Hi there AAC

Recently I've been dabbling into IoT solutions being as low power as possible. In my more recent adventures I'd like to introduce an alternative generation in the form of wind generation. The IoT product I'm intending to use requires about 0.1Wh per day ( which is about 4,2mW steady smoothed out ).

For testing purposes I've selected and tried using this motor/"wind" generator.
https://www.aliexpress.com/item/DC-...erator-Blades-Best-Promotion/32799339070.html
Generation is however very poor, to no ones suprise I presume. I get about 10mW in a wind tunnel when impedance matching the motor (100O), about 1V and 10mA.

I get about 1V 9.3mA with 450rpm (which about matches the wind tunnel generation). With 1600rpm I get about 3.6V 34.5mA (very unrealistisch(?)).

I've tried 3d printing some HAWT based rotor designs as VAWT appears to be very inefficient, but these perform much worse(?).

I for example tried this one, generating about 3mW.
https://www.thingiverse.com/thing:1767153

I'm now looking into printing this one as it is actually rated for some power, 5W.
https://www.thingiverse.com/thing:2060281

But it appears that he recommends using a stepper motor? That sounds odd to me, aren't these very poor for generation?
Should I perhaps get a different DC motor? Or use some gearboxes? Or am I missing something?

I'd like to use wind for charging a supercap so it keeps working, with perhaps the help of some solar panel as secondary generation.

As I'm an electrical engineer and I think this is generally more electronics related, I've put it into this subforum. Please move if necessary.

Thanks!
Regards,
Thom

 

Welcome to AAC!

Should I perhaps get a different DC motor?

Looks like you need a bigger motor than the one you've done the measurements on. Bigger blades, too.

 

Welcome to AAC!

Looks like you need a bigger motor than the one you've done the measurements on. Bigger blades, too.

Bigger blades I can print to some extent. The ones in the second thingiverse are a tad bit too large for the printer, but this can be resolved with a soldering iron and some glue.

I do have more motors, I have a stepper, common band bicycle dynamo ( tore that one apart, literally a magnet in some coils or something, you probably know ) and a bike hub dynamo. The bike dynamos require a lot of force to turn, especially the band dynamo. The stepper I'm a bit concerned about efficiency.

 

Hmm, I'm not seeing an edit option. The reason I haven't looked into these motors yet is that the stepper require me to get a rectifier and the others my gut tells me require too much torque.

Do tell if there's an edit button.

 

You might also benefit from a very efficient solar boost converter that will help make more efficient use of the power that is available. Read the datasheet and other info at the link below. I don't know if this exact one will work for the power level you're dealing with, but the general idea may help:

https://www.kr4.us/sparkfun-sunny-buddy-mppt-solar-charger.html

 

I have a very sophisticated energy harvesting engineering sample available optimized for harvesting from kinetic sources. I can set mptt of 50%, 65%, 80% and 100%. It's just that it was most effective to set this at 100% and use a 100Ohms resistor for optimal conversion (this has been confirmed by the manufacturer).

Do you think I'm better off using mptt tracking?
100 Ohms gives me about 1.83mA @ 3.93V, 65% gave me 1.8mA @ 3.93V ( nearest ).

I think the part not directly related to generation is covered and can be left out of the equation.

https://e-peas.com/wp-content/uploads/2017/07/PB_AEM30940_REV1.1.pdf

 

Do tell if there's an edit button

Bottom left of your post.

 

Yeah, I noticed, you can tell at the bottom right. Appears that it goes away after like 10 minutes or so.

Do you guys think it's worth 3d printing the last thingverse link I posted in the OP? First thing I learned is to take the rating by a pinch of a pinch, rated for 10W, more like 1mW... But even if it generates on average 1000 times less I should be fine.

It's not like it has to generate 5mW, I can catch some of that with solar.

 

I've used a 24V stepper to just run an LED as a garden ornament. It has a propeller from a rubber band driven model aeroplane, 6 x high speed diodes as a 3 phase bridge and a filter cap. It ran for a number of years until a storm....
Using a stepper is a good idea as there are no brushes to worry about. Add a cowling to the back of the propeller to stop water getting into the motor. I must build it again as it was kinda fun to see it running

 

Alright, brushing aside (heh) the stepper, I got pointed to hobbyking dc motors for generation, e.g. this one.
https://hobbyking.com/en_us/quanum-mt-series-4010-370kv-brushless-multirotor-motor-built-by-dys.html

Low KV, low cost. I don't really know what to look for though!
Thoughts?

 

I would forget the 3D printing idea altogether, it's just not a match for the scale of what you are doing.
You need a super lightweight, strong fan structure that has enough surface area to catch some air.
Anything 3D printed is just too heavy and clunky.

Those 3D printed things look great, but that's about it.

I would make a super lightweight fan / turbine from thin sheets of plastic combined with other lightweight materials.
Next, boost the RPM's up with a simple belt or gear set to make the motor spin faster, it's like "impedance matching" the slow fan speed to the motor.

 

Hmm, I'm quite the potato when it comes to these things, for 3d printing I can fix it myself, but for that I'd need to ask my friend.
Are there things like drawins/schematics available for these?

 

What wind speeds can you expect?

 

Couple m/s.

 

5 mph is not much to work with; it suggests blades of about 1.5 ft. diameter for a final output of 200 mW.
I might go with just solar, say a panel of about 36 sq. in. for about 1 W.

 

The basic problem is that wind turbine makes a rather small rpm. However any motor-based alternator deman at least 100x larger rpm. But make a gear box means to loss 99,999% of energy into wear. Therefore stepper is rather smart choice because it will generate sth at ANY step what is couple of angular grades.

 

5 mph is not much to work with; it suggests blades of about 1.5 ft. diameter for a final output of 200 mW.
I might go with just solar, say a panel of about 36 sq. in. for about 1 W.

Probably going to look more seriously into just dropping wind. There are just too many problems and questions that need to be resolved.

The basic problem is that wind turbine makes a rather small rpm. However any motor-based alternator deman at least 100x larger rpm. But make a gear box means to loss 99,999% of energy into wear. Therefore stepper is rather smart choice because it will generate sth at ANY step what is couple of angular grades.

Yes and no. Stepper works nicely because it indeed always generates something noticeable.
Major downside however is significant retention torque which can be accounted for with gearboxes, but then a minimal speed is necessary as the stepper can not overcome the voltage drop over the rectifier.
I've tested mine, need at least 100-ish rpm to get anything remotely noticeable which is a nono considering I tested this with a drill ( ergo no regard for torque requirements ). Steppers are very "ampy" though, at 450 rpm I got about 3V 500mA what is way more current than my circuitry can handle right now (not like it's realistic to generate that with home sized rotor blades).
Purchased a gimbal motor. Might work better, may not. Heavily dependant on retention torque. Will post some results when I get it.

 

I think I use something like this on mine..
https://www.ebay.com.au/itm/RC-Mode...506189?hash=item4d44aa7f4d:g:tYIAAOSwjodaSrr5
And it was a small motor too.

 

What is true for all kinds of generators is that the efficiency never exceeds 100%. The result is that as the power out increases the power in must also be greater. This is why many of the devices require more torque, which is because they would put out more power. Of course, some devices are also less efficient and so they do take even more torque for the power that they put out. Higher powered stepper motors with the very small airgaps do take more torque but they will also deliver more power. Remember that it is the change in magnetic flux that creates the voltage and the bigger that change the more force is involved.
For increasing the speed , gears are not as efficient as the better belt arrangements, with the "V" belts being the least efficient because of their high running friction.
I am not sure of how much value these insights have to you, they are what I have gained by reading quite a few articles and taking a few engineering courses.