Stepper motor Alternator

[Rdean33422]

This was an experiment I did with a stepper motor mounted on my V-Twin engine.
I was not expecting this result.





And a video


Thanks for looking
Ray

 

[kuhncw]

Ray, how are the stepper leads connected to the outlet? You are generating alternating current?

Chuck

 

[Rdean33422]

Yes it is alternating current but high frequency.
The coils are connected in series with the free ends connected directly to the socket.

Ray

 

[ShopShoe]

Perferal Info FYI:

I have also heard of using an automotive alternator as a stepper. Did not save the article.

--ShopShoe

 

[Rdean33422]

I had not heard of that but it may be possible.
Ray

 

[kuhncw]

"Yes it is alternating current but high frequency.
The coils are connected in series with the free ends connected directly to the socket.
Ray"

Thanks Ray. How many leads were on your stepper?

I was really surprised at the voltage you generated.

Chuck

 

[Rdean33422]

Chuck
Not as surprised as I was. I expected maybe 25volts and had made a bridge rectifier for D/C uses but when I recorded the A/C voltage I just plugged a led desk lamp into it.

The stepper motor was a two coil type with a center tap on each coil. The center taps were not used and just isolated. The two coils were hoked in series.
The stepper motor rpms are just a little slower than the rpm of the engine so I believe the output voltage can be increased with engine speed. There are more tests that I need to do.

Ray

 

[kuhncw]

Chuck
Not as surprised as I was. I expected maybe 25volts and had made a bridge rectifier for D/C uses but when I recorded the A/C voltage I just plugged a led desk lamp into it.

The stepper motor was a two coil type with a center tap on each coil. The center taps were not used and just isolated. The two coils were hoked in series.
The stepper motor rpms are just a little slower than the rpm of the engine so I believe the output voltage can be increased with engine speed. There are more tests that I need to do.

Ray

Thanks Ray. I've been looking into rectifying the stepper output to DC, but had not considered the path you took.

Chuck

 

[MrMetric]

So... What you are saying is that we can justify our motors to our spouses now as being "Emergency Preparedness" devices for that rainy day when the power goes out.... I *like* it!

 

[bluejets]

The two coils would need to be connected start finish finish start with out on the two starts.
Frequency will increase with speed but the voltage will only get to a certain level and thats it.
Alternator as a stepper...dont think so......maybe a brushless dc motor with the correct driver

 

[Toymaker]

Most any PM (Permanent Magnet) motor can be used as a generator/alternator. "Spindle" motors, the kind that use variable frequency AC, make excellent alternators. The guy on Tech Ingredients (a YouTube channel) explains how he built a 2 KW generator using an "out-runner" motor commonly used on drones and quads, powered by a 4 cylinder RC engine. He gives a detailed explanation of what he did and why he did it.

 

[Bentwings]

So... What you are saying is that we can justify our motors to our spouses now as being "Emergency Preparedness" devices for that rainy day when the power goes out.... I *like* it!HAHA I like that just remember nothing is free Even a bike generator still needs food for the rider

 

[100model]

This was an experiment I did with a stepper motor mounted on my V-Twin engine.
I was not expecting this result.

I did the same thing with a stepper motor I got from photo copier. It generated high frequency A.C. at a high voltage. This was the beginning of my testing every motor as a generator and at the time I did not understand why that happened. I do now know why it generates a high frequency, if you dismantle the stepper motor you will see the the rotor is magnetic and has lots of tiny poles. These are very close to each other so it will generate the steps needed to work as a stepper motor. If you use it as an alternator it will generate a high frequency because there are so many field magnets to excite your stator windings. To generate high voltage there must be many coils of wire connected in series. Very old induction heating equipment had the same idea before solid state electronics became common

 

[Steamchick]

2 simple bits of Physics to help understanding here (- in case anyone is not sure of the Simple electro-magnetic laws that apply!):

#1: B = nI: For a fixed field "B" (e.g. a permanent magnet crossing a motor pole) the CURRENT "I" is related to the Number of turns of wire, "n", linearly. Twice the number of turns = twice the current, 4 times the turns, 4 times the current. So, More turns on each pole piece means more current can be generated. But remember the wire rating, as if you have too much current (e.g. a short circuit, or motor start or something) then the insulation on the wire melts, coils short to each other and the coil simply fuses and burns away a lot of wire. So, the Number of coils per pole determines the current that can be generated for any particular magnet source, but the thickness of wire limits the current because of heating of the coils and lacquer breakdown.
Connecting 2 coils that are the SAME PHASE (Change from N to S pole at the same time) in Parallel will double the current available - but not the voltage.

#2: Voltage is proportional to rate of change of magnetic field: I.E. How fast you change from N to S on any pole. Double the field for no change of "speed" and you will double the voltage. Double the "speed" of a rotary generator and you will double the voltage.
A 2-pole generator/motor when driven will have N toS and back to N on either pole in 1 revolution. I.E. the AC frequency will be the same as the rpm. A 12 pole generator will have 6 full changes of N=>S=>N on each pole per revolution (half the poles are N, and half are S). So will be 6 times the frequency of the rpm. But at the same rpm, the voltage will also be 6 times that of the 2-pole generator, as the rate of change of field will be 6 times faster.
Connecting 2 windings in series, that are the SAME PHASE (Change from N to S pole at the same time) will double the voltage - but not the current.

Connecting poles that are not in phase is complex and not for this explanation.

Simply, by understanding the voltage of each coil as a single pole change happens in the motor or generator you have, you can decide a suitable speed for your generator to get the suitable output voltage, and by connecting coils that are in-phase in parallel, you can maximise the current as well. Staying within the Designer's voltages and current - per coil - is necessary, otherwise you can fuse the whole thing in an instance. It is relatively easy to increase the speed to increase voltage, or reduce the number of effective poles by connecting specific coils in parallel to increase the current.
Anywhere from 50Hz to 2000Hz will operate resistive devices like simple bulbs etc, but most AC motors are designed to be frequency dependant. Rectification to DC is a good way to utilise any "variable frequency" generated power (Such as from a variable speed generator like a "Home-made" wind turbine?), but then needs conversion to 50Hz (Europe) or 60 Hz (USA) to power your home.

I hope that is of some use to someone?
K2

 

[ajoeiam]

2 simple bits of Physics to help understanding here (- in case anyone is not sure of the Simple electro-magnetic laws that apply!):

#1: B = nI: For a fixed field "B" (e.g. a permanent magnet crossing a motor pole) the CURRENT "I" is related to the Number of turns of wire, "n", linearly. Twice the number of turns = twice the current, 4 times the turns, 4 times the current. So, More turns on each pole piece means more current can be generated. But remember the wire rating, as if you have too much current (e.g. a short circuit, or motor start or something) then the insulation on the wire melts, coils short to each other and the coil simply fuses and burns away a lot of wire. So, the Number of coils per pole determines the current that can be generated for any particular magnet source, but the thickness of wire limits the current because of heating of the coils and lacquer breakdown.
Connecting 2 coils that are the SAME PHASE (Change from N to S pole at the same time) in Parallel will double the current available - but not the voltage.

#2: Voltage is proportional to rate of change of magnetic field: I.E. How fast you change from N to S on any pole. Double the field for no change of "speed" and you will double the voltage. Double the "speed" of a rotary generator and you will double the voltage.
A 2-pole generator/motor when driven will have N toS and back to N on either pole in 1 revolution. I.E. the AC frequency will be the same as the rpm. A 12 pole generator will have 6 full changes of N=>S=>N on each pole per revolution (half the poles are N, and half are S). So will be 6 times the frequency of the rpm. But at the same rpm, the voltage will also be 6 times that of the 2-pole generator, as the rate of change of field will be 6 times faster.
Connecting 2 windings in series, that are the SAME PHASE (Change from N to S pole at the same time) will double the voltage - but not the current.

Connecting poles that are not in phase is complex and not for this explanation.

Simply, by understanding the voltage of each coil as a single pole change happens in the motor or generator you have, you can decide a suitable speed for your generator to get the suitable output voltage, and by connecting coils that are in-phase in parallel, you can maximise the current as well. Staying within the Designer's voltages and current - per coil - is necessary, otherwise you can fuse the whole thing in an instance. It is relatively easy to increase the speed to increase voltage, or reduce the number of effective poles by connecting specific coils in parallel to increase the current.
Anywhere from 50Hz to 2000Hz will operate resistive devices like simple bulbs etc, but most AC motors are designed to be frequency dependant. Rectification to DC is a good way to utilise any "variable frequency" generated power (Such as from a variable speed generator like a "Home-made" wind turbine?), but then needs conversion to 50Hz (Europe) or 60 Hz (USA) to power your home.

I hope that is of some use to someone?
K2

Adding in a bit - - - see the following
Why isn’t there a standard electricity frequency around the world?

Things are a bit more complicated than presented.
The big hydro-electric resource - - - Itapu - - well - - - most of the production is 50 Hz but some is 60 Hz - - - turns out that Sao Paulo runs at 60 Hz but most of the rest of Brazil runs at 50 Hz - - - how's that for 'interesting'?!?

All this goofiness because when things were being developed - - - there was no agreement and someone made more money by not going with changes suggested when moving from DC to AC. (Argh!!!!!!!!!!!!!)

 

[Rdean33422]

I finally got some time to do some tests at different rpms and under load.

1250 rpm
85 volts
943 cycles per second

1450 rpm
92 volts
1080 cycles per second

1700 rpms
103 volts
1240 cycles per second

1850 rpms
115 volts
1330 cycles per second

All readings are approximate but what they do show is the volts and cycles follow the rpms. I don't have any readings higher than 1850 rpms but I would expect the output would increase in proportion to the rpms.
If the stepper motor was geared up I wonder how high the numbers would get. The load on the motor was not that high.

Food for thought

Ray

 

[100model]

Anywhere from 50Hz to 2000Hz will operate resistive devices like simple bulbs

I have tested a light bulb on 30,000Hz so I am wondering why 2000Hz is the limit?

 

[GreenTwin]

Adding in a bit - - - see the following
Why isn’t there a standard electricity frequency around the world?

Things are a bit more complicated than presented.
The big hydro-electric resource - - - Itapu - - well - - - most of the production is 50 Hz but some is 60 Hz - - - turns out that Sao Paulo runs at 60 Hz but most of the rest of Brazil runs at 50 Hz - - - how's that for 'interesting'?!?

All this goofiness because when things were being developed - - - there was no agreement and someone made more money by not going with changes suggested when moving from DC to AC. (Argh!!!!!!!!!!!!!)

As I recall, when they first developed AC systems, a lower frequency was used for motors (for efficiency), and a higher frequency used for lighting (probably to minimize flicker).
The 50/60 Hz systems were a compromise between motor and lighting needs.
It wasn't an AC/DC thing.

The 50/60 Hz is another story, and I forget exactly how that transpired, but I recall reading about it.
I am pretty sure the 50 Hz was for better motor efficiency, but check me on that.

.

 

[GreenTwin]

I have tested a light bulb on 30,000Hz so I am wondering why 2000Hz is the limit?

I would guess an incandescent light bulb would work on many frequencies if you maintained the same current regardless of frequency.

You may start inducing current into nearby metal things at higher frequencies, or perhaps damage the filament somehow, but that is just a guess.

.

 

[GreenTwin]

I finally got some time to do some tests at different rpms and under load.

1250 rpm
85 volts
943 cycles per second

1450 rpm
92 volts
1080 cycles per second

1700 rpms
103 volts
1240 cycles per second

1850 rpms
115 volts
1330 cycles per second

All readings are approximate but what they do show is the volts and cycles follow the rpms. I don't have any readings higher than 1850 rpms but I would expect the output would increase in proportion to the rpms.
If the stepper motor was geared up I wonder how high the numbers would get. The load on the motor was not that high.

Food for thought

Ray

Many electrical devices have iron cores, and you have to pay attention to over-saturating the iron core (if that is the correct term), or operating the iron core outside of its effective range, else you can lose capacity and may overheat things.

.