Using a welder for electroplating

I've heard of guys using MIG machines (CV) to do electrolytic derusting. In that process, the variables you have are strength of solution (i.e. 1/4 cup washing soda or the whole box?) also distance to the electrodes and to some extent electrode topology. In my most-used setup, I use a square 5-gallon bucket that once contained laundry detergent (itself mostly cut with washing soda) and two railroad track ties with 10 ga. wires soldered to the track ties. The track ties lean in the bucket against the sides, leaving a nice volume for workpieces, which I suspend via a wire/clamp through a stick over the top of the bucket. The problem with this setup is that it's a real hassle when your current isn't enough, or is too much. All I can do with a buzzbox car battery charger is toggle 6V/12V. With a MIG welder, however, I can crank the voltage wherever it needs to be to get the desired level of bubbling, and after the electrodes "load up" I can crank it up a little more to overcome the resistance.

That's a MIG welder, though. A CC source would be really great as long as you can really control the current. Most of the time I'm shooting for 3-15 amps (I'm sure what you really want is some value of amps per unit workpiece area, don't know what that is) and if you can hit that easily and controllably with a CC welder, why sure it will work.

I don't see you have much to lose. I suggest you give it a try and report back.

GWE

you mean tie plates (steel), right?

Makes sense.

Yes, I have a 100% duty cycle CC welder, where I can set amps to whatever I want. It can run for hours.

I will. Right now I want to do nothing big that would take my time away from the tig inverter project, but it will definitely be on my list of things to try.

i

Constant current is ideal for plating, anodizing and derusting -- if you can get the current low enough to be suitable for the job.

Thanks Don. I will try it later, after I am done with my current inverter project.

i

It's not a sensible thing to do. The voltage is too high and the overall output is enormous for any reasonable "rec.crafts" process.

Electronics is cheap these days. Do it right,

Andy, I will check my welder for what the minimum amperage of its output could be. My welding machine has digitally settable output current, although I do not know how low it goes. My guess is that I could get under 20 amps, maybe a lot less (like 10 amps).

The voltage on this constant current welder is automaticaly adjusted to provide desired current.

Assuming that it is the case, do you still have objections to this use?

thanks

i

Good TIG welders will happily run down to 5A output. The open circuit voltage may be ~30V, but it will be lower when under load.

Pete C.

The _voltage_ will be too high. You don't have any way of reducing this (for any welder I've seen) down to the low voltages required.

Besides which, electroplating is a foul process. If you're into the region where you need kW of power, then it's a serious chemical waste handling problem. For "backyard" scale work you can just lash something up from the junk pile.

Here's a piece of electroformed copper (the underlying skeleton is plastic) about 12" across - work by a friend of mine. Nothing more obscure electrically than scrap-box transformers.

You misunderstand the concept of constant current welders, such as my Hobart Cyber TIG welding machine.

The constant current welder adjusts the voltage, up to a certain amount, and down to almost zero, to produce desired current.

If I short the leads of the welding machine, the voltage drops to almost zero.

Similarly, if I was derusting and resistance of the setup was low, the voltage would drop to a very low value, so that the produced current does not exceed the current that I dialed on the welder's control.

Right. Right now I am mainly interested in derusting, using steel electrodes, which is environmentally safe.

That's very nice and artistic...

i

Plating wants a voltage of around 6-7V, with good control of current. This isn't a "constant current" source, because if it does vary (owing to workpiece conditions changing) then it's better if the source behaves as a constant voltage source, once set. Current needs good manual control though and is a crucial adjustment for plating.

Some processes want higher voltages: 12V for hard chrome, 16V+ for anodising and some quite high voltages for anodising titanium.

I've also not seen a welder that went down to this 6V level.

I'm pretty certain that it _is_ zero. The welder will detect this as a specific case and go into a "shutdown" condition.

We live in a world full of cheap scrap electronics. I just wouldn't use a welder for this, when I have any number of small compact 5V and 12V high-current PSUs just looking for new homes.

Car battery charger (old non-auto one). You only need maybe 5A tops at

12V for anything that fits in a dustbin. I've done boat hulls where I used an old computer PSU and about 60A.

I have seen this happen to my welder.

Nope. It continues to happily produce current, as evidenced by the DC ammeter on the welder. I tried this, a dead short as well as a short with a copper bar that had about 2 volts or so of voltage across it.

This is real, my welder is a constant current source that does produce required current and drops voltage to where is has to be for that.

But why would i buy anything else if my welder can do what I want.

That's interesting to know...

i

You can't have "a copper bar" with "about 2V across it". The power required to maintain such a voltage would be enormous.

There are no true "constant current" sources, outside of Norton and Thevenin - when you get to the limits, something has to give.

that was a 6mm by 1.6 mm by 180 cm copper bar, more properly called copper strip.

I thikn that this discussion became sidetracked. I have a constant current source that really is a constant current source within the relevant limits. That's not questionable.

i

I have used my AC oil cooled welder with an external rectifier to de-rust rebar at 50 Amps. I was using an 8'x1'x8" pond made up from plastic sheet supported by wooden railway sleepers and using a washing soda electrolyte with lead anodes. The only thing limiting me to 50 A was the bridge rectifier that I had ( I now have some 100A rectifiers). I did have to top up the water in the electrolyte several times over the 5 days that I was using the rig. I measured 15V across the electrodes and this gives 750W dissipation... the water was hand hot and steamed gently where it was not frothing over the rebar.

Mark Rand RTFM

That's interesting (lead anodes). Why did you decide to use lead? Is the resulting solution environmentally safe?

Wow, that's very impressive. I did not realize that even at 50A, derusting takes so long (and so much energy). I thought that at that sort of amperage, I could expect rust to disappear within minutes.

i

You most certainly can, it's essentially a current shunt. With a welder happily pumping 200A+ through the bar, you will develop a voltage across it based on it's resistance.

You've clearly never had any experience with a quality TIG welder before.

Pete C.

2V at 200A is just 400 watt, not too much. i

If he shorts his welder, the voltage AT THE SHORT is zero. You are correct, Andy. However, the connections and the welding lead have nonzero resistances, and so some current is still flowing through those resistances and generating a small voltage back at the welder. So he is also correct.

It's easy to think of a piece of welding lead as having zero resistance, because in many ways that's an excellent approximation. However, *nothing* has zero resistance except maybe a piece of superconductor.

His welder is a fancy one, too, one of those TIG stick machines.

GWE

Like I say, the amount of current you need is proportional to the surface area. In this case he had a lot of surface area so he used a lot of current.

I like the idea of lead anodes. Lead is quite insoluble and of course it is used in about a billion car batteries as an electrode ..

GWE