Motor unable to rotate with BTS7960 driver until manually started

Other Hardware Motors, Mechanics, Power and CNC
1

Hi,

I am working on a senior design project which involves a 24 V motor that is capable of rotating at 20,000 RPM. The Arduino I am using is an Arduino Uno. The application is to grind coffee beans. I need to be able to control said motor (link below) at specific points in a sequence. The power supply I am using is a Balluff BAE0006 (link below). It has a 24 V output with 5 A nominal current. The motor driver is a BTS7960 (link below) that states it can handle 43 A. I won't be pushing a nominal 43 A, but I purchased this for current spikes during start up.

I originally tested the motor by directly connecting the power supply to the motor to see if the power supply could supply the proper amount of current. I am aware that over time this will wear down the motor. I then tried using the Robojax library (link below) to power the motor on. Initially, the driver was able to power the motor from stop to full speed. Now, it is intermittent if the motor will start up by itself. When I say "start up by itself" sometimes it will start, but most of the time I will need to manually spin it slightly and it will start.

Initially, I thought the coffee beans were jamming it and it wouldn't start. After disassembling the coffee grinder and leave the motor shaft bare, it still would not start. This leads me to believe I am having issues with starting current.

Is there a way to enable the BTS7960 to output more current to start the motor? As a Mechanical Engineer, I have very little background in PWM and do not know if this is the solution I neeed.

Motor: https://www.amazon.com/gp/product/B07PG12VJW/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1

Power Supply: BAE0006 (BAE PS-XA-1W-24-050-003) Power supplies for the control cabinet - BALLUFF

BTW7960 Motor Driver: https://www.amazon.com/gp/product/B07TFB22H5/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1

Robojax Library: Control BTS7960 DC Motor Driver Module with Arduino - Robojax

2

It seems more likely to be the 5A power supply that is the bottleneck rather than the 43A motor driver. Motors often need 5 or even 10 times their nominal current on startup. Can you try it with a more powerful power supply?

Steve

3

As we are nearing the deadline (4/17/2020) we are unable to order a new power supply with the Corona Virus affecting ship dates.

Additionally, the power supply is able to provide enough peak current to power the motor when it is directly connected, as stated previously.

4

Sounds like a wiring problem, or the motor driver is fried.

You don't need an Arduino to test the motor driver/motor/power supply. Just set the motor driver inputs to apply full power to the motor.

5

The BTS7960 has 0.016 ohms of resistance, your wiring is probably several times this, its worth checking out
if that is the case.

The problem may be that you are stressing the power supply too hard and its only just working direct from
the supply. 5A is nowhere near enough for such a motor, sorry, but that's the case, I would suggest 20A
as a minimum.

Grinding beans probably has the highest torque requirement at starting up, since the beans will pack around the
blades and jam them in place. Torque requires current, so you probably need to give the motor maximum
current almost instantly to get the blades to break out from the log-jam state.

Another thing to check for is excess static friction in the drive system - if there is one.

Being a 24V 20,000rpm motor that means the motor constant is about 0.06, so that for each amp of current
you get 0.012Nm of torque. 5A gives a paltry 0.06Nm of torque.

The motor constant is the voltage per unit angular velocity (in radians/sec) in Vs/rad, and is also the torque
per unit current (in Nm/A) - thus a fast motor will invariably have less torque per amp.