On Aug 4, 2009, at 8:49 AM, Harry Veeder wrote:
----- Original Message -----
From: Horace Heffner <[email protected]>
Date: Tuesday, August 4, 2009 1:41 am
Subject: Re: [Vo]:Marinov BB motor test problems
[snip]
The nichrome coil is a resistor being fed a large current. P = i^2
*
R. Why does a hot plate heat up? Why does an iron heat up, a hair
dryer or an electric space heater? If you are wondering why the
coil
heated up visibly for the ordinary steel bearings and not the
stainless bearings, the reason is that with the rotating motor I
could leave the power on long enough for the coil to heat up. The
stainless steel motor shut down rotation very fast so I had to cut
off the power fast to prevent welding.
Yes, that is exactly what I was wondering. So does the coil would
heat up
faster if the fly wheel is locked?
harry
[snip]
OK, Harry, I was hoping maybe you might be talked into buying some
parts and experimenting with this to satisfy your curiosity.
I did a test to show how much time it takes to heat up the resistor
when the motor is running vs when stopped. I added a little green
LED just below the filament so you can see exactly when the current
comes on, and also provided a clock to see the time. Here it is:
http://www.youtube.com/watch?v=PWlVn-uqxig
Looks to me like about 9 seconds when the motor is running, and about
5 when stopped. This is yet another indication this is an ordinary
magnetic effect. The reduction in current can be attributed to a
back-emf. To some degree it might also be attributed to non-
conduction time when the motor is running, but the scope traces have
indicated pretty much full time current conduction in all runs since
the bearings were cleaned.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
