I had a problem with a circuitry component on an old potters wheel (probably 30 years old at least) dramatically burning out. A bang, Lots of smoke and breaker tripped. Traced the problem to a small capacitor placed directly across the 230v maybe where the mains first entered the control box. I have removed the capacitor and replaced all the wiring around it which was burnt through. The machine now send to function perfectly and my question is do I need to replace the cap and, if so, what type and value do you suggest? Any marks which there were on the old capacitor

The machine - a DC .33hp motor which states 1.9 A and 220v on the plate. Field and Armature connections into the control box which has a Variac, turned by mechanical linkages to a foot pedal. Two bridge rectifiers - one feeds the DC to the field, the other to the armature. There are also two small caps (which look similar to the one which burnt out). One is across the armature DC feed - the other across the AC connections to the bridge rectifier providing the DC feed to the armature.

There is a small inline fuse and a relay switch on/off circuit safeguarding the use

 

Photo of rogue capacitor

 

That capacitor is very probably to stop interference getting out of the controller onto the power wiring - it is not necessary for the operation of the controller.
If you find that it interferes with radio, TV, or other RF devices then you can fit a new capacotor. It should be rated for your supply voltage and it should be an X2 capacitor which means it is intended for permanent connection across the AC supply. The capacitance could be perhaps 0.1uF to 0.47uF.

 

That capacitor is very probably to stop interference getting out of the controller onto the power wiring - it is not necessary for the operation of the controller.
If you find that it interferes with radio, TV, or other RF devices then you can fit a new capacotor. It should be rated for your supply voltage and it should be an X2 capacitor which means it is intended for permanent connection across the AC supply. The capacitance could be perhaps 0.1uF to 0.47uF.

Thank so much AlbertHall. I'm grateful for your confirmation that it's ok to leave it out. I'll see how it goes in terms of RF interference

 

If you think you need to replace it, look up a 600v WIMA MKP4 type, they are designed for High AC pulse circuits.

 

If you think you need to replace it, look up a 600v WIMA MKP4 type, they are designed for High AC pulse circuits.

Thanks Max. Sounds like a good tip. I'll see how it goes on the RF front

 

Replace those other Capacitors in the Circuit,
they are going to fail from old-age soon.
30-years is really old for a Capacitor that was probably under-rated when it was new.

If the other Capacitors are AFTER the Diodes, You can replace them with larger value Capacitors.
The Voltage-Rating of any of the Capacitors must always be the same Voltage or higher.
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Replace those other Capacitors in the Circuit,
they are going to fail from old-age soon.
30-years is really old for a Capacitor that was probably under-rated when it was new.

If the other Capacitors are AFTER the Diodes, You can replace them with larger value Capacitors.
The Voltage-Rating of any of the Capacitors must always be the same Voltage or higher.
.
.
.

Thank you LowQcarb. I'd been wondering about that. I'll see if I can read any markings on the others