Change of capacitors in voltage multiplyer

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Discussion Overview

The discussion revolves around the effects of changing capacitors in a Villard cascade voltage multiplier used for biasing a photomultiplier tube in a plessey ratemeter. Participants explore the implications of replacing resin impregnated paper dielectric capacitors with polyester dielectric capacitors, specifically focusing on changes in ripple current in the DC output.

Discussion Character

  • Technical explanation
  • Experimental/applied
  • Debate/contested

Main Points Raised

  • Luc reports an increase in ripple current from around 7mV to around 30mV after replacing the original capacitors with polyester dielectric capacitors of a higher capacitance value (from 56 nF to 68 nF).
  • Another participant inquires about the equivalent series resistance (ESR) and equivalent series inductance (ESL) values for the two types of capacitors, suggesting these parameters may influence performance.
  • A participant mentions attempting to measure ESR using a 9kHz square wave but did not observe a discernible difference, expressing uncertainty about the accuracy of their measurements.
  • This participant also conducted simulations in LTSpice adjusting ESR and ESL values but did not replicate the observed increase in ripple current.
  • Luc later indicates that the increase in ripple current may not be related to the capacitor change, as they found lower ripple in a different ratemeter's high tension board, suggesting the issue may lie elsewhere.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the increased ripple current, with some suggesting it may be related to the capacitor change while others indicate it could stem from different issues in the circuit.

Contextual Notes

Participants express uncertainty regarding the measurement techniques for ESR and ESL, and there are unresolved questions about the specific causes of the ripple current increase.

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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