[TriEmbed] Low Voltage Stepper with A488 controller

[Rick]

Good morning all,

I think you will find the motor heating is due to the lack of "holding 
current" ... that is, it takes much less current to hold a stepper motor 
in position than it does to move it. Some of the stepper motor drivers 
lack holding current, or it is just not implemented. Usually, you need 
only about 10% of the moving current to hold the stepper in position.

Because you are still applying moving current, but not actually moving 
the motor, you are generating heat. One application we had at work used 
an inexpensive "hobby" stepper driver and I burned myself by laying my 
wrist on the stepper motor that had been in operation for about 20 minutes.

If your driver doesn't provide holding current mode, you can reduce the 
voltage to ensure the current drops to about 10% of full current when 
you are not moving. This is easily accomplished by having two different 
power supplies fed through diodes (common anode) to the motor driver 
chip(s), and shut down the higher voltage one after your move is 
complete (Mosfet switch run from a processor output line perhaps?).

Regards,

Rick



On 4/3/2015 12:41 PM, Grawburg wrote:
> I understand that the key issue with a stepper motor and the A488 controller is the current and not necessarily the voltage. I have a 9V power source that I use with the controller and a motor that seems to be rated for voltage in that realm since it does not get very hot (just warm) when I "play" with it. And it does not get hot (just warm) in idle position.
>
> However, I have another motor (from a printer) that gets more than warm sitting in idle.  Not TOO hot to touch, though.  That makes me wonder if I'm putting 9V into a motor that is designed for 6. (I cannot see any writing on the motor-some parts are behind frame from the assembly.) My concern is that I might eventually damage the motor.  Shouldn't I do something to reduce the voltage to the motor and see at what voltage it still works (it's not going to used for anything other than instruction)?  I already have a step-down board I made that reduces 9V to 5 (I think).
>
>
> Brian Grawburg
>
>
>
>
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