Practical Power Factor Application

I am slowly fixing all the annoying features of this house we bought. I may never get all of them corrected. But have a temporary solution
to one.
The house is mostly wired with 14 gauge wire and 15 amp breakers. So the drill press with a 1.5 hp motor will pop the circuit breaker if used for very long. The long term solution is to add a 220 volt 20 amp circuit, change out the motor for a three phase motor and use a VFD. But there are lots of other things that are more pressing.
So the temporary fix is to add a 40 ufd run capacitor in parallel with the motor. That corrects the power factor a bit and drops the current enough that the circuit breaker does not pop. The savings in power is pretty much nothing, but having the power stay on is priceless.
Dan
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Dan,
I know it would be much more expensive, but how about an active power factor controller? That would handle correction at all loads, and also wouldn't present that potential "dead short" across the line, should the cap decide to upchuck.
LLoyd
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On 7/8/2010 5:24 AM, Lloyd E. Sponenburgh wrote:

I stumbled across this Power Factor info just now: http://ecmweb.com/power_quality/resonance_adverse_effects_0201 / http://ecmweb.com/powerquality/capacitors_filters_resonance_0301 / It is a cogent read, notwithstanding the equation error on page 1 under "Harmonic and reactive currents".
[Reader's Digest Version: Low PF can *also* be caused by a 'current resonance' in the load, which can also have the effect of distorting the voltage waveform. (This is in addition to the more traditional 'impedance mismatch' cause of low Power Factor, addressed with parallel capacitance.)]
If you had a nifty Hall Effect current adapter, you could clamp it on to the line supplying your drill press and determine if your DP is trying to be a radio transmitter. :)
As you see at the end of Page 1, the author suggests that an RC filter tuned to snub the frequency of the 'current resonance' can reduce it significantly, improving system reliability.
--Winston
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Interesting. But I think that they are talking about non-linear loads, not electric motors.
Dan
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On Jul 8, 8:24 am, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:>

The cap is one I got at the recycling yard and did not cost me anything. Probably came out of a air conditioner. If it does short, the circuit breaker should keep things from becoming a disaster. Since the load is an electric motor, I am not sure how I could build an active power factor controler.
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There are commercial power factor controllers for motors that are usually lightly loaded, and only occasionally under normal load. They start at about $10.
I have one made many years ago -- "The Green Plug".
LLoyd
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On Thu, 8 Jul 2010 05:20:26 -0700 (PDT), " snipped-for-privacy@krl.org"

If you can change the voltage, leave the 14G wire and run it 240V 15A. Change out or blank off other outlets on that circut.
Thank You, Randy
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That is a good idea and I looked at the motor. It is a 120 volt non reversible motor. 8-(. The drill press manufacturer probably saved a dollar or two. Dan .
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Dan sez: "The house is mostly wired with 14 gauge wire and 15 amp breakers. So the drill press with a 1.5 hp motor will pop the circuit breaker if used for very long."
AFAIK, there should be no time limit as to how long a given load operates from a CB. Could it be your motor is defective and draws excessive current after it warms up? Figuring 1000 Watts per HP (Allowing for normal PF and efficiency) a fully loaded 1.5 HP motor on 120 volts should not trip a 15 amp breaker. The aproximate 12.5 amps is well within the 15 amp rated CB. It is highly unlikely the drill press will be fully loaded to 1.5 HP all the time it is on; thus it appears something is wrong with the motor or the CB is the real culprit.
Bob Swinney
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Interesting problem; What is the drill capacity? Do you REALLY need 1.5 HP on it?
These motors are notoriously inefficient, as are most split-phase motors.
Consider: 1.5 HP x 746 Watts/HP / .67 efficiency = 1670 Watts maximum demand. (I'm estimating the efficiency based on pool pump motors). Supply: 115 VAC x 15 Amps = 1725 Watts. Therefore pretty marginal set-up if the motor is loaded to capacity.
The circuit breakers have probably deteriorated over the years and the motor efficiency may very well be less than .67... But unless the motor is faulty or loaded to capacity, the breaker should not trip. Can you check the running current with a clamp-on meter?
Wolfgang
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The drill press has a #2 MT and I have a 5/8 cap chuck on it. And I really do not need a 1.5 hp motor on it, but I bought it used and that is what it had. I wanted to check the running current and have a clamp on adapter that is used with a regular multimeter. But the 200 mv range of my DMM does not zero. Otherwise I would have posted what the power factor of the motor is. The motor efficiency is probably well above .67, but the power factor is likely to be very poor.
Dan
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Looking in the W.W. Grainger catalog I find a 1.5 hp motors with full load amps from 15.2 to 19.8. I would not be surprised if the circuit breaker is off a little, but think the motor is the major culprit and has a low power factor.
Dan
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Household circuit breakers have a definite time based response to current. They have dual overcurrent sensing methods; thermal and magnetic. The thermal portion reacts to long duration overload situations and the magnetic portion reacts quickly to short circuits.
Any good breaker will carry an overload up to say 150% for at least several minutes without tripping. Higher overloads, say 300% should trip it in several seconds.
Being in the panel beside another heavily loaded breaker tends to reduce the breaker's ability to carry it's rated current due to mutual heating.
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Most residential services are billed in KWH instead of KVAR. I hope you are not in a KVAR billing area. That could make running rpc's expensive.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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œ
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    It happens when you talk them into running three phase to your house. :-)
    Enjoy,         DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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Don sez: "It happens when you talk them into running three phase to your house. :-)"
Which is the best reason to build your own 3-Phase system. And I don't mean buy an individual VFD for each machine. See many articles on Rotary Phase Convertors.
Bob Swinney
wrote:

Enjoy, DoN.
--
Email: < snipped-for-privacy@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
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On Sat, 10 Jul 2010 12:06:40 -0500, "Robert Swinney"

Im sure it depends on the specific utility and the tariffs it operates under, but I've had two small (100~200 amp) 3-phase services and also worked in shops with the same and none had a power factor penalty, or even service equipment capable of measuring power factor. On the other hand, the rate was a bit higher than residential, so perhaps the utility gets it's due that way.
--
Ned Simmons

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The term might be KVA. Too late to google, I'm up 4 hours past beddybye. Night. You all be safe.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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    It could make it worthwhile to go through the proper tuning of the RPC -- first to make the converison more efficient, and then to make the power factor optimum -- easy to do with AC rated capacitors, a clamp-on ammeter and a bit of time. It will also make it less likely to trip circuit breakers.

    KVA is the measurement unit. KVAR appears to be a brand of auto-tuning to optimize power factor/.
    KVA billing seems to be used mostly for industrial power users -- which encourages them to tune to opimize power factor.
    Here is an exampel of KVAR:
        <http://www.kvar.com/1000/home/
    Enjoy,         DoN.
--
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