[TechAssist] Re: Need 30mfd 330vac run capacitor
- From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Sat, 25 Oct 2003 15:53:57 -0400
Start caps are only engaged for a few seconds and then disconnected by a
relay or centrifugal switch. The specs, sometimes printed right on the cap,
are for it to be engaged for only so many seconds and to be cycled only so
many times per minute.
If you reverse bias an electrolytic capacitor a DC current flows,
irreversable chemical changes occur, and power is dissipated causing heat.
Capacitors are not supposed to dissipate power. The heat causes the water in
the electrolyte to vaporize and build up pressure.
The effect of reverse bias is none-linear, so that a small reverse bias, up
to 10 % of the rated voltage may not cause much current to flow, but above
that the current will increase rapidly. Assuming that you had the foresight
to put a current limiting resistor in series with the capacitor before
applying the reverse bias, and that the current is small, after a while the
current will decrease and you have to raise the voltage to keep the current
flowing. If, after doing this you measure the value of the capacitor, you
will see that the value has decreased. That is because the reverse current
is causing the cathode foil to become anodized, thus putting the anode
capacitor and the cathode capacitor in series. Having different capacitances
and different breakdown voltages on anode and cathode, the behavior of such
a capacitor is somewhat unpredictable.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "Tri-County Tv" <tricountytv@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Friday, October 24, 2003 11:46 PM
Subject: [TechAssist] Re: Need 30mfd 330vac run capacitor
> Greeting Everyone,
> 1) This cap may be a start cap as I
assumed
> it was a run cap because of the low mfd rating. Perhaps in this motor,
which
> operates a lift chair, so it runs for very short durations, 30-60 seconds
at
> a time. Perhaps this cap is a start cap. 2) Where my shop is located, we
> have very few companys that carry these types of caps. I will order a new
> one from Grainger 3) Even though this subject is about caps and motors,
as
> you can see besides reel to reels that have motors with caps so do many
> turntables and I though the subject matter would be ok. When I opened
this
> cap it has a tar like substance in it. I was not sure if an AC capacitor
was
> the same as a NON-Polar, if it was why don't they just call it a
non-polar.
> I tried 2 80uF 350 volt caps in series (neg tied together) to test and
see
> if the motor would run and it did, I also noted that the caps did not get
> hot or even warm, everyone is saying they will over heat, but they did
not.
> I do not under stand why if the caps are being reversed biased, they
should
> get warm. Sorry it took so long to get back, I've been on service calls
all
> day. Thanks
> Tom Berger
> Tri-County TV
> Robbinsville
> North Carolina 28771
> Ph--828-479-6043
> Fax-828-479-4868
> (tricountytv@xxxxxxxxxxxxx)
> ----- Original Message -----
> From: "George" <grndmstrg@xxxxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Friday, October 24, 2003 4:02 PM
> Subject: [TechAssist] Re: Need 30mfd 330vac run capacitor
>
>
> > Most likely an oil filled tub capacitor.
> >
> > George
> > Afana Electronics
> > Moreno Valley, CA
> >
> > ----- Original Message -----
> > From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
> > To: <Techassist@xxxxxxxxxxxxx>
> > Sent: Friday, October 24, 2003 12:13 PM
> > Subject: [TechAssist] Re: Need 30mfd 330vac run capacitor
> >
> >
> > > First, electrolytics cannot be used for a run capacitor or they will
> > > overheat and vent or explode. Electrolytics are only used for
> intermittant
> > > duty start
> > > capacitors. The run capacitors are film or paper capacitors. Second,
> > > electrolytics exhibit semiconductor behavior when reverse biased so
> > hooking
> > > two in series to make a none-polar causes unexpected strange behavior.
> > > Jerry Silverman
> > > Greentron Inc
> > > 4 Newland Ave
> > > Greenville SC 29609
> > > 864 232 3889
> > > Fax 271 2080
> > > mailto:greentron@xxxxxxx
> > > ----- Original Message -----
> > > From: "Tri-County Tv" <tricountytv@xxxxxxxxxxxxx>
> > > To: <techassist@xxxxxxxxxxxxx>
> > > Sent: Friday, October 24, 2003 11:29 AM
> > > Subject: [TechAssist] Need 30mfd 330vac run capacitor
> > >
> > >
> > > > Greeting,
> > > > I have a question, is a capacitor rated at 30mfd 330
> volts
> > > ac, this is just a non-polar cap right? Could I use two caps in series
> to
> > > make up this cap? Like two 60uf 450 volt dc capacitors in series. It
is
> a
> > > run capacitor for a motor in a lift chair. The motor runs on 110volts
> ac.
> > > > Thomas Berger
> > > > Electronic Home Systems
> > > > P.O.Box 309
> > > > Robbinsville N.C. 28771
> > > > Ph- 800-393-3997
> > > > Fax 828-479-4868
> > > > E-H-S@xxxxxxxxxxxxx
> > > >
> > >
> >
>
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