Newbie extension cord question

[matt7340]

I've got a Lincon 135 that I'm using at home, and I'm running it off a 100ft 12AWG extension cord. I've read that the 110V machines are more sensitive to voltage drops and I'm wondering if thats my problem.

I can lay a great bead at school using their 110V MIG, but I come home and it seems I can't get good penetration. I think I'm getting a "cold" bead. Hammer test causes a break right at the bead, using 14ga coupons.

So I think an extension cord may be the problem. Do I need to use a 10AWG cord to prevent voltage drop over that distance?

[Sandy]

Matt,

Yeh that's sounds like a border line situation if nothing else. Lot of "depends" type of issues here too. 100 ft of 12 awg shouldn't be a problem all by istself, but if your starting point is off the end of a long run of 14 awg to begin with or power in your local home area is running a little lower than the power at school is, or both of those combined ----bla bla bla, all sorts of things can be looked at.

There are voltage drop cals out there you could use to verify what your thinking. I don't have one handy right now, probably do at home and can check when I get there this evening.

If you have a meter you might take a reading at your school, then take one at your home panel, then another at the place you are plugging your cord into that would give some data to add to the problem to be solved.

[slamdvw]

At that distance, I'd say yes... go with the 10AWG cord. If it's similiar to my Miller 135 it'll pull close to 20 amp running full tilt. Just out of curiosity, what gas and/or wire are you using at home vs school? I would say you could cheat and use CO2 at home and it *might* help. Seems to burn hotter for me anyway.

[smithboy]

Here is a thought. If you have an outlet near a place you can weld, you could just do a simple test bead with and without the extension cord (keeping feeder settings unchanged). My guess is that if you are near some limit, you will notice a difference just by adding the 100ft of additional wire. Not 100% conclusive, but it is a quick and easy check. If the two welds are about the same, the problem may be at the line (voltage or whatnot) and might require more testing. Would you agree with this, Sandy???

[matt7340]

Pulled out my meter and checked in house (122V), outside outlet (123V) and at the end of the extension cord (also 123V). I'm not too familiar with AC but it seems like this is okay, since there is not voltage drop.

Smithboy, good idea, I should've tried that before posting. Hopefully Sat. I can do that.

Slamdvw, I'm using 0.025 and C25, school is 0.030 and C25, perhaps that difference is enough to throw me off (I'm still pretty new to this stuff).

Thanks for the ideas, now I've got some direction.

[Sandy]

If the two welds are about the same, the problem may be at the line (voltage or whatnot) and might require more testing. Would you agree with this, Sandy???

You're right ;) . Moving the welder is probably the quickest and the real acid test. Measuring sometimes can but doesn't always prove anything in advance.

Couple of reasons why; The voltage drop under load is really what you want. Open circuit AC voltage will drop very little with nornal household distances. Significant open circuit voltage drop in and of itself will indicate that you do or will very likely have a problem with something like this welder. Lack of a voltage drop does not necessarily mean that you won't. Probably not a problem but not a for sure guarantee. Open circuit AC voltage can walk right across a contact type joint and reflect almost no detectable loss. There is no current there to force the issue to the top. Once a load is put on where curent needs to flow these contact joints will start arcing and losing their ability to carry a load.

You need someone to watch the voltage under load at a known good point and determine what the acceptable voltage drop would be. Then move to the end and do the same test. There is usually a quick drop (lights flickering effect) then it comes up to just under open circuit and holds. With a bad joint it may drop drastically, then only rise somewhat and possibly waver. Wavering is tuff to see on a digital meter.

Bad joints might be where two wires are only butted together and a wire nut put on loosely, or a wire run through multiple recepticles with the back stab type connections. Things like that. Things that would never show with light loads like bulbs and such.

That's why the voltage drop calculators help a lot. Pick your wire size, pick your distance, pick your load guestimate and see what the drop will probably be.

[awright]

Great recommendations above.

My handbook shows resistance of copper wire at room temperature to be very close to 1.64 ohms per 1000 feet of #12 wire and 1.0 ohms per 1000 feet for #10 wire. For a 100 foot extension cord (at room temperature, 20 degrees C), the total length of wire is 200 feet, so resistance of the wire alone (neglecting contact resistance of the plugs/receptacles) would be 0.328 ohms for #12 and 0.2 ohms for #10. These would result in voltage drops at the machine drawing 20 amps of 6.56 volts for #12 and 4 volts for #10. The difference is not trivial, but not all that large, either. While larger is always better for long extension cords, it's hard to believe that a 4 or even 6.56 volts drop would affect your bead that much unless you were already right at the limit of the machine's capability.

Contact resistance could be a more significant factor. Do the plugs feel like they are making solid contact when you push them together? Is your receptacle, house wiring, and circuit breaker rated for 20 amps? A 20 amp house receptacle will have one straight slot and one T-shaped slot. Two straight slots indicate a 15-amp receptacle (although it may be supplied by a 20 amp breaker and #12 wire). How long is the wire from the breaker to the receptacle, and is it #12 wire?

Having someone else read the meter (or using a digital voltmeter with a min/max memory function) while you are welding is the proof of the pudding.

awright