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They measured a whopping 4.5mW. The windmill RPM was only about 860 then it was rotating at only about 14.3 revs per second. The "generator" was a cheap little DC brushed high RPM motor.
Just now I connected a cheap little DC brushed motor to an LED and spinned (spun?) it as fast as my fingers could. It did not light.
Most helpful? I've seen no evidence of that in this thread. Lots of irrelevant comments and comments that the project can't work.
I pity the poor kid trying to sort the tiny bit of useful information from the noise in this thread.
[Note to moderators: delete this if you must, but consident my point. Ban me if you wish.]
View attachment 98576
Of course he could, his problem is in not spinning the motor at any kind of reasonable speed - small DC motors work pretty well as generators, but you have to make them rotate
Can you honestly read through the posts here and believe the student doing this project is benefiting from most of them?
The options given have been to use a meter instead of a light, an energy-harvesting circuit to flash an LED once every 6 weeks, etc, etc.
My wife's Nissan has one of those awful CVT transmissions with "infinitely variable" ratio to optimize RPM. Maybe it could work on a windmill to optimize power transfer.I was thinking the same. Use a continuously variable speed belt drive on the generator (like some cars have) and set it for your country's wind speed.
| DC motor | DC Motor | DC motor | -------- At light load -------- | ------ At medium load ------- | ------- At heavy load ------- |
| Voltage | Amps | Watts | RPM | Load ohms | Volts | Gen Pwr | RPM | Load ohms | Volts | Gen Pwr | RPM | Load ohms | Volts | Gen Pwr |
01 | 0.5 | 0.2 | 0.1 | 650 | 25 ohms | 0.15 | 0.0009 | 620 | 15 ohms | 0.13 | 0.0011 | 600 | 5 ohms | 0.10 | 0.002 |
02 |
03 |
|
|
|
etc.
Ok. So we've established that it is indeed a brushed motor and not a brushless one. But that the speed at which it's being driven is probably too slow to produce a useful output.
I think the thing to do now is to do a little experimenting.
Equipment needed:
1) One DC motor identical to that which is in the turbine. We will call this the Generator.
2) A second DC motor. It may be the same or different. If different it should be larger. We will call this the Motor
3) A varaiable voltage DC power supply.
4) A tachometer, or some method to measure RPM.
5) A voltmeter.
6) A variable resistance to use as a load. As a first order approximation, I would select something that could go from about 4 Ohms to ~25 Ohms in ~0.25 Ohm steps. A 25 Ohm rheostat should do that nicely. In the following procedure, increasing the loading means reducing the resistance so that the current increases.
Setup:
1) Mount the motor and generator with their shafts coupled together.
2) Connect something to the shafts that the tacometer can read.
3) Connect the power supply to the motor. Set the output voltage to zero Volts to start.
4) Connect the voltmeter and resistive load to the generator. Set the resistive load open, or to it's highest resistance.
The purpose of this exercise is to find where the useful RPM operating range of the generator is. At each step you need to observe and record the behavior in both unloaded and variable loaded conditions. The amount loading will be determined empirically at each step to find where the useful power range is. To do so, you will adjust the resistive loading down while watching the voltage. As the resistance is lowered, the current increases, but the voltage will also decline. The voltage will be highest with no load. But, since that current is zero, the output power is also zero. You need to find the sweet spot where the Volts times the Amps results in the highest Watts. Enter a wide range of measurements into a spreadsheet program and graph of the results.
1) Adjust the DC power supply so that the shafts are spinning at a rate equal to that of the turbine. Record the reading of the voltmeter and a range of loaded values.
2) Increase the voltage to roughly double the RPM. Record the results.
3) Continue until you reach the upper voltage limit of the motor.
Your table will look something like this:
The values in the DC motor Watts column is calculated from Motor Volts x Motor Amps. Gen Pwr is calculated from Volts^2 / OhmsCode:| DC motor | DC Motor | DC motor | -------- At light load -------- | ------ At medium load ------- | ------- At heavy load ------- | | Voltage | Amps | Watts | RPM | Load ohms | Volts | Gen Pwr | RPM | Load ohms | Volts | Gen Pwr | RPM | Load ohms | Volts | Gen Pwr | 01 | 0.5 | 0.2 | 0.1 | 650 | 25 ohms | 0.15 | 0.0009 | 620 | 15 ohms | 0.13 | 0.0011 | 600 | 5 ohms | 0.10 | 0.002 | 02 | 03 | | | | etc.
Data in line 01 is an example, and is not to be used in your table.
Disclaimer:
The procedure above is how I would go about determining the best speed change ratio for the gear/pulley requirement for your system, and is my first think through of a new process of which I don't have an existing history. Once in the process, I usually come up with variations as I see how things are going. Feel free to vary this process as you see fit at the time of testing.
Have fun, and good luck.
Chris
Hi JonSea,Spec, you are exactly right. A thousand pardons.
Please explain to me how you're going to read a book in the dark by the light of a meter or an LED flashing for a microsecond every 6 weeks. I'm kind of slow on the uptake, so please explain in great detail.
Most helpful? I've seen no evidence of that in this thread. Lots of irrelevant comments and comments that the project can't work.
I pity the poor kid trying to sort the tiny bit of useful information from the noise in this thread.
[Note to moderators: delete this if you must, but consident my point. Ban me if you wish.]
Hello,
Isnt that just harsh judgement? Not to mention rude at the very least.
I ignored your rude reply in my thread and i am betting other people will start to ignore you too if you continue to act with such indiscretion. Maybe think a little before you reply.
I agree.JonSea , Please don't leave the thread. You were providing some very useful information.
In all honestly, several of AG's posts were not related to the actual question, and were going against the requirements specified by the OP. I expect this is what JonSea was referring to. That being said, the way he pointed it out was a bit rude. Let's try to be more polite here from now on.
JonSea , Please don't leave the thread. You were providing some very useful information.
In the other thread there was no teacher wannabee rudely insulting and criticising me.