Cheap Spot Welder Teardown | Hackaday

2022-10-28 20:56:04 By : Mr. James Li

It used to be hard to dump enough electricity through two pieces of metal to meld them together. But a lithium-ion battery can do it. The question is, should it? [The Signal Path] takes a cheap battery-based spot welder apart to see what’s inside and tries to answer that question. You can see the teardown in the video below.

The cheap welder has some obvious safety problems so the first thing was to trim down some wires and also retinning some of the PCB traces to ensure they are the lowest possible resistance. Of course, the less resistance in the wiring, the more current is available for welding. Aux Cable For Mobile

Cheap Spot Welder Teardown | Hackaday

The welder did do a good job securing a metal strip to a battery. After a successful weld, the video shows how to measure the current using a clamp-style ammeter with an inrush function. The resulting pulse was 960 amps, although it immediately drops over the 50 millisecond pulse, but still impressive.

The safety issues were worrisome, but easy enough to deal with and we’d suggest you do the same examination if you buy one. Some commenters mentioned that their version of similar welders didn’t have the same problems, but it is worth the effort to check before you burn your shop down.

We have had our own concerns about cheap spot welders, before. This isn’t the first piece of cheap gear we’ve seen that bears a safety inspection before first use.

Wonder if those similarly-sized battery-bank car starters could be turned into a spot welder? Safety is part of their design.

Many videos on welding with just a battery.

A lead acid car battery can weld. A neighbor of mine used to weld with one.

2 or 3 car batteries in series and a stick welder end will do really lovely welds in the field.

A ReadyWelder spool gun with flux-cored wire is the posh way to do it.

Yes it can do it but it is really hard on the plates. I have used a series of batteries myself for an emergency small job. The big deal with those emergency jump starter packs is they DO NOT have a timer circuit built in to pulse the current. As the video showed the pulse was only a few milliseconds and to go beyond that can be disastrous. They don’t have a disconnect switch to stop the current flow so that can be another safety issue. You can however use one of those booster packs to recharge the welder pack for extended use in the field or on the bench.

I have had trouble with those EC5 plugs/sockets that are used to plug in the probes.

The idea is that you have a 5mm hole and a 5mm plug is cut along its length into 6 sections of 60 degrees. The gap of the cut will allow the plug to compress a small amount so that for example a 6.001mm plug will fit into a 6.000 hole and still maintain a contact surface area along it’s length and the curve of its arc (segment of circle).

Some manufacturers cheat as it’s hard to get such tight tolerances so they turn the plug smaller and splay the 6 sections out to give a positive feel (friction) that it is connecting properly. However it is only connecting on the end of the plug and the rest of the surface area is lost because the plug is significantly smaller than the hole. Electrically this means the plug cannot carry the specified current and fill fail in burn slightly causing even more resistance.

To check just take one single side of the plug set without the plastic cover and plug one plug into one socket. Try to move one end and if you can move the axis of one in a different direction (offset axis) to the axis of the other then though it in the bin.

Unfortunately this is another example of when something for a very specific prepose (high current connector) can be made cheaper but however be completely incapable of serving its intended (specified) purpose.

A cheap and easy way of protecting the battery and limiting the current-draw from it is to use supercaps instead as the current-source for the welding-process; just charge up the supercaps from the battery through a current-limiter. Supercaps won’t have any trouble handling a couple hundred amps pulse.

When I was a young kid I found a 12V car battery laying around and decided to file the poles (but, WHY?) and make then brighter. They too much bright when I accidentally touched both poles with the file that immediately got welded in place: in a few seconds the file went red-hot and when I had already fled, it (the file) blew up with great red iron blobs. Scary cheap fun. Yes, a car battery is good for welding, i understood!

That is why you always connect “+” first and then “-” if you jump start a car from another car. -> no chance of accidentally creating a short while connecting the “+” clamp. (Disconnect of course the other way around.)

Shouldn’t that be weld or melt? Not a native speaker, maybe meld exists?

Originally meant declaring a selection of cards in a card game but sometime in the 20th Century the new usage, a blending (melding?) of the words melt and weld came into use as a verb meaning the thorough mixing of several components. The new usage is now quite widely accepted.

“Meld” implies a joining together without specifying how that physically happens.

As in Star Trek’s “Vulcan mind meld”?

Call me paranoid but I consider any device with lithium batteries of unknown origin to be unsafe and not welcome in my home.

Likewise grey import mains-powered devices.

that’s probably a fair and safe attitude. There are a lot of different “Lithium” technologies now and there not all as bad as the earlier technologies that seemed to delight in exploding.

On the second point I agree absolutely. Our safety regulatory systems are failing with the much higher scale of import / export of sub standard goods.

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Cheap Spot Welder Teardown | Hackaday

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