SHIELD-MD10 warming up at 24V/1A, diode smoking

[Demolux_D1]

Hello!

I recently purchased the SHIELD-MD10 to control a low-intertia 24V/6A PMDC Servo Motor which draws 0-0.6A at 0-24V running idle. The motor has analogue tachometer and I want to control its speed via PID. So the first step was controlling speed via a potentiometer without any feedback in one direction (B).

I did this with an Arduino Uno and the MD10 as shield. The motor is connected successfully and I am able to control it with the two switches on the MD10. Now I tried using PWM for adjusting the speed:

1. I used native PWM frequency (about 500Hz). The motor was turning but due to its low inertia also made a very loud sound. At 50% PWM duty cycle, the motor draws 2.8A in idle! In addition to that, the 7812 voltage regulator on the MD10 heated up very quickly!

2. I set up fastPWM to about 7.8kHz to control the speed of the motor. The motor runs alot quiter (acceptable), but still draws 1.8A at 50% duty cycle. Still, the voltage regulator heats up quickly.

3. I set up fastPWM to about 15kHz - I know the MD10 supports only up to 10kHz considering the manual. However, the motor runs even quiter but only up to about 15% duty cycle. After that, it suddenly gets loud and the amperage is at about 2A. Also, the voltage regulator heats up quickly.

4. With not much hope I went higher: fastPWM with 62.5kHz. To my surprise the motor runs quiet and smooth over the whole duty-cycle-period and it also never draws no more current than 0.7A. BUT: Still, the voltage regulator heats up quickly, becoming too hot to touch even with no motor attached, it gets warm and the shield draws 0.1A at 24V - quite alot if you ask me.

I am scared to damage my MD10 by firing up the 7812 voltage regulator when using the motor. I guess the heat is not normal isn't it?

UPDATE: I ran the motor at about 15% duty cycle and played with it for a minute or so... when suddenly the diode in the picture started smoking. I immediatly turned off the motor. Shield still works but this is definatly not normal. What am I missing?

Here is a picture

By the way: In this thread the heat-problem was also asked about:
https://forum.cytron.io/viewtopic.php?f=7&t=12951&p=26513&hilit=MD10#p26513

[waiweng83]

Hi,

The 7812 voltage regulator warming up is normal when the motor driver is powered by 24V. It's hot to touch but still under the spec of the motor driver.
So please do not worry to much for that issue.

And for the smoking of the diode, it's due to the high PWM frequency which is over the maximum rating of the motor driver.

Can I have the specification or model of the motor you use? I think you have a motor with very low inductance. This is quite common with high performance low inertia motor.
This type of motor need to be driven with very high PWM frequency. Since it's not possible with the SHIELD-MD10, we can connect a high power inductor in series with the motor.

For a quick start, you can try with connecting 2 x 33uH inductor with the motor in series and see how it goes.

Hope this helps. Thanks.

[Demolux_D1]

Hi,
thank you very much for your response and help!

I just ordered 33uH inductors, will take a few weeks until they arrive. Here are some pictures of the motor in the meantime. To make it easier I wrote out the data here:

Catalog Listing: 33VM52-220-1
Torque Constant: 5.7 OZ-IN/AMP
Rotor Inertia: 00047 OZ-IN-SEC²
Terminal Resistance: 0.85 OHMS
Rated: 24 VOLTS
Rated: 6.7 AMPS (RMS)
SERIAL: 406045580

I hope you maybe can gain new information based on the pictures? I don't have really any expertise in electric motors...