low buck tig foot pedal build for old Mag Amp Lincoln

[sd455dan]

Wanted to weld aluminum with the old Lincoln that I picked up,as a back up for my little inverter welder.

Originally thought it would be easy because my sister has a newer Tig 300 with a foot pedal she was willing to lend me.

Unfortunately my old lincoln is a Mag amp controlled unit which requires a wire wound rheostat for current control. So had i hooked up the newer foot pedal and tried to weld the variable resistor would have been damaged.

This led me to search the internet for home built foot pedals since no ancient factory K 746 foot pedals seem to be available. I was able find an old military surplus Rheostat with the correct 1000 ohm resistance and ordered it.

Hooked it up with a test cord and sure enough the weld current could be controlled with no over heating of the the rheostat.

So threw together a wood based pedal to test the viability, ( please don't laugh to hard) know it looks like ----


Using a couple brackets supporting a pin vice clamped on the control shaft. the pin vice has a hole through the shaft to maintain the rheostats position.
Any way it worked. The only real problem was the heavy duty carpet thread stretched, so replaced it with 10 # steel fishing leader line.


Feeling fairly sure it was going to be ok , I purchased some 10 and 11 gauge steel from leftover cut offs from our local Pacific Steel.
Scribed some pieces out and plasma cut them with my lotos combo unit which did a decent job with fairly minimal dross to knock off.



Next added the rheostat and fishing line , springs and such

and here it is next to the Lincoln foot pedal


my first attempts at welding some Aluminum .065 circular punch outs with the new pedal


I have a lot to learn and lots and lots of practice to do, but i was able to stick 2 Aluminum pieces together without blowing huge holes :cool2: (at least not on all of them:laughing

The total cost for the pedal was under $ 40. and ended up with about 1/2 of the 11 gauge steel unused.


I think this pedal will also work for my Lotos, LPTDC2000 for tig since the variable resistor in it is also a 1k unit.

The rheostats are electrically noisier- but going to try it, so ordered up some aviation 5 pin connectors that match the inverter welders connectors.

So far the pedal is working great and will also add a micro switch to free up my tig hand to concentrate on the arc and not holding the button down.

I really enjoyed building this

 

[Mysfyt]

Me like! Love it when people roll up their sleeves just like you did and build it themselves. How did you find the resistance value?

 

[sd455dan]

Me like! Love it when people roll up their sleeves just like you did and build it themselves. How did you find the resistance value?

Thanks,
as for the value, It made sense that the resistance would match the value of the main amp control in the machine.
After checking the newer model foot pedals resistance and comparing it to lincolns schematics for the SCR controlled Tig 300s they were a match @ (10,000) ohms.
The older Mag amp controlled units are much lower- in this case 1000 ohms.

 

[Big Barn]

Nice work!! And great photos.

I LOVE it when something comes together so well AND saves money to boot!

Terry

 

[sd455dan]

I think this pedal will also work for my Lotos, LPTDC2000 for tig since the variable resistor in it is also a 1k unit.

The rheostats are electrically noisier- but going to try it, so ordered up some aviation 5 pin connectors that match the inverter welders connectors.

So far the pedal is working great and will also add a micro switch to free up my tig hand to concentrate on the arc and not holding the button down.

I really enjoyed building this

Update:

Ordered up a micro switch (normally open) and mounted it into the foot pedal, also replaced the pin vice with a more robust shaft to actuate the Rheostat.

Sourced some 5 pin chinese (aviation) connectors that match the Lotos 3 in 1 inverter and then tested the footpedal on the Lotos tig,

It works great.
varies amps from 11 to 200 and the foot pedal also triggers welder current:cool2:

Next hooked up the 5 pin receptacle in place of the 3 pin Leviton industrial receptacle on the Lincoln tig 300 300. ( hard to find 3 pin plug) and the only source I could find was $35... Ouch
the new paired 5 pin units were a total of $3.50 and that is for 3 SETS male /female Including the shipping. This also allows either foot pedal control of welder trigger, or using the button on the torch.

I found repair job to do of an aluminum alloy scoop shovel that was used (over zealously) clearing snow.
The footpedal and lincoln did great and the 2 piece shovel is now one, could not have done it without the footpedal to control the amps.

Next going to wire up another 1 k Ohm resistor or rheostat on the side of the foot pedal the Lotos,
this should allow a % of max amps to be set for the current meter and allow the foot pedal to operate within the range set without modifying the internal wiring of the inverter- (so that the warranty is not voided).

Not sure if this will help others with 2 welders that have the same value Rheostat/variable resistor- but it did work for me,
and may be a way to get their old mag amp controlled welder to work with a home built foot pedal if they can't source a new /used one.
cheers

 

[Millnturn]

Brilliant job, love the outcome! One suggestion: if you find it's too sensitive (short pedal throw), you could add a larger pulley to the rheostat shaft. The larger the pulley, the more pedal travel required to turn the rheostat (less sensitive, more precise control).

 

[sd455dan]

Brilliant job, love the outcome! One suggestion: if you find it's too sensitive (short pedal throw), you could add a larger pulley to the rheostat shaft. The larger the pulley, the more pedal travel required to turn the rheostat (less sensitive, more precise control).

Thanks- when I did the re- wire with aviation plugs, re- sized the rheostats shaft size larger.

Here is a comparison of the factory Lincoln foot pedal/ and home built unit at extreme travel :

The range matches the Lincoln very closely, and I really like the way Lincoln designed their pedals , such that you can put a full weight on the pedal and just rock your foot either way a little to adjust.

Most of the units sold for the chinese built units have a combersom large box that is hinged at the heel end of the pedal.
That style looks like it would be very uncomfortable to use for very long-, since you can not put any real weight on it and the control cannot be accomplished by foot rocking.
Any way the pedal is working fine for both welders -but do want to put another 1 k ohm rheostat in series so that the Inverter welder can be set at any desired max amp and then vary with foot pedal with in the range dialed in.

 

[arkydog]

i have got an old airco ac/dc heliarc high frequency tig welder with no provision for foot pedal. is there anyway to figure a foot pedal something like yours? if not, no problem. just have to start and stop with flip of wrist.

 

[sd455dan]

i have got an old airco ac/dc heliarc high frequency tig welder with no provision for foot pedal. is there anyway to figure a foot pedal something like yours? if not, no problem. just have to start and stop with flip of wrist.

The first thing I would check is if the airco has a control rheostat, and what the wattage or alternatively the current rating is.
If it is not to high powered a smaller version may be available . Would also need to determine the Ohms across the outside terminals.

when I was doing research on the Lincoln, ran across some posts about aircos and at least one model had a huge high powered rheostat
Hopefully yours is one with a small rheostat.

You mentioned that the unit has no provision for a foot pedal? So no remote switch? and no place to plug in a foot pedal?