Makings of a generator

[Steamchick]

Hi Tony,
I have been looking back on your post #9, but cannot find the power/current rating of the dishwasher motor stated anywhere? - I did note you said it was a 240V motor. I agree it should be run as a 3-phase motor - I guess in the dishwasher it had a variable speed 3-phase drive module controlled by the programmer?
It is a similar design to Car alternators, but I guess from it's size it could be anything from a 100W to a 1kW motor, as the forced draught cooling makes a big difference to motor ratings, and these open stator coils are easy to keep cool with a good draught from a fan. The rotor will be a permanent magnet (6-poles) with probably neodymium magnets, as almost all small motors use them now.
Have fun!
A really fun project.
K2

 

[TonyM]

Hi Ken. No actual info on this pump motor but the replacement is specified at 200v. 3ph 0-175Hz 100W.

 

[BaronJ]

Hi Ken. No actual info on this pump motor but the replacement is specified at 200v. 3ph 0-175Hz 100W.

Hi Tony, Guys,

First an apology I've just realised that the the number that I quoted for the diodes should be 1N400x I didn't realise my mistake until I read your post about you finding 1N5400 's The only real difference is the current rating.

Once you have converted the output from your generator to DC adding a capacitor across it will give you a much smoother voltage and enable you to more accurately measure the voltage. The actual capacitor value isn't at all critical, 10 to 1000 uf electrolytic one will do, but do make sure that its voltage rating is at least the same or higher than the generator output voltage. Make sure to connect an electrolytic the right way round, they are polarised devices.

As ken says, bulbs make good testing loads ! I tend to use surplus car headlight bulbs for testing. Wired in series or parallel as required.

Thanks for the videos. Looks like you have a winner there

 

[wce4]

Use Schottky Diodes in high-frequency applications. These diodes are perfect for high-frequency applications because they offer faster switching speeds and a lower forward voltage drop than conventional silicon diodes.
Schottky diodes are typically chosen when high frequency operation, fast switching, and minimal forward voltage drop are crucial. However, when reverse breakdown voltage is high and reverse leakage current is low, traditional diodes perform better.
Just my 5 cents worth.

 

[Steamchick]

Thanks Baron,
As Tony could be dealing at 100V or above, I suggested domestic bulbs as more like the resistance values he would find useful, as well as capable of the high voltage when things go "bang". I have never seen what 100- 240V, with potentially 100W available, does on a 12V bulb... should something go awry... - It could get "lively"?
Would one of these on each AC phase do the job properly? - The 3 x 12V DC outputs should then be able to be connected in parallel to charge a battery - or light a 12V Bulb I guess?
https://www.ebay.co.uk/itm/12474386...7779&msclkid=0bae2a49fc441d3f89634d7d8055d93c

K2

 

[Steamchick]

While it is difficult for the body to detect 12V DC, and it rarely forms a health risk, any Voltage over 50 V (AC or DC" is only considered "safe" in the UK when a trained operator is on the job. Certainly I have seen a trained and certified electrician take a "Belt" from a single phase of a 440V 3-phase installation, but he was wearing rubber soles, standing on a concrete floor, and that restricted the current to earth, but he still jumped involuntarily a yard or 2 away from the box of wires, falling to the ground, and explained "that hurt!", in words of some foreign language... I do not recommend anyone tries this potentially lethal trick! He had asked me if I wanted to be the one to turn on the system, to which I declined suggesting he "prove it was safe"... which it wasn't!
I do not know what 100V AC, with potentially 100W of available power from the generator, could do if applied hand-to-hand...
Stay safe, write more "enjoyable posts", not obituaries.
K2

 

[TonyM]

Absolutely agree Ken. Moreso with us "oldies" whose tickers tend to be a bit weaker than your average 40 year old.

 

[mcostello]

Worked at a place that had a 440 volt motor starter refuse to stay turned on. One of the Guys said He would fix that. He held the button in and it shot a grape fruit size fire ball out just missing His Head. Another Guy was poking around in a small electric box and We asked if everything was shut off. He said it was only 110 volt there by safe. We walked away and He poked His fingers in again and a fire ball came out and fused 2 fingers together. I am not an electrician, just a walker by at the right time. Other stories possible.

 

[TonyM]

So I put some load on it as suggested. I tested Volts and Amps using two 12v 21W bulbs in series and also using one 12V 21W bulb. I have no Idea what these results mean with regards to the output / usefulness of this as a generator so any expert advice warmly welcomed. To me the output is very low @ 2480RPM with barely enough to power a 21W bulb

 

[Steamchick]

I think I understand,

• at 2480 rpm you have 0.89A. on 2 x 12V 21W bulbs in series:
• at 2480 rpm you have 5V. developed across 2 x 12V 21W bulbs in series:
• at 2480 rpm you have 3.2V. developed across 1 x 12V 21W bulbs:
• at 2480 rpm you have 0.9A. developed across 1 x 12V 21W bulbs:

SO the generator windings - on a low resistance of the 21W 12V bulb - is developing a limiting current in the generator windings of 0.9A. - That is a Generator limit. Simply because the windings have an impedance of ~ 100 Ohms. And although the generator is trying to develop "100V" (or whatever you had with an open circuit) most of the voltage is developed across the generator, leaving a very small voltage across the LOAD (~5V.).
The POWER available, from your experiment - is about 4.5W... At 2480 rpm... = Not a very useful generator for the steam engine. But it may charge your phone? (converted with a full-wave rectifier).
I am a bit surprised, but not very surprised. The Motor is intended to have 240 V across it.
Perhaps this motor runs up to 10,000rpm in use in the dishwasher - or something? - so your limit of 2480rpm is to slow to be useful?
BUT it may be down to the way you have coupled wires from the generator to the bulbs... It is a 3-phase motor - see post #42 = "specified at 200v. 3ph 0-175Hz 100W."
Have you fed the output of the 3 motor wires through a rectifier like post #19 instructs?
Not visible on the videos...

I am sure the electrical guys can correct my errors here?
K2

 

[TonyM]

Thats exactly how they are connected

 

[Steamchick]

Seems like I had the right idea for my sums - based of RMS AC or DC. Hopefully, someone with generator experience can teach us more? (Correct my errors first of all!).
Ta,

 

[BaronJ]

Seems like I had the right idea for my sums - based of RMS AC or DC. Hopefully, someone with generator experience can teach us more? (Correct my errors first of all!).
Ta,

Hi Guys,

Lets start again !
I'm making the assumption that the motor you are using is not 3 phase but a dual voltage 110/220 volt one. The voltages that you have measured between the wires L1/L2/L3 would be what I would expect from a 3 phase motor ! Or a dual voltage single phase motor. And your rectified output would be the the sum of the output if all the windings were correctly phased !

But they are not ! Unless the magnets that you have used to make a new rotor are correctly placed and in the same magnetic direction to energise each phase 120 degrees apart the output voltage and current will suffer.

I would find the common point of all three windings and then measure the output voltage from there. I suspect that you will find that one of the outputs will be much lower than the others. For the time being forget the diodes, they are only useful to create a DC output.

The motor that I have is a single phase washing machine pump motor and the rotor appears to have three magnetic poles and has just a single coil without any other connections. The magnetic poles also seem to be bar magnets since they extend about two thirds of the way along the rotor.

HTH.

 

[TonyM]

Hi Baron, It is the original 6 magnet dishwasher pump rotor with just the shaft replaced.
So it is the complete original dishwasher motor just in the older motor casing.
I can add a connection to the common and measure between that and each of the three terminals tomorrow and see what I get. I don't have much I can use in the way of a load other than the auto bulbs.

 

[BaronJ]

Hi Baron, It is the original 6 magnet dishwasher pump rotor with just the shaft replaced.
So it is the complete original dishwasher motor just in the older motor casing.
I can add a connection to the common and measure between that and each of the three terminals tomorrow and see what I get. I don't have much I can use in the way of a load other than the auto bulbs.

Hi Tony,

If its the original rotor having six magnets, and that they are centered in the coils then I would have thought that you would have more voltage output ! Assuming that the wiring is correct. The only other thing that I can think of is a bad winding.

When I spin the rotor on mine I will measure the output voltage.

 

[TonyM]

Hi Tony,

If its the original rotor having six magnets, and that they are centered in the coils then I would have thought that you would have more voltage output ! Assuming that the wiring is correct. The only other thing that I can think of is a bad winding.

If I spin the rotor on mine I will measure the output voltage.

So I connected to the common. Measured resistances of coils. Common to L1, L2, and L3 all 24.6 ohm. Measured across coils
L1-L2, L2-L3, L1-L3. All showing 49 ohm.
Checked the output with the 12V 21bulb and the voltage now 2.5vAC 0.8amp.

Thinking it's probably back to the drawing board.

 

[BaronJ]

Hi Tony, Guys,

There is something definitely wrong !
The resistance readings that you are getting are correct for a star or delta connected 3 phase motor.

I ran my pump motor up this morning. Using a battery electric drill at about 550 rpm, I measure nearly 15 volts no load, with a 100 ohm resistor added across the winding I get just over 12 volts, which suggests about 100 to 120 milliamp output current, about 1.5 watts. I do know that the voltage will increase as the speed increases, 550 rpm is as fast as I have. My coil resistance is a bit higher than you have measured at 58 ohms.

I wonder if the magnets on yours have lost their strength ?

 

[BaronJ]

I think I understand,

• at 2480 rpm you have 0.89A. on 2 x 12V 21W bulbs in series:
• at 2480 rpm you have 5V. developed across 2 x 12V 21W bulbs in series:
• at 2480 rpm you have 3.2V. developed across 1 x 12V 21W bulbs:
• at 2480 rpm you have 0.9A. developed across 1 x 12V 21W bulbs:

SO the generator windings - on a low resistance of the 21W 12V bulb - is developing a limiting current in the generator windings of 0.9A. - That is a Generator limit. Simply because the windings have an impedance of ~ 100 Ohms. And although the generator is trying to develop "100V" (or whatever you had with an open circuit) most of the voltage is developed across the generator, leaving a very small voltage across the LOAD (~5V.).
The POWER available, from your experiment - is about 4.5W... At 2480 rpm... = Not a very useful generator for the steam engine. But it may charge your phone? (converted with a full-wave rectifier).
I am a bit surprised, but not very surprised. The Motor is intended to have 240 V across it.
Perhaps this motor runs up to 10,000rpm in use in the dishwasher - or something? - so your limit of 2480rpm is to slow to be useful?
BUT it may be down to the way you have coupled wires from the generator to the bulbs... It is a 3-phase motor - see post #42 = "specified at 200v. 3ph 0-175Hz 100W."
Have you fed the output of the 3 motor wires through a rectifier like post #19 instructs?
Not visible on the videos...

I am sure the electrical guys can correct my errors here?
K2

Hi Ken,

I had a play with the pump motor that I have (pictures earlier). On 245 volts it runs at 1445 rpm, which suggests that it is a four pole motor and that there are four magnets in the rotor.

I put my results in the reply No:57 to Tony. My motor seems to be on par with what Tony gets from his motor, but I don't have the variable speed drive.

 

[Steamchick]

I may be on the wrong tack...
BUT:
a 50 Ohm winding, generating v volts, - is short circuited will only permit I = V/r = 5 /50 A = 0.1 A.
So your 15 V O/C across a 58 Ohm winding at SHORT-circuit can only permit 0.26A...
Or 12V across a 100Ohm resistor will be 0.12A.. (but resistors are not linear, so change resistance with temperature, I.E. Current!).
I think the limiting factor is simply the windings are high resistance (small wires for many turns in a small space) and that limits the power that the generator can supply. , at the particular voltage developed by the speed of the motor.
With a fixed magnetic field (I.E. a P.M. motor) the thing is quite simple, in that the Field B = n I. where B is field, n = no of turns and I is the current that is in the windings.
The Voltage is based on rate-of-change of field (dB/dt) - hence rotor speed related. In old Trams, locos, etc. they would "switch-up" the turns from 32 poles, to 16, to 8, to 4 poles as the vehicle accelerated to keep the motor field change versus speed at an optimum. (Sounded like changing gears!). Now we use 3-phase and variable frequency to do the same.
It is quite "sensible" for a manufacturer of motors to tune the motor design for 15,000 rpm, 240 V (RMS) running, which means a 0.79 A motor is 190W (1/4 H.P.). Ok for a domestic appliance. And making 10,000,000 a year means they are cheap. But are limited to 0.8A at whatever speed you use them as a generator.... so if running at 550rpm, you get 240 x 550/15000 = ~9 V. = 9 x 0.8 = 7W. So it all adds-up as it is just simple calculations. (in my head at least!).
Therefore if that motor fits your model (size, appearance, etc.) and you are developing enough power and torque from the steam engine, it will happily run at 550rpm and deliver the 9V and 7W to LEDs, etc. for a display.
Tony, what power and voltage do you really want from the generator? Maybe a bicycle wheel hub generator will do a better job, as it is designed for "an Amp" at low rotational speed, and enough power for an array of small LEDs?
Or Baron's 1445rpm motor is a "better device" than a higher speed motor. as running at 500rpm as a generator should still produce about 85V if that's what you want? And supposing it is a 1/4H.P. motor (~190W) that would be about 190/245A, which at 85 V is about 66W. = What a beast for the model steam engine to drive! ~60W is car-headlamp power! Or a yard-long string of LEDs...?
K2

 

[BaronJ]

Hi Ken, Guys,

I don't disagree with your logic, though I don't see where you got 15,000 rpm from ! My pump motor only runs at 1,445 rpm on 245 volts. Based on that speed and 50 Hz suggests that my motor has four magnetic poles. I didn't attempt to measure the short circuit current, preferring a known load resistance. In this case the voltage across a 100 ohm wire wound 1 watt resistor.