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#1
08-21-2012, 01:48 AM
 soutthpaw WeldingWeb Artisan Join Date: May 2010 Location: Fountain, CO Posts: 3,377
Tig pedal question. 15 vs 20 ohms

Ok so I got my 330abp up and running today with an old off brand pedal that had 2x 20 ohm circular wound resistors in it wired in series. I changed them to a parallel setup for 20 ohms instead of 40. But my 330 abp specs a 15 ohm resistor.
The 3 prong plug arrived today and I got to test the pedal out and it seems to work fine. Just wondering if anyone knows what difference or if there is any negative effects to running it on 20 ohms instead of 15?
I have a 15 ohm resistor from an old 3 phase miller I scrapped if needed but would require quite a bit of pedal modding to make it work which I am trying to avoid
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#2
08-21-2012, 09:48 AM
 blasphemy000 WeldingWeb Journeyman Join Date: Sep 2011 Location: Home, PA (Yes, that's the name of the town.) Posts: 189
Re: Tig pedal question. 15 vs 20 ohms

(2) 20Ohm resistors in series will give you 40Ohms. Where as (2) 20Ohm resistors in parallel will only give you 10Ohms. The formula for calculating total ohms in a parallel setup is:

1/((1/R1) + (1/R2) + (1/Rn)) for as many resistors you have wired in parallel.

So for (2) 20Ohm resistors in parallel you would have:
1/((1/20) + (1/20)) =
1/(0.05) + (0.05) =
1/ (0.1) = 10Ohms

As far as how it will effect the welder using a different ohmed resistor than is specified. I don't really know. When I ohmed out the potentiometer in the foot pedal on my Airco I got a total resistance of 23.7KOhms, but when I bought a new potentiometer for it I replaced it with a 25KOhm one without any problems.
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