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    Default Can anyone identify these parts?

    Gíday everyone, Iíve received a 3 phase 12 channel stage lighting dimmer. Upon firing it up smoke came out of it. I took it apart and found these devices () with cracks in the side and liquid oozing out. Can anyone tell me what they are? Iím looking for some sort of a replacement for them. Iím thinking theyíre older metallised polypropylene capacitors just by looking at the jaycar catalogue. Cheers all



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    yes they are what you thought . but you are likely to find they are not the fault and it will be the triacs or the diacs at fault , it is possible these have failed as they are rated at 250 v but the need to be at least 350v rated , iirc they are a suppression cap on the output of the devices and as a result have 240vac rectified to 325v and are below rating . good luck ? What brand ? don
    are you a self appointed hypocrite sheriff or just a nasty person

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    Those caps are metallised paper, encased in an epoxy resin.

    They have a long history of failure, mostly due to the absorption of moisture over time.

    They can be replaced with polypropylene equivalents.

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    Bloody hell, those caps brought back some memories. We used to use them in customer's telephone lines with a diode for STD barring! (Slightly higher capacitance, though). Anyway I'll leave you in mtv & hinekadon's capable hands! Just remember don't let out the smoke nothing works when that is let out!
    I'm out of my mind, but feel free to leave a message...

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    Cheers for all the answers. In reply to Donís post I think the triacs/diacs are in good working order. When we last used the dimmer it worked fine (smooth dimming etc) it was only the caps that were the problem. Thatís again everyone

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    You MUST replace them with X1 rated capacitors !
    I see none at Jaycar, they only have X2 which is safe for household equipment but not suitable for 3 Phase lighting systems.
    You can find them at element14:



    @Hinekedon, a 250V AC rated capacitor and would need to handle at least 600V DC but in reality these X1 types can handle transient spikes well over 2kV !
    You are right that they need to be higher rated than 250V but the X1 specification covers that.
    Generally triacs will not fail because of a leaky suppression cap. It did not look like much current went through them either because otherwise you would just see lumps of molten aluminium.
    Last edited by Uncle Fester; 29-06-19 at 01:39 PM.
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    Quote Originally Posted by lsemmens View Post
    Bloody hell, those caps brought back some memories. We used to use them in customer's telephone lines with a diode for STD barring!
    Yep, that was my first thought too. I'd be confident that I have a box of this exact type in the back shed somewhere.
    But these days, I'd just replace them with the 0.1uF 600V polyesters like nomeat suggested. I've got an even bigger bag of them somewhere. I use them for Walton Cockcroft multipliers so I know they can handle a good 3kV. Usually the 1N4xxx diodes let loose before they do.
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    Quote Originally Posted by hinekadon View Post
    yes they are what you thought . but you are likely to find they are not the fault and it will be the triacs or the diacs at fault , it is possible these have failed as they are rated at 250 v but the need to be at least 350v rated , iirc they are a suppression cap on the output of the devices and as a result have 240vac rectified to 325v and are below rating . good luck ? What brand ? don
    These are specifically designed for spike suppression. They do not see any DC.

    A Jands Dimmer Rack for sure. Common fault.

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    Quote Originally Posted by trash View Post
    Yep, that was my first thought too. I'd be confident that I have a box of this exact type in the back shed somewhere.
    But these days, I'd just replace them with the 0.1uF 600V polyesters like nomeat suggested. I've got an even bigger bag of them somewhere. I use them for Walton Cockcroft multipliers so I know they can handle a good 3kV. Usually the 1N4xxx diodes let loose before they do.
    Polyesters should never ever ever ever be used in this application. They are totally unable handle the AC plus spikes. Lots of smoke and fire.

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    Quote Originally Posted by rothackerben8 View Post
    Cheers for all the answers. In reply to Donís post I think the triacs/diacs are in good working order. When we last used the dimmer it worked fine (smooth dimming etc) it was only the caps that were the problem. Thatís again everyone
    When you replace the Caps, make sure you check the series resistor as that usually suffers.

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    Quote Originally Posted by Reschs View Post
    Polyesters should never ever ever ever be used in this application. They are totally unable handle the AC plus spikes. Lots of smoke and fire.
    I've never put any serious thought into it Reschs. The caps I used may not be polyesters, they have more of a white ceramic case, I just call them polyester.
    They've never caught fire or exploded or let go. Else I'd just re-apply them for that job.
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    Quote Originally Posted by trash View Post
    I've never put any serious thought into it Reschs. The caps I used may not be polyesters, they have more of a white ceramic case, I just call them polyester.
    They've never caught fire or exploded or let go. Else I'd just re-apply them for that job.
    The ones you are using are fine for your application.
    The X Series are a totally different capacitor and are for direct mains voltage, plus high current spikes.

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