electrolytic capacitors: potential on case

[electricuwe]

The case of an electrolytic capacitor is usually connected to one of the terminals.

As far as I know this is always the negative terminal.

One of our suppliers of SMPS claims that the type he uses has the positive terminal connected to the case.

Can this be true ?

 

[buzzp]

I see now reason to have the positive applied to the case. Please post your findings. Thank you.

 

[MMAshwin]

Hi,

The electrolytics capacitors in SMPS supplies aren't
your run of the mill electrolytics. If they are they
quickly dry out and fail an ESR test and you supply goes phht.

Saying that it would seem logical to have the can at the
lowest potential possible from a safety point of view. So if you using the capacitor for a high negative voltage and the +ve is at earth potential I would like the can to be at earth as well (which is the +ve terminal)
The reverse is true also for high positive values. I would question, why have the can at any portential and not just floating around ?.
Any help ?, yes no let me know.

Regards

 

[nbucska]

The housing is negative -- this is dictated by the electrochemistry. <nbucska@pcperipherals.com>

 

[buzzp]

Please clarify nbucksa!

 

[nbucska]

The first electrolytic cap-s consisted of an anode foil
folded into a star ( /\/\/\/\/\/\.... folded around the axis
of the cap, held by two rubberbands, immersed into a liquid
eletrolite in an Al container, which acted as the cathode.

To reduce the R and eliminate liquid spills later they used a cathode foil, which -- whenever the case was metall, i.e. Al, -- was connected to the case, so insulation was not necessary.

The anode must be very pure Al to maintain the quality of
the oxide -- the housing may be alloy and it may be contaminated during the MFG process. The Cathode does'nt
need time consuming forming (growing the oxide layer ).


<nbucska@pcperipherals.com>

 

[electricuwe]

I have checked it myself by removing the capacitors outer isolation-sleeve. The case was on negative potential.