Re: (ET) So how hot can a drive motor get?

["David Roden (Akron OH USA)" <etpost drmm net>]

On 5 Jun 2011 at 15:13, Chris Zach wrote:

> So what's the max external and internal temps for an E12 shunt motor?

The motor's nameplate should have a temperature rating.  These are letter 
codes from A to H (oddly, C, D, E, and G seem to be never used), and they 
specify the manufacturer's limits on internal temperature rise before the 
insulation breaks down and the motor lets its smoke out.  The rule is that 
if you maintain these temperatures the motor is supposed to last 20,000 
hours.   Each 10 deg C increase above the maximum in routine operation 
cuts 
the expected life by half.  

Class A insulation shouldn't exceed 105 deg C

Class B (common in household appliances), 130 deg C

Class F (common in industrial motors), 155 deg C

Class H (often used in road EVs), 180 deg C

These are the temperatures measured at the windings.  It's a bit more 
complex than this, with other limits on ambient temperature and motor 
temperature rise, but that's the gist of it.  

Note that the armature windings may be hotter than field because the field 
has that big hunk of metal attached to it, acting as a heatsink.  Thus to 
the cut to the chase, the general guideline in road EVs (usually class H) 
is 
that if you can't keep your hand on your motor after a run, you're getting 
it too hot.