Change of capacitors in voltage multiplyer

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SUMMARY

The discussion centers on the replacement of capacitors in a Villard cascade voltage multiplier used for biasing a photomultiplier tube in a plessey ratemeter. The original WIMA Durolit resin impregnated paper capacitors were replaced with polyester dielectric capacitors, changing the capacitance from 56 nF to 68 nF. This modification resulted in an increase in ripple current from 7mV to 30mV in the DC output. Further investigation revealed that the increase in ripple current was not solely due to the capacitor change, indicating potential issues elsewhere in the circuit.

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lucvh
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Hi,

I have a supply for biasing a photomultiplyer tube in a plessey ratemeter. In the supply there is a voltage multiplyer of the Villard cascade type, with a filter after it.

The voltage multiplyer is supplied with a 9kHz supply of 300v p-p.

We replaced the original capacitors, which were a resin impregnated paper dilectric (WIMA Durolit) with a polyester dilectric capacitor. The value of capacitange has changed from 56 nF to a preferred value of 68 nF.

When we changed the capacitors over, we notived an increase in ripple current in the DC output from around 7mV to around 30mV.

Can anyone shed any light on what may have caused this?

Thanks, Luc
 
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lucvh said:
Hi,

I have a supply for biasing a photomultiplyer tube in a plessey ratemeter. In the supply there is a voltage multiplyer of the Villard cascade type, with a filter after it.

The voltage multiplyer is supplied with a 9kHz supply of 300v p-p.

We replaced the original capacitors, which were a resin impregnated paper dilectric (WIMA Durolit) with a polyester dilectric capacitor. The value of capacitange has changed from 56 nF to a preferred value of 68 nF.

When we changed the capacitors over, we notived an increase in ripple current in the DC output from around 7mV to around 30mV.

Can anyone shed any light on what may have caused this?

Thanks, Luc

What are the ESR and ESL values for the two types and values of capacitors?
 
I couldn't find the values in the specification sheets so i tried to measure the ESR the other day using a 9kHz square wave but i couldn't see any discernable difference between the two, although i cannot garuantee my test was completely accurate as i have never preformed it before.

I have run a few simulations on LTSpice adjusting the ESI and ESR values but it did not seem to have the magnitude of increase in ripple current that i am seeing in reality.
 
Disregard this thread, the increase in ripple current is caused somewhere else, i checked the HT board in another ratemeter and found there to be a much lower ripple.

Now i just have to find out where the damn voltage is leaking from.
 

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