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I need a bit of help from someone who owns an unmolested unit. My machien and pedal were PROBABLY never meant to work together, and the PO modified atleast one (pretty sure both) to make things work out. The pedal is spotty but before I just launch into finding parts I want to verify what is custom and what I can actually get from lincoln if I feel like paying 300 bucks for a resistor (not gonna happen).

My pedal is a K870 Amptrol, so if you have one I would LOVE it if you could spend 10 minutes to pop the cover off and snap a picture for me. If you have an volt meter and an extra 10 minutes, you could help even more by letting me know what the voltage on the pot is when you weld at some current.

My hero would be if any of you out there owned a K746 pedal, but as far as I can tell, such a thing never actually existed... Or the K-745 hand control for that matter. Lincoln doesn't even know what I am talking about...

oh and to open it up, all you have to do is push the two pivot pins in on the sides of the pedal, they are spring loaded.

Now, one of my welders at work had apedal go bad. Took the cover off like you described, and found abad spot on the potentiometer.
long story short, replaced pot and cap, and back in bidness.

yeah, only issue is the pot in my pedal is DEFINATLY not factory, and I am trying to figure out what on earth is correct for my welder. The one that is in there has so much friction to spin I had to seriously re-enforce the springs to get hte pedal to return more smoothly, but its far from good.

heck I even have a spare one of those pots, still a stiff sumbith to spin

Shoot a pm to piledriver. He deals with industrial electrics for a living, and can probably help you.

Offhand, we took the numbers off of the pot, verified the min/max ohm readings, and found one online for $10 in about 15 minutes.
Lincoln just wanted to sell a whole pedal, which we did purchase immediately as the welder being down represented a loss of revenue in excess of $1500/day. Then we repaired the broken one, and kept it as a spare.
it floored me that they were making that much a day per welder and did not have an entire spare entire machine.

I may do that, but I figured I'd give him a chance to notice the thread first, I pester him enough as it is! I strongly suspect my machine sends a lot more current thru the pedal than a typical machine, hence the huge pot causing me all kinds of headache. normal ohm ratings, but huge power rating.

I always hit the site using a "new posts" link--- I like to try and limit the spammers, or at least run along behind them with a broom.

I suspect you need a PWM control setup of some sort if you are ever going to get any reliability/control.

Millers of that era used a 130W rheostat, and IIRC used that current to control some movable vanes or some sort of saturable reactor setup--- Very 1960 tech, and expensive HD parts.

It would not surprise me in the least if Lincoln copied the setup Miller used or vice-versa.

Miller has pretty good documentation available.

But... rather than copy, you could probably make up a PWM control setup for a few bucks that would achieve the same control with less heat and it will probably last forever. If it's AC (and it would not surprise me) you might even get away using a HD dimmer//speed control setup.

You could probably even fit one of my finger pressure amptrols into it.
(basically just a pressure sensitive resistor setup)

pile, probably true. My current pedal has a 6 or 12 amp 10k pot in it, wierd that it lists current not power cause power is what matters, but the PN stamped on it doesn't turn up any datasheets. I assume it is an AC signal as well tho. I have the schematic, just need to consolidate it. Couldn't geta good pic of teh whole thign so I am working on a mosiac lol.

ok so i finally dug into the internet and found specs on the retrofit rheostat in my current pedal, it was a 25 watt unit. remember it is NOT stock so no way of knowing if it is proper, but since it is not on fire, it gives me a minimum value at least. I wonder if I need to strike an arc ot measure the operating voltage on the pot in the pedal, or if I can just measure it "open circuit" at the leads. my photos of the schematic did not come out too good, will try again w/ a wide angle.

got a response from lincoln, they confirmed that the original pedal was 10k unit, but didn't give me wattage. I am probing a bit harder to see if they will just give me the literature. there was a hand control avail at one point, so I am gonna try and get some paper on that as well, but I think I am barking up a tree that has been long chopped up for toothpicks.

Can you get the schematics for the actual WELDER?

WeldingWeb is very good, I would register and ask a bit over there, much more likely to find someone that has a similar//same welder or that pedal.

If they had a factory finger control it can't be that bad...

I have a schematic, no values, although I guess I should post it here. Pile, that is my thought too, but maybe they have a finger control w/ some kind of creative slaved box that handles the current? there is no photo or diagram or anything of the hand controller.

on the productive/non-noodle side of things, I got the springs I needed to R&R the pedal for the "last" time. After I recover from ahlloween, I smell some melting metal in my future...

reactors are confusing... Getting closer but still missing it, but so far I am getting the feeling the 25 watt pot is overkill. Pedal feeds the mag amp directly, should be moderately low current but easy enough to just measure voltages and find out.

This look right for the parts breakdown ? (got link from drawing #, L4546 is machines code)
http://www.lincolnelectric.com/assets/s ... n1/p66.pdf

Here's something to make notes on... (schematic L-4546 , R click, save as)
http://weldingweb.com/attachment.php?at ... 1364270996

Found Here: http://weldingweb.com/showthread.php?26 ... ig-300-300
Seems to be a fellow or two who knows them well in that thread, might want to visit.