Hi, I am having trouble with a project using an Arduino Uno and an mg995 servo controlled by it. It works fine when I run the servo from the 5v output of the arduino while its plugged in to my pc from usb, but I need the final version to run off a battery charged by a small solar panel. I have wired the solar panel to a TP4056 charge module, which is wired to an 18650 battery holder and it works fine at charging the battery. Since the battery only works at 3.7 to 4.2 volts I understand I need to increase the voltage to run the Arduino. I wired the output of the TP4056 to an XL6009 step up module, which I set to output 5V. However, when I plug the output of the step up module to the 5v port of the Arduino without anything else connected to it, the voltage measured on the output of the module drops to 2.3V, which I don't understand. I also tried setting the step up module to 12V and using the Vin pin on the arduino, and the voltage also drops to around 8v. I don't know if there's a better way to make the arduino and servo run from the same battery. I would appreciate any guidance or help as I have no experience with electronics before this project. Thanks for taking the time to read this, hope you have a great day.
That is No, No. Never use a controller board as power supply for motors, servo etc.
Please post the schematics of it!
Thats because the XL6009 input needs to be between 5V and 32V
It will not work at 3.7V
The datasheet for that boost converter says its minimum operating voltage on Vin is 5V. That wouldn't be a good match for a maximum of 4.2V from the charger or battery.
Have you tried running the Uno directly from the battery to the Uno's 5V pin, and separately connecting the servo to the battery?
Note that servos often draw lots of current when first powered up.
And I guess I would be curious how much the battery voltage drops if you connect the servo alone to the battery, with the control line disconnected from anything. (Don't try to measure servo current with your meter - if it's too great you will blow a fuse in the meter.)
Anyway, it may just be that you have the wrong boost converter. The MT3608 is the typical choice.
Thanks for your reply. I understand it's not correct to run the servo off the arduino power pin, which is why I want to increase the voltage of the battery properly and use it to power the servo and arduino simultaneously. This is my attempt at a diagram showing the circuit.
Understood, the website I bought it from said that it was good for 3-32 volts, but searching further you seem to be right. Thanks for your help!
Thanks for your reply, the voltage drops even when just connecting the arduino without the servo, so I haven't tried to run both at the same time. As you and others have commented I'll try to change the converter to the model you suggested.
Don't buy an adjustable boost. The pots are not high quality so the set voltage may not be stable. Buy a fixed voltage output type but don't go overboard with the current, a 3, 4 or 5A model would be good
Very good!
I miss the servo but guess it will use the 5 volt from the XL6009. Hopefully it supplies the current needed.
You've got 2 good replies already.
You should never power a servo or motor from the 5V output. The 5V output is a convenience, designed for a couple of LEDs or low power sensors at most.
Power motors and servos separately, but connect all the grounds. Like this:
Just understand that when the charger has charged the battery, it will shut down. That will leave the battery powering everything even though the sun is shining brightly. Then when the battery drops to about 4.1V, the charger will turn on again. So the battery will be cycling between 4.2V and 4.1V when it shouldn't really need to.
Also, the charger shuts down when the constant-voltage charging current drops to 10% of the full constant-current setting. That's how it detects that the battery is fully charged. But if the Arduino and the servo are drawing more than that, then charging will never terminate, at least until the sun goes down, which is not a good thing. You can deal with that by building in sleep periods when current draw drops to very low levels.
Thanks for the comment again. I switched to the MT3608 boost converter you suggested and the arduino runs ok on its own and the voltage doesn't drop, however I've run into another wall with the current, as the Mg995 servo can draw up to 1.5 Amps, and even without any load, it struggles to barely move when I have both the Arduino and servo running from the boost converter output. When I power the Arduino itself from usb and the servo with the converter it works fine. I'm kind of at a loss as to how to continue, should I just duplicate the power system, and have two solar panels, two batteries with their respective chargers and two step up converters? I'd appreciate any suggestions, thanks again for your time.
When a 5V boost converter is providing 1.5A start/stall current, the power output is 5*1.5 = 7.5 watts.
To produce that the converter, operating at 80% efficiency, has to draw about 7.5W/3.7V/0.8 = 2.5 Amperes (9.25 watts) from a 3.7V source.
If the servo is struggling, either the source cannot provide that amount of input current, or the boost converter is not capable of drawing that amount.
Pololu has a good collection of boost converters, and very importantly, they describe the maximum input current for each model, as that is often a limiting factor.
Tip for beginners:
There is more to electrical circuits than "VOLTS".
Or connections are so flimsy, they won't support surge currents.
Have you tried connecting the servo directly to the battery, bypassing the converter? That shouldn't work per the datasheet since the voltage is too low, but it might be worth a try.
Anyway, it sounds like you should be able to add a second MT3608, and power the Arduino from one and the servo from the other.
That is why I suggested that you don't use the MT3608 as I also suggested you don't use the XL6009.
See post #8
Hi, @m3ntecle
Have you been monitoring the battery voltage when you have the problem.
Don't forget the battery current into the DC-DC converter will be almost twice the current out of the DC-DC converter.
Tom.. 
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