Appliance trips MCB

[Bonny]

I am seeking help with an old Silvaseam carpet joining machine, I have an electrical fault when connecting the clamps to the silva joining tape and switch on the tape starts to warm up but then gets to hot and trips the MCB in the circuit. I would think it is a problem with a thermostat. I wondered if anybody had similar experience, there doesn't seem to be an obvious thermostat visible but there is a circuit board which may incorporate one.

 

[PrenticeBoyofDerry]

Is it a MCB that trips or is it a RCD, RCCB or RCBO?

 

[Bonny]

Thank you. Sorry I was just assuming, but had a look, it is the RCCB. does this help.

 

[PrenticeBoyofDerry]

That would indicate the likely issue is a heating element on the appliance.

 

[Bonny]

Thank you once again. i have never seen a machine like this it is very heavy and two transformers inside, one is huge and heavy along with a printed circuit board and the cables which contain the heating clips are 1/2" dia but the tape used for the carpet joining is very thin with glue on one side and a foil back which the cables heat up and melt the glue it seems to be over engineered to me but there must be a reason. Surely the heating must be regulated by a thermostat but the only thing I see is two tiny type 1/2" dia items on the circuit board with adjustment in the centre. I haven't tried adjusting them as surely a current required to heat them cables would not (I thought) be regulated through a PCB. If you have any ideas I would appreciate any suggestions I could send photo's if that would help.

 

[crystal ball]

Photos might help, the temperature may be regulated by a simmerstat type controller, the items on the circuit board sound like potentiometers

 

[Bonny]

 

[Taylortwocities]

Pictures are a bit blury but there is a lot of dust and crap on the components.
If it is the RCD tripping then there may be tracking over the crud. First job is to vacuum out the innerds so its all nice and clean.

After that, its a bit tricky to suggest anything, could be a capacitor that is failing, or one of the transformers may have a faulty winding.

 

[Bonny]

Thanks to all I will give it a good clean and see if I can check the components on the pcb is there any way I can check using continuity on the windings of the transformers.

 

[bernardgreen]

The current through the foil is controlle by the device labelled IR ( International Rectifier ) which is a pair of thyristors which are switched on and off to control how long the current flows. The current flows between the AC terminals with control inputs on the G (Gate ) terminals.

It is possible that the temperature is not measured. Provided the correct tape is used then the temperature can be fairly accurately controlled by how much current is passed through the tape.

Without a circuit diagram and some hands on diagnostic testing it is near impossible to determine what if anything is wrong with the machine

 

[stillp]

If it's tripping the RCD, then surely it has an earth fault, so the temperature of the foil doesn't matter. As you said, needs a circuit diagram, and an IR tester.

 

[Bonny]

Looking at the picture of the IR there is an red disc and it is marked 340V 3.6mA is this a capacitor and the white one above (which you can see in the other picture is marked .047 uF. when I opened the machine at first the red one had a leg not soldered to anything and I thought it was from where I have soldered it now but this had no effect so has someone replaced it with the white one. I haven't got an IR tester but would I be able to remove the one that is on and purchase another. or is it part of the transformer.

 

[bernardgreen]

340V 3.6mA is this a capacitor

Almost certainly a surge suppressor, this would not cause any earth leakage

is marked .047 uF.

This is a capacitor ( 0.047uF is a value of capacitance ) and may have been part of the circuit or may have been added later.

If the 0.047 capacitor is connected the the "terminal" I have ringed in red and that "terminal" is the earthed mounting bolt for the IR module then that could be the reason for earth leakage currents

 

[JohnW2]

If the 0.047 capacitor is connected the the "terminal" I have ringed in red and that "terminal" is the earthed mounting bolt for the IR module then that could be the reason for earth leakage currents

True, but only a very small 'leakage current' - at 50Hz a 0.047 μF capacitor has a reactance of around 68 kΩ, hence a 'leakage current' of only about 3.4 mA at 230V - far too little to trip an RCD.

However, the capacitor might be faulty ('leaky'), in which case anything is possible.

Kind Regards, John

 

[bernardgreen]

There is also a resistor to the same "terminal".