RE: power factor correction capacitors (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Mon, 2 Jul 2007 11:20:40 +0100
From: Colin Dancer <colind@xxxxxxxxxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: power factor correction capacitors (fwd)

You need charge to flow in and out of the caps, so I don't think blocking
diodes will work.

You could try two caps in series, the two caps opposite way round, each with
a diode across their terminals such that the +ve terminal can't go more than
a diode drop more negative than the -ve terminal (i.e. on each half cycle
one cap is bypassed by a diode, and the other in use).  

Having said that, I wouldn't like to comment on the lifetime of your caps.
An electrolytic is normally rated for a limited ripple factor, and in this
case you'll be going all the way to the peak line voltage and back to zero
every half cycle!

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx] 
Sent: 02 July 2007 04:15
To: tesla@xxxxxxxxxx
Subject: Re: power factor correction capacitors (fwd)


---------- Forwarded message ----------
Date: Sun, 01 Jul 2007 21:57:59 -0400
From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: Re: power factor correction capacitors (fwd)

Considering that I don't get to the junkyard everyday (sadly), and since DC
capacitors are relatively cheap for their voltage/capacitance rating, could
I use two parallel strings of DC caps, each protected by a diode to keep the
power flowing the right way, or would this not work (or if I grounded the
strings)?  For my power supply, Java TC is suggesting I need a 295 uf cap
size, and considering how low the values of motor run capacitors generally
are, I would need a whole lot of them!  Thanks.
Scott Bogard.


>From: "Tesla list" <tesla@xxxxxxxxxx>
>To: tesla@xxxxxxxxxx
>Subject: Re: power factor correction capacitors (fwd)
>Date: Sun, 1 Jul 2007 17:25:04 -0600 (MDT)
>
>
>---------- Forwarded message ----------
>Date: Sun, 01 Jul 2007 12:33:25 -0400
>From: David Speck <dave@xxxxxxxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: power factor correction capacitors (fwd)
>
>Scott,
>
>IMHO, it's not worth it to try to build a PFC cap.  You can get metal 
>can (oval or round) oil filled motor run caps for free from dead air 
>conditioners, refrigerators, some furnaces, or dehumidifiers at your 
>local recycling center.  Usually, the bigger the original device, the 
>bigger the cap.  They are also available from eBay.  Even microwave 
>oven caps work, but at only 1 uF each, you would need several in parallel.
>Motor run caps will have a definite capacitance value, like 6 uF at 
>some voltage, stamped into the case.
>
>Do not use round black plastic encased electrolytic motor start caps -- 
>they are intended for a duty cycle of only a few seconds, and get hot 
>and explode if run continuously.  Start caps usually have a very wide 
>range of capacitance printed on the case, like 50 - 120 uF at some 
>voltage.
>
>Dave
> > Hey everybody,
> >      Can anybody tell me where I can get, some capacitors to use for
>power
> > factor correction (and how much it would cost me)?  Would it be 
> > insanely difficult to build one?  Could I use motor start or run
capacitors?
>Thanks.
>
>
>

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