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Old 31st October 2006, 07:45 AM   #1
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Default Capasitor above chassis

I using the obligato caps from diyhifisupply in a psu PI filter in my El34 project, aming at B+ og 450-460 volt. The obligato cap will come up through the chassis. On the top of the cap the plastic casing does not totally cover the aluminum can of the capasitor.
I cannot find any references to wheather a capasitor aluminum can can be a safety risk if possible to touch in Morgan Jones book or searching via google.

Should I for safety reasons

1. Make sure the aluminum can is connected to the chassis via the clamp and screws through the top chassis plate.

or

2. Cover the aluminum can of the capasitor totally with isolating substance.

I thinking that if I do 1. the aluminum can will be at 0 volt potential and it will not be unsafe to touch the aluminum can. If I do 2. the aluminum can is not possible to touch.
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Old 31st October 2006, 08:38 AM   #2
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Clamping the bare capacitor can to chassis will make it safe but almost certainly cause hum problems because of hum loops. Totally shrouding the capacitor in plastic (as many modern electrolytics are made) will make it safe and avoid hum loops. I assume that you don't have enough room to put it inside the chassis. Some imaginative constructors have sprayed tins intended for tea and used them to cover unsightly/dangerous components.
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Old 31st October 2006, 08:54 AM   #3
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Hum loops if aluminium capsel is grounded: I have seen projects from very competent people where the capsels were connected to ground to avoid hum/noise. I think it had to do with capasitors in the signal path, though. I`ll ask the constructor about this..
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Old 31st October 2006, 09:55 AM   #4
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I was wrong about capsels connected to ground, they were only mechanically connected to the chassis. I am told that my question about capasitor capsel rely on the contruction of the capasitor itself. I`ll send the cap supplier a mail and ask the same question.
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Old 31st October 2006, 02:13 PM   #5
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I can personally assure you that touching the can on a Panasonic electrolytic (top is exposed) is a SHOCKING experience. The can seems to be at a voltage that is somewhere between the potentials on the two terminals. In my case it was about 200 volts on a 350 volt cap.

I would not ground the can because this may cause an undesirable internal leakage current inside the cap. Insulate it from contact.
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Old 1st November 2006, 10:24 AM   #6
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This is a "film in oil" capasitor and I have now lately been advised to groud the can as its plates should be isolated from the can, and grounding will prevent from shock hazard when the can is exposed.

I cannot find connection from the terminals to the can with an Ohmmeter, but I do not have the option of measuring capasitans terminal/ can. If a leakage current arise inside when I do this, will it be possible to measure?
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Old 1st November 2006, 10:51 AM   #7
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If it is a film capacitor in a metal can then there is no problem at all in connecting the can to chassis. With this sort of a question, when you don't know exactly what the component is, a photograph helps get the correct advice instantly.
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Old 1st November 2006, 11:12 AM   #8
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Point taken. Here is a photo (if I now manage to do this) Click the image to open in full size.
It is the big black 30uF I have bought. They where bought due to the price. I do not know much about the quality.
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Old 1st November 2006, 07:31 PM   #9
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There will be no problem at all if the case is connected to the chassis.
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Old 1st November 2006, 10:31 PM   #10
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I have a pair of this huge momma 30uF I have not been able to use yet.

A friend of mine was *shocked* from an aluminum cap whose cover was ripped off in a vintage amp.

I never thought this would be the case for the film cap Obbligato and thanks to this thread for the confirmation.
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