Power Factor Correction Capacitors

Touche, I shall and goodbye.

There's a reason this forum has lost many knowledgeable members.

JonSea said:

Geez oh grief. Suraj asked a question about power factor correction, and many of "most noted members" here proceeded to attack him. Nobody asked why he wanted to correct the power factor, but instead told him it was a waste of time! This forum seems to be filled with a bunch of grouchy old men, shaking their canes and yelling at the kids to get off their lawns!

As to the question of why, I have a similar problem. I have an industrial UPS connected to a bank of golf cart batteries to provide some backup power during power failures. It keeps the network gear up (got to have priorities you know), the small bit of power required to run a tank less gas water heater and the gas furnace.

The furnace blower motor is surprising small...a quarter or third of a horsepower...but it uses almost all of the capacity of the 1000VA UPS because of the power factor (and a frightening 50 amp draw on the battery bank). When YOU are the utility, you are paying the price of a crappy power factor.

So maybe keep an open mind, answer the question asked, and STFU if you have nothing to add?

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Most of us old grouches get grouchy because we know that there should be far more info provided than what the OPs give us which thus leads to all the speculation and disgruntlement with them.

BTW I'm only in my early 40's so I can still hit pretty hard with my cane!

I did ask if he was VA limited, which is valid concern.
.
" Are you trying to run it from a VA limited inverter? Then it might help to reduce Amps. "

I can see frustration from experts who are waiting for more details necessary Such name & part number of equipment or pertinent details driving this, to be able to clear up false assumptions.

So far the OP has not been forthcoming. HOpefully he will define the precise voltage source and motor in his next response.

Putting a switched UPS onto a large capacitor can induce large short circuit currents if not switched during the zero crossing. Switching voltage to a motor causes most motors to induce a load current not as fast, but within 1 cycle equal to the peak voltage over the DC resistance of the motor which is usually 5x to 8x the steady state current of the motor, so possible tripping the over current of the implied VA limited voltage source. Depending on the equipment characteristics, a PTC surge limiter may be required at the expensive of a longer startup time.

Modern furnaces use DC motors and constant current drivers to provide quiet start without exceeding the steady state capacity of the supply. Otherwise we get what I s called load regulation voltage error, current surges followed by and steady state power factor inefficiency or excessive excitation current in the motor stator for the unknown supply.

Load regulation is when a load drops the voltage when switched on and can occur from either caps or motors. The motor's impedance rises as it's speed increases due to the back EMF, then it drops while more work is being done with pushing . Some induction motors have an RPM controlled centripetal switch to boost starting current with a capacitor coupled coil, then it cuts out after approaching target speed.

We won't know until the OP specifies both the source and then motor precisely, what is the best solution. So far he has only stated steady state current without a pf result and no mention of what happens , which he wants to avoid.

What source is it and what load ...specify exactly.

Tony Stewart said:

I did ask if he was VA limited, which is valid concern.
.
" Are you trying to run it from a VA limited inverter? Then it might help to reduce Amps. "

I can see frustration from experts who are waiting for more details necessary Such name & part number of equipment or pertinent details driving this, to be able to clear up false assumptions....

Click to expand...

Actually, I think the OP was quite complete in his question.

Suraj143 said:

Without a line voltage (230V/50Hz) parallel capacitor, my refrigerator shows Power factor = 0.62 & It takes current exactly 1A.
I loaded a 5uF/450V capacitor to the same power outlet & the power factor increases to 0.82 & the current takes drop down to 770mA.

I have two questions

1) Is there any way to increase the power factor closer to 1?

2) When the refrigerator off (no load) the capacitor takes 350mA current which is too high.How to reduce this standby current?

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He spelled out the issue and asked how to further reduce the power factor. You all decided to jump on his and tell him it was unnecessary, useless or a waste of time without knowing anything about the application. He didn't ask for your opinions regarding the validity of doing so. Perhaps posting a link to this power factor correction calculator would have shown him the information needed to determine a suitable value capacitor and allowed him to calculate the value.

Or you might have helped him with the second part of the question. Yes, ideally the cap would be connected across the motor. It's in a refrigerator so it may not even be possible to get to the points needed to tie in the cap. The OP wants the cap in a box at the plug. So how can he do that? Perhaps a Hall effect switch driving a relay to connect the capacitor when current flow is detected?

So far in 2 pages of posts where the experts have spoken, neither of the OP's 2 questions have been addressed...until now.

But I have been told to STFU, so I'm done here.

JonSea said:

But I have been told to STFU, so I'm done here.

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You said that already then came back.

Having a bad day?

It seems obvious now that it is a homework question.

Last line shows a useful formula. Q is the apparent power in VA which originally was 220 VA
https://rapidtables.com/electric/Power_Factor.htm

It is not very economical to add capacitors to fridges and would required ZVS triac switches to prevent surge and lights flickering, although Motor start caps are plastic with higher ESR than general purpose plastic caps. The 8uF at 50Hz is near 400 Ohms and Dissipation factor around 10% can be expected for no name caps.

He can do the homework calculation to increase the cap size.

JonSea said:

Actually, I think the OP was quite complete in his question.




He spelled out the issue and asked how to further reduce the power factor. You all decided to jump on his and tell him it was unnecessary, useless or a waste of time without knowing anything about the application. He didn't ask for your opinions regarding the validity of doing so. Perhaps posting a link to this power factor correction calculator would have shown him the information needed to determine a suitable value capacitor and allowed him to calculate the value.

Or you might have helped him with the second part of the question. Yes, ideally the cap would be connected across the motor. It's in a refrigerator so it may not even be possible to get to the points needed to tie in the cap. The OP wants the cap in a box at the plug. So how can he do that? Perhaps a Hall effect switch driving a relay to connect the capacitor when current flow is detected?

So far in 2 pages of posts where the experts have spoken, neither of the OP's 2 questions have been addressed...until now.

But I have been told to STFU, so I'm done here.

Click to expand...

Excellent words & thanks for your kind attention.You and some few others understood my question. Your hall effect driving relay is a great idea.I'd think it a bit.

Thank Jon & Tony for the support.

Suraj, the simple answer to make your motor near unity power factor is to add more capacitance.
How much total is very easy. You need a cap that can deliver 380 VAR.

Since you have 0.62 p.f. @220V*1A=220VA you have inductive reactance stored energy of 380VAR then add -380VAR of capacitance to neutralize. Since Voltage lags current in caps, it is negative. Then your Power can be as low as 0.65 A *220Vac or slightly higher due to imperfect cancellation of harmonics. You can look up how to compute C from 380VAR at 50 Hz and 220V.

If your source does not have low impedance i.e. <5% of the motor coil DC R, you may see a load sag on startup. To avoid this a 1A ICL (inrush current limiter) from Digikey or other, , which are cheap, in series with the cap. all in parallel with the motor. The Cap must be rated for at least 650V or more and a large ferrite series filter will protect it somewhat from 1us rise time lightning surges. This is necessary to protect the Cap and the total cost is why you don't see these parts in fridges.

The LC resonant frequency will be well above 50 Hz but should not be on an odd harmonic.
You can compute this as well using basic engineering.

Is is worth reducing 770mA to 650mA? Only you know thus answer.