Capacitor polarity

[gabriel/norfolk]

I got a batch of caps which are electrolitic everything is marked on them, except the polarity which is not to be found anywhere on the cap or stamped on the leg the can is isolated from either leg, no form of identification on the rubber bottom.

Any idea how I can find the polarity simply?

Thanks

[Sonusthree]

Maybe they're bipolar electrolytics?
They don't have a line running down the side?

[auplater]

If one leg is noticeably shorter than the other, that's the negative lead.

Are these axial or cans?

John L.

[gabriel/norfolk]

Hi John L

They are cans and the legs are the same lenght.

I was told to charge the cap up a couple of volts, + on one leg and to time its discharge, then discharge it and charge it up with + on the other leg , the way it held its charge the longest time that leg was the + side of the cap. There is a time difference but it does not inspire me with confidence. they are rated at 50 Volts and the rail voltage is 35V what I do not want is them going off like a string of fire crackers

Gabby

[gabriel/norfolk]

Originally posted by Sonusthree
Maybe they're bipolar electrolytics?
They don't have a line running down the side?

Hi Sonusthree

they are 100uF @ 50V do bipolars come as big as that? all the markings are in line with one leg as if that is where the black line should be, other half side of the can where the other les is is totaly blank

Gabby

[auplater]

Originally posted by gabriel/norfolk
Hi John L

They are cans and the legs are the same lenght.

I was told to charge the cap up a couple of volts, + on one leg and to time its discharge, then discharge it and charge it up with + on the other leg , the way it held its charge the longest time that leg was the + side of the cap. There is a time difference but it does not inspire me with confidence. they are rated at 50 Volts and the rail voltage is 35V what I do not want is them going off like a string of fire crackers

Gabby

depending on cost and how many you have/need, you could always guess on one of them, run it up to ~30 volts (or until it gets hot, sizzles, pops, or starts to draw additional continuous dc). That'd be the wrong polarity

If you get lucky and pick correctly, it should charge up and stop drawing current... if not, you'd be out 1 cap but would no which way is which...

hope this helps.

John L.

[dave_gerecke]

Hello Gabriel, If you could post more information about the cap or pictures, someone here should be able to figure the cap out. Complete description of the writing on the cap can provide a lot of clues and may allow one to find the datasheet for the cap.

Peace,

Dave

[Minion]

If you have a DMM with a capacitance tester then you can use that to find the Polarity...With the DMM on Capacitance you will only get a reading if the polarity is correct...That is with Polarized parts....

Cheers

[gabriel/norfolk]

Originally posted by auplater


depending on cost and how many you have/need, you could always guess on one of them, run it up to ~30 volts (or until it gets hot, sizzles, pops, or starts to draw additional continuous dc). That'd be the wrong polarity

If you get lucky and pick correctly, it should charge up and stop drawing current... if not, you'd be out 1 cap but would no which way is which...

hope this helps.

John L.

Originally posted by dave_gerecke
Hello Gabriel, If you could post more information about the cap or pictures, someone here should be able to figure the cap out. Complete description of the writing on the cap can provide a lot of clues and may allow one to find the datasheet for the cap.

Peace,

Dave

Originally posted by Minion
If you have a DMM with a capacitance tester then you can use that to find the Polarity...With the DMM on Capacitance you will only get a reading if the polarity is correct...That is with Polarized parts....

Cheers

auplater:

Lots of caps spare, your idea tied up with the charge and delay method. The problem being the forward velocity of the cat meant it's skin went forwards so quick that it's skeleton exited from the hole at its rear. there was a dreadfull smell from the cap and I am still picking bits of what looks like cotton wool up.

Dave

Thanks for the suggestion, the site is new to me and I would have problems up loading a photo.

Multi meter worked a treat as well I feel this is now the prefered method from now on.

Thank posters for your help

Gabby

[Mooly]

Easy Use a current limited PSU set to say 20 ma max current. Correct way and the voltage on the cap will rise to the voltage the PSU is set to. Wrong way and the voltage will "stop" at say 7 volts as the dielectric film breaks down and the cap will draw current-- non destructively.
There you go, safe, quick, foolproof, and you can use the PSU to "form" the caps as well if the voltage is high enough