Reversing polarity on small welder

[mudtoy67]

I've got an old Astro Power Powermig 130 I want to use as a flux-core welder. When trying to use it the other day, it was welding horribly, so I did a little research and found the welder appears to be wired for DC electrode positive polarity, while the wire I'm using requires DC electrode negative. There are a few flux core wires out there that run DC+, but the ones I have seen are pretty specialized and not usefull for everyday/all position welding.

I want to just swap the ground (38) and electrode (51) wires around, but the problem I'm running into is the switch to turn on the feed control (30) gets its signal at A1 from the lead going to the electrode (51). This means that if I switch the ground and electrode wires, the current going through the switch and A1 is also going to reverse direction. So I was thinking I need to rewire the welder as seen in the lower diagram. The only problem I can see with this is that the wire going to the A1 terminal of the feed control (30) is now on the opposite side of the transformer (32) as it was before. Do you think this will cause problems?

If this can't be done the only other options I could come up with is to install a microswitch in the stinger which would then be separate of the electrode power. Or get a new stinger with a switch already built in. Or don't even mess with it.:p

http://i267.photobucket.com/albums/ii297/mudtoy67/wiring.jpg

[agjohn02]

is that your modified schematic or one you found somewhere?

[agjohn02]

drink your coffee, then ask yourself this. does a switch care about polarity?

[agjohn02]

in the modified version, A1 is still wired the same and A3 is wired the same but on the opposite side of the transformer

[mudtoy67]

is that your modified schematic or one you found somewhere?


drink your coffee, then ask yourself this. does a switch care about polarity?


in the modified version, A1 is still wired the same and A3 is wired the same but on the opposite side of the transformer

A new thought every three minutes huh?:flipoff2:

The "factory" schematic is the wiring diagram in the manual for this welder. The modified one I did myself.

I realize a switch does not care about polarity, but the thing I'm having trouble with is the fact the A3 wire will now be on the other side of the transformer. I'm worried that I'll send too much juice through the feed control.

I might be overthinking things though. IIRC welders are typically operate on constant voltage, right? So if the voltage is the same, and the resistance in the feed control is the same, then the amperage running through the feed control should also stay the same.:confused2

[sasquatch]

yes. I=v/r

[Reckless]

I know on some welders, like hobart, the wires are in the spool housing and its just a matter of switching the wires. But im going to take it that they arent in there.

[mudtoy67]

correct

[agjohn02]

I might be overthinking things though. IIRC welders are typically operate on constant voltage, right? So if the voltage is the same, and the resistance in the feed control is the same, then the amperage running through the feed control should also stay the same.:confused2

Mig is a constant current operation. stick and tig are constant voltage. Thats why you can change the heat (amperage) of a tig or stick weld by changing the arc length (resistance).

by altering the location of the transformer, you are just changing the voltage potential across the switch. transformers dont create power. i was going the say that same thing you just said about amperage staying the same and it not damaging the switch but i didnt want to be wrong and be at fault for damaging your welder, but i think you are correct. do it and report back.:flipoff2:

[robertf03]

if it uses a FET to trigger the motor, as any fine chinese welder should, switching the polarity will make it not work, as will too high a voltage at the gate.

leave the switch wired as is, and run an external wire to and from it if you have to

[mudtoy67]

I anticipated the polarity change, that's why I swapped the wires at A1 and A3. But the voltage was a major concern.

I stopped at radio shack on the way home and picked up a microswitch. I'll wire it up and let yall know if it works.

If you don't hear from me I've dun been electrocuted.:gigem:

[AggieTJ2007]

can you not dissonect the wire from the back of the feeder and switch with the ground. Probably to easy for this crowd but there had to be somewhere where the lead connects to the gun,

[agjohn02]

whoa, i saw a TLA in there. id go with that as im thinking in simple electronics terms.

[robertf03]

whoa, i saw a TLA in there. id go with that as im thinking in simple electronics terms.

tig?

[agjohn02]

haha, i knew i wasnt actually on your ignore list. you can't quit me.


Three Letter Acronym

[robertf03]

ur so smart

[mudtoy67]

Mission Accomplished!

I gave in and picked up a microswitch from radio shack. I figured this was the safest way to wire this welder and not burn it up. So I reversed the electrode and the work, then installed the microswitch in the stinger on its own circuit.

This was the problem. The single wire coming from the trigger got its power from the weld current and switched on the feed. Reversing the current put this switch on the high voltage side of the weld.
http://i267.photobucket.com/albums/ii297/mudtoy67/DSCN1979.jpg

Here's the new switch installed. I wrapped some tape around the conductor to make sure the switch wires wouldn't short to it.
http://i267.photobucket.com/albums/ii297/mudtoy67/DSCN1985.jpg
http://i267.photobucket.com/albums/ii297/mudtoy67/DSCN1986.jpg

Here's some practice welds. On the far right is the practice weld I did the other day when the polarity was wrong. Welds: (left to right) 1. grooved w/ two passes 2. flat surface pulling 3. grooved w/ one pass 4. flat surface pushing.

It looks to me like it's got good penetration, and they are pretty good looking welds (clean) for flux core.
http://i267.photobucket.com/albums/ii297/mudtoy67/DSCN1990.jpg
http://i267.photobucket.com/albums/ii297/mudtoy67/DSCN1991.jpg

[AggieTJ2007]

welds look good I like to clean them up with a wire wheel on the grinder and skip the chipping hammer

[DRAGOONRANCH]

jitterbug