This is not a test result for an actual battery, but a test specification with criteria for “test passed”.
Note that “does not vent” or “does not spew electrolyte” or “cell performance still meets specifications after test” are NOT listed as pass criteria.
That is, a cell passes this test even if it vents and spews out electrolyte and is dead afterwards. It must just not ignite and not explode or pop. Controlled venting and terminal damage is allowed.
A high-current cell without PTC (like the VTC5A) will usually vent on an extended low-ohmic short (if the shorting wire can take the current and doesn’t melt after a second). At the very least, the cell is damaged afterwards.
Ohm’s law: 200A current requires max. 20mOhms total resistance for a fully charged cell. That is, internal resistance plus contact and wiring resistance plus welding point resistance. So it could be possible to get the required current out of a VTC5A for a fraction of a second, but maybe not very wise to do this repeatedly. And if the welder fails to end the current pulse (FET shorted or the like), you can only hope that some other component will melt faster than it takes your cell array to start venting.
Edit:
Actually, this is a requirement specification for an “over current protective circuit” (7.2.4.3), not a performance specification of the cell.
I can completely relate on both counts separately, and on the statement as a whole.
Stick a VTC5 in a dead short contraption until failure to get a baseline for worst case scenario, then build the thing if you aren’t scared off by the results of the first test.
Oh an Youtube results (of at least the first test) please.
if you really need to use “batteries” for a spot welder, then only a automotive lead-acid battery than safely provide that momentary high current needed. A larger good quality cranking battery can provide 1000+ amps of current, as they are designed to do. One problem is weight & size.
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.
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.
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
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.
