I need some help from a person that knows electrical problems. I have a used welder that I am refurbishing. I have made a repair to the interface board that had a blown capacitor. When I turned that welder on it seemed that everything was okay with the fix so I am testing the weld capabilities. As I don't have it set up for the tig yet, I am just testing the "arc" functions. When I selected AC and used a 7018 3/32" rod I was able to run a bead. When I selected DC (straight polarity) or DC (reverse polarity) and turned the welder on it flipped the circuit breaker. The question(s) that I have:
1) Is this a dead short in the rectifier bridge? diode? If so how can I check the fault?
2) Can can check to see if the high frequency works using the "stick" function?

Thanks for any help.

Al

It doesn't indicate a dead short. A 250 amp bumblebee welder draws
a hefty initial current. What kind of circuit do you have it plugged
into?


hd_74al wrote:
I need some help from a person that knows electrical problems. I have a
used welder that I am refurbishing. I have made a repair to the
interface board that had a blown capacitor. When I turned that welder
on it seemed that everything was okay with the fix so I am testing the
weld capabilities. As I don't have it set up for the tig yet, I am just
testing the "arc" functions. When I selected AC and used a 7018 3/32"
rod I was able to run a bead. When I selected DC (straight polarity) or
DC (reverse polarity) and turned the welder on it flipped the circuit
breaker. The question(s) that I have:
1) Is this a dead short in the rectifier bridge? diode? If so how can I
check the fault?
2) Can can check to see if the high frequency works using the "stick"
function?

Thanks for any help.

Al

Mike: The AIRCO 250 AC/DC welder is single phase 220v, nothing real special on this part of it. After I posted this I took the Bridge rectifier out of the welder to test the power diode and the SCR's. This welder has two SCR's (hockey puck style) mounted in the aluminum heat sink.

Here's were I need some help. I tested the power diode with a multimeter and only got a reading one way. That should mean that the diode is okay?

To test the SCR's I used a 12v car battery, a 12 volt light and made two connections from the positive lead; one with a resister (1k 1/2W) to trigger the gate (white lead) and the other with a resister (100, 2w) to the device (red lead). The negative lead was to the metal case of the device. With the connections intact I took the one lead (white) and was able to get the lamp to light but not stay on. It should stay on with a good SCR, correct?

The other SCR did not light at all. Am I on the right track?