welding dc inverter repair

[Mono Electronic]

Hi friends
I want to repair a welding dc inverter that after one minute work,the warning light(o.c) turn on and the output cut.
I need to help...

 

[Reloadron]

Gee since you provide no schematic or make and model number I will just take a wild guess or two. Could the problem be thermal? Does the unit have fans? If the unit has fans what do the fans blow on? Does the unit have heat sinks for rectifiers? If yes, are they clean and heat sinks clean?

With the information you provided nobody can even begin to make an educated guess so I made a few uneducated illiterate guesses. That is as good as it gets unless you provide more and much more information.

Ron

 

[dr pepper]

As Ron.
A common cause of failure esp in the cheaper ones is grinding dust on the pcb shorting things out, though that would stop the unit from workign altogether not work for a while then stop.
Try cleaning out any crud from the heatsinks.

 

[Mono Electronic]

• ohhhh.excuse me.you are right...
• device model: MMA 200(220A-from beta company)
• the device have a fan and when device turn on,fan work correctly.
• the unit have heat sinks for rectifires and they are clean.
• is these information is enough?

 

[Reloadron]

From the little bit of data I could find unfortunately there was no schematic or drawing. I did read something about a maximum continuous duty cycle of 60% I think it was. The main reason machines like this shut down is thermal. Something gets hotter than it should, the machine shuts down, then once the machine cools down it will run again and the same thing happens. I could not find an owners manual online either.

So my guess is possibly a thermal issue where the duty cycle is being exceeded? Possibly the thermal sensor which senses over temp is faulty or the controlling circuits for over temp shutdown. Without a good schematic and drawing it is just about impossible to say why this model is doing what it is doing.

Ron

 

[Mono Electronic]

i agree
but ...where is temperature sensor?is it on the heat sink?
i checked the supply board.i find a ptc that faulted.dose the ptc fault is effective?

 

[Reloadron]

Normally yes, an overtemp switch or thermal sensor is placed on the heatsink but without seeing all of this and a drawing it is all guess work and speculation. Apparently the unit runs and then stops. Once it cools down it starts again, that leads me to believe there is a thermal issue or a thermal sensor issue. Since I don't know what the ptc actually does I can't say what a faulted ptc would do.

Ron

 

[tcmtech]

Another common cause if that is having a bad solder joint or connection point that goes open circuit once it warms up a bit and causes what appears to be a false overheat shutdown.

Just for a heads up typical duty cycle ratings are based on a specific current output over a 10 minute period so your machine should be good for doing roughly 6 minutes of continuous work at or below a certain output rating how ever if you are running above that the duty cycle gets lower and in the case of many low end cheaply built machines run at or near the maximum output could have less than a 10% duty cycle.

 

[Reloadron]

Another common cause if that is having a bad solder joint or connection point that goes open circuit once it warms up a bit and causes what appears to be a false overheat shutdown.

Just for a heads up typical duty cycle ratings are based on a specific current output over a 10 minute period so your machine should be good for doing roughly 6 minutes of continuous work at or below a certain output rating how ever if you are running above that the duty cycle gets lower and in the case of many low end cheaply built machines run at or near the maximum output could have less than a 10% duty cycle.

Another good point and possibility.

Ron