On 7/17/07, damon henry <[EMAIL PROTECTED]> wrote:
I've got no ideas about your DC to DC, but this is why I always recommend
the 6.7 inch series wound motors over Eteks. It's not that they can't do
the job, but they are too easy to fry. Too many amps either undoes all the
solder or demagnatizes the magnets. Yes they are small, and yes they are
efficient, but the lack of thermal mass is a big part of the reason why they
are easily destroyed.
damon
I'm very heavily on Damon's side on this one. The Etek seems to be a
wonderful device, but it is very intolerant of operation outside its
design envelope. An EM leans on that envelope pretty hard.
I believe there's a design flaw in the Etek. Without having seen one
up close I'm speculating a bit, but apparently there is a bunch of
copper clippy bits on the periphery of the armature that are heavy
because they have to carry big currents. They are held in place only
by solder.
Big mistake. You *never* use solder as a mechanical attachment method
in a critical application where there are any significant forces
involved. (Per numerous government studies on military electronics.)
Centrifugal force at 1000s of rpm acting on chunks of copper is pretty
significant.
Further, those government studies found that the best way to get
solder to fail is to put it through lots of low-level temperature
cycles while under load. In other words, it's not necessarily the
event you're in the middle of that makes it fail - you could have been
setting the stage for failure for quite a long time. Wasn't there
someone on this list who had one fail a short time into the first ride
of the day?
If I had an EM running an Etek I would waste no time in making sure it
runs cool under *all* circumstances. Really cool. Run it hard, then
put a thermocouple directly on those copper clippys. (I don't know
what is an acceptable temperature, but cooler is better.) Keep making
changes until the temperature under heavy use goes *way* down. If the
case makes it difficult to get air where it's needed, I'd look into
cutting the case.
I wonder if the new brushless version has those copper clippys? My
guess is no - I'll bet B&S has received lots of complaints and did
what they could to make them go away.
Chris
P.S. Just took a look at Mike's pictures. I wonder if you could wrap
the armature with a Kevlar band to take some of the load off the
solder joints?
