# 3 phase alternator is generating a voltage, but no current

## Main Question or Discussion Point

I made a permanent magnet alternator out of a 3hp 3 phase induction motor. I am getting voltage, but no current at all. The alternator is wired delta and feeds a capacitor bank wired in a wye, to create a neutral. I have even tied the neutral into the alternator and still no current. I connected the alternator to another motor and it is as if they were mechanically connected but still no measurable current. Can anyone tell me why? I am not an electrical engineer or even an electrician.

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How are you measuring voltage & current ?
What value capacitors are you using to get your AC neutral / common ?
Have you tried a safe resistive load between a phase and neutral ??

russ_watters
Mentor
I connected the alternator to another motor and it is as if they were mechanically connected but still no measurable current. Can anyone tell me why?
Are you saying you electrically connected the alternator to the motor and the motor spun? If so, there must be a current -- but if there is no load, the current will be small. Try loading the motor.
The alternator is wired delta and feeds a capacitor bank...
Once the capacitors are charged, I would think the current should be zero.

Yes, the alternator was electrically connected to the motor , I even added a load to that motor and still I am measuring 0amps, no watts used, yet 140 volts on each leg. I have a meter connected and I have also used my fluke inline and nothing. The capacitors are Cobb-65r 440v standard run capacitors. I was about to put a light bulb in place of the motor to see what happens. I am really stumped here. When I say 0, I mean 0. There was no current flowing, crazy, even with the motor loaded. Took a little longer before it started turning but it did and still 0.

Baluncore
If your capacitors are too small, or you spin it too slow, it will not generate power.

The idea is to select capacitors that resonate with the motor inductance to generate the frequency required. You must be able to spin the induction motor at about 5% above that resonant frequency.

To measure the inductance of the motor you could do a locked rotor measurement, or you could run the motor and slightly overcompensate the power factor with the capacitors you will use.

I even added a load to that motor and still I am measuring 0amps, no watts used, yet 140 volts on each leg.
It is a bit crazy question (at least it matches how crazy the situation is) but are you sure your equipment can properly measure AC current at the required frequency?

Baluncore
I assume you have replaced the armature in the induction motor with permanent magnets.
1. How have you arranged the magnets as an armature, do you have a diagram or picture showing magnetic poles?
2. How much of the original armature squirrel cage remains?
3. What RPM was the induction motor originally specified to run? That will tell us the number of poles on the stator.

anorlunda
Mentor
I even added a load to that motor and still I am measuring 0amps, no watts used, yet 140 volts on each leg.
Something is wrong with this description. Forget the motor. Put 140V AC voltage across a capacitor and current should flow. Also, why would you expect nonzero watts for an ideal capacitor?

I agree with others. Tell us the details of your measurement instruments and setup.

Fluke multimeter. Magnets are arranged in 4 rows of 4 . 4 north, 4 south fallowing the original pattern of the rotor. Not a lot of the rotor survived. Each row is made up of 4 1/2” round 1” long magnets. The power meter is a cheap eBay model that is why I have the fluke, neither is measuring any current. After running the alternator I use a resistor to drain the capacitors and when I do there is barely a spark connecting it.

Sorry, 4 poles 1800 rpm, running it just a bit faster than that.

What is a locked rotor measurement?

russ_watters
Mentor
Fluke multimeter.
What model? Is it a clamp on? Does it require 60hz to get an accurate reading? How fast is the motor spinning?

Fluke 18b I will measure the exact speed tonight, have to work now...

russ_watters
Mentor
Fluke 18b I will measure the exact speed tonight, have to work now...
Ok, and let us know how you are connecting it, because that doesn't look like a clamp on.

....there is a danger of damaging the multimeter here (though it has a fuse).

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anorlunda
Mentor
After running the alternator I use a resistor to drain the capacitors and when I do there is barely a spark connecting it.
Wait a minute. An induction generator is AC. Discharging the capacitors is something you do with DC.

Confirm, you mean 140 VAC, not DC.
I made a permanent magnet alternator out of a 3hp 3 phase induction motor.
What does that mean? Did you make new windings? Did you put diodes in?

An AC 3 phase induction motor can be run as a AC 3 phase induction generator with no modifications at all. What did you actually do?

Baluncore
What is a locked rotor measurement?
That measures the momentary current when stalled. It is used for induction motors, not for alternators.
Your three capacitors as a load on an induction motor/generator threw me into thinking you were running an induction generator, but you actually have a synchronous 3 phase AC alternator.

I expect your PM armature should generate two cycles of voltage on each phase per revolution.
2 poles x 1800 RPM / 60 sec = 60 Hz.
The AC voltage and frequency generated will be proportional to RPM.

Capacitors are only needed for induction generators, not PM alternators. You do not need capacitors to generate DC from 3 phase. It will require 6 diodes in a bridge to rectify the AC to DC before it is used, or stored as DC in one capacitor.

I am really stumped here. When I say 0, I mean 0. There was no current flowing, crazy, even with the motor loaded. Took a little longer before it started turning but it did and still 0.
Very probably something is wrong with measurement or you managed to make perpetuum mobile

Tom.G
On pg. 12 of the the Fluke 18B User Manual, there are instructions for Testing the Fuses . Please do these tests and report the results here. (The User Manual can be downloaded here: https://dam-assets.fluke.com/s3fs-public/18b_____umeng0100.pdf)

You say the motor was slow to start. This could be from only two phases being energized; from either an open winding somewhere or an open ammeter.

Do you get any different start-up or load responses when you are not trying to measure current? That is without the meter in the circuit.

If there really is no current flowing, disconnecting one or more motor leads will have no effect. Try it and let us know the results.

Try wiring an incandescent light bulb in series with one or more motor leads to see if it lights. Try various wattage bulbs until you find some that dimly light .

To verify correct meter operation and wiring, disconnect the motor and replace it with light bulbs; three bulbs if the motor is Delta connected or 4 bulbs if Wye connected. Measure the current drawn by each of the bulbs and let us know the results.

Measurement. I had to translate the manual from Chinese. Still working on it...

davenn
Gold Member
I had to translate the manual from Chinese. Still working on it...

What do you mean by that ?? Why?

Tom gave you a link to an English version

Meaning I am leaning toward measurement as my problem. The capacitors are creating a neutral as the motor was wired as delta, did not know I could grab a neutral out of the delta.

I hope you are measuring current the right way?
Because you say there is output voltage, now thinking logically if you managed to measure a voltage across a capacitor that means there also must be a nonzero current, I bet your capacitor is not ideal so it draws so current,

that is why I am asking how did you measure the current? Simply turned to current setting and left the two probes across the capacitor or put the probes in series with one of the output wires?

since you have a permanent magnet rotor as other here said you don't have an induction generator anymore you instead have something that hopefully resembles a synchronous generator, in such case you simply take some say 100 ohm resistor connect it in series with your multimeter probes and then connect those probes across each two of the generator outputs, switch to current measurement and you should get a number of non zero value. Maybe you need less than 100 ohms for the resistor but then you have to calculate using Ohm's law as I don't know your parameters.