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Re: PFC current load



Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jonathan,

As far as I know there is no standard.  Usually the case markings have
little triangles and squares and a little digaram or note on the cap
telling how to hook it up.  If you have an ammeter, you could hook it to
the AC line and see how much current it draws.  Be sure these are the
"motor run" or true PFC caps that are made for full time AC, unlike the
motor "start" types.  If the cap is not the right type, it will quickly
over heat and explode.  I always wear saftey glasses and stand back when
hooking any cap to the AC for the first time.  The wrong or defective caps
make a very big bang!!

Cheers,

	Terry

At 03:55 PM 11/18/2001 -0800, you wrote:
>Terry,
>
>Thanks a bunch, with about 300uf max PFC for my 15/120 I'll defintly go the
>relay route, I have a 15 amp ice cube laying around. I appreciate you
>reducing the formula to a ratio for me! Another PFC question, I have multi
>value caps, 20/36uf, and they have three tabs, marked A,B,C. Is there a
>standard for the internal arrangement of this type of cap? My meter only
>reads up to 2uf, so I would have to string em all together to figure out
>which is which.
>
>Thanks again!
>
>Jonathan Peakall
>
>> If you place a cap directly across the AC line, like for a PFC cap, the
>current
>> is:
>>
>> I = Vac x (2 x pi x F x C)
>>
>> I is the RMS current
>> Vac is the RMS line voltage
>> pi = 3.14159...
>> F = 50 or 60 Hz.  AC line frequency
>> C is the capacitance in "Farads"
>>
>> So a 100uF cap is:
>>
>>  I = 120 x (2 x 3.14159 x 60 x 100e-6) = 4.52 Amps RMS
>>
>> It is proportional so a 50uF cap is 2.26 amps and a 200uF cap is 9.04
>amps.
>>
>> Cheers,
>>
>
>