Using welder as power supply

I purchased a $150-$200 or so Chicago Electric welder from Harbor Freight some time ago, and realized it didn't make a very good welder even when using the 240V off a generator. It wouldn't get much past the striking and ignition for a few seconds. Maybe I was using it wrong, but it did seem to have the current (about 90A max they say). It was enough when using off my home, it kept throwing the 120V breaker when I had it on that setting.

I was thinking of using it's output or power supply for some laser work, but was wondering if the output on these is enough to pump a gas laser.

It sounds like an arc welder (the type with the consumable electrodes or "sticks") If so, its probably a fat variable transformer in a box i.e low volts but high current out with a big croc clip to clamp on the steel. Not sure if you'd be able to use it it fire an argon without a lot or messin about though.

Yes, it's an arc welder. I believe it's rated from 90-120A.

I'm open to taking it apart and such, but definitely with caution.

I'm wondering if I ran the transformer backwards, if then I'd get more volts instead.

Quote:

---

Originally Posted by nanoWatt

I'm wondering if I ran the transformer backwards, if then I'd get more volts instead.

---

You'd actually get less voltage :)

The way transformers work is they have a primary and secondary coil. Ever see a tesla coil? In a tesla coil there is a bottom coil that is maybe 10-20 turns and the secondary coil (the big mast part) that has thousands if not millions of turns. If the ratio of turns is 1:10 you will (in theory, neglecting losses) have a 10x voltage increase. That is 120v input would equate to 1200v output, and so on. This allows the really high 90-120amps on a standard 20amp 120v circuit. because 120amps at 1200v is really 10amps (again neglecting the losses from the magnetic transformer) on the 120v circuit.

Now if you reversed it 120v into the secondary coil you now have a 10:1 ratio, and you would inefficiently step 120v down to 12v.... so you could start your car or something.

If anyone notices any errors please correct me. It's been a long day :D

-Max

Quote:

---

Originally Posted by mliptack

You'd actually get less voltage :)

The way transformers work is they have a primary and secondary coil. Ever see a tesla coil? In a tesla coil there is a bottom coil that is maybe 10-20 turns and the secondary coil (the big mast part) that has thousands if not millions of turns. If the ratio of turns is 1:10 you will (in theory, neglecting losses) have a 10x voltage increase. That is 120v input would equate to 1200v output, and so on. This allows the really high 90-120amps on a standard 20amp 120v circuit. because 120amps at 1200v is really 10amps (again neglecting the losses from the magnetic transformer) on the 120v circuit.

Now if you reversed it 120v into the secondary coil you now have a 10:1 ratio, and you would inefficiently step 120v down to 12v.... so you could start your car or something.

If anyone notices any errors please correct me. It's been a long day :D

-Max

---

Assuming for simplicity it's an isolated 10:1 step-down transformer, not an autotransformer, the secondary would produce 12VAC at a 100A capability. Reversing this would cause it to simply blow up, or blow a breaker, because the transformer core would reach magnetic flux saturation well before the primary reverse EMF could limit the input current. (it's just not designed for that.)

Quote:

---

because 120amps at 1200v is really 10amps...on the 120v circuit.

---

http://hacylon.case.edu/fail.jpg

Power must be conserved, with a 1200V secondary, you would get 1A MAX.

For example, the lower number of windings in the secondary decreases the available voltage at the secondary, but increases the available amperage. Likewise in a tesla coil, the secondary has a few orders of magnitude higher voltage, but at the cost of a few orders of magnitude lower amperage available, compared ot the primary.

Just have a look at one of the old fashioned soldering guns:
http://hacylon.case.edu/soldering_gun_1.jpg
The secondary is a few turns of very thick copper wire, which allows a huge current (at low voltage) to heat up the thinner soldering tip.


To the OP: Without some real measurements and knowledge of your transformer, it's not a good idea to use it as a power supply.

Hmmm maybe I should get some sleep... hahaha... not tonight... got too much to do...

Thanks for correcting me... thats why I put in that little disclaimer :)