[AMRadio] HV Capacitor question


Donald Chester k4kyv at charter.net
Mon Jul 17 12:19:58 EDT 2017


Maybe it's acting like an electret condenser.  I recall (in early 1960s Popular Electronics I believe), an  article on how to build an electret.  You melted a specific kind of wax and poured the molten material between two plates of tinfoil while a high DC voltage was applied.  After the wax cooled, the HV was removed, and the two plates retained a permanent HV charge.

I have also noticed that with HV oil capacitors, once you discharge them by shorting out the terminals, they will recover after the short-circuit and the charge will bounce back, sometimes enough  to cause a painful shock.  That's why oil capacitors are usually shipped and stocked with a wire connected between the terminals. 

> I just learned another characteristic that I've not found anywhere in print. If I
> take a DVM, and clip the leads across the capacitor (used bad ones), I will
> measure a voltage!! Maybe something like 20mv, and varying with
> temperature by just grasping the device with my fingers. Now the kicker,
> wave the device with a heat gun, and as the device warms up, the voltage
> increases upwards rapidly to 1 volt!! A good (used) capacitor, same type, will
> never go beyond 20mv, hot or cold. 


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