running motors on a bench PSU

I am trying to simulate running 10-12 motors using two batteries and a power expander. I have a small PSU and the motors stall very early. An example is 4 high speed motors connected to a 1/35 gear train and the motors can’t even turn the wheel. I believe the PSU isn’t generating enough current but I’m not sure how much the battery set up can actually provide. I’m pretty sure the current limit of my PSU is 3A and that is why it is stalling, I need confirmation and a guide as to what current max I can run. I’m guessing if each motor is maxed at 2A and I have 12 it should be around 24A? Can the batteries supply that? Does 3000mAh mean I can run at 12A for 15 minutes or 24A for 7.5 minutes? Can someone please explain how I can do this, I am just trying to bypass having to program and run through the cortex while prototyping.

I’ve included a pic of the model and motor modules I designed and am trying to test.

The opposing module polarities are reversed so that the motor rotations are combining to rotate the wheel. I tested them individually to ensure the rotations are correct.
motor module.JPG


The 3000mAh battery can output 3 amps for about an hour. As the current goes up, the capacity will go down, so at 6 amps it will last less than 30 minutes.

The VEX EDR 393 motors have a stall current of about 4.8 amps at 7.2 volts. So your 3 amp Power Supply is current limiting. The motors have internal Positive Temperature Coefficient (PTC) devices that will open up like a circuit breaker when high current is drawn for a long enough time. It varies over temperature, but you can pull about 0.9 amps through each motor for a two minute match. Instead of instantly going to 100% throttle, have your code ramp up in speed to keep the currents lower.

The VEX ARM® Cortex®-based Microcontroller has one PTC that is shared between motors 1 through 5 and another shared between motors 6 through 10. The VEX Power Expander has one PTC that is shared among all 4 of its motors. It varies over temperature, but you can pull about 4 amps through each PTC for the whole match.

You are probably pulling too much current through your 393 motors with your current gear ratio. Ideal gear ratios for different flywheel setups have been discussed at length on a number of other threads.

Thank you!