Quote:
Originally Posted by Uncle Bulgaria
Questions: - I have seen reference on here to testing capacitors with a 'Megger' type machine for breakdown resistance. I might be able to stretch to one of these as the older ones are cheap. Is this worth it? At the moment all I can do is test for continuity and/or turn on the machine with the capacitor I want to test and see if the smoke comes out.
- I like dual cans, but the right values are not available. My calculations suggest replacing the (for example) 8mFd + 16mFd PSU filter/reservoir capacitor (C24 & C26) with a 16+16mFd would not adversely affect the filtering. There are a couple more of these. Could I use 16+16mFd in all these locations? (C9/C13 & C11/C12)
- There is a 0.1mFd, 350V 'MICAMOLD' capacitor between the AC contacts of SW3, the motor switch. Is this purely to prevent arcing? As it is on a mains AC line, though the capacitor is not between LN or L/N and Earth, should this be an X/Y type?
- C3 is marked as 0.02mFd 360V, but in the unit it is bypassed by a resistor and a 3100pF(? - value half illegible) 'Suflex' (picture attached). What is the reason for this not being on the circuit diagram? Is it a pre-calculated snubber circuit for the speed control switch?
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1) A megger is down to personal preference, myself I would not use one for testing run of the mill capacitors but might use one if it was a large can paper type and I wanted to know of any electrical leakage problem.
2) 16uF for the reservoir should be ok.
3) "MICAMOLD" capacitors are notorious.
4) Suflex types have been known to go open circuit or partly open circuit (very high ESR) and sometimes short circuit if there's a high voltage across them in my experience.
Lawrence.