# Consensus Opinion

I am using a DC gear motor to drive an epoxy dryer that will rotate at from 5 to about 30 RPM. I have a 24V gear motor rated at the correct speed, but cannot find anyplace what the current requirements are. I can measure the no load current, and sorta measure a load current which will give me some insight.

But what I really need is a consensus opinion. I know I can control the motor with an L298N motor controller, H-Bridge, and transistor to name a few methods I have read about. But what I need is a consensus as to what method seems best.

The dryer will have to rotate for up to 24 hours or as short a time as 15 minutes. I need to be able to control the speed and direction of the rotation. I have used dc motor controllers in the past to do some of these things, but it requires a lot of wiring and switches, it seems to me an Arduino approach may be a little more "elegant".

Thanks for any insight you might have.

The last motor driver that I would us is a L298. They are ancient and inefficient technology. Pololu has many modern drivers. Choose the driver to match or exceed the stall current and rated voltage of your motor. Use PWM to control the speed.

Thanks for the advice. I will go look at Pololu and see what they have. As for the stall voltage, I have no idea what that would be since there is nothing written on the motor itself and I got if off ebay and they don't publish much with their motors.

Guess I could do some testing to see what I get, or just use a driver that is rated for voltage higher than the motor.

Thanks again.

The term is stall current or locked rotor current. It is important to know as that is the current that the motor draws, briefly, at start up. You can estimate the stall current by measuring the motor winding resistance and using Ohm's law to calculate the current. Stall current = motor supply voltage / measured winding resistance. You need to make sure that the driver that you choose will handle the, brief, start up (stall) current as well as the continuous (running) current and the rated motor supply voltage.

groundFungus:
The term is stall current or locked rotor current. It is important to know as that is the current that the motor draws, briefly, at start up. You can estimate the stall current by measuring the motor winding resistance and using Ohm's law to calculate the current. Stall current = motor supply voltage / measured winding resistance. You need to make sure that the driver that you choose will handle the, brief, start up (stall) current as well as the continuous (running) current and the rated motor supply voltage.

Got it. Thanks. Now I can do the math and match the controller to the motors.

ov10fac:
I am using a DC gear motor to drive an epoxy dryer that will rotate at from 5 to about 30 RPM. I have a 24V gear motor rated at the correct speed, but cannot find anyplace what the current requirements are. I can measure the no load current, and sorta measure a load current which will give me some insight.

Do you have any estimate of the required torque ? From that you can determine the
mechanical power and thus estimate the electrical power the motor will need (allowing for
gearing losses - a factor of 2 should cover most gearing setups).

mechanical power = torque x angular velocity
electrical power = voltage x current

(SI units throughout for sanity)

MarkT:
Do you have any estimate of the required torque ? From that you can determine the
mechanical power and thus estimate the electrical power the motor will need (allowing for
gearing losses - a factor of 2 should cover most gearing setups).

mechanical power = torque x angular velocity
electrical power = voltage x current

(SI units throughout for sanity)

OK. I can estimate the torque which will be very low. The dryer will only hold fishing poppers made from balsa and these will be mounted symetrically, so weight will be pretty much equally distributed. So the only torque required will be to overcome the inertia and friction at start up. That should be less than a ft/lb of torque.

I'll take some measurements and see what I get.

Torque is a product of a force and a distance, not a ratio. Use SI units if you want to
convert to power without much grief. Nm and rad/s