On 03/21/2013 08:57 AM, Bimmer Owner wrote:
On Wed, 20 Mar 2013 23:17:36 -0700, jim beam wrote:

analyze the actual problem - don't just waste money replacing stuff.

That's exactly what we've done - yet - we need help since nobody to
date has figured out HOW to test an FSU that is fried.
http://www.bimmerfest.com/forums/sho...d.php?t=678534

it's like testing a dead light bulb.



Note: It appears to be an active component, but it probably does
dissipate 100W.

it dissipates Vd x Im where Vd = voltage drop across the unit output,
and Im = current drawn by motor. it will indeed get hotter when running
the motor slower because of the greater voltage drop across the unit.
that's why pwm is the better solution - the semiconductors are either
fully on [minimal heat dissipation] or fully off [minimal heat
dissipation]. the only time they get to dissipate heat is during
switching which is a sub-millisecond event and a tiny percentage of the
base time.


--
fact check required