Change of capacitors in voltage multiplyer

AI Thread Summary
The discussion centers on a voltage multiplier used for biasing a photomultiplier tube, where original resin-impregnated paper capacitors were replaced with polyester capacitors, changing the capacitance from 56 nF to 68 nF. This replacement led to an increase in ripple current in the DC output, rising from 7mV to 30mV. Initial inquiries focused on the equivalent series resistance (ESR) and equivalent series inductance (ESL) values of the capacitors, but measurements did not show significant differences. Simulations in LTSpice did not replicate the observed increase in ripple current. Ultimately, the user determined that the ripple current issue was unrelated to the capacitor change and is now investigating potential voltage leaks elsewhere in the system.
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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