RV on a single phase AC motor US (120vac/60hz)

[mramos]

I took a fan (motor with a fan blade) that was single phase 120VAC and 60 Hz (like the title).

Used 12uF and 14 uF caps (400+ volts AC of course) and popped them in and out.  I did the 12 and 24uF also hoping to see something as there is a magic combo there.

The draw went from 126 (stock from the store and plugged in to an outlet) to 127.5 watts (higher power draw from the power company) with the same fan and outlet with the best combination. 

I did not have a tach or ann meter.  But the air flow was the same to me.  And if someone wants to pop in and tell me I had more air out that is OK (sure someone will have something to add).  But I was shocked the load went up after all I read on it.

I figured it would drop the power draw (and the air flow).  But it went up in power draw and I do not think there was an increase in RPM (would bet on it based on RPM and watts pulled)

I can measure the RPM or air flow but sad to say the RV did not impress me and I will not bring the meters home.

Ash, some input to make it work better?  I think you are the expert here.  What went wrong?

I did not do any math, I did as I read.  It did not work.  It was pretty simple.

[ashtweth_nihilisti]

Hi mramos, Sorry this is late man.

Okay Jason and Gene are currently the only ones who have tested the single phase RV, so there isnt much data available, we do how ever know based on what Jason has reported works.

So Im not sure if this can be applied to your set up, I have included the exert from the compilations, perhaps this might help? let me know man

It is possible to run 1 PH motors in RV mode however in single phase configuration it requires 200mF 370 VAC caps (as an average to go into resonance) at 12 Ohms impedance, but will have a low Q which varies a lot, and needs further lab experimentation. A single phase demands more to run in RV mode as is lower impedance than a normal 3PH motor.

You can wire one phase motors to 460 VAC and can run them in RV mode vectoring the START phase at the proper angle (45deg). It will however be a bit less effective than a 90DEG 3PH force vector but it will be effective, all 1 PH motors can be run RV mode this way.

Other Research and development idea includes using them as an RV Type reverse induction alternators.  230 VAC one phase motors can self excite with cap to self resonance. Values range in 40 to 100mF 370 VAC oil caps.

The principle for the single phase is of course the same - one winding is connected directly to mains and the second through the caps. The caps make sure that there
will be ca 90-degree phase shift between the original input voltage and second winding voltage. The 90-degree windings will create a revolving magnetic field, which will start to drag the squirrel-cage rotor along.

For a Single phase RV 28VAC, use a 120VAC to 28VAC trafo (transformer) it will work de-rated, use the same cap value. With 230VAC motors use 48-52VAC. As it generates power factor correction to line across transformer that will have an interesting effect Single phase is not as effective as 3 Phase but it still works as "tuned wideband dipole.



Credits to Jason

For single phase power savings you can do easily just run about 60 uf (for 1/3hp motor), uf will have to be adjusted for best results, use a cap bank then after you find out what value works for your set up (drill press etc.) you can pick up a single cap (or two). Use 370v oil run caps.

Place caps parallel to line in close to motor. Most small motors have a centrifugal start cap (or winding) and I have found no need to mess with them. This works well with my drill press and other small load motors. I could not find a big savings on my air compressor but I did have the caps at the end of the plug and have not tried it close to the motor which seems to be desirable. A drop from 6-7amps to 2-3 amps is normal.

Use a 4 to 1 trafo, 120vac in and 30vac out. Use a cap bank of 370v oil RUN caps. Put caps after trafo parallel to line and adjust to lowest current draw.

-------------                        --------       ---       ----------
Line in            [transformer]                Cap      cap              Motor
-------------                        --------       ---       ----------

Most small motors I [Jason] have found have a start winding or capacitor that turns itself off after it is up to speed (centrifugal switch).You know for sure you have RV effect when you have a higher circulating voltage Amperage between the cap bank and motor then you have watts from a battery to inverter. Also, a magnet vibrates violently 4? away from motor housing. A single phase can work as alternator as well

[ashtweth_nihilisti]

This is the answer i got from a more experienced RV engineers

"
* RV RPM is very near to nominal RPM, it does not depend on amps (there
exists a small slip and in some occasions over speeding though)
* RV is not a DC motor that speed is input V or A controlled, so it is
stupid to measure fan air flow
* caps must be tuned to the load, it requires some patience, 100W is
normal for the fan at ca 3600RPM. It is not the way to measure OU,
complicated.
* lube the balls, take the fan off to see how small can be made (size
matters)
* learn something about 3PH and RV
* no lube proby brake with ass cheeks recommended to measure the shocking
power

[jjbeamish]

Hello mramos,

Perhaps I missed it but are you using a capacitance decade box? So you can easily switch capacitance in and out to find the lowest draw? Also, are your caps close to the motor? They need to be fairly close. Also, what size single phase motor are you using? What RPM, HP? If your draw without the caps was only 125watts I am assuming it was a small motor (under 1/3hp) I have not tried on anything that small. My motors (over 1/3 hp) all draw around 500 watts or more unloaded. I have gotten them down to run on 4watts (hp rating greatly reduced).

I would guess you are using a really small motor or not using a cap box to switch up and down. Or, if you have a 1/3hp or bigger motor that is running on 125watts, now this is just a guess, your centrifugal start mechanism (if it has one?) is not functioning correctly, in effect keeping the start cap ?on? when running at full rpm instead of shutting off, this would explain the small current draw you have, but that?s a guess.

Jason

[jjbeamish]

"Used 12uF and 14 uF caps (400+ volts AC of course) and popped them in and out.  I did the 12 and 24uF also hoping to see something as there is a magic combo there."

You really have to use a switch box with 5uf increments to switch up and down in 5uf (.5 even better). There is a window but too much capacitance and current draw will go up, back it off a few uf it  goes down, too little and it does nothing.

Jason