humming lincon welder

Hello RAYSLENN

Over many years Lincoln Welders have been excellent products.

You don't advise the actual model of the Lincoln MIG welder.

My guess is either:

1. The wire feed motor has a short circuit, or is partly burned out.
2. The transformer has partly burned out.
3. Either of above has developed a short circuit to ground (Earth Connection)
   

In cases (1) and (2) there would be the characteristic smell of burnt insulation.

In any of the cases above, neither a Diode Tester, nor a DVM would establish that there is a fault, you would need a 500V "Megger" or tester which places high voltage DC on the Windings.

Reply please, with with model # of the Welder, and advise made in US or "elsewhere".

Kind Regards....

Replacing all the diodes is a good move as when one goes open circuit it throws extra loading on the remaining ones, these could fail later due to this.

As you have replaced them all and still have circuit breaker tripping double check you have not fitted the diodes with polarity reversed this would short the transformer output.

The other thing to try is disconnect the transformer output from the welding circuit and trigger on if the transformer still hums and it trips the circuit breaker your transformer is shorted.

Cannot think why disconnecting the relay would solve anything usually this only proves whether or not you are getting full voltage into the primary.

I believe the reversed polarity of the diode(s) is a good place to start, this would most assuredly cause the problem you are having. I would not megger the windings however with 500V as welders are designed for high current and low voltage output, if the insulation rating of the windings is lower than 500V, you would burn up a good tranformer and make things worse.

The current of Meggers is too low to damage anything- in this case the most likely cause is shorted windings in the transformers- all these welders have a duty cycle- eg- 25%- exceed this &overheat of the windings occurs breaking down the insulating enamel so that s/c occurs drawing excess current- a shorted turns tester is needed or r/p of tx to prove- obviously this is general as I haven't seen the set .

Welding utilizes current, but meggers utilize voltage for testing dielectric strength of materials.

It has nothing to do with megger current, and everything to do with megger voltage when testing insulation dielectric strength. High or low current is not what passes through the insulation, voltage exceeding the insulation rating is, and when it does, the insulation is damaged by arcing or heat causing a breakdown in the insulation dielectric strength. Once the isulation of the windings is compromised, the xfmr is junk.

Oh-excuse me for my misconceptions- I am referring to the tx windings which are usually enamel covered- now when work is done, the windings heat up- if overheated, the enamel burns off & the windings are now in contact-ie shorted turn/s- now in a welder, if you want to weld thicker metal, you turn up the amperage- this increased current heats the windings more, so you must observe duty cycle- stop to let the heat dissipate. This is true in anything using enamel covered windings-eg electric drill- overload the motor to excess & burnt windings are certain. My megger(500 & 1000v) passes a current of 4mA- it is laughable to suggest this can damage anything!. B/r, Neil.

Normally you would test windings of a transformer or a motor at twice its rated insulation, say if its a 230v supply you would test in the 500v range.

The following is for your info.

Also you say its a friends welder, in the UK their is a difference between circuit breaker types B, C, and D ; a type D is suitable for a welders use, as it has a different time curve than a B or C type. What this does is allow for the inital inrush or surge of electricity when you first turn on the welder, if you have say a B type fitted it can cause the circuit breaker to trip. Added to this if you have an RCD or Earth leakage detector fitted this will also cause nuisance tripping.(unsure of what you call them in the US)

Saying all that most welders come with a wiring diagram on the inside cover which should help you to trace your fault.

Sorry guys I did not get back sooner I have not bean over to friends to get #'s but to add to above I Isolated feed motor and still the same hum if I hold the Trigger for a few seconds it just hums let go and no hum no blown breakers hold it on pop.

so have to believe it is trans coil ?can i soak coil in something like lacquer or shellac to re insulate it and save it some how?

Hello again RAYSLENN

If your problem is a shorted turn, or a breakdown to the earth connection, you would have to repair that, or risk a fire at some later stage.

If you were rather closer, I could test it for you, free.

Perhaps you have a friendly electrician locally, who could take a quick look at your problem.

Kind Regards....

Thanks Sparkstation if ever in new Zealand will stop by for a free test Thanks for the offer as to re-dipping coils not good idea or Even possible?

Hi Rayslenn- unfortunately when a shorted turn/s occur, the actual winding/s are welded together- if you can find & seperate, then yes enamel can be reapplied- if can't seperate, don,t even try!. In tv repair if we have a buzzing tx, we sometimes use lacquer to quieten- b/r,Neil.