects to the live grid and with those large currents things can blow it inside of it, so I’d rather deal with non lethal voltages in range up to 16V.
The cable from the welding energy source (18650 VTC5A in the initial proposal) would be perhaps 50cm long 6 to 10AWG cable. So not many feet away, just the minimum needed to reach the object of the welding.
you do not need 1000 amps for battery tabs. i think even low quality spot welder from china will be safer than shorting out li ion cells,
worst thing welder can do, is pop the fuse, li ion otoh will do a lot worst, you can get seriously hurt if you breathe that smoke.
now i do recommend you have class D (yellow) fire extinguisher, it is the only type that deals with metal fires, no powder, water, or co2 will do anything to burning lithium.
actually there are few good diy spot welder plans on instructables.
unless you need it to be mobile, not tied up to ac lines, than use lead acid, they do not blow up with no warning, they heat up swell before so you’ll notice if there is an issue.
also i would not recommend marine batteries, they are deep cycle, and have solid plates, that means you can discharge deep, but screen plates or starting batteries, will give put out more current, that is when you compare 2 same size\capacity batteries.
You have not seen the people who have been harmed by li ion battery explosions or people who die in fires, have you?
There is a difference between challenging dogma and attempting to create unstable explosives and hoping they do not explode
machinist/welding is what i do for a job/profession. i should not need to say more.
allright all, let’s relax a bit, I have a family, experience, education, I’d like to blow up things just for fun but I will not put people or property in danger.
I initiated this to get some feedback. Feedback received. I will not use liIon cells as the power source. I might torture test a VTC5A in a safe manner to document what happens.
That all said - dogmas and laws of physics and everything else should be always open for challenging. That’s the only way forward. Don’t get irritated if your opinions are challenged, it can provide learning possibilities.
Anyway now I need:
1. a capacitor with low ESR (rockford fosgate seems ok, 1F 1.2mOhm ESR)
this guy tested a few of them
2. MOSFETS (ordered a bunch of these)
3. MOSFET gate driver. I have no clue yet how to do this but I don’t think I can drive 10 200A fets directly from Attiny85. Something bad will happen.
4. protective glasses & gloves
Allright! Thanks for participating!
What is your opinion why spot welding of battery tabs should not be done at home?
options are:
- capacitive discharge spot welder (capacitor+MOSFETS)
- tranformer spot welder (either microwave DIY or a chinese spot welder such as sunkko 709A)
- car starter battery spot welder (lead battery+MOSFETS)
what are the risks, safety or otherwise, that you think need to be addressed?
Glad to hear you’ve decided against this
We should challenge things such as trickle down economics and racism/elitism, but testing explosives should be left to professionals.
Spot welding battery tabs? as in the contact strips & tabs that connect Li Ion cells together in laptop packs? The only Spot welder i used is the Miller MSW-41 110 Air cooled unit, (factory made) and have neber built a hme made unit, but many people have done so as mentoned above using transformers & caps.
Agree with the use of a L/A starting battery but I’ve known 2 of them to blow up with me on the scene and I have heard from a few totally reliable people who have also had or seen them blow with no prior warning. In all cases the batteries were installed in cars and that may have set off the chain of events which caused them to blow up. From what I can gather from my limited online research, the usual cause of car batteries exploding is a faulty internal ‘strap’ connection between cells. This part can become loosened by hard jolts and vibration- and cars get that kind of treatment. But an almost new battery was involved in one explosion I heard about which indicates a factory defect- that was a cheap battery brand with a high rate of warranty failures according to my car-battery expert who stopped selling that brand once they saw how bad it was.
But fear not- I’ve known dozens of people who use car and deep-cycle L/A batteries to power their Ham radios and to date only one person had a problem- they were sensitive to the fumes. I do that myself for short-term back-up power, just a used car starting battery kept on a float charge and checked maybe twice a year (and immediately after bringing it into use). I’ve also used a 1/2A charger similarly in the past but it tended to need water added every couple months from the overcharge. I’ve paralleled them across radio power supplies of various outputs up to 25A. Never an explosion, and never heard of a one though rumors abound. Yes there is a risk- hydrogen is dangerous. But like keeping a LiIon cell in a hot car it’s your call and it is beyond generally stated safety rules so if you do it, you’re on your own. Me, I’m not worried,
And now something useful: Take the center rod out of a dead carbon-zinc D cell and hook it to a car battery. Hook the opposite side of the battery to a steel plate and get upwind. Touch the rod against the plate and in about a second it will be red hot at the tip. The electrolyte fumes will mostly burn off after first use (LOL!). Now you can solder starter brushes to the heavy steel cases of automotive starters, an otherwise nearly impossible task as you can’t put a flame there without destroying the coil’s insulation and no commercially made electrical soldering iron can generate enough heat to not give a quickly-failing cold joint. It’s almost a spot-welder in itself and it will melt thin metals but it puts a huge amount of concentrated heat where you need that ability. Not quite a short (think carbon resistor) and you can solder a couple dozen brush sets before you need to recharge the battery. Don’t use jumper cables; the clamps will melt. Use lead battery terminals on all but the grounded lead which clamps directly to the cleaned starter case with cheap vice-grips. Wedge the carbon rod into a terminal as best you can. Do NOT try this with LiIon or NiMh cells; the heated spot is far too large and far too hot for that purpose but it may prove handy for other uses.
Thanks to George W. my second cousin (RIP) who repaired starters as part of his employment for showing me the trick along with a few others which have saved me tons of money through the years.
Phil
You misquoted me, I didn’t write that.
Callies customs tested a low current cell equipped with current limiting PTC. And the short wasn’t low-ohmic (thin wires, poor connection).
A PTC-less high current cell ist a totally different story. The wires would have burned within seconds.
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.
yes my thoughts exactly, VTC5 would behave quite more violently than that.
If anybody has a thermal vision camera I’m offering 10$ or a VTC5A to perform the following experiment:
- charge VTC5A up to spec and discharge with 3A to verify capacity
- charge VTC5A to 4.25/4.3V with termination current <30mA (to get as much charge in as possible)
- connect firmly mechanically to dead short with at least AWG 8 cable and maximum connection quality
- film the results using cam & thermal cam
- if battery survives test capacity again as in the first step
Anybody willing? I would do it if I had access to thermal vision cam.
I did almost exactly that to this 18650. It was running at 3A and I used the thermal camera.
Send me money! hehe