I collected some comparative data just now to illustrate....

Green, spun from dryer as described. Voltage measured from meter. No diodes. Max out is ~0.55v
Yellow, spun from dryer as described. Voltage measured from meter. No diodes. Max out is ~7.85v

*that* is the difference that I am concerned with. Specifically, how to characterize that difference from a data sheet. In these two cases, however, there are no markings at all on the motors - I don't hink that I spent more than $2 on either.

I'm getting there, but it will take a while.

 

Do you have an oscilloscope? Since the motor has a finite number of poles it is likely that there will be periodic peaks in its output when driven as a generator. The 'scope would make these visible and the peak interval would give you the shaft speed, if the number of poles is known. This number is usually discoverable by rotating the motor by hand and sensing the cogging.

I do have a toy oscilloscope and a frequency meter and maybe I could rig something - not a bad idea.

 

Why did you put a Full Wave Bridge on the output of the DC Motor with green blades?

Because he didn't want to use a puny single diode rectifier!

 

If you are interested in low voltage energy harvesting, look up LTC3105 and LTC3108 boost converters.

 

I collected some comparative data just now to illustrate....

Green, spun from dryer as described. Voltage measured from meter. No diodes. Max out is ~0.55v

.

Is there any way you can detect the nature of the motor, does it appear to have brushes?
If you short the leads together, is it harder to turn when spun?
Max.

 

If you are interested in low voltage energy harvesting, look up LTC3105 and LTC3108 boost converters.

Yeah, I have heard of those chips and I would add to them the S6AE102A/ S6AE103A from Cypress. I ran into these when playing with their solar beacons - https://www.allaboutcircuits.com/te...-ble-solar-beacon-from-cypress-semiconductor/ and https://www.allaboutcircuits.com/pr...-ble-humidity-and-temperature-sensor-monitor/ Later, @Mark Hughes wrote about their evaluation kit https://www.allaboutcircuits.com/te...ing-cypress-s6ae102a-s6ae103a-evaluation-kit/ It is a cool chip.

In a sense, the energy harvesting interest, particularly with respect to wireless (BLE) did give rise to the instant case and objectives. Sometime ago, I used a beacon to signal when an HVAC motor came on using a simple sail switch to power the beacon. Then, when the beacon on/off was detected, IR was sent to a TV to raise and lower the volume to overcome the additional noise of the AC [the #1 rule of energy harvesting in my view is to use less - in this case, moving one's butt off the couch to find the remote and turn the volume up and down). I had a thread about this https://forum.allaboutcircuits.com/threads/question-on-using-a-current-sense-transformer.147508/

It still works and I have just recently rebuilt it, dumping the Arduino and the HM-11 in favor of a Linklt 7697 which works very well and I am 99% confident that it will make it from breadboard to permanent case. In so doing, I started thinking more about the issue and whether it would be easily possible to substitute the beacon's coin cell battery+sail switch with a wind generator.

I like the idea of using BLE beacons as simple sensors - especially when you need simple feedback and do not need immediate or complex information (I turned the heat on - is air circulating? Is the light on? Did the pipe burst? - that kind of thing). When I say, not immediate, I mean, for example, that you do not always need a room's temperature 10 times per second.

The anemometer is just another example. A leak detector is yet another possibility.

I like BLE and I think beacons can be valuable for more than bad location information used as the basis of even worse advertising through an app glued to eyes and mind of a generation.

More than you needed to know - eh?

 

Is there any way you can detect the nature of the motor, does it appear to have brushes?
If you short the leads together, is it harder to turn when spun?
Max.

I don't know Max, these are dirt cheap toys:

https://www.banggood.com/DIY-Techno...p-1120341.html?rmmds=myorder&cur_warehouse=CN

https://www.ebay.com/itm/DIY-Mini-D...m=163136691438&_trksid=p2047675.c100005.m1851

as far as harder to spin when shorted - no, not that I can notice.

 

The Bangood one is very low quality, but it does look like a simple brushed motor.
The second one is slightly better, you would need to rotate it at 6000 rpm to get 5vdc out of it.
You get what you pay for!
Max.

 

The Bangood one is very low quality, but it does look like a simple brushed motor.
The second one is slightly better, you would need to rotate it at 6000 rpm to get 5vdc out of it.
You get what you pay for!
Max.

Yes, of course I saw those "specs" when I bought it. I would never count on those specs being accurate - in fact, I can already get more than 5.5v out as I posted.

How would you derive those specs (and additionally a little better information on the relationships - like even a curve or two):

Output voltage : DC 0.01v - 5.5v
Output current : 0.01 - 100mA
Rated speed : 100 - 6000 rev/min

From data sheets, like the one I posted as an example. That is what I am trying to determine.

 

This is not over for me, but I have been reading about it all day and this is where I am at.

I started out with the notion that a motor is also a generator and a generator is also a motor. Any motor can be a generator and any generator can be a motor. Now, I don't mean this literally in all case and all motors and all generators.

From there, I had only DC motors and I made some disappointing tests, like what was reported for the green motor. Then, I got the yellow one and saw a very different performance profile. So, I am still trying to understand that and will continue doing so.

Simplistically, what I want is a data sheet for the same device as a motor and as a generator. I'll likely not find that.

This posted link:

Looking around (not too thoroughly) I found this which looks fairly authoritative.

https://electronics.stackexchange.com/questions/152171/dc-motor-as-a-generator-voltage-and-current

is starting to make some sense to me.

While looking around, I am finding much on micro-generators - sometimes as concept devices and sometimes with references to watches and the like.

I am also finding a few demonstration devices, including the yellow one that I posted pics and links to. These usually have some specs (as posted) and those specs, for right now, are probably the best that I can do - that and some educated estimate as to how to consider the amount of "wind" that will produce how many RPMs.

I like this one https://www.amazon.com/CrocSee-Brus...NJKZHXEQ17G&psc=1&refRID=6G87B5CY3NJKZHXEQ17G including the answered questions.

But, the yellow one I have may work - I will find out and post the story if/when I get around to it.

 

I had a small motor running LEDs for a few years until the wind blew it over,
But the motor I used was a small stepper. And it had a 3 phase bridge rectifier too so you can get to use 6 diodes in stead of 4
Low drop Schottky diodes work well.
A stepper has no brushes to worry about but may be harder to get spinning.
If you can find a small 24V stepper, try that.
On the one I used, it had a model plane propeller, rubber band powered variety.

 

Hey @Raymond Genovese,
You can sit around and harvest energy at lower voltages for longer periods of time -- from air currents -- from WiFi -- from photovoltaic sources -- if, you are willing to wait long enough and have an energy source that accumulates energy at a greater rate than your storage medium dissipates it. The energy-harvesting chips use capacitors tied to boost-converters to increase the voltage to usable levels. You can usually back that up with some off-the-shelf batteries. Use the fan as a source of energy harvesting, and it won't matter much which one you choose.
Then, instead of using the fan as the trigger -- consider using an accelerometer to trigger movement -- or since you are working in a duct -- a barometer.
The real trick is how much energy you use during transmit....and nowadays I imagine it isn't very much at all. When I was a teenager, I made a 555-timer circuit that flashed a LED once every five seconds for a fraction of a second. It ran for many years off of a single C-cell battery....I want to say 6-8. If you augment the battery with an energy harvesting IC and a super-cap -- you should get even greater mileage.
Best,
Mark

 

Hey @Raymond Genovese,
When I was a teenager, I made a 555-timer circuit that flashed a LED once every five seconds for a fraction of a second. It ran for many years off of a single C-cell battery....I want to say 6-8. If you augment the battery with an energy harvesting IC and a super-cap -- you should get even greater mileage.
Best,
Mark

There used to be a great chip, the LM3909 that would flash an LED using less than the self discharge of an alkaline cell. I guess you can still get them, but at a very high premium from old stock. I loved those things.

[EDIT: just found a pair for $8.95 delivered, so I ordered them. I don't need them, but now I will have them. ]

 

@Yaakov,
That IC number sounds awfully familiar -- perhaps I'm remembering wrong.

 

@Yaakov,
That IC number sounds awfully familiar -- perhaps I'm remembering wrong.

You may be, the LM3909 uses a cap, and was hot stuff when it was new.

 

You may be, the LM3909 uses a cap, and was hot stuff when it was new.

What I do remember is burying that thing in a sock drawer -- and having a blinking LED after 2-3 apartment moves. Whoever made that IC deserves a raise!

 

That's the chip...and I still have one...

 

Hey @Raymond Genovese,
You can sit around and harvest energy at lower voltages for longer periods of time -- from air currents -- from WiFi -- from photovoltaic sources -- if, you are willing to wait long enough and have an energy source that accumulates energy at a greater rate than your storage medium dissipates it. The energy-harvesting chips use capacitors tied to boost-converters to increase the voltage to usable levels. You can usually back that up with some off-the-shelf batteries. Use the fan as a source of energy harvesting, and it won't matter much which one you choose.
Then, instead of using the fan as the trigger -- consider using an accelerometer to trigger movement -- or since you are working in a duct -- a barometer.
The real trick is how much energy you use during transmit....and nowadays I imagine it isn't very much at all. When I was a teenager, I made a 555-timer circuit that flashed a LED once every five seconds for a fraction of a second. It ran for many years off of a single C-cell battery....I want to say 6-8. If you augment the battery with an energy harvesting IC and a super-cap -- you should get even greater mileage.
Best,
Mark

Yes.

One point worth consideration is that in the Auto Volume on HVAC operation, it is important that the transmission rate is as short as possible. This is, of course, programmable on many beacons. For this application, I have it set at the highest rate - 100 ms as I recall. I want an instant response. That is going to consume much more power.

In other applications, you don't need that at all - case in point are the solar beacons I mentioned - getting temperature every few minutes is fine for many applications.

 

That's the chip...and I still have one...
View attachment 171576

That is exactly the source of my first one.
Brings back memories.