# Charging a cell phone with a mini wind turbine

#### Orlando S. Ferrassoli 1

Joined Dec 10, 2015
5
I made a mini wind turbine using a stepper motor as a generator, and I would like to use it to charge my cell phone when I am camping or out in the wilderness. The stepper motor has the following specs:
-From the diagram, It has two separate / independent coils inside, and one permanent magnet core.
-Size NEMA 17
-Phase voltage: 6.0 VDC
-Phase current: 0.8 AMP
In winds of approximately 15 to 18 MPH, I have measured an open voltage of up to 70+ (seventy) volts.
Using only one of the coils (two of the four wires), I put it through a step-down transformer, which gives me a voltage of 10 to 12 volts - then, through a full wave bridge rectifier (RS203L), then through a voltage stabilizer (M2940ct) - then two capacitors to smooth out the ripples. At this point I get a steady 5 V output. The amps stay around 250mA / 330mA (depending on the wind speed). But never more than that. An Iphone does not charge if you don't have at least 0.5 Amps.
Question: ...and here is the thing I am trying to understand...even if I connect the other two wires from the second coil to the transformer, I don't get more than the 330mA final output. I thought the potential for this motor/generator would be 0.8 Amps * 2 = 1.6 Amps...minus all the losses, of course. So, is there a way to obtain more than 0.5Amps with this? What am I missing or doing wrong? Your comments will be greatly appreciated.

#### wayneh

Joined Sep 9, 2010
17,167
It's hard to tell where your pinch-point might be. You could be limited by your step-down transformer. Your bridge and regulator have adequate specs but we cannot see how you hooked them up.

How are you measuring your output current - what is the load? Are you measuring turbine rpm while you measure output? How does your turbine rpm compare to the specifications, where the 6VDC and 0.8A are given.

And hey, why is the turbine rated at 6VDC? Is it not putting out AC?

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#### Orlando S. Ferrassoli 1

Joined Dec 10, 2015
5
Wayneh,
Thank you for addressing my question so quick. It's really appreciated.
-The transformer is a Signal Transformer DPC-40-600 / 115/230V 20/40VCT Class B 50-500 Hz 24.0 VA.
-Measuring the output current: I connect my Innova 3320 multimeter, with the DC mA or the DC 10A setting. I have tested the Amps with different small motors that I have, small incandescent light bulbs and of course the Iphone. They pull different Amps, but the Iphone is always in the range of 250mA to 330mA
-I do not know the RPM and don't have the means to measure. I have connected the shaft of the stepper motor to the shaft of my desktop fan (via a plastic tubing, very snug) and measured the output AC voltage at 42 Volts steady at the low speed setting...if this serves as a source of information.
-The rated 6 VDC is on the spec sheet of the stepper motor, I believe because when used as a motor, that's what the input is...just my guess.
-Perhaps my biggest challenge is to figure out how a motor that produces 70 volts AC (and can actually give me a shock...) can output a 5 Volt 0.5Amp. Thanks again

#### AnalogKid

Joined Aug 1, 2013
9,956
It is hard to tell exactly what you are doing without a schematic. 300 mA at 5 V is 1.5 W. It might be that this (plus the circuit inefficiencies) is all the energy the turbine can extract from the wind. If the 2940 you mention is a linear regulator, then another option is a switching buck regulator. The $2 wonders on ebay are ok for most things, but to wring out every erg you will need one of the new generation controllers that can run as high as 96% efficient. ak Thread Starter #### Orlando S. Ferrassoli 1 Joined Dec 10, 2015 5 It is hard to tell exactly what you are doing without a schematic. 300 mA at 5 V is 1.5 W. It might be that this (plus the circuit inefficiencies) is all the energy the turbine can extract from the wind. If the 2940 you mention is a linear regulator, then another option is a switching buck regulator. The$2 wonders on ebay are ok for most things, but to wring out every erg you will need one of the new generation controllers that can run as high as 96% efficient.

ak
Thank you,
Hello AK, I uploaded the schematics of my project to the best of my ability.
Is this enough information for you to analyze?
I look forward to your comments. This has been a frustrating experience for me, because it seems to me like the outcome is possible (obtaining 5 Volts and 0.5 Amps or more) from this system (wishful thinking might be a better way to say it...), and yet, everything I've tried hasn't worked so far. Please note that this generator has 2 coils inside, and I am using only one of them.
Thank you again,
O

Moderators note: removed white space and the over number of pictures

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#### wayneh

Joined Sep 9, 2010
17,167
-The rated 6 VDC is on the spec sheet of the stepper motor, I believe because when used as a motor, that's what the input is...just my guess.
Ah, I see. You are running a 4.8W motor as a turbine and getting 1.5W out, after losses. I don't think that would surprise anyone.

An iPhone might need 5W to charge and I don't think you can expect that from your motor.

Not that it matters, but you could try mapping the power output against the applied load. For a given rpm, there will be a peak where the load and the turbine are matched and maximum power is produced. I suspect it will be at a much higher voltage and much lower current than you want. That's why you might want one of those fancy DC-DC converters, to let the turbine run at maximum power with a larger current, low voltage load.

FWIW, I've used a drill press to give a fairly repeatable rpm, when testing a generator.

#### Orlando S. Ferrassoli 1

Joined Dec 10, 2015
5
Wayneh
Your numbers helped me see the project far more clearly. I really enjoy the learning process.
Since this is a 6 Volt x 0.8Amps = 4.8 Watt motor per phase, is it correct to assume that, because it has 2 (two) coils inside, it has a theoretical capability of producing 4.8 Watts x 2 coils = 9.6 Watts total (minus losses, of course)?
Thank you for the suggestions. Do you have a recommendation on a DC-DC converter?
I have seen several DC-DC converters on Amazon, but I am not sure which would be the right (or better) match. Would you have a suggestion?
Thanks again,

O

#### AnalogKid

Joined Aug 1, 2013
9,956
Since this is a 6 Volt x 0.8Amps = 4.8 Watt motor per phase, is it correct to assume that, because it has 2 (two) coils inside, it has a theoretical capability of producing 4.8 Watts x 2 coils = 9.6 Watts total (minus losses, of course)?
Unfortunately, no. The energy a motor consumes is almost completely unrelated to how much it can produce when operated as a generator, mostly because it is designed to be an efficient motor, not an efficient generator, and the electromechanical requirements of the two are different.

ak

#### wayneh

Joined Sep 9, 2010
17,167
Yup, AK nailed it. There's little connection between a motor's draw specifications and what its specifications might be when turned into a generator.

I have only a slight hunch that you'll get more power from your motor by putting the 2 phases in parallel (assuming they are truly in phase with each other, they may not be). This should double its current capacity instead of its voltage, which you seem to have plenty of already. I believe the DC-DC conversion that follows will be more efficient if the voltage and current conversions are not so large. But this is really just a hunch. Data beats all.

#### AnalogKid

Joined Aug 1, 2013
9,956
Also, you might try a smaller transformer. Without getting into mutual inductance and poynting vectors, it seat-of-the-pants makes sense that it takes more energy to wake up a large transformer compared to a small transformer. Figure out or measure the frequency of the AC out of the motor. If it is up in the audio range, try a small audio transformer. The higher the frequency, the more efficient the transformer will be and the less efficient the diodes will be. Life is choice.

ak

#### Orlando S. Ferrassoli 1

Joined Dec 10, 2015
5
I used plastic tubing to connect shaft-to-shaft of my stepper motor/generator to my pedestal fan, lined them up as perfect as I could, with almost no vibration, secured generator with rubber bands to a box at the exact height from my desk to the fan shaft. Used speed setting # 3 (fast)
I then connect the two coils of the generator in parallel. The detent torque, or cogging was too strong. Couldn't use that combination.
Next, I measured the voltage output of one individual coil, say coil A:45 V steady
Then, measured the other coil individually, say, coil B: 45 V steady
Next step, connected them in series A+B, output was 60 V steady (hmmm, interesting, I expected close to 45V x 2 = 90V!) - Detent torque / cogging was no more than when I used one individual coil...minimal.
After using a small transformer (thanks for the suggestion), full wave bridge rectifier, voltage stabilizer, electrolytic cap I could run small motors, LED lights, etc...but Iphone charged backwards (it lost one volt every few minutes..)
So, I finally connected the AC 60V from the generator directly to the Iphone charger pins, the pins that we normally insert in the wall outlet, and ran the fan motor (speed #3)...to my surprise, the Iphone went up one volt 85V to 86V...I left it there and after a while, it went up another volt..86V to 87V.
I used Google stopwatch online...and timed the next change...87V to 88V in 4 minutes and 10 seconds.
Right after dinner, I came back and repeated the same set up...got the same results..charging one volt every 4m:10s (give or take a few seconds for each change). Apple's proprietary internal circuitry may allow for a wide range of situations, which my home made circuitry may not be compatible with. I will continue this project, I still have a lot to learn.

#### wayneh

Joined Sep 9, 2010
17,167
You're braver than I am. It's interesting that the stock charger can accept your input directly from the generator, but you are placing some expensive equipment at risk.

#### AnalogKid

Joined Aug 1, 2013
9,956
Almost all standard small device chargers are offline switchers designed with a universal AC input voltage range that extends down to at least 85 Vac. Throw in some design margin and light loading and I'm not surprised that it runs at a much lower input. Usually these things are too low cost to include an undervoltage lockout. Still, a lot of tech for \$5.

ak

#### djsfantasi

Joined Apr 11, 2010
8,256
How much current does the incandescent lamp draw?

How are you connecting the iPhone to the generator? It expects a certain voltage on the data pins to charge normally. There are many references to this online.

Here's a circuit as an example.

#### tcmtech

Joined Nov 4, 2013
2,867
Next, I measured the voltage output of one individual coil, say coil A:45 V steady
Then, measured the other coil individually, say, coil B: 45 V steady
Next step, connected them in series A+B, output was 60 V steady (hmmm, interesting, I expected close to 45V x 2 = 90V!) - Detent torque / cogging was no more than when I used one individual coil...minimal.
After using a small transformer (thanks for the suggestion), full wave bridge rectifier, voltage stabilizer, electrolytic cap I could run small motors, LED lights, etc...but Iphone charged backwards (it lost one volt every few minutes..)
Your motor is a two phase unit with each winding 90 degrees off phase from the other which is why they don't add directly together to give you 90 VAC output.

Ideally to get a wider working range and higher output voltage you would be best off to put a full wave bridge rectifier and capacitor ( 100+ VDC 100+uF) on each phase and then stack their DC output together. By doing that you should be able to get up to 100 - 120+ VDC output which your universal input phone charger will take just fine even though its DC.