# Need advice for Solar cell to DC Motor circuit.

#### Maxzgrr

Joined Apr 4, 2016
1
Hi,

I'm working on a artistic project which involves solar energy. They asked me to find a solution to run from a couple small solar cells a small low voltage dc Motor (product page).

I managed to run the motor directly from 15 solar cells in parallel. This gave me enough current to start the motor, but 15 cells are to many for our project, and we need a lot of light. When it's cloudy we need to start the motor manually, sometimes it doesn't start at all.
As I understood motors need enough current (A) to start, and in a certain way voltages (V) would set the speed (rpm).

I have found some interesting solutions with B.E.A.M. bots. The B.E.A.M circuits allowed us to get a burst of energy discharged after being stored in a capacitor. Since we need constant motion, even very slow, this didn't fit to our requirements.

Another solution, which is more appropriate, would have been to make something similar found in solar pumps. Solar pumps are active at slow speeds very early and very late in the day, running at full speed in full daylight. All the circuits designs I've found are for much higher voltages than what we need for our project. I believe, correct me if I'm wrong, such circuits are called "Buck converters" ?

In practice I need to find a way on how to decrease voltage and increase current so that i can have enough current to start the motor in dim light, and run it even at very slow speed.
Do you know any schematic design that would help me in this project? Or could you maybe point me in the right direction? Any hint?

Your help is very much appreciated!

#### Kermit2

Joined Feb 5, 2010
4,162
Any scheme which takes your solar panel power and converts it in ANY way will be less efficient than the direct connection you have now.
That said, you have to select a motor that will operate well with the power you can give it.
If you must use fewer solar panels you need a motor that will work with less power.
Maybe gear reduction could increase your motor torque without the higher current draw.

#### wayneh

Joined Sep 9, 2010
16,513
I think the last sentence is the solution. Gearboxes lose some energy also, but could free you from doing any electrical transformations. The overall efficiency might even be better. Making an electric motor go slowly is not easy.

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#### ronv

Joined Nov 12, 2008
3,770
Hi,

I'm working on a artistic project which involves solar energy. They asked me to find a solution to run from a couple small solar cells a small low voltage dc Motor (product page).

I managed to run the motor directly from 15 solar cells in parallel. This gave me enough current to start the motor, but 15 cells are to many for our project, and we need a lot of light. When it's cloudy we need to start the motor manually, sometimes it doesn't start at all.
As I understood motors need enough current (A) to start, and in a certain way voltages (V) would set the speed (rpm).

I have found some interesting solutions with B.E.A.M. bots. The B.E.A.M circuits allowed us to get a burst of energy discharged after being stored in a capacitor. Since we need constant motion, even very slow, this didn't fit to our requirements.

Another solution, which is more appropriate, would have been to make something similar found in solar pumps. Solar pumps are active at slow speeds very early and very late in the day, running at full speed in full daylight. All the circuits designs I've found are for much higher voltages than what we need for our project. I believe, correct me if I'm wrong, such circuits are called "Buck converters" ?

In practice I need to find a way on how to decrease voltage and increase current so that i can have enough current to start the motor in dim light, and run it even at very slow speed.
Do you know any schematic design that would help me in this project? Or could you maybe point me in the right direction? Any hint?

Your help is very much appreciated!
The usual way to do this is to use a battery to store the solar power. Then the battery can supply the current needed to start the motor.

#### Bernard

Joined Aug 7, 2008
5,719
Can you give us the specs. on one of the solar cells, open circuit V & short circuit I in full sun and expected shade?
What speed do you need ?
What is the load on the motor ?
With variable supply V, suggest using a tachometer to control motor speed.
Use something like B.E.A.M. bots, or solar gleaner, to start the motor.

#### John P

Joined Oct 14, 2008
1,860
I think what you want is a geared d.c. motor that draws very low current, like this:
http://www.ebay.com/itm/15mA-DC-3V-...ash=item2a3e308a93:g:73IAAOSwyZ5UlW3z&vxp=mtr

You can get all kinds of gear ratios with this type of motor. But of course it's not perpetual motion--there is a need tor a certain amount of power! You'd better figure out what your solar cells can supply, and you also need to know whether you can tolerate a speed that changes according to the amount of illumination. But it wouldn't be hard to put in a low-dropout regulator to limit the voltage to the motor, and thus the speed.