Electronics > Beginners

Help in replacing a high voltage capacitor.

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Atomillo:
Hi:

I recently became the owner of a Keithley 246 HV precision supply. I turned it on briefly to check that the tubes and transformers worked fine, but I turned it off quickly because I found a cap that was leaking quite badly in the resistor divider board. In spite of this, the supply worked perfectly when it was turned on.

I am in the process of ordering new capacitors, and I originally wanted to replace all of them. However, in the voltage doubler part there are two big 0.5uF 3kV capacitors. Those are quite expensive (by a big margin the most expensive component I need to replace). However they both have the correct capacitance. I'm aware that simply measuring the capacitance of a cap is no guarantee, so I wanted to know if this type of capacitor (picture attached) is prone to failure or if it would be safe to leave them on.

Many thanks

Atomillo:
Hi:

Looking a little bit more at Mouser I found this: https://www.mouser.es/ProductDetail/WIMA/SNMPW034708H4AKS00?qs=sGAEpiMZZMsh%252B1woXyUXjycuPj0va9qfWPnmcAWL6q4%3D

Could this be an appropiate replacement? As stated previously, it is used in the HV doubler right outside the transformer.

Manul:
I would not mess with non-electrolytic capacitors without explicit knowledge that they are prone to failure. Capacitors randomly picked from mouser might be even less reliable then the old ones.

wraper:
As I understand some rubber sealed paper cap was leaking somewhere else. Then why would you replace high voltage hermetically sealed cap? Waste of time, effort and most likely can only possibly make things worse.

Gyro:
The leaking 50nF capacitor clearly needs to be replaced but, unless they are actually faulty, I don't see that the 0.5uF ones do. They are hermetically sealed and from the name (Plastic Capacitors Inc) I would say that they are plastic film rather than paper in oil and probably extremely reliable. Blanket capacitor replacement is rarely a good idea, apart from obviously faulty ones (I would replace all of the 50nF ones if one has started leaking like that).
 
As this is the beginners section, I should warn you that the large high voltage capacitors could be holding a potentially lethal amount of energy, certainly enough to scare the hell out of you. They can also recover a proportion of their charge if left disconnected (dielectric absorption) so use care when handling them.

EDIT:

--- Quote from: wraper on September 16, 2021, 03:55:25 pm ---As I understand some rubber sealed paper cap was leaking somewhere else.

--- End quote ---

Yes, can you clarify where the leakage is coming from, it's not clear from the photos. Is it actually from the 50nF?

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