Gotta love Naudin's work on this -- it's so clear... Couple things, from a very quick skim of the new version of the page.
** Introductory text in a box at top of page: > The current required to get the temporary depolarization of the magnetic > domains of the ferrite is fully independent of the mechanical torque > produced on the motor shaft. As I mentioned previously, this isn't entirely true. The torque produced by the shaft must depend on the strength of the permanent magnets used, and the field generated in the core when the coil is energized must be large enough to 'swamp' the field of the permanent magnets, so the current needed must be larger when using more powerful permanent magnets. So, the (minimum) current needed in the coils does indeed depend, in a gross way, on the torque produced by the motor -- but increasing the current beyond that minimum won't increase the torque, and the system is (probably) putting far more than the minimum required current through the coils. Consequently effects such as changed minimum current requirement as a result of minor changes to the magnets won't be apparent. ** Test 3, Canceling Back EMF in the toroidal coils -- He's not measuring back EMF here. He's measuring induced EMF in an unenergized coil (the "fifth wheel" which is used as a sensor). In the context of BEMF, the only time induced EMF is interesting is when there's current flowing through the coil. Otherwise, the induced EMF does no work. In fact, in the actual stator coils, the change in the external field takes place either when the coils are shut off (as the magnets approach) or when the cores are saturated and unresponsive (as the magnets leave). My expectation, then, would have been that the BEMF would be zero whether or not there's sloppy alignment in the system. That would have to be measured by mis-aligning one of the actual stator coils and measuring BEMF. I haven't as yet read the page carefully enough to see if he does that, nor to understand why he thinks there would be BEMF in that case. ** Test 7: Test of effect of a load on the current The "high powered LED panel" has unspecified power consumption. That makes it impossible to tell, a priori, if we *should* be able to see a difference in current through the coils. But we can take a guess at the LED draw, and come to some tentative conclusions. Small LEDs draw typically on the order of a dozen mA, and run at a couple of volts. So let's say this is 20 mA * 2 volts = 40 mW. The rig seems to be running at about 10 volts applied, according to scope traces elsewhere on the page. At 400 mA current, that's 4 watts. So, the drain of the LEDs is on the order of 40 mW/4W = 1% of the input power. That would translate to a difference of 4 mA. Looking at the dial on his analog meter, that should show up pretty clearly. It clearly doesn't. So, he's right, this indicates no BEMF. The video with the digital meter is actually less clear than the analog video, as the bottom digit on the digital meter wanders all over the place and could easily varying by .004 A. At the same time, there is one other piece of information which is missing, which makes it hard to judge the significance of the lack of measured change in the current: Does the motor slow down when the LEDs are turned on, and by what percent? If we assumed constant friction in the bearings, that would tell us what percent of the output power was being diverted from the bearings to the LEDs. However, the speed doesn't seem to have been measured in that test. On 02/15/2010 11:33 AM, Harry Veeder wrote: > Feb. 14 update > > Naudin finds the current through the toroïdal stator coils does not change > when a load is applied: > > > http://jnaudin.free.fr/steorn/indexen.htm > (towards the bottom of the page) > > Harry > > > > __________________________________________________________________ > Be smarter than spam. See how smart SpamGuard is at giving junk email the > boot with the All-new Yahoo! Mail. Click on Options in Mail and switch to > New Mail today or register for free at http://mail.yahoo.ca > >
