little idea helped in electrolytic derusting problem

I picked up a little sheet metal roll with 30" rolls recently. It is old and had been neglected. There was rust on the rolls. I disassembled the machine and decided to do electrolytic derusting on the worst of the rolls, followed by polishing in the lathe.

The first problem was what vessel to use. A workpiece 32" long and slightly less than 2" is quite awkward. I wound up cobbling. I used two 3' lengths of scrap 4x4 wood tacked together on the ends with scrap 1x4 wood to make a frame of sides only. Then I took a garbage bag and put it down inside the frame so it hung over the edges, then stapled it down. I placed sheet lead down the length of my "gutter" with tabs that stuck up for connection points, then put little wood spacers at each end and put the workpiece in. I filled it with solution from my regular bucket, clipped on the leads from the battery charger, and fired it up. It bubbled nicely but the ammeter was clipped on high even on the 6 volt setting. In a few seconds, the overload in the charger tripped. I took the workpiece out and bailed out most of the liquid and replaced it with plain water, hoping to dilute the solution.

That got it down to about 16 amps, but the little charger is only a 10 amp unit so after several minutes it popped again.

That's when I got my little idea!

I put a 20A variac in front of the battery charger and turned it down so the charger only saw about 60% of its input voltage. Ah hah - can set the current right on 10 amps! There were two drawbacks with using a $5 garage sale car battery charger. One is that it won't deliver a whole bunch of current to do e.g. a truck bed. The other is you only have one switch to control the current - the 6V/12V toggle. Sure, you can monkey with your solution, or your topology, but in this case monkeying with the topology would have meant starting over.

This is another handy use for the variac.

Grant Erwin Kirkland, Washington

Reply to
Grant Erwin
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Another idea is to use a PC power supply. Look on Wikihow for more info. I needed a 12 volt supply good for 12 amps and none of my old supplies were rated that high. So I spent $2 at St. Vincent de Paul and got a supply rated for 15 amps at 12 volts. For derusting you might be able to use the 5 volt output ( 20 amps ) or the 3.3 volt output ( 18 amps).

Dan

Reply to
dcaster

This took me 3 minutes! You want me to go buy something ELSE? Besides, I wanted 10 amps at 6 volts .. my idea is to avoid replacing the supply.

Of course, you can build/buy another DC supply, Dan. You are entirely correct as usual.

Grant

Reply to
Grant Erwin

Reply to
David Billington

I was not suggesting that you buy something else. But if someone needs a supply for derusting, they might consider a supply from a PC. Of course a Variac won't work with a PC supply, but you do have different voltages available.

Dan

Reply to
dcaster

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