Fitting a 14 pin remote control to an engine drive welder

I've recently acquired a newish (early '90's) Miller Legend AEAD-200LE welder and subsequently an HF251D1 arc starter with a TIG torch. The welder does not have remote control, and by all
accounts a footpedal (or equivalent) current control is nice to have.
Miller apparently offered a 14 pin remote as an option on the welder, but it was never common and hasn't been available for some years now. Much Google searching reveals considerable interest in adding a remote control to Miller Legends, but no indication of how to do it (nor any hint why it can't/shouldn't/won'twork) be done emerges. The welder manual shows a schematic complete with component values, but without knowledge of how both the welder and the remote control are intended to work it's not trivial to duplicate the functions of the board.
I've been unable to find aftermarket remotes for the Miller Legend, though units do exist for larger Miller and Lincolnmachines. I inquired of one vendor and was rebuffed with surprising speed, saying simply they don't have the part. It's hard to believe the Legend is all that different.
Does anybody know what the impediment is?
bob prohaska
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wrote:

I've fitted a remote control (pedal) to several Chinese made welders. In every case the hand amperage control has been a simple rheostat and what I did was add a switch and external socket so that either the welder circuits or the foot pedal could be selected.
I don't remember the ratings but it turned out that the welders had the same capacity internal rheostat as a Miller foot control that someone had given me.
--
cheers,

John B.
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That seems like an eminently reasonable thing to try. What I can't figure out is why nobody says so, or says no. They behave as if they're afraid to speak.

The rheostat on my welder is 30 ohm, rated 100 watt. An old fashioned sewing machine rheostat might do the trick..... I wonder if they can still be found. Might be worth a try.
You don't happen to have a model number for that Miller foot control, do you?
Thanks for your help!
bob prohaska
Thanks for reading,
bob prohaska
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wrote:

I tried that and it didn't work although my "trial" was simply to connect the Singer pedal and step on it,
I'm not sure what value rheostat I used and I'm a long way from where the welder is but 30 ohms sounds sort of like what I remember although I'm really not positive.

No I don't have any idea. I asked at a welding machine vendor if he had any "foot controls" and he fished this used one out of the back room and gave it to me. It turned out to be the same value rheostat as the welder so I used it. And it worked :-)

--
cheers,

John B.
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I have a engine driven welder, and this welder has a generator. It is a similar miller welder. "250"
There is no way to stop the generator from producing welding electricity, while the welder is running.
If yours is the same way, I cannot see how a remote control could work.
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My welder uses a tapped inductor for coarse current control and varies the field current (effectively adjusting the open-circuit output voltage) to set the fine current. I think this is fairly standard. In principle one can adjust the output current all the way to zero by opening the field current circuit. In practice the range is more limited, so a contactor is used to terminate the arc. Completely opening the field circuit should do much the same thing, but far as I can tell that method isn't used. One fairly basic puzzle is why not. Possibly other components in the welder react badly to a loss of field current, but nobody has offered an explanation. That is the error I'm trying to avoid.
Thanks for reading!
bob prohaska
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You have a good welder, do not make it into a bad welder by messing with its most basic principles of operation.
i
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Agreed entirely! That's why I'm seeking knowledgeable counsel. What really surprised me is that nobody on the Miller Electric welding forum has been willing to comment. A simple "won't work, here's why...." or " can be done, here are the pitfalls/limitations...." would suffice. Thus far the silence is deafening.
bob
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On 3/10/2016 9:49 PM, User Bp wrote: ...

Probably because there is residual magnetism in the stator that would give some output voltage.
Bob
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Possibly you meant residual magnetism in the field? The idea makes sense, but I'd think it too feeble to maintain an arc. It's one of the many things I don't yet know.
bob p
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On 3/11/2016 9:34 PM, User Bp wrote:

Well, I meant "residual magnetic field in the stator".
The voltage across a tight arc is much less than the OCV, maybe 10 - 20v. Whether the residual field could produce that - I dunno, but maybe.
Bob
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It's a simple enough remote setup.
A not connected to B, contactor open, no weld voltage. A connected to B, contactor closed, weld current enabled. Just possible (description vague) that this is inverted, but unlikely.
C provides 4.5V to one end of the remote (current control) pot. D is the control circuit common on the other end of the pot. E is the wiper of the pot (value of the pot will typically be 5 or 10K, and is not critical, as the voltage, at little current, is the control signal. The remote pot is NOT a high-power unit.
K is chassis ground.
Order a connector and go. It's not rocket science. Or are you saying the welder does not have the remote socket/internal board? In either case, the above is how the remote works, and Lincoln remotes are quite similar.
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Aye, there's the rub. No contactor and no remote board. No OEM remote boards available, nobody willing to tell me how to adapt a generic board or why it can't be done.
bob prohaska
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On 03/09/2016 08:09 PM, User Bp wrote:

I went to the Miller web site, and pulled up the users manual and schematic, and it looks like they show how the fine current control adjustment works. You could put a double pole, double throw switch that would substitute your foot pedal variable resistor for the fine current control. Or you could use the switch to put your foot pedal resistor in series with the existing fine current control resistor which is how my old Dialarc 250HF did it. The parts list shows a 30Ohm 100W resistor for the fine current control.
The last version of the users manual showed the schematic for the remote control version of that machine. It used a board to control the field instead of the 30 Ohm power resistor for the remote. The 14 pin foot pedals have a small 5 or 10 KOhm pot in them (1/2 watt or so) so you would need the control board to use that style foot pedal.
The old Dialarc 250HF used a 24 or 30 Ohm 100Watt variable resistor to control the current. They used a 3 pin connector for current control and a 2 pin twist locking connector to control the contactor. A pedal like that would work without a control board.
I think that the foot pedal that you want is the Miller RFC-23A
Good Luck, BobH
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(Amazon.com product link shortened) It's the diameter of a coffee cup. The reviews of some similar ones call out the brush as a weak spot.
--jsw
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That's what I found also.

The control board is what I don't have, can't find and can't learn how to adapt. Their scarcity makes me wonder if maybe they didn't work all that well and Miller simply wants to banish the bad memory....

That's a good clue, at least I have something to look for now. I'll poke around a little.

Thank you!
bob p
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On 03/11/2016 07:55 PM, User Bp wrote:

You're welcome.
If you look at the schematic for the unit without a remote board, it just shows the variable resistor for the fine current control (R1 on the schematic I looked at). A Double Pole Double Throw switch would let you swap the remote resistor (foot pedal) in for R1. A contactor would give you the make/break for the on/off. My Dialarc used a big 3 phase contactor, but it was the highest maintenance part of the machine.
You may need to figure out how to trigger the "Idle Up" from the contactor control, or it will be awkward starting. I didn't see any link from the remote board to the idle control, but there may still be one that I didn't notice.
Looking at the HF-251D-1 manual, it looks like all that it cares about from the foot pedal is the contactor control. That contactor option they offer would be really nice if it were installed, it would take care of the on/off part with the HF control.
If you are planning to TIG weld outside, you need really good wind breaks, or you lose the shielding gas around your weld. My luck with TIG welding outside has not been great.
Good Luck, BobH
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I'm starting to think that's the only viable approach. Absolutely nobody offers the OEM remote control board, nor will anybody offer guidance on how to improvise one.. I've been studying the schematic for several days and still don't understand how the voltage regulation scheme works. The schematics aren't the clearest, but even if they were it's a real brain teaser. Some things just don't make sense yet, and one poster observed that the schematics "aren't always right" 8-( At some point I'm going to break out the meter and start measuring voltages while running.

I'm hopeful that a big enough resistance in place of R1 will reduce the output voltage to the point of extinguishment. It turns out one can still buy carbon pile rheostats rated 4 amps on Amazon, sold for controlling univeral-motor tools. For $20 it seems worth a try, but I want to be fairly sure of not doing damage with the experiment. It seems no harder on the machine than having a brush go open, but still I'm cautious.

Oddly enough that problem seems to be solved. The welder revs up when it detects a load on either the weld terminals or the 100Hz accessory outlet. Pressing the trigger switch for the HF251 makes it draw enough current to rev the welder.

I did manage to find a contactor listed for sale, but at more than $400 it seems worth trying to live without, at least to begin with. I can't help but wonder if a few starter relays in series with varistors across them might be a usable substitute.

I have the luxury of waiting till the weather is nice 8-)

With my thanks!
bob prohaska
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snip

snip

Digikey lists a 25 Ohm, 100W watt rotary variable resistor from Ohmite for about $92. This is what I used when I built a foot pedal for my Dialarc. They don't stock them, but at least they still exist. Surplus might be a better choice if you could find one.
You might try open circuit for a big enough resistance for extinguishment. Increasing the value of the variable resistor value a lot will compress the useful range of adjustment to a very narrow range of motion.
The contactor on my Dialarc was just a big 3 phase unit, I think it was an 80 amp unit with all 3 circuits in parallel.
I will take another look at the schematic on the circuit board. When I looked at it, I was more curious what the output looked like than the control aspects.
If you want to take this conversation to email, my address needs a little editing.
Regards,
BobH
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I've ordered the carbon pile rheostat foot control, just to try it. For $25 it seems a reasonable gamble.

One of the nice features of carbon piles is that they go open, or nearly so, when pressure is released. Whether the non-linearity will happen in a useful range remains to be seen. They're prone to flakiness, but at this stage I don't think it matters much, and they distribute dissipated power more evenly over the volume of resistive material.

Sounds like it must have been on the mains side....

There are two big puzzles for me: The first is that the voltage regulator gets signal from two places. One is a center tapped transformer that samples the 60 Hz AC when in generator mode. That signal appears to supply both a voltage sense and power to a 15 volt regulator that powers the op amps and biases the transistors. It goes away in weld mode, because the relay upstream disconnects the power windings while welding. Meanwhile a second signal comes from a dedicated "regulator power winding" that's always active, whether generating or welding. It seems intended to merely turn the field circuit full on, though just how it does so isn't obvious. I guess that competition between the two inputs provides regulation when generating, lack of signal from the center-tapped input lets the regulator run wide open.
The other puzzle is the importance of the CR3 contacts paralleling R1. It seems logical to suppose that CR3 would close while generating, giving field control to the regulator to produce output voltage. However the instructions explicitly state that the fine amperage control must be at 100% while in generator mode. The purpose of CR3 is thus unclear. The "Idle Lock" mode is intended for exclusive generator operation, but the fine amperage control must still be set to 100% per the operator manual and according to the schematic "Idle Lock" disconnects CR3 entirely.

We can take it off the record if you like, but I'd have been very happy to find a thread like this one.
bob prohaska
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