Too high voltage on the generator

Hello,

i'm working on the motorized pinwheel project form the Arduino projects book and decided to change it a little bit. I've connected a second motor to the first one and it should function as a generator. The first motor is controlled with PWM.

The components i used are the standard ones coming with the arduino starter kit. The MOSFET is the IRF520,1N4007 Diode, 9V battery and both motors are CC motor 6/9V, datasheet http://arduino.cc/documents/datasheets/DCmotor6_9V.pdf

The problem is that i measured a 7.3 V on the generator when setting the PWM to 255 (for the first motor). Since the motor (generator) operating voltage ,according to the datasheet, is 1.5 - 6.5 V this could damage the motor. I would like to read the voltage using the arduino analog input. Would a voltage divider suffice , and how should I proceed if not ? Thank you.

Yes, voltage divider will suffice to read the voltage. A multimeter is excellent too - every experimenter should have one.

ManFish: The problem is that i measured a 7.3 V on the generator when setting the PWM to 255 (for the first motor). Since the motor (generator) operating voltage ,according to the datasheet, is 1.5 - 6.5 V this could damage the motor.

I assume the PWM signal is applied to motor A and the voltage is measured on Motor B acting as a generator? I presume there is no electrical connection between motor and generator?

That voltage won't do the generator any harm. If it was 100v I might worry about damage to the insulation. What will damage the motor/generator is excessive current causing it to overheat. The voltages specified for the motor are those which allow it to work as a motor without a too high current flowing. When used as a generator I would expect the motor to be very inefficient and only capable of producing a very small current at 7.3v.

...R

Robin2:

ManFish: The problem is that i measured a 7.3 V on the generator when setting the PWM to 255 (for the first motor). Since the motor (generator) operating voltage ,according to the datasheet, is 1.5 - 6.5 V this could damage the motor.

I assume the PWM signal is applied to motor A and the voltage is measured on Motor B acting as a generator? I presume there is no electrical connection between motor and generator?

Correct.

Thank you both, you've been very helpful.

ManFish: The MOSFET is the IRF520

That's not a logic-level MOSFET and won't work properly from 5V

MarkT:

ManFish: The MOSFET is the IRF520

That's not a logic-level MOSFET and won't work properly from 5V

Hm but it's used in the motorized pinwheel schematic. Which one should i use then ?

ManFish:

MarkT:

ManFish: The MOSFET is the IRF520

That's not a logic-level MOSFET and won't work properly from 5V

Hm but it's used in the motorized pinwheel schematic. Which one should i use then ?

IRL520 would be the Logic Level part.

The problem is that i measured a 7.3 V on the generator when setting the PWM to 255 (for the first motor).

Hi, that measurement is an unloaded voltage from the generator motor is it. You need to draw some current from it to see what power you can generate, that voltage will drop due to internal resistance of the generator. You need to experiment and do a load graph of the output.

Tom....... :)