electrolytic caps without polarity markings that are not Bi-polar

[pucho812]

How can one tell the polarity of an eletrolytic cap that is in use and does not have any markings other then the value on the top.  The caps are radial and the value is off to one side.  I think the value on one side is the key but I would not know if that is positive or negative.

 

[MagnetoSound]

Can you post a photo? I have never seen a polarised cap that didn't have some kind of indication.

 

[okgb]

usually one lead is longer

 

[ruckus328]

The positive lead is longer, but that doesn't help if the part is already mounted.  If it is mounted, if you can figure out what signal each pin is connected to, it will probably help with determining the orientation.

 

[pucho812]

Can you post a photo? I have never seen a polarised cap that didn't have some kind of indication.

I will when I return from holiday around Dec 30th. I left yesterday and this has been puzzing me  as a client brought in a bunch of original 550's that were recapped long ago and they are due again.  The guys who recapped it used these lytic caps that have no indication of positive or negative lead.  Other then the value like 220uf/16V are on one side of the radial only. Also the value is only printed on 1 time.

usually one lead is longer

Correct and the longer lead is positive. there is also a stripe line going down to indicate the negative lead usually.

The positive lead is longer, but that doesn't help if the part is already mounted.  If it is mounted, if you can figure out what signal each pin is connected to, it will probably help with determining the orientation.

Correct.  Yeah it's looking like I need to finds the right schematic rev of the unit and go from there.  I would make a guess and say that since the value is on one side of the radial cap, it would indicate something but not sure if that is positive or negative indication.

 

[gemini86]

I wouldn't make any assumptions, since they've already broken the convention. Trace out the board and see where it's going, if it's a filter cap, one side will be going to a fairly obvious ground trace.

 

[pucho812]

Tracing sounds like a great idea. Will most likely do that

 

[CJ]

put an ohm meter on there, leakage for a polarized cap will be more one way than the other, problem is, i forgot which has the most leakage, reverse polarity i would guess, so if the minus lead of the ohm meter is connected and shows a lot of leakage, the cap is reversed biased and so the positive lead will be connected to the neg lead of the volt meter,

if anybody knows which way is leakier, chime in,

does this test ring a bell?

thats right, exactly like the diode polarity check only different, 

we don't want poor ol pucho to blow this thing up,

why is he working during christmas, are times that tough?

heck yes,  :-*

 

[mad.ax]

If it's a coupling cap, then you can measure the DC offset on both side of the capacitor. Most positive is where the '+' pin needs to be connected.
If it's a // cap, then a bit of tracing will tell you which side is closest to ground...

Axel

 

[pucho812]

cj

I'm going to take all these cays and toss them down the hole.Maybe a flaming tennis ball or two just for good measure.