electrolytic de-rusting power supply questions

I finally tried electrolytic de-rusting and I like it. I tried it on a sheet metal blower housing off a lawn mower and I was really
impressed with the results. The pitted areas of the metal were blasted completely free of rust and the process removed most of the paint as well.
The downside is that I now have a dead Harbor Freight battery charger. I found a 24 V forklift battery charger that runs on 220 or 440 and will deliver 12.5/25 amps. the guy wants $20 so this might be a good deal.
Is this a good candidate for making a dedicated power supply for an electrolytic de-rusting set up?
I know that a cheapy little battery charger will work but I assume that the forklift charger has much heavier internal components so it should last.
I also understand that the power requirements to de-rust vary depending on the surface area and the conductivity of the solution. Would it be easy to tweak this charger to make it so I could dial in an optimal setting?
Also, what sort of fuse or other safety should I be sure to build into the supply?
Roger Shoaf
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RS at work wrote:

If it actually works, then yes, it's a hell of a deal. (i.e., good.) :-)

Yes, as long as you have control over the current delivered.

Agreed.
Only the seller can tell you that.

If it isn't already fused, breakered, or current limited, I'd say based on the 25 Amp spec, a 30A slow-blow should be fine. When I worked for the battery charger manufacturer a few years ago, they used fusible link wire. :-)
Have Fun! Rich
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RS at work wrote:

What you want and need on the output is a "PWM controller" . Stands for Pulse Width Modulation . Google that for more info , but the net result is current/voltage control . I use one to control the temp of my 'lectric motorcycle gloves . They are also commonly used to control DC motor speed . Kits can be had fairly cheap , mine was around $35 including case . You can also find them on eBay ... As far as fusing , I'd think you'll rarely draw more than rated amps , say fuse it for 15 with a 220 supply . I'd fuse it at the output of the PWM though - unless your PWM is rated less than the supply's output spec , then I' d fuse the input .
--
Snag
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I've been using a no-name charger for "wand" derusting for ten years. (Ted Edwards' recipe:
http://www.metalworking.com/dropbox/_1999_retired_files/E-CLEAN.TXT
I blew a fuse once when I slipped and touched the probe to the work (actually, my piece of cotton batting wore through).
At first I put my big Variac in front of the charger to fine-tune the amperage, but I soon found it wasn't necessary.
--
Ed Huntress



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All you need is a charger that isn't a complete piece of crap (horrible fright being a near-guarantee of a complete pice of crap barring the occasional planetary alignment - so killing that is an upside if you get a better replacement.)
Use weaker solution or more distance between electrodes or a smaller electrode if you are pulling too many amps for the charger.
I use my regular charger (don't recall the brand, but not Chinese) and have had no trouble in 20 years - I can switch that one to 6V if it gets too excited on 12V.
--
Cats, coffee, chocolate...vices to live by

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A linear adjustable current regulator is not difficult to build.
I think there's a research project in the PWM idea. Does it work as well as continuous current? Does it work better? Is high voltage (current), low duty cycle an advantage? A quick Google search didn't find any data. Mikek
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If you can find a surplus Variac or Powerstat you can make an adjustable supply from a transformer and rectifier. A built-in current meter is useful. You can clip on an external voltmeter because its leads don't have to pass high current and it isn't nearly as hazardous if a lead clip falls off.
I don't think this will work with an automatic charger unless it's blown and you are salvaging only the transformer and rectifier.
jsw
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The place to find out more about a forklift charger is from the manufacturer, if the model isn't too old. I've looked up several brands/models, and the basic schematics/wiring diagrams (and jumper settings) were available online.
Old F-L chargers vary considerably from newer charger models.
Any of them can likely be modified for other purposes (spot/resistance welding, arc welders etc) with some additional control circuitry that replaces the original controller.
Newer charger controllers are microprocessor/firmware driven (the circuit board may only be about 3x3"), and unless you really know electronic design, it's likely to be much easier to just replace the controller with something that's much more simple, but also reliable and safe.
--
WB
.........


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