Power Factor Correction Capacitor

[[email protected]]

Hello- I am running an AC refrigeration compressor on a sailboat using
an inverter. By determining the DC watts and the AC VA i figure a
power factor of about .5 . I would like to correct this power factor,
and have calculated that I need a 150 uF capacitor to do so. My
question is, what kind of capacitor should I get with that capacitance
that will handle 120 V AC? I appreciate the help. John

 

[Homer J Simpson]

Hello- I am running an AC refrigeration compressor on a sailboat using
an inverter. By determining the DC watts and the AC VA i figure a
power factor of about .5 . I would like to correct this power factor,

Why?

 

[John Popelish]

Hello- I am running an AC refrigeration compressor on a sailboat using
an inverter. By determining the DC watts and the AC VA i figure a
power factor of about .5 . I would like to correct this power factor,
and have calculated that I need a 150 uF capacitor to do so. My
question is, what kind of capacitor should I get with that capacitance
that will handle 120 V AC? I appreciate the help. John

You need an AC rated capacitor, oil filled or polymer film capacitor
or bank of paralleled capacitors.

But be warned that your inverter may not like having a power factor
capacitor connected across it.
Example of oil filled type:
http://cgi.ebay.com/28-5-UF-330-VAC...oryZ4662QQssPageNameZWD1VQQrdZ1QQcmdZViewItem
Example of film capacitors:
http://dkc3.digikey.com/PDF/T063/1303.pdf

 

[[email protected]]

Hello- I am running an AC refrigeration compressor on a sailboat using
an inverter. By determining the DC watts and the AC VA i figure a
power factor of about .5 . I would like to correct this power factor,
and have calculated that I need a 150 uF capacitor to do so. My
question is, what kind of capacitor should I get with that capacitance
that will handle 120 V AC? I appreciate the help. John

As has been pointed out it would serve no useful purpose and may cause
you additional problems. By the way, how did you arrive at the 150uF
figure?

 

[[email protected]]

Thank you all for your help. First of all the reason I wanted to
correct the problem was because I have both a DC Ammeter and an AC
ammeter on the electrical panel, as well as an AmpHour battery monitor,
and its just nice for them all to correspond if at all possible. But
if there's a chance that it will hurt things to add a capacitor I
definitely won't do it. The only thing I really care about is the DC
Ammeter and the DC battery monitor. My question is are these DC
readings still accurate as far as true amount of amps being drawn from
the battery banks even when the inverter is putting out way more power
AC? Right now to run the compressor I get about 45 amps DC and 9 amps
AC... so should the 45 amps DC be accurate? Thanks again for your help.

 

[John Popelish]

Thank you all for your help. First of all the reason I wanted to
correct the problem was because I have both a DC Ammeter and an AC
ammeter on the electrical panel, as well as an AmpHour battery monitor,
and its just nice for them all to correspond if at all possible. But
if there's a chance that it will hurt things to add a capacitor I
definitely won't do it.

The problem is that the inverter probably outputs a waveform with some
fast rising and falling edges, rather than a smooth sine wave. Even
if it did produce a perfect sine wave, there is a fast edge every time
you turn it on, or connect the capacitor. The current through a
capacitor is proportional to the rate of change of voltage across it.
Fast edges imply large currents.

I have seen power factor capacitors added by having small inductances
in series, to limit the peak current, but it is tricky to keep the LC
resonance from being excited by any harmonic in the system (which
would also produce large current at that harmonic frequency).

The only thing I really care about is the DC
Ammeter and the DC battery monitor. My question is are these DC
readings still accurate as far as true amount of amps being drawn from
the battery banks even when the inverter is putting out way more power
AC?

The DC meter should represent an accurate measure of load on the
battery. AC power factor current represents energy borrowed and
returned each half cycle, so it heats the inverter up a bit, as it
sloshes back and forth through it, adding to its losses, but it
doesn't change the average DC load much. It just adds ripple to it.
But a DC meter should average that ripple and give an accurate average
answer.

Right now to run the compressor I get about 45 amps DC and 9 amps
AC... so should the 45 amps DC be accurate? Thanks again for your help.

It is an accurate measure of battery drain. It might drop a few
percent if you could eliminate the power factor current, because the
inverter would be wasting a little less power because the borrowed and
returned energy would be sloshing back and forth between motor and
capacitor, instead of between motor and battery, through the inverter.

 

[Homer J Simpson]

But
if there's a chance that it will hurt things to add a capacitor I
definitely won't do it.

Old rule: "If it ain't broke, don't `fix' it". It's good advice.

 

[vasile]

Hello- I am running an AC refrigeration compressor on a sailboat using
an inverter. By determining the DC watts and the AC VA i figure a
power factor of about .5 .

Did you measure it ? There is tool called "cos fi" meter.
But it does measure correct only sinusoidal shapes (as your AC
voltmeters and ammeters) There is a coefficient of 4.44 to 4 (shape
coefficient) between sinusoidal and rectangular waves.
About power factor, if you have a regular energimeter in your house,
and such a small cos fi, there is no compensation required because
there will be no effect in the money you'll pay for your energy...

If you gave an active energimeter and also a reactive energimeter in
your house (I have doubts you do) then it worth the trouble of mounting
capacitors...

greetings,
Vasile


I would like to correct this power factor,