# Why does this solar panel powered dc motor not spin?

I am a complete beginner at electronics and am encountering this problem with connecting a solar panel to a dc motor:

According to some demonstration videos, the dc motor starts spinning right after the wires are connected. Can anyone help troubleshot what I am doing wrong, and why the dc motor does not spin at all, either indoor with room light, or outside in partially cloudy sky, please?

EDIT: got it working at last, but i used a battery in the end and latched on the solar cell just for the visuals.

• No, DC motors don't run on any random voltage. The voltage specification must be followed and applying a very low voltage to motor terminals than the rated voltage will not spin the motor at all and can damage the windings by heating up (let say when you apply 1V to a rated 5V motor) or if you provided very high voltage (like 15V to a 5V rated DC motor) it can give you the smoke. Jan 4 at 6:45
• The voltage generated by PV cell is not a constant at all, its a variable and highly depends on the intensity of light falling on the surface of PV cell Jan 4 at 6:46
• what is preventing you from placing the solar cell in very bright light? Jan 4 at 6:53
• "They both come from the same kit" - Which kit? Were any specifications provided for the motor or solar panel? Jan 4 at 7:49
• hold the solar cell close to a bright lightbulb Jan 4 at 8:17

"Partially cloudy sky" and especially "Indoor light" are not a good recipe of testing a PV module.

It may sound somewhat surprizing, but human eyes are not very good at estimating a total amount of light even to an order of magnitude. In a sunny day one may get as much as 1 kW of light per sq. meter. Clouds may lower it to as low as 10W per sq. meter at noon. Indoors your room may be lit by ~1W light in total and you will still be comfortably reading.

Your PV module is expected to catch the available light at its surface, convert it to electricity (it has 20% efficiency at best and your is likely 10%) and then you can do something with this electical power.

There is no dimensions in your picture, but I dare to imagine that the motor is a phone vibration motor that requires few miliwatts just to barely rotate.

In order for this to happen, yout electricity source must be capable of this power and be somewhat matched to the motor in terms of voltage and current. Your setup probably fails at both.

p.s. if you really want to get into electronics, get a strong habit of looking at your parts' specifications. This usually consist of looking for a part number written somewhere on your part and then looking up in the Internet for a datasheet. In some cases, it is harder.

Having an educated guess about the circuit parameters may not be enough and the guess needs to be educated in the first place.

• @ fraxinus thanks, i tried it on an AA 1.5v battery, and it did spin... So it's probably something to do with the amount of light falling on the solar panel... Jan 4 at 7:32
• OK, the motor works. What to do next: get the cheapest possible (like \$5) mutimeter and try to measure the voltage the panel generates. Jan 4 at 9:37
• @ fraxinus thanks, i got the dang robot assembled at last, but used a battery in the end as it's just so much easier. Jan 4 at 11:23
• If you're going to continue with electronics a multimeter is an absolute must. Even just to check that 2 wires are properly connected (there's a feature for that). But if you really want solar on your little robot, just use a bigger solar cell, it'll eventually move.
– csiz
Jan 5 at 3:44

PV's and motor's both have an impedance.

1. Z(PV) = Voc/Isc

Motor Z(RPM) = 2)DCR + L * RPM* 2pi * 3600// mechanical load. Is much lower.

What did you compute? energy? Or power or impedance ratio?

Measure 1) & 2)

What did you measure? Where are your specs !!

Try full sun or bright 4W LED up close

• @ Tony I'm just starting out so have not done any calculations. They both come from the same kit, so I assumed they are pretested to compatible... (?) The voltage generated from the photovoltaic cell, are they constant voltage, or light dependent? Can dc motors run at any voltage? Jan 4 at 5:43
• Voc is open circuit and Isc is short circuit which is light dependent. The optimum at full bright sun is around 82% of Voc , or 70% at 10% full brightness. Max Power Transfer or MPT occurs when source V/I matches load. So you need full sun probably to get enough solar energy to drive the energy needed by the motor. Take some measurements taking care not to exceed DMM fuse rating so use the 10A scale input. For Impedance or simply resistance is Voc/Isc= Vmpt/Impt when loaded at matched point between 70 and 82%. Jan 4 at 12:56
• Its just like matching the torque and RPM of a 10 speed bicycle. With low torque (solar power) it is like you are starting in 10th gear , so measure Voc, Isc then measure motor winding resistance and compare Jan 4 at 13:01

As a general rule of thumb: there is always a transition between "on" and "off".

For your solar cell that means: no light -> no voltage , a lot of light -> maximum voltage, maximum current.

You can try this yourself, if you equip yourself with a cheap multimeter and use this as a replacement to the motor in both: current mode and voltage mode.

You will see changes in your readings, if you change lighting conditions.

When you think about your motor, the same rule applies: no voltage (=no energy) no movement. Rated voltage -> rated movement.

Exchange the solar cell with a standard battery cell (1,5V). It should move.

Add your multimeter in between in current mode. You will notice, that the current depends on the friction you apply to the motor.

Get yourself a "adjustable battery" (adjustable power supply) to play with the voltage applied to the motor. You will notice, that you need a minimum voltage to get the motor spinning. This is mostly always the case in physical systems and called friction. You have to apply enough force to overcome friction. In the case of a motor: you will have to supply enough voltage and your energy source will have to be able to supply enough current to start the motor spinning.

If you want to start playing with the motor, without waiting for a adjustable power supply: try to get it running with the battery cell and then add some thin wires in between. You will notice, that the motor speed changes and you will notice some dependence of the diameter, length and chemical composition of the choosen wire.

• @ toka thanks for the ideas! I tried touching the wires onto a AA 1.5v battery, and the motor did spin... So i guess the trouble is with getting enough voltage from the solar panel... Didn't realize solar cells can be quite finicky to work with... Jan 4 at 7:29
• In summer light you will have more success playing with the solar cell ...
– toka
Jan 12 at 4:20