On 03/21/2013 08:08 PM, Scott Dorsey wrote:
In article , jim beam wrote:
On 03/21/2013 07:23 PM, Nate Nagel wrote:

*why* is it overheating?

because it's linear, retard. if you don't know what they means, ****
off until you find out.

Nothing wrong with linear motor control, it's just inefficient and
produces a lot of heat.

right, but what's the point in using 140W to run a 60W motor? and
/certainly/ not when the devices to do so are so cheap and abundant. i
can see doing it back in the day when there weren't any other options,
but today there are, and there have been for 20+ years.


I used to work in a place with a 1.2 MW DC
motor whose field coil voltage was controlled by a couple rooms full
of cast-iron resistors. The resistance array lasted nearly 80 years
before the whole facility was taken down.

As long as you keep within the safe operating area of the semiconductors,
you're fine. If you exceed them, bad things happen.

right. but again, we're dealing with mba's here. as an engineer,
you're going to design with reliability and a safety margin built in.
as an mba, you're going to cut and keep cutting until it meets "business
objectives".


But we don't know
if the semiconductors are failing on these things, or if it's just
ordinary RoHS solder failures; the RoHS crap doesn't like thermal cycling
so well.

very true. but at the end of the day, that's still heat. and a linear
semiconductor controller is just stooopid when a wire coil will do the
same job more reliably and at a fraction of the cost.


--
fact check required