Welder Problem Part 2

[DRussell]

The welder is a Century AC/DC 295. You can read the post below for more info as well, but the DC side of the welder will not weld, there is no spark at all on the DC side. The AC side works fine.

Pardon what might be considered a stupid question, but I'm a total newbie on this kind of issue. I've attached a couple of pictures of what I think are the diodes in the welder. Can you confirm that these are the diodes? There are four of them in there. I've placed yellow arrows pointing to them. The size of the round part of these would be about 1 inch high and 1 inch wide and the wire coming off of them is about 3-4 inches long.

I did inquire with a local shop that works on welders. Just an estimate to figure out what is wrong with it is 110 dollars and I was told the price to fix it would very likely be more than the machine is worth. Getting into this level of electrical diagnosis is outside of my comfort zone for sure.

These appear to be very easy to remove, just a nut on the diode end and a bolt through a wire strap on the other end. If these are the diodes, how do I go about testing them to find out if they are bad?

 

[old]

That may well be one of the diodes can't really see it all that well

 

[Jeff NWOH]

Those are your diodes. You should be able to check them with a multimeter. They should have continuity in one direction but not the other.

 

[Janicholson]

Take off the braded lead, then Set the meter RX-1 (lowest Ohms Setting) and measure with red lead on the base mount, and the black lead on the braid. Record the reading. The do the opposite and record. In one direction the meter should read less than 1 ohm. in the other more than 100 Ohms. 2 of the 4 can be reversed in polarity, but all should be about the same readings. Jim

 

[DRussell]

Thank you for the detailed instruction. I will test it and report back, might be a day or two though.

 

[DRussell]

Assuming the diodes are bad, what makes them go bad?

 

[old]

Age or over heating due to not giving the machine rest periods. One need to be sure to use a welder as per it's duty cycle

 

[MarkB_MI]

You need to disconnect one side of each diode to test it. Otherwise you'll probably be reading a short circuit through the transformer. A good diode will have continuity in one direction only; they're basically a check valve for electricity.

Note that most digital multimeters have a 'diode check' range, as the normal resistance ranges may not work on a diode. The diode check range actually displays voltage drop rather than resistance. A good diode will have a drop of about 0.7 volts when forward-biased, and will be open when reverse-biased.

Diodes usually fail from heat. Typically caused by too much current for too long. The failure mode is typically first a short-circuit, followed by the diode opening. You'll probably have one or more diodes open, but you could have just a shorted diode.