Is a motor also a dynamo?

[ratstar]

I tried soldering (ed: the shafts) two motors together and connecting an led to one of them, and powering the other, but I didnt get the led to light up.

I read this thing on faradays law which said you can rotate inside a magnetic field to get a current, but it didnt work two motors connected at the shaft.

does anyone know the deal here?

 

[ratstar]

 

[Audioguru]

Your video is too fuzzy to see anything. The video sounds like you are spinning the motors mechanically very slowly.

You provided no details about the motors or your circuit:
1) Are the motors DC with permanent magnets?
2) How many volts do they normally run at? How many volts (from a battery?) was spinning one of them?
3) What was the voltage generated by the dynamo motor?
4) Was the LED connected with correct polarity?
5) If you did not use a current-limiting resistor in series with the LED then did it instantly burn out?

 

[(*steve*)]

I could hardly tell anything from the video, other than you sound like a sandgroper.

It is possible that you rotated the motor the wrong way and damaged the LED, the motor produced insufficient voltage to light the LED, the LED is infra-red and you couldn't see it light up, or the motor doesn't have permanent magnets in it.

If you have a multimeter, the best test is to connect it to the leads of the motor (in either a voltage or current mode) and rotate the motor by hand to see if anything happens. This is one of those rare cases where an analog meter works best.

 

[ratstar]

geeze, no need to be so rude! what the hell is a sand groper?

1) they have a magnetics to them, they constantly stick to things.
2) not sure, they are small hobby motors. i had the power supply flat tack for a little bit.
3) havent got a multimetre.
4) i had back to back diodes - so current would go both ways.
5) i checked the leds are still alive.

 

[(*steve*)]

You say you had back to back diodes, I presume you mean LEDs?

Did you mean they were in inverse parallel, or wired be back to back in series? You want the former, the latter won't work.

Damage to LEDs can be non obvious. A damaged LED may be slow to turn on our require a higher than normal voltage or current to turn on.

What color are the LEDs? Red, green, or yellow would be better than white or blue.

 

[ratstar]

yeh sorry, meant leds. yes they are parallel, opposite polarities. (im actually quite experienced, ive done many experiments by now. but it all still confuses me.)
red and yellow. red one could be damaged, but it still works with a 9v battery, theres about half the life of the battery left, got a hunch.

interesting... how things never bloody work!

 

[Minder]

Why not measure the voltage first?
Just about any P.M. motor will generate when back driven, a DC brushed motor will generate a voltage equivalent to the voltage required to rotate it at that rpm.
A BLDC motor will generate a 3 phase sine wave.
M.

 

[ratstar]

Yes, i might go get myself a multimetre - but it should be enough to light the leds, especially if i hammer the back of the motor with watts right? I got no response at all, gets me superstitious.

Just one last question - the output is dc from a dc motor, because of the commutator right?

 

[(*steve*)]

The output should be pulsed DC.

And I hope you are using a series resistor when you connect the led to a 9V battery.

 

[ratstar]

Yes shucks.

 

[Chemelec]

To get any Useable Power out of the Motor using it as a Generator, You need to Spin it at a Reasonably HIGH RPM.

 

[ratstar]

Its probably useless saying it, but they were smoking out of my VPS.
I guess ud get more if you could spin more than one, but one did not work at all.

 

[Minder]

Just one last question - the output is dc from a dc motor, because of the commutator right?

The generated voltage is obtained from the commutator coils passing under each of the fields, either wound or P.M.
In your case it will be P.M.
The degree of voltage out will depend on its RPM/voltage rating.
Just to test if it is actually generating, short the two leads and try and spin the shaft, if generating, you will feel resistance.
M.

 

[ratstar]

The generated voltage is obtained from the commutator coils passing under each of the fields, either wound or P.M.
In your case it will be P.M.
The degree of voltage out will depend on its RPM/voltage rating.
Just to test if it is actually generating, short the two leads and try and spin the shaft, if generating, you will feel resistance.
M.

holy **** your right!!! haha, ill try again!

 

[ratstar]

yep, its working. thanks that last tip was the one.

 

[Doug3004]

A brushed motor doesn't have the brushes set at an ideal phase to produce output electricity. Yes, it works, but not real well.

If you need a "mini-dynamo" for something, try using a plain (nema) stepper motor or an RC-brushless motor instead. If you attach an LED to the leads of one winding a nema-17 motor, you can see the LED light up if you spin the motor shaft even just a bit with your fingers. If you want a mildly-pulsing DC output, use some schottky diodes as rectifiers.

 

[Minder]

A brushed motor doesn't have the brushes set at an ideal phase to produce output electricity. Yes, it works, but not real well.

.

Where did you get that from,??
Every DC generator I have installed or worked on has the brushes set at 90° to the field, just as DC motors do that are capable of bidirectional control, and generation, which is the vast majority.
Including Edison's original!
M.

 

[ratstar]

A brushed motor doesn't have the brushes set at an ideal phase to produce output electricity. Yes, it works, but not real well.

If you need a "mini-dynamo" for something, try using a plain (nema) stepper motor or an RC-brushless motor instead. If you attach an LED to the leads of one winding a nema-17 motor, you can see the LED light up if you spin the motor shaft even just a bit with your fingers. If you want a mildly-pulsing DC output, use some schottky diodes as rectifiers.

I should experiment more then, getting more efficiency is probably possible since im only sitting at a dribbly ~ 6% output watts to input watts with what ive got now. plenty of room for improvement.