welder idle control?

I have an old Miller welder with a bad idle control module. It's supposed
to energize an electromagnet-type (pull) solenoid mounted on the carburetor
which pulls the governor arm to the idle position, and to sense when there
is weld current, in which case it deenergizes the idle solenoid. The idle
solenoid still works. The bad part is obsolete and unobtainable.
I'm wondering if there isn't a way I could rig a remote switch to turn on
or off that solenoid by hand. It would be a pain, but better than having
no idle control at all.
Ideas?
Grant Erwin
Reply to
Grant Erwin
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Mebbe take the module to a TV shop, A tech there MAY be able to 'shoot it and repair the problem (bad caps, prolly). If it's an IC, fergetit. JR Dweller in the cellar
Grant Erw> I have an old Miller welder with a bad idle control module. It's supposed
Reply to
JR North
Hi Grant, Is the obsolete/unobtainable part a complete board or is it a specific part on the board? If it is a complete board, is there any information available on the board like maybe a schematic? Also, is the board accesible or is it potted in epoxy or something similar?
I would not expect that module to be horribly complicated and if you can get to the components, it should be fixable. Lack of docs would make it harder, but probably not impossible. Also, there are shops that sell idle control modules. These guys advertise some:
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BobH
Reply to
BobH
Grant, if I had the problem you state, I would try to find out from Miller or others what were the parameters that triggered the solenoid, and try to replicate the circuit using modern components. what is the solenoid coil operating voltage. What model welder is it. It does not appear to be a very complex circuit. I would hate to have to manually throw a switch every time you stopped welding. Sorry I cannot be any more help, not knowing the details. See what the others in the group have to say.
Best Regards,
Ray R
Reply to
ramray
Precision Welder Repair has a shop in Portland they send broken obsolete boards to for component level repairs. We had some boards from South Seattle repaired there.
Reply to
Ernie Leimkuhler
If you can't find the parts you could probably adapt the unit from a normal generator to it. Just find one with automatic idle. My smaller Generac has it.
Reply to
Steve W.
Even then, as long as the label hasn't been burned off or erased for "trade secrets" it would likely be something standard. This sounds like a REALLY simple circuit. An op amp, maybe, senses a small voltage across a resistor and switches on/off a power transistor. Shouldn't need more than 10 - 15 parts.
Jon
Reply to
Jon Elson
Miller gives out full circuit board schematics on their welders, so they should have one for this module. You may have to dig DEEP into their obsolete product files.
Jon
Reply to
Jon Elson
It's potted, and weldtron discontinued their Miller II board. :-(
Grant
Reply to
Grant Erwin
I know guys who do board level work too. But this one is a module, potted in epoxy. Later Miller boards were open i.e. repairable.
Grant
Reply to
Grant Erwin
Sounds like a mess, Grant.
Can you cut the epoxy off from around the module so that you can get into it?
You could always reseal with a fresh tube of epoxy later.
Just a thought.
"Grant Erw>> Precision Welder Repair has a shop in Portland they send broken obsolete
Reply to
jp2express
I would be tempted to build my own, using the ole MOT (microwave oven transformer). Remove the *primary*, put a couple of turns of welding cable in its place. The secondary energizes a relay which controls the idle solenoid. The trickiest part would be getting it to work with the whole range of welding currents.
And 'course this only works on AC! Unless the leading edge of the DC current is sharp enough to give you a pulse the could pick a relay that would then be latched until a negative pulse on the trailing edge. Probably not reliable enough.
Bob
Reply to
Bob Engelhardt
Admittedly, I wouldn't have much to lose .. it's a thought, all right. Lots of times when modules are potted it's to prevent component damage from vibration.
Grant
Reply to
Grant Erwin
Can you provide a link to these full schematics? I didn't find them on their site. They have the owners manuals, which include a "circuit diagram", but that is *not* a complete schematic by any means, really just a wiring diagram.
Reply to
Pete C.
Yup, it looks like there have been some changes in the web site. I was there maybe 2 years ago, and the detailed service manuals were "findable" on a link for service parts, I think. You had to look in a non-obvious place, and then search through a HUGE list of PDFs for the older machines. They had both the operator's and the service manuals in there. I poked around for a while, found some more stuff like all the literature blurbs on-line, but no service manuals. I'll bet they are STILL there, but you need to know the exact URL to get to it, and they only tell this to their authorized reps. (There's a "partner login", maybe that's the way in, but you'd need a password.)
Jon
Reply to
Jon Elson
OK, throw the module away and start over. Is there a separate inductor on the welder output? Probably a chunk of laminated iron with 5 -10 turns of one of the output lead wires wrapped around it? You can probably work a reed switch contact in there so it gets enough of the welding magnetic flux to close the reed contacts. Then, you need a simple transistor circuit to turn on a power transistor when the switch is open. You might add a 555 timer to delay turning on the transistor and solenoid until there's been no weld current for several seconds.
Jon
Reply to
Jon Elson
If it is potted in RTV, with a plastic cover, it is quite easy to get into it and pick off the RTV. If it is potted in hard epoxy, it is a major hassle to get in there, and extremely hard to do so without causing major (additional) damage.
Jon
Reply to
Jon Elson
If all else fails, you can reverse engineer it from the bits after you chip away the epoxy (and confirm the schematic if it ever shows up) and make a new one.
If it's simple as it sounds, you don't need a PC Board - just a chunk of generic Protoboard, or even point-to-point wiring if it's only discrete components. And once it's working and debugged, pot it again for moisture and vibration - but use clear resin so you can see the workings next time without destroying it again.
Bump the voltage ratings on the parts, and make sure there's enough heat sinking on any transistors - they try to skimp at OEM because they can toss the ones that blow out and grab another from the bin, you only want to do it once.
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Reply to
Bruce L. Bergman
Since (I think) this is a constant current stick welder, it might be easier to sense voltage rather than current. Open circuit voltage is high, welding voltage might be 1/3 to 1/2 of OCV, and the voltage will be even lower when the welding rod touches off at idle.
One potential problem I see with reacting to current is that the generator may not produce enough current at idle for a simple sensor to discriminate between closed circuit idle and zero current.
Reply to
Ned Simmons
Hi Jon
Would a simple system like this work? If I had this problem of needing to throttle up when the stick starts to strike, I'd try to build an adjustable throttle stop that could be easily set to the engine speed desired for the stick being used. The engine could throttle up with a *on-off* solenoid when current is drawn. I suppose the welding cable from the machine to somewhere near the stick holder could be used as a voltage source to tell the throttle solenoid to pull to the stop.
Jerry
Reply to
Jerry

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