Stepper motor Alternator

[Steamchick]

Thanks Ray, but when I enlarged the label picture I could not read what it says. Maybe as you are closer than my poor eyes you can type the volts and amps it says? All I could get was a blur. - possibly DC 5.4V and 1.5A ??? But I did see " 2 phase" clearly, but not the "step" bit.
My worry is that if it is rated for less than 50V, you really should not try and run it over 50V. (Based on my experience of 12V car wiring being designed to resist a voltage "spike" of 50V without puncturing). The lacquer on the windings is very likely to fail due to switching voltage "spikes" if running at anything over 4 times the rated voltage - in my manufacturing experience... After the lacquer has failed, the windings will rapidly - usually catastrophically - fail.
So the question may be: How slow can you run it to get the voltage (around 5 volts) for USB charging? - put the AC output across a diode bridge and measure the DC voltage...
K2

 

[Toymaker]

In the first post there is a picture of the stepper motor that has all the information printed on it.

The engine is capable of higher rpms but first I must find a way to secure it to the work bench.

Ray

Looking at your first post, your workbench top looks like metal,...steel or aluminum?? If it is metal, I suggest you drill and tap a few holes in strategic locations that will allow you to bolt your current, and future projects securely.

If the top of your work bench is wood, you might consider adding some threaded steel inserts to the top of your work bench. I did this to my work bench years ago when I first built it and I've used them many, many times. The inserts turn your workbench into a large fixture plate, allowing you to easily bolt things down. I've mounted my grinder and vise to smaller wooden plates and can quickly add or remove them from the bench. Choose a regular spaced hole pattern that works for you. Also, if you have a milling machine, try to find inserts that use the same size internal bolts and threads as your mill's clamp set, as that will allow you use your mill's clamp set on your workbench

I put inserts on the corners of the table, which work great for the grinder and vise, but I need to put some in the middle of the table where do most of my work. Make sure they're recessed or flush with the surface and they'll never be in your way. The only problems I've run into is that occasionally you'll have to fish a small screw or nut out of one of the holes; but that's a small price to pay for the added utility they bring to your workbench.

 

[Rdean33422]

Steamchick: You have all the numbers right and the step is 1.8 degrees.
I run 36 volts D/C to the stepper motors on my CNC router with no problems.

Toymaker: Nice setup on your work bench and I will figure something out.

Thanks for the replies.
Ray

 

[100model]

The laminated iron cores used in most motors, including steppers, when used as alternators, will become less efficient as the frequency increases. This is mostly due to eddy currents within the iron laminations. Higher frequency typically requires the use of powdered iron core or ferrite materials.

The really old induction heater/furnace was a motor generator set up using a three phase motor to spin a single phase alternator to generate 10,000 Hz and the high frequency alternator had steel laminations in it. So the cut off point to where ferrite materials must be used is above that frequency. Car alternators are designed to run at 600 Hz before the three phase A.C.is rectified to D.C. A car alternator can safely run at twice that speed it so it can generate 1200 Hz with no problems to the electrical system.

 

[Toymaker]

The really old induction heater/furnace was a motor generator set up using a three phase motor to spin a single phase alternator to generate 10,000 Hz and the high frequency alternator had steel laminations in it. So the cut off point to where ferrite materials must be used is above that frequency. Car alternators are designed to run at 600 Hz before the three phase A.C.is rectified to D.C. A car alternator can safely run at twice that speed it so it can generate 1200 Hz with no problems to the electrical system.

From what I've read, there's no one distinct frequency above which iron laminations cannot be used, but it seems to be somewhere around 10kHz to 20kHz. Manufactures have also started to use thinner laminations in motors and transformers which allow even higher frequency operation. Other examples are the transformers in switching power supplies, which all operate above 20kHz and all use ferrite cores.

 

[Jeffro]

Car alternators are designed to run at 600 Hz before the three phase A.C.is rectified to D.C. A car alternator can safely run at twice that speed it so it can generate 1200 Hz with no problems to the electrical system.


That's good to know, I was worried my setup might cause a horrendous overpower energy release that could threaten the world !!!!

Actually I am in early testing mode with a 21W 12V bulb to see if this thing will actually run. Pleasantly surprised 15 -17V and engine still hit and missing.
Looks like I can gear up the alternator a bit. Field input is just a variable resistor at the moment. I am hoping to take the AC out of it later for fiddling with.

 

[Steamchick]

Sounds like you are generating up to about 40W to get such high voltages across that bulb? - but I am guessing without knowing how that filament changes resistance with current/temperature.
My point about voltage destroying the insulation... nothing happens until there is a big "bang". Failures often occur when the surge when you switch an inductance "On" (Inrush current) after an "Off" (or many repeated "Offs") has generated a voltage spike to puncture the varnish insulation on the windings.
I can only warn of possible failure modes when such devices are used outside their designed voltages. I cannot say "When", not how catastrophic such failures can be, as that is for you to experience. My advice is simply "Do not go far beyond any rated voltages, as the "guarantee expires" when you exceed those limits". I have heard many tales that simply said "Everything was fine until it broke/crashed/failed/went "boom"..."
"A little knowledge is dangerous; a lot of knowledge can be hugely dangerous!" (I think that was a remark made by or about J.R. Oppenheimer?). - But the same applies to voltages above 50V (which can kill humans).
Just so you don't misunderstand my messages.
Cheers! - and be safe when fiddling!
K2

 

[Rdean33422]

I bolted the motor down to the work bench today and got these results at 2400 rpms.

All the following tests done under load and at approximately 2400 engine rpms

25 watt light bulb
45 ohms measured
65 volts
94 output Watts


40 watt light bulb
27 ohms measured
35 volts
45 output Watts


60 watt light bulb
19 ohms measured
20 volts
21 output Watts

The unloaded voltage did increase at higher rpms (140 volts seen) but the output watts went down.
It looks like there is a point in rpms where the output drops off. The 25 watt bulb did better at a lower rpm but I don't have any readings for the other bulbs.
The 40 watt bulb did glow about 1/4 of its normal brightness and the 60 watt bulbs filament did show red.

So what does this tell us?
I am somewhat confused

Ray

 

[Gary C]

Some general info:

https://www.e-jpc.com/stepper-motor-voltage-explained/



http://www.reuk.co.uk/wordpress/wind/electricity-with-stepper-motors/

 

[Rdean33422]

This is from the above article and I do agree.

A good rule of thumb is to use between 10 and 24 times the motor’s nameplate voltage for the system bus voltage.

I didn't understand all the information but it did answer some of my questions.

Ray

 

[100model]

So what does this tell us?
I am somewhat confused

A meter that measures voltage and amps etc will not give an accurate reading of voltage with a crappy wave form and also are not designed to measure voltages with a higher frequency than 50-60 Hz To prove this point get two the same wattage light bulbs, connect one to a 12v battery and the other to your generator. The one connected to your generator will always be dimmer even though the meter says 12 volts. I went through all these problems 20 years ago experimenting with all sorts of motors and car alternators for model engines.

 

[Toymaker]

This is from the above article and I do agree.

A good rule of thumb is to use between 10 and 24 times the motor’s nameplate voltage for the system bus voltage.

I didn't understand all the information but it did answer some of my questions.

Ray

The above rule-of-thumb is for when you apply a voltage from a DC power supply to a stepper and use it as a motor, not as a generator.

 

[Toymaker]

I bolted the motor down to the work bench today and got these results at 2400 rpms.

All the following tests done under load and at approximately 2400 engine rpms

25 watt light bulb
45 ohms measured
65 volts
94 output Watts


40 watt light bulb
27 ohms measured
35 volts
45 output Watts


60 watt light bulb
19 ohms measured
20 volts
21 output Watts

The unloaded voltage did increase at higher rpms (140 volts seen) but the output watts went down.
It looks like there is a point in rpms where the output drops off. The 25 watt bulb did better at a lower rpm but I don't have any readings for the other bulbs.
The 40 watt bulb did glow about 1/4 of its normal brightness and the 60 watt bulbs filament did show red.

So what does this tell us?
I am somewhat confused

Ray

Your 3 readings are telling you that as the load increases, the output power decreases. Smaller resistance values represent greater loads to the generator, so as the resistance decreased from 45 ohms down to 19 ohms, the voltage from the stepper-generator also dropped, which is exactly what one would expect to see from any generator, but steppers are worse than standard PM motors. When used as a motor, steppers are designed to move to one very specific point of rotation, and hold that position very precisely until directed to move to another very precise location. In order to achieve this precise motion, the magnetic lines of flux inside a stepper are very narrowly focused points. When used as a generator, these narrow points of flux produce a triangle wave instead of the much preferred sign wave; bellow is a pic of the actual unloaded wave form from a single winding on a stepper:


If you placed a load on the stepper-generator, the voltage of the wave shown would drop and the triangles would begin to narrow. That's important because, when looking at a wave like the one above, power (watts) is represented by the area under the wave, so a smaller (shorter), more narrow triangle will have less area below the wave, which means less power.

 

[minh-thanh]

A meter that measures voltage and amps etc will not give an accurate reading of voltage with a crappy wave form and also are not designed to measure voltages with a higher frequency than 50-60 Hz

When used as a motor, steppers are designed to move to one very specific point of rotation, and hold that position very precisely until directed to move to another very precise location. In order to achieve this precise motion, the magnetic lines of flux inside a stepper are very narrowly focused points. When used as a generator, these narrow points of flux produce a triangle wave instead of the much preferred sign wave;

Simple graph showing the relation of frequency, voltage, power
Same voltage but different frequency

 

[Steamchick]

Hi Minh Thanh: Just a quirk. For the same shape of waveform, at different frequencies, you are correct saying there is less energy beneath the single waveform of a higher frequency (single cycle: single triangle). But if compared to the same waveform at a lower frequency, then surely "per second" the power is the same? - Power being the integral of the energy all the waveforms in a unit of time?
100model: Of course, meters are design for sinusoidal waveforms for measuring AC voltages (to give an RMS voltage, not peak voltage), whereas (demonstrated by M.T. on his oscilloscope) the stepper motor generates a triangular waveform.
Correct me if I am wrong, the RMS of a sinusoidal voltage is 1.7321/2 x peak voltage = 0.86 x V peak, whereas the triangular wave RMS voltage is 2/3 of the peak voltage = 0.66Vpeak? (A long time since I did this, so may be up the Swanee!) - So, the peak voltage of a stepper motor is 50% above the meter reading.... (It is voltage and temperature that damages insulation) whereas the rating plate for DC relates to the actual voltage the insulation is designed to withstand. Of course, manufacturers build in factors of safety: in this case the switching peak voltages that can be generated can develop very much higher peaks, and the insulation is adequate for their design limits. But watch out in case you develop "insulation puncturing voltages" - you may find out that has happened when there is a big bang...
And - just a repeat of the safety message - voltages of 50V and above (Peak or DC) can seriously damage your health if applied to nerve tissue. It can be literally heart-stopping. So "Please do not touch" ANY live electrical conductors unless you are sure they have no voltage. USE a probe and wire to earth to be sure.
Stay safe,
K2

 

[Toymaker]

Hi Minh Thanh: Just a quirk. For the same shape of waveform, at different frequencies, you are correct saying there is less energy beneath the single waveform of a higher frequency (single cycle: single triangle). But if compared to the same waveform at a lower frequency, then surely "per second" the power is the same? - Power being the integral of the energy all the waveforms in a unit of time?
100model: Of course, meters are design for sinusoidal waveforms for measuring AC voltages (to give an RMS voltage, not peak voltage), whereas (demonstrated by M.T. on his oscilloscope) the stepper motor generates a triangular waveform.
Correct me if I am wrong, the RMS of a sinusoidal voltage is 1.7321/2 x peak voltage = 0.86 x V peak, whereas the triangular wave RMS voltage is 2/3 of the peak voltage = 0.66Vpeak? (A long time since I did this, so may be up the Swanee!) - So, the peak voltage of a stepper motor is 50% above the meter reading.... (It is voltage and temperature that damages insulation) whereas the rating plate for DC relates to the actual voltage the insulation is designed to withstand. Of course, manufacturers build in factors of safety: in this case the switching peak voltages that can be generated can develop very much higher peaks, and the insulation is adequate for their design limits. But watch out in case you develop "insulation puncturing voltages" - you may find out that has happened when there is a big bang...
And - just a repeat of the safety message - voltages of 50V and above (Peak or DC) can seriously damage your health if applied to nerve tissue. It can be literally heart-stopping. So "Please do not touch" ANY live electrical conductors unless you are sure they have no voltage. USE a probe and wire to earth to be sure.
Stay safe,
K2

If you draw both triangle wave and sine wave with the same frequency and peak voltage on the same graph, it becomes clear the triangle wave has less area under the graph lines (& therefore less power), compared to the sine wave. Even worse, as the stepper output is loaded, the straight sides of the triangle begin to curve inward towards the peak; this is the result of steppers focusing most of the lines of magnetic flux into a single point. I tried to show this in the pic below, and if you look closely at the wave on the O-scope, you can see that the leading edge of the triangle wave is already slightly curving inwards, without any load.

As Ray has demonstrated, steppers can be used to generated electricity, but as the resistive load increases, a stepper's power output drops off rather quickly.
A much better motor to use as a generator is the outrunner BLDC, as they produce a 3-phase sine wave, and they have lots of poles like a stepper. Below is a typical outrunner BLDC motor,....notice the large number of magnets and coils.