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Solar Motor Control

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nwolfman

New Member
I was wondering if someone could help. I'm trying to figure out how to make a DC motor turn one way when light isn't available, then turn the other way when light returns. The only thing I've been able to figure out is it will need a photoresistor. Can any one help?
 

MikeMl

Well-Known Member
Most Helpful Member
Photoresistor in a four-arm bridge circuit, opamp as a differential comparator; followed by a H-bridge to reverse current in the motor.
 

nwolfman

New Member
Thanks, but I guess forgot to mention I'm completely electronic stupid. Could you explain further or a sketch would be helpful.

Thank you!!
 

MikeMl

Well-Known Member
Most Helpful Member
What are the motor specs:
Voltage?
AC/DC?
Amps?
 

MikeMl

Well-Known Member
Most Helpful Member
Couple of more questions:
Do you have the photoresistor? If so, model number or specs? I need to know its resistance at the range of illumination you want it to reverse the motor.

What will you be using as a power supply? A regulated AC-powered wall-wart? Batteries an motor do not seem practical?
 

nwolfman

New Member
Unfortunately I don't have any parts yet. Basically I’m trying to get it to function like a solar light, just without the light. When the sun sets, the motor will turn one way, when the sun rises the motor will turn the other. So it can run on 1 or 2 rechargeable batteries, and the solar panel can recharge them.

Thanks again Mike for all your help!
 

zoodlewurdle

New Member
This isn't likely the expected answer but it might be the best. I read it somewhere, I forget where..

Set a tiny 6" cell at 90° to the main panel, and have it directly drive the motor. When the panel is full on to the sun, the small cell will be edge on, so the motor will stop. It tracks perfectly because the small cell has a shape that is inherently precise in response to light from one direction. I never saw, or figured out, the detail of how it gets aligned right for the next day, but the idea is surely to eliminate complex circuitry and keep it as simple as possible so it needs no maintenance. It might be possible to add a small mirror or something to prompt it to return to start when the sun appears next day.
 

MikeMl

Well-Known Member
Most Helpful Member
You will need a pretty big solar panel and batteries. Measure the motor running current, and size the panel and batteries accordingly.

I assumed ~100mA for the motor.

Look at the circuit and plots. The simulation shows how the motor gets reversed. If the motor turns the opposite way, just reverse the motor connections at M1 and M2.

If your PhotoCell is other than near 100KΩ at the illumination level where you want to reverse the motor, you will have to change R5. At the trip point, R5 = R10.
 

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MikeMl

Well-Known Member
Most Helpful Member
So, is your requirement that the motor runs one way while the battery is charging, and runs the other way when the sun goes away until it depletes the battery?

If so, you will need a solar panel much bigger than one suitable for charging a battery to just run a LED. You never answered the question about how much current it takes to run your motor. I'm guessing that it is on the order of ~50 to 100mA, while a LED lamp runs on ~10mA.
 

nwolfman

New Member
Yeah it can work that way. I'm not sure about the motor. I was just going to pick up one I seen at radio shack. They don't give to many specs on it. And the LED isn't needed, so I guess I can just cut it out. And now that I think about it a bit more, the motor will need to turn one way when the sun goes away and then stop at a certain point, then when the sun returns the motor will spin the other way and stop at a certain point. I'm just trying to make it simple, something I can make from parts at radio shack.
 
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