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in need of a capatior

Posted: Fri May 02, 2003 2:24 pm
by myp71
I was wanting to know if anyone would know of a place to get one capatior 100volts non polalized 5 uf or like a 4.7uf<p> Thanks in advanced.
Ryan

Re: in need of a capatior

Posted: Fri May 02, 2003 3:07 pm
by Externet
Hi Ryan.
By canibalizing the abundant defunct computer switching power supplies you may find 1 to 2 uF / 250V, use some in parallel if you cannot find the capacitors at a store.
Miguel

Re: in need of a capatior

Posted: Fri May 02, 2003 6:40 pm
by russlk
That is like a motor starting capacitor. Any electric motor repair shop should have some, probably a higher voltage rating.

Re: in need of a capatior

Posted: Fri May 02, 2003 9:06 pm
by analogee
Sure thing! Get 2 50V 10 uF electrolytic capacitors, and hook them in series, plus-to- plus (or minus-to-minus, doesn't matter).<p>The result will be a non-polarized capacitor with a voltage rating of 100 V and a capacitance of 5 uF.<p>Or, places sell these as non-polarized electrolytics; they are essentially the same as what I told you to do, all in one nice package.<p>Regards,
Todd<p>[ May 02, 2003: Message edited by: analogee ]</p>

Re: in need of a capatior

Posted: Fri May 02, 2003 9:17 pm
by myp71
Hi guys, thanks for the help this cap is going across a transformer ac voltage I still might try a motor shop see what the have they are hard to find these caps 100volts non polarized of course this is a happen town with lots of shops NOT.<p>thank you everyone for your help, this forum keeps me busy
Ryan :D

Re: in need of a capatior

Posted: Sat May 03, 2003 4:05 am
by rshayes
If you are going to connect two polarized electrolytic capacitors back-to-back, eack capacitor should be rated for the full voltage. Electrolytic capacitors act something like a diode, and will conduct with low voltages of rerversed polarity. Electrolytic rectifiers were actually used in the 1920's before vacuum tube rectifiers became common. You can get an idea how poor they were by noting that silicon rectifiers replaced selenium rectifiers, which replaced vacuum tube rectifiers, which replaced electrolytic rectifiers.<p>Motor starting capacitors are rated for AC use, but usually for intermittent operation. They are often quite bulky, similar to "computer grade" electrolytics.<p>Some paper or plastic (polyester or polypropylene) tubular capacitors are made up to the 5 or 10 microfarad size. Usually these are rated at 100 volts or above. I would look for these in the Mouser or Digi-Key catalogs or in surplus catalogs.<p>If you have a substantial AC voltage across the capacitor, check to see if the capacitor has a ripple current rating. Most electrolytic capacitors will not stand high ripple currents. Metal cased tantalum capacitors tend to make a loud noise (temporary hearing loss level) when they fail, as well as imbedding the pieces in nearby objects. Aluminum electrolytic capacitors scatter shredded aluminum foil and electrolyte around (possibly corrosive). Metalized foil capacitors usually fail by burning the foil open, but may not actually explode.<p>Be especially wary about connecting capacitors across the AC line. Only a very few parts are approved for that use by UL and the other standard setting agencies (CSA, DIN, etc.).

Re: in need of a capatior

Posted: Sat May 03, 2003 5:34 am
by Chris Foley
Possibly this has to do with the intercom circuit in a previous post? You might want to try scrounging one from an old phone with an electromechanical ringer -- I think they all had them.

Re: in need of a capatior

Posted: Sat May 03, 2003 12:26 pm
by k7elp60
Ryan,
You might try Mouser electronics. WWW.mouser.com
There current catalogue lists a 4.7uf 100V non-polarized as part# 140-NPAL100V4.7.
Ned

Re: in need of a capatior

Posted: Sun May 04, 2003 7:49 am
by Carl Pugh
For motor-run capacitor try Grainger, www.grainger.com

Re: in need of a capatior

Posted: Sun May 04, 2003 7:34 pm
by myp71
Wow thanks everyone for all your help I will start looking around the advice you guys gave me and see what I can find<p>
thanks again,
Ryan :D

Re: in need of a capatior

Posted: Wed May 07, 2003 8:43 pm
by analogee
stephen -- thanks for the correction on the back-to-back capacitors. I know I've done this before when I needed a non-polarized cap, and didn't have any at hand, but I probably never got anywhere near the voltage limit. Didn't think about how the leakage of the reversed polarity unit would basically apply the full voltage onto the properly biased capacitor.<p>Regards,
Todd