Treadmill dc motor controller - Page 1
Forum section: electronics / projects

author: Airton
author_rank: Newbie
timestamp: February 20, 2021, 12:16:44 am
content: Hello everyone!I'm fixing my old treadmill, but the original circuit is gone to the trash long time ago, so I bought a PWM controller and want to do some modifications to improve the control and safety.There is no identification on the motor, but is a DC motor with 2Ohm, measuring I found out that the motor start at 30Vdc, and found an old picture of the advertising of this threadmill saying that is a 0,8Hp motor.The PWM that I bought has an output from 10Vdc to 220Vdc (but I'm connecting to 127Vac, so the maximum would be 127Vcc I believe) and a maximum of 20Amps.With this PWM I would having a maximum 40Vdc before pops the fuze. (40 V/2 Ohm = 20A)I'm using a 680uF 400V electrolytic capacitor in parallel to the motor, I found out this formula but I'm not shure how to calculate the motor efficiency. (I tried to calculate and endup with a 300uf Cap, this is right?)C=(P(kW)*3,18*10^6) / (U²*CosFI*n)P = Motor power (800W)U = lower motor voltage (30V)CosFI = Cosen of the constant Fin = motor efficiencyI need some ideas to improove/implement this:-On the motor start there is a peak on the current, the new capacitor could improve that?-I want to make the circuit safer, so I don't die wen running on the threadmill, so the first thing would be to ground the metal shield of the pwm and I want to isolate this potentiometer, maybe with an arduino, but I don't have any idea wat could be used to replace this potentiometer that could be controlled by an arduino. Any ideas how to do that?Attachet is some pictures of the PWM.Thanks!

author: amyk
author_rank: Super Contributor
timestamp: February 20, 2021, 02:54:06 am
content: Quote from: Airton on February 20, 2021, 12:16:44 amThat's not how it works... there's a little thing calledinductanceback-EMF....and a formula that involves the power factor is definitely wrong for a DC motor.In short, I recommend you learn a ton more about electricity before you burn something.

author: WattsThat
author_rank: Frequent Contributor
timestamp: February 20, 2021, 05:41:48 pm
content: The original controller that ended up in the trash was a regenerative dc drive. The replacement you purchased is more suited in the trash than the original drive as that was most likely repairable.The replacement PWM controller is not capable of controlling a treadmill. No matter how much you modify it, it will not work for the required application. Even if you could get it to spin the motor, the moment you attempt to run on the treadmill, the controller would go bang and then it too will be in the trash. More likely it will go bang when first applying power with a capacitor having been removed from board and a big electrolytic added somewhere.A treadmill drive requires operation in two quadrants. It must provide positive torque to move the belt and it must absorb negative torque when the user is running on the belt. That requires a regenerative dc drive. That is not what you purchased.Look on eBay for a used treadmill controllers. You’ll see they are significantly different than the device you purchased which is not capable of the task at hand.

author: Siwastaja
author_rank: Super Contributor
timestamp: February 20, 2021, 05:51:02 pm
content: Sorry to sound harsh but electronics does not work by buying random parts, connecting them randomly, and plugging random numbers into random formulas.As WattsThat wrote, likely your "PWM controller" does not work for the purpose.Obviously do not connect a capacitor in parallel with the motor. Where did you get this idea? The motor controller will see this as an AC short circuit and blow up the capacitor.A proper motor controller supporting two-quadrant operation (running and braking) would work here, but I have no idea where you could get a properly engineered replacement module. I'm sure there is aftermarket for fixing broken treadmills, hence look for treadmill motor controllers.

author: Zero999
author_rank: Super Contributor
timestamp: February 20, 2021, 07:45:58 pm
content: It's not a PMW controller. It appears to be phase control. I don't know why it uses two bridge rectifiers, when only one is necessary. A proper schematic would make it more clear.