Capacitors

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domnic

Senior Member
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Electrical Contractor
WHAT is the rule of thumb for capacitor uf per hp for motor start and run ?
 
ActionDave said:
For a guy like you yes. For a guy like me, I'd rather just have your phone number.
Click to expand...
It'll cost ya pal! International rates plus my exorbitant fee.........$1/hr......

Slightly more seriously, I have a couple of spread sheets I use.
Yes, I can do the calcs from scratch but I'm an indolent old git.
Do it once. Set up a spreadsheet with the arithmetic/trig so that subsequent visits to it just need the data to be keyed in.
 
Besoeker said:
It'll cost ya pal! International rates plus my exorbitant fee.........$1/hr......

Slightly more seriously, I have a couple of spread sheets I use.
Yes, I can do the calcs from scratch but I'm an indolent old git.
Do it once. Set up a spreadsheet with the arithmetic/trig so that subsequent visits to it just need the data to be keyed in.
Click to expand...

Doesn't it depend on the relative impedance (resistive and inductive) of the windings and the line frequency? (and maybe the geometry of the windings?)

SKYPE is cheap!
 
Domnic...

Following is a table of Start-Cap values taken from a text I used teaching Electrical Technology in a NYC Community College, many, many years ago:

Table 10.1: Typ Caps for 60-Hz, 1725-RPM, 1-Ph. Fractional Hp, Start-Cap, Split-Phase Motors

Hp 1/8 1/6 1/4 1/3 1/2 3/4

C, uF 80 100 135 175 250 350


The Text was: I.L. Kosow's "Electric machinery and Control"

Resulting phase displacement between the "Start and "Run" windings was approximately 80 Deg.

Do you need additional detail?

Regards, Phil Corso
 
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fmtjfw said:
Doesn't it depend on the relative impedance (resistive and inductive) of the windings and the line frequency? (and maybe the geometry of the windings?)
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Depends on the power and the power factor of the motor and the desired corrected PF.

This is how I do it:



And how the formulas take the strain in the main an let you see what you gain:





fmtjfw said:
SKYPE is cheap!
Click to expand...
But I'm not, I'll have you know!!!
:p:lol:
 
Golddigger ... you certainly exhibit a typical PTP's impatience!

Domnic...

The Run-Cap requires more discussion. Size and type will vary depending upon function. For example, is it used in a:

1) Duplex-cap scheme, fulfilling separate Start and Run requirements?

2) Single-cap scheme, fulfilling both Start and Run requirements?

3) Single-cap scheme, fulfilling a Reversing requirement?

4) Single-cap scheme, fulfilling a Braking requirement?

5) Single-cap scheme, fulfilling four requirements, i.e., start, run, reverse, and brake?

6) Single-cap scheme, capable of altering its start and run values?

Regards, Phil

ps: I will provde an answer to Domnic's ROT query, if he wants it!
 
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