In the normal course of events with a DC motor, the initial inrush is very momentary, as soon as the armature starts to turn, even a little, it starts to generate a back EMF voltage.
It is only if you anticipate an actual stall for a prolonged period at full voltage that you should worry, and any amount of heavy duty driver is not going to save the inevitable burn out.
If you anticipate a stall with normal operation, the drive should have a current limit protection.
Max.

 

My concern is in the rare event when a tennis ball becomes jammed between the throwing wheels (each wheel has one of these motors attached). Commercial tennis ball machines have a push to reset button on the back of the machine when this happens. Would the over temperature and current limitation of the 43a BTS7960 driver be enough to protect the motor in the event of a stall, or do I need to think of something else?
Thanks

Michael

 

My concern is in the rare event when a tennis ball becomes jammed between the throwing wheels (each wheel has one of these motors attached). Commercial tennis ball machines have a push to reset button on the back of the machine when this happens. Would the over temperature and current limitation of the 43a BTS7960 driver be enough to protect the motor in the event of a stall, or do I need to think of something else?
Thanks

Michael

How is it freed/released just by re-starting the motor?
Or is the jam freed some other way first?
Max.

 

The user just pushes the jammed ball out by hand.
The first minute of this gives you an idea:

Michael

 

Not sure from the documentation just how the BTS7960 handles the O/V , but you want a device that removes power until a manual reset, not one that resets automatically when the load is suddenly removed.
There is simple panel mount push to reset C.B.'s If the board does not shut off completely and wait for a reset then this option may work.
Max.

 

I've attached the datasheet for the BTS7960 43A driver if that's any help to you?

Michael

 

I get the impression from that the O/C condition is automatically reset on removal of the O/L, that may prove a little hazardous in this application?
Max.

 

Well, in the event of a jam, could I just turn the power off to the motors, then remove the ball and switch it back on? That would be fine

Michael

 

What if someone releases a ball and the motor starts again?
Max.

 

My concern was always with the damage done to the motors in the time it took to get to the machine from the other side of the court.
As I'll likely be the only user, turning the machine off before unjamming a ball would be acceptable. Do you think doing that in conjunction with the over current protection of the BTS7960 driver would work adequately?

Michael

 

Personally I would pursue a C.B. that cuts power and has to be reset.
Max.

 

Ok, would that be a separate module which would be put in the circuit with the motor and BTS7960 driver?

Michael

 

See TE W57 style, Digi key etc, but look at the trip point chart for the time it takes for the C.B. to trip, I would think you would not need more than a 1 sec delay until the O/L operates.
What you really need is the average and peak operating current of the motor/operation, and size the O/L from there, not the stall current figure you have been chasing.
Max.

 

Thanks for that, I'll look into the circuit breakers you mentioned.

As a guess, I imagine the motors draw little current when they're spinning freely but then there is a spike in the current draw when the ball is fed through due to the resistance (the gap between the wheels is quite a bit smaller than the size of a tennis ball). How would you go about measuring something as sudden as that?

Michael

 

If you monitor the current, anything that happens around 1 second long can usually be seen on a meter, but I would size for 1 sec max before trip.
If you have one in operation it should be possible to measure some kind of average/peak current.
Max.

 

Would it be ok to buy the 43A BTS7960 driver to use with the motor - then set up a test rig to measure the current? At the moment I don't have a motor driver

Michael

 

From the spec's it looks like it would do the job, how are you controlling it?
Max.

 

The idea was to connect that driver to an Arduino Uno with a potentiometer as the input for motor speed. Does that sound like a good idea?
Michael

 

Never used an Arduino, but I assume it would be the same as a Picmicro.
Max.

 

I'll look into ordering the driver and other parts to set up a test rig so I can measure the current.

Looking ahead, one of the issues I have read can be with the motors/throwing wheels not recovering their speed quickly enough between ball throws. I think commercial tennis ball machines do something with the back EMF to maintain the speed of the motors between throws. Would this be complicated to implement? The other option I was going to try was to create a feedback loop and use PID control with the Arduino.

Michael