Power is good from Arduino, but not LiPo.

I have an Arduino Nano wired up to a MOSFET and my multimeter shows me the voltage going up and down, however when I attach a motor to it, it struggles to do one rotation. When I have a LiPo attached to the MOSFET with the Arduino still giving values to the Ground, I no longer get a varying voltage output, but the full voltage of the power.

Any reason this would happen? As soon as I change it to the 5V rail from the Arduino everything is nice and good again. Odd!

Hi leito, There are some very cleaver people on this forum, but not of them are mind readers (or are they?) What we need to know is What FET! how is it connected? What lipo battery/cell.

We need to see your schematic or a good clear picture and your code. Then perhaps we can help!!



haha, yes sorry.

So I'm using a 3.7V, 600 mAh battery connected to a HUF76423P3 MOSFET (https://www.fairchildsemi.com/datasheets/HU/HUF76423P3.pdf)

PWM pin 3 is connected to the first leg (the gate). The middle leg is where the 3.7V is connected, and the last leg (furthest from the dot) is connected to the +ve lead of the motor. The -ve lead from the motor is connected to the -ve rail.

This one is connected to the 5V pin from the arduino, and the voltage goes up and down: |500x280

This one is connected to the LiPo and stays stuck at 4.09, even though I've done nothing to the data pin: |500x280

Not sure if that helps a bit?


edit: It seems like depending in the input power it affects whether the FET plays nicely or not. Interestingly, powering the arduino from the LiPo makes the FET play nice.

Hi leito,
I have always use an N channel Fet and put the device I want to drive, ie. Motor, lamp etc, between the Fet and the positive supply! like this: Motor pos to V+ supply, motor neg to Fet Drain, Fet Source to Gnd, Arduino pin to Gate, also a 10-100K resistor from Gate to Gnd, this keeps the Fet OFF when there is no signal from the Arduino.

Is that Nano a 5v or a 3V if you’re only using a 3.7V lipo?

You can’t switch power the way you have things connected, the Fet in not in control, it works like a switch, but needs to be in the right place.

Here’s part of a schematic that shows what I mean… Yes you also need the diode to protect the Fet from high back voltages from the motor, when stopping, etc



FetRelay.pdf (13.2 KB)

With out looking at the data sheet, Is your MOSFET logic level?