Welder won't excite

[busy44]

I was given a miller 225 bobcat that runs good but wont produce ac or weld no current. I have megged the windings and seem good. I tried to excite with a 9v battery no luck. My question is does the engine alternater have anything to do with the initial voltage? nothing seems burn't and the guy that give it told me the circuit board had been changed. any ideas where to start. Do i need to ohm any thing? I have the schematic. I hate to throw it away.

[maddog]

If you have a schematic you're half way
there. You should be able to answer your
own question with that in hand.

JMO

[Thrud]

Check the rectifiers if this is an AC/DC machine - they could be pooched.

Otherwise get a meter out and start checking for voltages from the generator forward.

[GMSteve455]

I'm not sure I understand your question about the alternator. Initial voltage of what? I'm not too familiar with this machine but have worked on a number of AC motors and generators.

Do you get anything out of the receptacles on the front? I've worked on a generator where I was getting minimal voltage around 3 volts. I found one faulty steering diode in the circuit and I had to re-excite the armature winding to get it to work. The low magnetism in the armature was enough to produce the 3 volts out but not enough to excite the armature to the point where it would break over to full output.

Basically the way my generator worked was that the armature had some residual magnetism which excited the field. The field windings fed back to the armature through steering diodes and at a certian RPM, the voltage going back to the armature was enough to get it to breakover and start making normal output voltage. After replacing the diode, I was able to charge the armature and magnetize it with a variable output power supply. I left it "charge" for a few hours till I thought I had enough residual magnetism to get it to work and it did.

Hope that made sense. I'm not sure if this is the same setup as your bobcat or not but it should be similar. I'd check to see if there are any diodes in the generator circuit. Forget about the welder circuit and see if you can get the generator working, once that is fixed, the welder will probably work as well. If you want to send me a picture of the schematic, I might be able to help you more.

Good luck!

Steve

[mattc]

on my blue star it has a switch that you switch between welder and generator and the governer is manualy switched also if they are not set the same nothing will work (possably stating the odveous but easy to over look)


Matt in AK

[busy44]

thanks guys for the help great site

[ahidley]

Busy44 if your throwing it away, please throw it my way.... willing to pick it up if its not too far.