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madman
07-29-2008, 07:32 AM
I been looking for three big rectifiers to use in my Lincoln Arc Welder to derust a old 1938 Pickup Truck Body. Usually im apretty good scrounger but with the Insurance at scrap yards in our area no ones allowed into the yards anymore. Makes it hard to get good cheap junk nowadays.

2ManyHobbies
07-29-2008, 08:00 AM
Big and cheap are moving targets these days when you talk about rectifiers. The prices on new ones may surprise you. What voltage and current ratings?

Just Bob Again
07-29-2008, 08:12 AM
Brand new 275A 400V rectifiers are only like $25 (Digikey). Make sure to get something with several times the voltage and maybe double the max current rating of your welder if you want it last a while. Add a nice chunk of metal for a heat sink. Square foot or two at least. It will dissipate a hundred watts or so at 200A and you don't want it too hot.

Evan
07-29-2008, 09:43 AM
I want to know what you are using for a tank. A swimming pool?

Lew Hartswick
07-29-2008, 09:59 AM
I want to know what you are using for a tank. A swimming pool?
Good one Evan. :-) I realy laughed at that even had to tell the wife
what I was laughing about.
...lew...

Dawai
07-29-2008, 11:00 AM
Mike..

Check with GA EWEN to see what he did with the big uns I sent him..

THE state of Canada charged him a huge import fee. I had charged him what I paid for them back ( I had sold the welders to a scrappie). I guess they have a book there in the customs office with pictures of things and guesstimates on what to charge you poor canucks.

Fasttrack
07-29-2008, 07:32 PM
I'm with Evan - I want to see how you manage to do this. I hope to see lots of pictures!

JCHannum
07-29-2008, 08:35 PM
Lots of the old tractor restorers use large watering troughs, feed tanks or tanks lined with poly to de-rust engines and even complete tractors.

Dawai
07-29-2008, 09:54 PM
http://bbssystem.com/viewtopic.php?t=1260

I don't care how they do it in california.. This is how a Hillbilly does it..

Fasttrack
07-29-2008, 11:53 PM
Hey David! Thanks for that. I enjoyed the .pdf on de-rusting the Chevy. That was awsome! I'll keep that in mind next time I take on a rust-bucket.

lazlo
07-30-2008, 12:57 AM
Great job David - I love that article :)

Madman, these should do the trick: 400V, 50A bridge rectifier, $6 each. I used these in my EDM:

http://www.mpja.com/prodinfo.asp?number=5254+BR

http://www.mpja.com/images/5254.jpg

Just Bob Again
07-30-2008, 07:00 PM
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=12848

Another option for you. Schottky 400 Amp 45 Volt for $3 each. Just make sure the open-circuit voltage of the welder is under 45 volts peak. around 30 RMS.

madman
07-31-2008, 09:24 AM
Yeah lots of great Information .Thanx a bunch,. I will be using the Dave Cofer Hillbilly Mode of rust removal, Ha Ha Evan well to be serious yes the one neighbour is moving in a month has a nice pool and yeah we considered just sneaking on over and derusting the body in it and sneaking on off into the night with our derusted parts. This old opickup is very small and not too heavy. Anyhow a rubbermaid container will be used to derust the truck.

pcarpenter
07-31-2008, 11:40 AM
I suppose I risk hijacking this thread, but I have a related question about electrolytic rust removal. I did it some years back to remove rust on an old hand plane I was restoring and had good success using the 12v supply in an old and fairly large computer power supply. This was from an old mid-frame computer back in the days when disk drives were large enough that they used more current and as such the power supply would deliver more than a typical PC supply.

What I really want to know is whether this might be a decent solution for *paint* removal on some old machine tools. I am struggling to find an auto machine shop that can hot-tank larger pieces....I am thinking of the base of my Sheldon shaper for example. I think I recall that there is "some risk" that paint would be removed as a layer of the iron underneath is lifted by electrolysis. On the other hand, the plane I refinished did not loose its japanning as I recall. My shaper has several layers of paint and hand stripping is a pain and doesn't work well in all the crevices etc.

If I can buy a plastic tank big enough to dip that baby then I am all set if electrolysys can be made to lift the paint. Someone here advocated boiling in TSP solution as a great way to strip something that size, but finding and manipulating a metal tank that large, much less a source of heat, makes that difficult.

Paul

lazlo
07-31-2008, 05:35 PM
What I really want to know is whether this might be a decent solution for *paint* removal on some old machine tools.

Yep, it pulls the paint off too.

andy_b
07-31-2008, 11:05 PM
if you add some lye to the mix it soften the paint and it comes off in big sheets. you don't need much. one bottle of Drano (make sure it is the lye type) will last for several batches. i've used the process on some old farm tractors and it works well. the tractors were in pieces, i didn't drive them into a swimming pool. :)

andy b.

Dawai
08-01-2008, 10:37 AM
HI Mike.. Hope you and Audrey are well.. eating good. Tell her Lex and I miss her cooking.

OK.. NOW on to making this deruster last more than ten minutes?

Cooling.. ok.. a big block of aluminum, one per stud rectifier or on each full wave rectifier..

First off.. Buying cooling heat sinks are sometimes sixty to seventy dollars.. take a large chunk of aluminum and face it off flat.. most are curved.. then cut some cooling slots everywhere except where it bolts to the rectifier.. ON stud type, the stud and heatsink are "HOT" and will short out against the other phases so they must be isolated and the heat sink can or could be used as a connection point. Use heat sink compound to transfer the heat.. just smear it on and wipe it around.

Cousin THRUD, he suggested at one time using old computer heat sinks and cooling fans on the lil stepper drives I was playing with.

THE one that laid around here for years? I had it mounted on a chunk of white UHMW plastic.. isolated from each heat sink.. but the 200amp stud diode rectifiers were connected in the manner to make full wave.. I sent it to a guy in Illinois that does Willis car builds... I don't think he ever got off his butt and used it thou. There is a diagram there on that metalillness site of how I connected them.. right below the link to the redneck derusting pdf..

A FULL WAVE lil square job like the picture above for $5 is the easiest to connect.. NOBODY says you have to just use one thou.. you could mount half a dozen on a strip of aluminum.. the wiring is laid out on the terminals.. the lil wavy line on the cube is the ac inputs.. the negative is the minus symbol and the notch or the plus is the HOT off the lil unit. THEY are actually 4 diodes made up in that lil square block.. cooling is a concern thou or they will heat up, and smoke.. Matter of fact, more square jobs with multiple connections to the part are better.. don't have to be two huge single points.. can hook a dozen wires to it..

OLD hyster battery chargers are a godsend to the man doing a big cleaning job.. if you can buy one for $5 go for it.. A cheap dc welder is as good but dangerous..

Playing with electricty around water is dangerous.. Living is dangerous, if you are not careful mowing the yard can kill or cripple you.

madman
08-08-2008, 08:32 AM
I want to be able to weld with my unit also and do derusting. I figure ineed 200 or 400 amp models. So far all ive found is 80 amp on ebay??? Still searching Tanx for the advice guys. Mike