Capacitor above chassis

[andRookie]

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.

 

[EC8010]

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.

 

[andRookie]

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..

 

[andRookie]

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.

 

[Tubelab_com]

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.

 

[andRookie]

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?

 

[EC8010]

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.

 

[andRookie]

Point taken. Here is a photo (if I now manage to do this)

An externally hosted image should be here but it was not working when we last tested it.

It is the big black 30uF I have bought. They where bought due to the price. I do not know much about the quality.

 

[EC8010]

There will be no problem at all if the case is connected to the chassis.

 

[arnoldc]

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.

 

[Wavebourn]

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.

I second that!

Once during a workshop there was a hot sunny day and we vere half naked, without t-shorts. Suddenly I saw a smoke going from the amp on the edge of stage. I come and removed cover. Smoke was going from uderneath of the chassis. I pulled the amp, bent over it trying to spot where the smoke is going from... And suddenly tauched by belly a can with about 450V on it....

Put some isolation cap on it.

 

[pinkmouse]

What about the exposed leads? If they're outside the case they really need proper insulation.

 

[EC8010]

I'm assuming (perhaps incorrectly) that a hole is to be punched in the chassis and the capacitor will poke through with the leads inside in traditional valve amplifier style...

 

[andRookie]

EC8010, assumption confirmed. Not easy to drill those 51mm holes so a pro helped out. A bit dissapointed about the caps though as the can was bulky and ugly underneath the plastic. Filler and paint is needed to make them look good (as is a goal of mine), but aluminum is not your friend in that case. Any suggestions?

 

[EC8010]

It's easiest to use a chassis punch for holes bigger than 9mm. No suggestions I'm afraid for making the capacitors look pretty.