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  1. #11
    Co-Pilot ArthurG's Avatar
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    Are you sure it's an electrolytic? I can't make out all the details but it looks like a metallised paper one to me. Bosch stopped making them in the 90s IIRC, so no data is available online to check.
    The best argument for the status quo is a five minute conversation with Russell Brand.


  2. #12
    Co-Pilot Arielarts's Avatar
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    You could be right. Is there any sign of a polarity marking (the sure sign of an electrolytic). If not, your metallised paper suggestion could be correct (I do see an 'MP' in the part description). If it were mine, I'd disconnect one wire, short out the pins to ensure no remaining charge, then measure its resistance. If greater than 1Mohm, it's probably okay. Could also try charging it to say 12v, and monitoring the decay of voltage. Assuming you have no capacitor tester.


  3. #13
    Wannabe Pilot Trident's Avatar
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    Looking at the photos, I think it could be a relaxation oscillator driving the coil which then produces the very high output voltage. There seems to be a voltage multiplier circuit in the 4 red diodes. I would think you might be able to use a lighting or motor-run capacitor to replace the large one if indeed it has failed. They are usually available in some obscure values to provide power-factor correction and phase-shift for induction motors:
    https://uk.rs-online.com/web/p/polyp...itors/4515398/ or perhaps https://uk.rs-online.com/web/p/polyp...rs/2508489300/
    I expect with the tolerance on the capacitance it would be close enough for them to work in what appears to be a non-critical application such as an impulse generator.
    Comfortably Numb......


  4. #14
    Co-Pilot Wexfordair's Avatar
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    Good ideas guys, thanks. I don't see any sign of polarity but as you suggest it does say MP, which I thought meant multi purpose! (Shows how much I know about these things). I'll do the test on it when I get the chance and then probably do as Trident suggests above.
    Cheers.


  5. #15
    Co-Pilot Wexfordair's Avatar
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    Just checked the big capacitor and got open circuit across the terminals.
    I guess that confirms it then...


  6. #16
    Wannabe Pilot Trident's Avatar
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    Not necessarily. A capacitor will show open circuit if you use a normal multimeter, but it depends on how you test it. Essentially, if it is fully discharged when you first test it, the meter will start by showing a very low resistance which will gradually increase (depending on the capacitance value) and settle at some figure of maybe a few tens or hundreds of kilo-ohms. Again the final value can depend on the type of capacitor, the value, age (if it's an electrolytic type) and storage conditions. If there's doubt about the condition and it's very old and been stored in damp conditions, it's probably shot and needs replacing. Without the spec sheet which will show leakage current values, it's very difficult to test without a capacitance meter.
    Comfortably Numb......


  7. #17
    Co-Pilot Wexfordair's Avatar
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    Right,

    The big capacitor has arrived but it has a weird connection on top. Can this be just split open to solder on the wires and is there a polarity?
    Attached Images Attached Images


  8. #18
    Co-Pilot ArthurG's Avatar
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    No polarity.Don't split it if you can avoid it. Just push in a (stripped) wire into the socket and it should grip and hold it. If some disaster occurs PM me and I'm sure I can post you something suitable.
    The best argument for the status quo is a five minute conversation with Russell Brand.


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