Powering two SM-4315R servo motors + arduino nano w/ 6 volt, 3.5 watt solar cell

Hi I’m implementing this dual axis solar project I found on instructables.com by geobruce

user spellmal used continuous servos so I used his code and setup.

I used an arduino uno with a prototype breadboard and everything works fine when i plug a 9 volt power supply and hook it up to the pc via usb.

I basically set up my circuit similar to what user Spellmal has and my code works too.


However after I switched to the arduino nano and used a 6 volt, 3.5 watt solar cell things didn’t work fine. The nano gets powered by the solar cell but the servo motors don’t move when the photoresistors are blocked or when a shadow is cast over them.

Is there something wrong with the way i’m grounding things?
Should I use a resistor to limit the amount of current going from the solar cell to the arduino nano?
Please see pictures attached below of my wiring. Thanks.

Powering two SM-4315R servo motors + arduino nano w/ 6 volt, 3.5 watt solar cell (ideally 583 mA)

The site below provides an approx usage of 165 mA with there controller. I am assuming this power draw is the same with the nano

Most instructables are written by people who don't know what they are doing, and this one is no exception.

Servo motors briefly draw the stall current when they start up, and that can be well over 1 ampere. If the 3.5 watt rating of your panel can be believed, it cannot provide more than about 550 mA at 6 V.

I can't find a definitive stall current rating for your servo, but this page claims 1.8 amperes or 0.417 amperes at 5 V, depending on the controller. At 6 V, it will be proportionally higher.

Either buy a bigger panel, use two in parallel, or have the panel keep a battery charged so that the servos get enough current to start moving.

Thanks. Hmm… the instructable was pretty good and got loads of good reviews.
It works great with the small micro servo 9g but that motor is not continuous.

I know it works for my application when I use spellmals code.
It works when I have a 9 volt 1 amp power supply hooked up to it when it’s hooked up to the usb port. I can’t recall when it worked best either when I had a 4 pack of aa rechargeable batteries along with the USB port plugged into the uno board + the prototype shield or the 9 volt power supply along with the USB port plugged in. (I was able to measure a 40 ma output from the 4 pack of aa batteries with my multimeter and touching the ends of the pins of a jst connector )

Thanks for the input with regard to the stall current. However my motors aren’t under any load so will they still draw that much current in the beginning? I’m just wondering since the motors were working fine with my 4 pack of rechargeables

I guess I’ll have to look for a solar cell with greater amperage output. Or a battery with good capacity and large current output.

I’ve attached the front and backside of my arduino nano circuit.

I think there may be also something wrong with the way I have my voltage being split from the solar cell and my ground connections. I was thinking of putting a resistor to the nano board to limit how much current is being sent to it from the solar panel.


If you want to be successful in this hobby, you really need to learn the very basics.

Voltage is not "split" and current is not "sent".

A device draws current, according to its particular characteristics and the voltage of the source.

Solar Panels behave like current sources and are not suitable for directly powering things unless you grossly
oversize the panel or use the Solar Panel to charge a small battery and run your project off the battery.
Solar panels are specced at STC conditions , which is 1000 w / sq metre solar irradiation and cell temp of 25 C.
Easily obtainable in a Lab, but not many places otherwise.
Measure the voltage from your Solar Panel when the Servos are trying to start.
You will find the voltage collapses.


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
Not a fritzy diagram.
Reverse engineer what you have and draw a proper diagram.
You have described so many changes that we need a current schematic of what you have.
Include your panel, LDRs, and servos.
What are your current servo units.

Tom.... :slight_smile:


I attached a picture of a circuit which I’ve drawn to the best of my knowledge.
I’ve also attached my code.

the servos I am using are sm-4315r from springrc i believe.
the reason I got them is because they have high torque but I don’t think i will need much force to turn my dish via gt2 pulley and belt drive.

The circuit is similar to geobruces and spellmal’s setup
except I don’t have an lcd or potentiometer hooked up like they do.
I am also using different pins due to my pcb layout and wanting to minimize circuit foot print size.
i was able to fine tune random movement of the servos by adjusting their rest point positioner.

I really wanted to avoid using a battery because I wanted this to be completely powered by the sun.
I am going to try using small stepper motors 28BYJ-48 with uln2003a driver board
instead and hopefully they won’t have the same issue with respect to stall current as the servos do.

arduino.solar.tracker.two.servos.4LDRs.nolcd.for.parabolic.dish.ino (2.43 KB)