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Simple electronic question



I am a software developer dabbling for the first time in some electronics using Gadgeteer, perhaps a dangerous thing! Anyway, we are working on a project for Halloween that involves flowing fake blood. I have a 12v pump that I’d like to run at 6v so that it goes slower. It’s max rated current is 350 mA. I suspect that I will want to put a couple of resistors across the negative and positive feeds? If so, what size would I want?

Thank you for the help!


Not that I’m an expert for this, but I don’t think that putting some resistors in row with an Motor would reduce the voltage by half. A motor is not just an resistor on speed, it’s an inductive load.
I would use a 6V power supply and switch it on and off using a relay.


@ CodeGreen - With a little time before you need what you are asking for I would suggest a Gadgeteer motor controller that you can drive using PWM for provide the control. You can feed this with 12V but use PWM to produce a 50% duty cycle what would reduce the speed. This will also provide the additional components to ensure the drive electronics doesn’t blow up as you try and turn the motor.

This is what I suggest:



My plan is to use a 6v power supply controlled by a relay (the Load Module), I just didn’t know if I would also need to put resistors on it.

Jason, I actually already have one of L298 modules, hadn’t thought of using that (haven’t actually ever used it yet). That is a really good idea, I could experiment and maybe by ramping it up and down create a nice grisly effect!


The resistor option would work, but it’s a bit wasteful as it’s just dumping all the unwanted power as heat. You also need a fairly beefy resistor too so that it doesn’t burn out.


Realize, I am not trying to reduce the voltage, I would be using a 6v power supply. My question is that if using a 6v supply for a 12v motor (wanting it to go half speed), do I need resistors, and if so what size? Would that still create a lot of heat? And if I use the L298, does it handle all of that for me and I can just control the speed using that?


I would suggest the PWM route with 12V as this will allow you to control the speed to what you need. PWM pulses at 12V ensure you get more torque from the motor. Lowering the voltage often means the motor has less torque.


Excellent, so it is a plan, I will use the L298.

As always thanks so much, this group is always extremely helpful!