RE: [CAD_CAM_EDM_DRO] operating temp of stepper motors

The short answer is that hot temperatures are normal for a motor driven
at full amperage and high voltage. The motor I have next to me has a
plate rating of 90 deg C max and that is typical.

The long answer is that there are 2 sources of heat. One is just the
current flow through the motors. You can reduce your current and in
virtually all cases not affect your performance. This will reduce
heating over the lower speed range. The reason this is the case is that
once you start turning the motor much of any speed (The engineering
types can give more details on how to figure out the speed) the current
becomes limited by the inductance and you are then not running up to
full set amperage anyways. When you decrease the amperage you will lose
low speed torque, but normally we use oversized motors to maintain the
high speed torque so we have torque to burn at low speed. The other
source of heating is iron losses. This is pretty proportional to the
over voltage you use to drive the motors. I think Mariss's white paper
covers this, but the summary is that at the low end of the 10 - 25 X
voltage range we use the majority of heat will be form copper (the first
reason above) and at the higher end the major loss will be iron.

With all this said most home CNC types don't like the idea of motors
that you can fry eggs on (or your self). So we tend to not push them to
the limits. I generally tend to stick in the 15 - 20% range for over
voltage and I set the current to about 65% of the rating. Performance is
slightly reduced (but not that bad as when you look at the curves you
see that diminishing returns set in as you approach the limits), but
parts last longer and I don't have any NEMA shaped burn marks on my
forearms.

Tim
[Denver, CO]
Sherline products at Deep Discount
Mach1 & DeskCNC with credit card ordering
www.KTMarketing.com/Sherline

> -----Original Message-----
>
> I've not had the opportunity to run long jobs in the past but now
> that I am beginning to run longer jobs I noticed that the stepper
> motors run quite hot and wondered if this is normal. I measured the
> case temp of my stepper motors measureing 150 degrees F. These are
> 23 sized motors wired in parallel at 4.1 amps.
>
> Should I be worried about this temp or is this normal?
>
> Ken
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html