# Question about which DC motor will suit project.

#### Benjamin0904

Joined Oct 3, 2020
22
Hi! My project goal is to build a DC Generator that produces minimal output. Here is the scenario:
I have a wheel constantly spinning at 1500 rpm. The wheel has semi-low torque.
I want to power a circuit that requires a minimum input of 5v, 220mah.
If I use the spinning wheel as a generator, what motor should I use to create 5v 220mah DC?
I have looked at different motors, but many are too hard to turn, and some don't produce enough.
Let me know what you think.

Thanks,
Benjamin

Joined Jul 18, 2013
22,038
Hi! My project goal is to build a DC Generator that produces minimal output. Here is the scenario:

If I use the spinning wheel as a generator, what motor should I use to create 5v 220mah DC?
I have looked at different motors, but many are too hard to turn, and some don't produce enough.
Let me know what you think.
Not sure what motors you have been trying, but practically all DC and BLDC motors will generate when back fed, the voltage level generated is almost directly identicle to the voltage level required to operate as a motor at the same geven rpm.
The ones that are hard to turn sounds like they are gear motors?
The BLDC variety generate a 3ph AC signal so would require a 3ph rectifier bridge.
Max.

#### Benjamin0904

Joined Oct 3, 2020
22
Hi MaxHeadRoom! The thing is, a treadmill motor will produce more than enough at 1500rpm. I know that.
Although the torque of the wheel is pretty low, therefore it would not be able to spin a treadmill motor, which requires torque.
I am experimenting, so what is above I am not sure about. What I need is a really good DC can motor that is easy to spin.
Thanks,
Benjamin

Joined Jul 18, 2013
22,038
A T.M. motor is typically 90v DC at 2hp - 3hp. so a little over kill to generate 5v. Also easy to spin at that current.
Why not look for a lower voltage motor, there are many surplus and new L.V. motors out there.
Max..

#### Benjamin0904

Joined Oct 3, 2020
22
So would a 12v DC motor spun by 1500rpm and semi-low torque produce 5v, 220mah?
I don't have one on me so I'm just wondering.
Thanks.

Last edited:

Joined Jul 18, 2013
22,038
The 12v dc motor when ran at its normal operating voltage will rotate at a certain RPM as shown on the motor plate, if same motor is rotated at this same RPM, then approximately 12vdc will be generated.
The current capability should also be shown on the plate.
Max.

#### Audioguru again

Joined Oct 21, 2019
2,406
Your electrical load is 5V at 220mA which is 1.1W. The motor as a generator produces some heat which increases its mechanical work to maybe 1.3W. Depending on the size of the motor, 1.3W might be a lot of needed torque.

Why 220mA? If you decrease the current then the amount of needed torque also decreases.

#### Benjamin0904

Joined Oct 3, 2020
22
Thanks everyone!
I found the perfect motor after days of searching. Its a 12v, 2750rpm, 100W DC motor. And it is decently easy to spin. And I'm pretty sure that when I spin it at 1500rpm low torque I will get 5v++ and 220ma++. That is exactly what I need.
Thanks,
Benjamin

#### BobTPH

Joined Jun 5, 2013
2,747
You do realize, I hope, that when you connect your 220mA load, the torque required to spin the motor will increase dramatically.

Bob

#### Benjamin0904

Joined Oct 3, 2020
22
Hi Bob! No I didn't realize that. I just tested it myself and learned the consequences. I will have to consider that.
Thanks.

#### Audioguru again

Joined Oct 21, 2019
2,406
Try shorting a DC electric motor then try spinning it for it to generate a few hundred milliamps. That is how an electric motor is used as a brake. Frequently the "short" is using the generated current to charge a battery.