Capacitor Problem?

Please see the attached pictures of a capacitor on the mains line filter of a microwave/oven combination appliance. The filter board is powered by 240V AC, and I've gone though 2 boards where that capacitor has blown. My questions are:

1. Is it a problem that the capacitor only indicates 175V or would the voltage be lower at that point in the circuit?

2. If it is a possible problem, could I replace it with a higher voltage?

3. What type of capacitor is it? I was thinking it was ceramic, but if the "595" means 5.9 µF then I guess it is some other dielectric.

Thanks in advance for any input or suggestions.

It may be a surge arrestor.

But the voltage certainly seems too low. It's unlikely that the voltage is lower than the mains voltage at that point. It should have at least a 350V rating for a 240VAC circuit. The 175V rating seems more appropriate for a 120VAC circuit.

bdpead said:

Please see the attached pictures of a capacitor on the mains line filter of a microwave/oven combination appliance. The filter board is powered by 240V AC, and I've gone though 2 boards where that capacitor has blown. My questions are:

1. Is it a problem that the capacitor only indicates 175V or would the voltage be lower at that point in the circuit?

2. If it is a possible problem, could I replace it with a higher voltage?

3. What type of capacitor is it? I was thinking it was ceramic, but if the "595" means 5.9 µF then I guess it is some other dielectric.

Thanks in advance for any input or suggestions.

Click to expand...

Buddy 595 means 5,900,000 pF. for an 220v circuit you must use the capacitor value greater than the RMS value of 220v.
regarding dielectric material you can use ceramic or polyester. It can work man.

I think it is a PolyFuse (like these, but not this exact part).

bdpead said:

Please see the attached pictures of a capacitor on the mains line filter of a microwave/oven combination appliance. The filter board is powered by 240V AC, and I've gone though 2 boards where that capacitor has blown. My questions are:

1. Is it a problem that the capacitor only indicates 175V or would the voltage be lower at that point in the circuit?

2. If it is a possible problem, could I replace it with a higher voltage?

3. What type of capacitor is it? I was thinking it was ceramic, but if the "595" means 5.9 µF then I guess it is some other dielectric.

Thanks in advance for any input or suggestions.

Click to expand...

I am positive that it is a surge arrestor MOV. Looks like it exploded, that will happen, only with LARGE voltage/current spikes!

You might be able to get away with a higher clamp voltage MOV, but other parts, like the large high-voltage transformer might not be able to take 240volts without frying!

-Ben

crutschow said:

It may be a surge arrestor.

But the voltage certainly seems too low. It's unlikely that the voltage is lower than the mains voltage at that point. It should have at least a 350V rating for a 240VAC circuit. The 175V rating seems more appropriate for a 120VAC circuit.

Click to expand...

Maybe it is meant only for 120 volt use, so 240v blows it.

-Ben

I think what you are looking at may be a varistor.

If it has a part number it may look long and odd.

VE07M00131KDC is an example of a varistor part number

A varistor os a semiconductor device that behaves a bit like a bi-directional zener diode.

Below its trigger voltage it has very high resistance (looks like a small cap), if the voltage goes above the trigger voltage, above the stand off voltage or the voltage rises very fast it goes short cct, to stop high voltage spikes.

This device is used to protect electronic devices from high voltage spikes on mains supply, AC and DC. Be aware that even if a fuse blows, if the cct it is protecting has much inductance around it the inductance will generate a back emf and therfore voltage spikes.


------- coil ----------------------------
|
AC Varistor device or CCT to protect
|
--------- coil -------------------------------


Without seeing the device in front of me it can be difficult to see exactly what you are liking at.

ben7 said:

Maybe it is meant only for 120 volt use, so 240v blows it.

Click to expand...

Since he is using the Microwave on 240V I assumed it should have been designed for 240V.

There's no way they can use 175v X2 type caps on 240v.

Generally they use 275v X2 caps on 240v mains.

It's probably a fuse or a MOV. Can you tell if it is across the input or in series with it?

That looks like a MOV.

for 240 Volts there are 275 V rms MOV's available.

The Cap looks like a X 2, probably still ok

The MOV blew up because it is designed to do so.

A 175 Volts MOV will blow up at 240 volts AC.
Main reason is to take out the appliance fuse and protect the rest of the appliance.

MOVs will blow up sometimes!