Adapting a foot pedal

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Does anyone know if the miller rcfs 5 foot pedal can be adapted to work as an rcf23a foot pedal?  They both have the same number of wires and both work on the older millers, just different older millers.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Does the manual for both include schematics?  If they do, I can tell you one way or the other.-Heath
Reply:Nope.  No schematics available.  I found a cheap pedal on ebay and thought I'd give it a whirl.  I figured it would probably work on either my dialarc or powcon or I could just re-sell.  Little projects....I thought I had found a good old rcfs5, but I am having second thoughts about that now.  It looks like the same thing as the rcf 23 ("2" pin connector + "3" pin connector), but it has a single 5 pin connector.  Several folks I have talked to so far have said that the rcfs5 and rcf23a are very different.  The 5 uses a potentiometer, where the 23a uses a a high watt rheostat.  Now I am no electronics expert, but when I look at the innards, it dont look like a pot to me.  I might take pictures of the inside and post just to be sure.  More later on this.Smithboy...if it ain't broke, you ain't tryin'.
Reply:A potentiometer and a rheostat are nearly the same damn thing.  I bet it could be made to work.I'm probably going to punt when it comes time to get a foot pedal and just use a guitar volume controller with custom innards.-Heath
Reply:I had been thinking sewing machine pedal myself...until I saw this one.  The big difference I am currently reading on other sites is that the pot. is used on solid state machines and acts almost like a sending unit or relay.  It adjusts "a signal" that is read by the circuit board and the board adjusts the amps....so, in that case it can be a very cheap (low capacity) pot.  Whereas, the older rheostat based pedals control the amps directly without the circuit board as an intermediary.It sounds suspiciously like miller is saying early on, the pedals were expensive because the parts were so heavy-duty and expensive...now they are expensive because everyone is used to paying that much...so, why change and upset "the force"...I have looked carefully at the pot. on the powcon.  They look like something that could easily come out of a stereo or buy at radio shack for $3.  My miller hand control (rhc3) has a big mutha of a pot./rheo. that is just about the same as what is in the dialarc itself...in fact, it may be the same part for all I know.  It looks pretty expensive, might weigh a pound or two and is made mostly of copper or plutonium or maybe kryptonite.  One thing I do know is that after an hour or so of pretty continuous welding, it gets pretty hot. and, so, a simple little $3 pot would not work for long doing that job.I am going to take my pedal apart tonight and take a bunch of pictures and post them so at least the next person will have something more to go on.Smithboy...if it ain't broke, you ain't tryin'.
Reply:I believe that on the Powcon units, the remote control signal is 0-10VDC and I don't think there's very much current at all.  If someone were using a rheostat to handle the entire welding current then I can imagine that part would cost a damned lot of money.  Good high current rheostats can run well over a hundred bucks each.  Get some photos, and I'll see if I can come up with something.-Heath
Reply:Here are the pictures of the interior of my new old pedal.  It looks like a big honkin' pot/rheo or what ever you call that thing.  There are 5 wires.  3 go to adjust the amps, and 2 go to a switch for whatever you want to turn off and on (high freq, shop lights, food processor...whatever).  This doesnt look like a $250 accessory does it???  But that is what it costs new.To me, It looks pretty hefty.  It doesnt look like something you might find in a stereo...I am guessing it should work fine for controlling the amps directly, but a bit of reassurance would be nice...I know the switch is heavy duty enough for high freq.  Heck, just about any switch is.This looks pretty easy to build.  Depending on what that big white thingamabob costs (technical jargon), seems like you might be able to rig up something pretty easily.Note: in the picts, the foot pedal part is on the bottom.Another note:  There is a second opening in the casing for a second wire.  Looks like the same housing used here is used for the 23a.  I bet the only difference is the connector.... Attached ImagesLast edited by smithboy; 10-20-2005 at 02:20 PM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:What you have there is essentially two parts.  There's the switch, as you noted, and the potentiometer (not a rheostat).  The big white thingamabob is a wire-wound resistor, probably made of carbon.  As the wiper arm moves up and down the resistor, the resistance between the green, black, and white leads will change.  I can't quite tell how the foot pedal goes on, but as its shown in the photo, the resistance between the green and white leads would be low and the resistance between the green and black leads would be high.  As the wiper moves down, the resistance between the green and white leads will increase and the resistance between the green and black leads will increase.  That particular foot pedal can likely be adapted to work with any kind of welder.  What would be required depends on the resistance of the pot.  If I understand correctly how most TIG welders are controlled, there's a 10VDC lead coming from the welder and a 0-10VDC lead that goes back into the welder.  That could likely be directly connected to the pot with the 10VDC +V going to the green and white lead and the 0-10VDC feedback going to the black lead or vice-versa depending on where the zero position of the wiper is.  If you seriously want to give this a whirl, I can help.  You'll need a multi-meter, and I'll need to know what power supply you want to control and I can probably come up with an appropriate schematic for you.-Heath
Reply:Also wanted to add, that yes, something like this would be pretty easy to build.  I could spend five minutes and five dollars in an electronics surplus store (common in the silicon valley) and come up with something suitable for the purpose.-Heath
Reply:The welder is a dialarc 250 (an "old school" ac/dc welder) with no computer-type printed circuits.  I have a hand control that has a similar "wiper/resistor", I think.  It's just roundish (for a knob) rather than long and straight (for a pedal).  It also uses three wires to control the amps.  I wired a switch to control the hi-freq.  The hand control works fine.It might be a simple plug and play switch for the three wires.  My hand control activated by a switch on the welder that takes the main control out of the loop and places the hand control into the loop.  I have a wiring schematic for the remote plug.  I was able to install it pretty easily (years ago) and its very simple.  I think maybe all I need to do is put the right plug (three prong) on the three wires comming from the resistor.  Then add a second plug for the hi-freq switch to go to my HF unit.I guess I am just wondering if this "resistor" will handle 30-250 amps, like my hand control.  How can you tell if a resistor can handle big amps other than test by fire, so to speak?BTW, If you could make these for less than $20, you could start a pretty lucritive business just in supplying these for old welders.  These old ones often go for $100 on ebay...sometimes for more.  I talked to the fellows at the welding repair shop, and they said they sell them for $150 whenever they can get them.  Appearently, even though these things are as big as a concrete block, they tend to get misplaced or something.Thanks for the info, by the way.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Just based on the size of the pot, I suspect that it can handle a great deal of current.  If you have photos of the hand control components, I could give you an accurate description of how to adapt it.  You probably want to use a meter to measure the resistance of each one.  If the resistance isn't high enough, you could potentially end up with too much current going through the foot pedal and let the smoke out of it.-Heath
Reply:Here is some more info about the foot pedal and hand control for reference.  The resistance, as measured with my multimeter, for the foot pedal goes from .943 (not depressed)to .001 (fully depressed).  The hand control goes from .18 at the lowest setting to 0.0 at the highest setting.  I am not sure what the units are on my multimeter, so I dont know if it's ohms, kohms or what, just keep that in mind.  So, based on this, the foot pedal should have a much greater effect on the welding current, right (wider adjustment range)?  I know I cant currently shut the welding current off with the hand control.  I can only reduce the welding current to a fraction of the max current setting on the welder's main control (at least that appears to be the way it works).  The resistor in the foot pedal has a rating of 1000 ohms (see picture).  Attached are pictures of the interior of my hand control (this is the one recommended for my dialarc and it works...It just doesnt have a wide range of control).Even if I cant end up using this foot control on my welder, I think posting these pictures will be helpful for folks looks into foot pedals.  Miller and lincoln do not post any information about how these things work.  The user manuals are all but non-existant on the web. Attached ImagesLast edited by smithboy; 10-22-2005 at 08:10 PM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Isn't the foot controll switch often used to start the current flow?  At least that's how mine is....Although, it would be prety cool if it started a food processor.As for the resistor, it's 1k which is common, but of a high amperage, which can get expensive if you mess up 2 or 3 of them...
Reply:Yes, it is.  But on my welder, I don't have a remote for current control.  So on this pedal, the switch won't be used for this, unless I hard wire it that way.  I think on the dialarc hf, there is a remote current control, but mine is not the hf...it has an external add-on hf box.  Since I mostly do aluminum when I tig with my dialarc, I just figured I could make it start the hf.  It is not actually necessary, cause I could just flip the hf on and use the pedal for amp control.  I just have this problem with having an extra couple of wires and a switch not controling anything.  My main concern is controlling the amps without burning up the resistor.  The switch can remain unused.Or,.......I could put a disco ball, lasers, and a cd player with Frankinstien cued up on that switch and really get my moneys worth out of that thing.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Halbritt,I snagged a link to the miller manual for the rfc23a.  Man, these things are hard to get out of miller sometimes.  It looks like my pedal is the same as the 23a, except the 23a separates the wires into two connectors.  The internals look the same.http://www.millerwelds.com/om/o826t_mil.pdfI have included the link for anyone else who might be interested.  Does anyone make these big variable slide resistors anymore???  Or, is there a better thing to use now.  I was actually thinking of building one for the machine (also a dialarc but OOOlder) I gave my dad as a little project....Smithboy...if it ain't broke, you ain't tryin'.
Reply:Just looking at the AWG requirements of the cord it doesn't look as if the foot pedal takes the full welding current.  10AWG at 100' sounds more like 20-30 amps to me.  If you get this one working, you can throw a clamp meter on one of the leads to see how much current it's really pulling.  That'll help you size the adjustable resistor required.  It might also be nice to see what kind of voltage is passing through as well.I'll poke around for a pot or adjustable resistor suitable for this purpose.  I'm sure someone makes 'em.-Heath
Reply:I think you are probably right on the current.  There is no way all current could flow through the wires in the foot control and remain in a solid state.I was kinda surprised when I got a reading on my ohm meter of .001 to .943 given that the manual says from 0-15 ohm for the 23a and 3a.  Maybe I dont know how to read my own meter.... I have got to read more about electricity anyway.  As much as I am around it, I should educate myself.  Is there a good book or website for learning the basics (or advanced basics) of electric circuitry and stuff.  I really dont know where would even be a good starting point.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Odd, I posted something earlier to this thread, but I guess it didn't stick.  I'm poking around the different places to see if I can find a source of these pots.  I'll also ask my EE friends and see if they know something.  I'd wager that guy can handle 20-50 amps or so.It'd also be possible to build one, but that would be a bit of a pain unless you really, really cared.-Heath
Reply:Results of the foot pedal conversion:Well, it was a snap.  I cut off the 5 pin connector and put on the 3-pronged plug (noting wire colors in the manual from miller), and added a second home-brew plug for HF.  I plugged it in and went to town.  I tested it using stick, cause I could not find a single piece of nice clean scrap, but I noticed that the amps adjustment with the pedal appeared to be more non-linear than the hand control or the main control on the machine.  The amps came on slow early in the pedal and quickly toward the end.  The other pedals I have used were more linear in thier adjustment of amps.  I guess this is better for thin stuff cause it gives more adjustment at the lower end of the amp range, but I guess I'll have to see how it works for thicker stuff.  I wonder if this is simply a characteristic of resistor-based controlers versus other types or if it was designed that way to begin with. After testing it, I realized that I was welding near lots of flammable stuff, so I decided to clean up my shop before starting anything serious.Last edited by smithboy; 10-31-2005 at 10:46 AM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:A current meter might help you figure out the range more accurately, but just based on what you're describing, I suspect the problem is that there's a lot of resistance over the range of the rheostat than what your welder would normally have.  It probably starts off with much lower current than you would expect.  You can fix this by putting a power resistor in parallel with the rheostat.  Sizing is going to be important, so it'd be really nice to know how much current and voltage is flowing through it.  If you have a decent multimeter, it should have a shunt current meter that's capable of something like 100A.  Otherwise, you'll need a DC clamp meter, if you have one.  I'm betting that there's 20 amps or so going through that.  Measuring the voltage through the range will also be needed.Assuming your initial reading was correct and the max resistance is .943 ohms, then a 1 ohm resistor in parallel will make your max resistance somewhere closer to .5 ohms giving you more granularity in the range that you're looking for.  If you really wanted to get clever with it, you could throw in a couple of pots and build a voltage divider network that will allow you to set a min and a max range and get a great deal of granularity through that range.If you have difficulty finding a power resistor that's suitable locally, I can send you something.  New ones aren't really cheap, and I have several.  If I don't have what you need, I can pick one up at an electronic surplus place that I visit frequently.  Generally, they run a buck or two for precision ones potted and mounted in an aluminum casing.-Heath
Reply:I am looking into the clamp meter.  I only have a cheap home depot $10-$12 multi-tester and it appears to be on the fritz...especially the ohm meter.  I can hit it and it works....then it doesnt again.  Sounds like I got what I paid for.  Is there a clamp meter that would be good for use with both household current and welder currents.  I looked at the Flukes and they seem overpriced for the features, but they also seem to sell pretty well.  I have been looking at the Ideal 61-734, because of its 400 volt capacity.  Here is one that I was looking at...http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7557631356I noticed that there is a pretty large price differential for clampmeters that do all four, ac and dc amps and volts.  Most do volts, but only the pricier models do dc amps.  Would having that option be a very valuable thing?  Any recommendations???Smithboy...if it ain't broke, you ain't tryin'.
Reply:I've been looking for one myself that does DC amps.  The problem with DC amps measurement is that a current transformer won't work.  I think they use a hall-effect sensor for that.  Otherwise a shunt ammeter would work for relatively low currents, but not quite as well for welding currents.  Radio shack has some decent multi-meters for cheap.  I really hate to recommend their stuff, because it's mostly crap, particularly the electronic components, but they have a decent multi-meter that's $50 that does RS-232 data logging which is a feature that can't be find on anything short of a $250 Fluke.Having a decent DC clamp meter would be a nice feature to have to measure welding current.  I'm going to get one at some point so that I can make a decent door chart for my welder.  As I stated, a shunt ammeter in a standard multimeter might suffice for this particular application.-Heath
Reply:I had a similar problem not to long ago and this is what I came up with:http://bbs.homeshopmachinist.net//Fo...ML/013711.htmlMy pedal had a 2500 ohm rheostat in it and I needed a 1000 ohm. Man, that 1000 ohm slider you have could have saved me some work...You need to call Miller and talk to someone in the parts/repair department and find out the wattage and ohms of the pot in the pedal. It took me a few days of calling to get the info. My welder is a Lincoln so I can't really help you with the specs of your Miller. I just hacked up a Miller pedal  My old Idealarc is of similar vintage to yours because it has the 2 big plugs that go to the welder.Good luck! At least that big honkin' pedal has plenty of room in it for modification!
Reply:Wow!great post and pictures.  That slide-gear thingie is a hoot.  I might have one of those myself.  NEW PROJECT!!!Last edited by smithboy; 11-03-2005 at 10:08 AM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:If you need 1000ohms and you have a 0-2500 ohm resistor, you can put a 1500ohm resistor in parallel with it and get 0-937.5ohms rather than 0-2500.  You can use this tool to calculate parallel resistance:http://www.1728.com/resistrs.htmBoth parts should be able to handle the full amount of current as there'll be a current imbalance between the two.-HeathWow, so I could have just gone to Radio Shack and soldered in a resistor to get it working?Oh well, it was fun to build and it works...
Reply:Yup.  Though you would've probably needed something a little beefier than what's available at Radio Shack, but that's about the sum of it.-Heath
Reply:Those are neat sites.  I'm going to cut down the code the the bare basics and put them on my palm pilot to make a calculator function.Smithboy...if it ain't broke, you ain't tryin'.