Swp 271 single phase

[Baron@williams]

Hello, l have SWP217 single phase welder has started splattering really bad you can find tune into range 12 but all other ranges it is impossible just spluttering like crazy so I’m starting to throw parts at it I’ve just bought four caps not fitted yet so I don’t know if this will fix it next it will be diodes I should think but I’m not electrical engineer or have experience. Am I going down the right road?

 

[eddie49]

It is unlikely that the capacitor bank is causing this problem, but it could be the diodes. A short or open diode would cause partial AC on the output.
I would suggest starting with a voltage check from the torch tip to the work clamp at each position of the range switch. The output should start at about 15 volts and rise incrementally to about 32v DC.

 

[Baron@williams]

It is unlikely that the capacitor bank is causing this problem, but it could be the diodes. A short or open diode would cause partial AC on the output.
I would suggest starting with a voltage check from the torch tip to the work clamp at each position of the range switch. The output should start at about 15 volts and rise incrementally to about 32v DC.

Hello, I have found out it is the diodes and I want to rebuild the bridge rectifier and I don’t know if they are forward or reverse thank you for your response

 

[eddie49]

Yes, those diodes have definitely failed!
I do not know why they fail in that way, with the wire "popping off". Maybe the diode shorts, overheats, and a soldered connection melts?
Perhaps it is just the heat of normal operation that causes that to happen.

I like the way that the busbars of the capacitor bank are bolted directly to the rectifier. Replacing the whole rectifier with a new generic unit would probably mean finding an alternative way to make that connection, for example with heavy cables.
Rebuilding your failed rectifier would be a difficult task. Have you tried contacting SWP and asking them if they can supply the correct new rectifier? Alternatively, maybe Les Ford at Tec-Arc in York could rebuild it.

I think that each of the four aluminium plates represents one of the four diodes in a bridge rectifier. and there are 6 diodes in parallel on each plate. That means each diode is nominally rated at about 50 Amps. Press-fit diodes are available as "automotive diodes", for use in car alternators. E.G.:

Pardon our interruption...

The wire leads on those diodes are probably not long enough to reach the internal connecting points, and this may be a problem with most of the components that are available.
Obviously new diodes would have to be the correct diameter to fit the original plates. They would have to be pressed in using a spacer - e.g. a deep socket, and a press or a vice.
I think all the diodes may be the same polarity, which is commonly defined as normal or reverse, or "stud cathode" or "stud anode". There may be part numbers printed on the diodes. If you can find a diode that is not defective, then test it with a digital voltmeter set to the "Diode Test" range. The meter will show conduction, indicated by a reading of "400" to "700", when the red test lead is connected to the anode, and blocking, indicated by "OL" or "1." , when reversed, with the red lead on the cathode.

 

[Baron@williams]

Thank you for your reply. I am trying to source the correct diode for rectifier, but the numbers have worn off. So I’ll probably just buy a new rectifier. And get spares, thank you, Eddie.

 

[Baron@williams]

Hello Eddie I was on the phone to Lez ford very helpful and he going to send me out a rectifier to me and a bit of upgrade for a £100 just wanted to say I appreciate putting me forward for Technical Arc at York thank you very much Baron