Hi!
The water trough saved me a lot of money! :-)
I gave a follow-up in December, it's at the bottom of Gary's Build-it-solar website page if you go look for it. Now that winter's over, some concluding remarks are in order.
I think you can see the saturation when you view the result in FEMMVIEW. I like to play around with the upper and lower bounds so that the colors are more meaningful. For example, by default you typically get a set of lower and upper limits based on the min and max flux in the results, so it can be something like 0.000237 to 2.7188573. This plots out a nice spread of colours, but the legend on the side takes on 20 increments between those two numbers. So before plotting the flux density, change the limits to "0.000" to "2.000" and then hit OK. That range divided into 20 intervals will give you nice round numbers. Now the colours start to mean something.
Also, the stuff over 2T will all be purple, so you can tell right away what's saturated. Some iron is actually saturated at about 2.2 or 2.4T, so you could use that as your upper bound instead. Then adjust the lower bound accordingly and the intervals on the legend will still be round numbers.
Is 2T necessary? Well points here and there don't add up to much, really what you want is a "surface" with the flux maximized. Have you tried the Integration functions yet? There's a button in FEMMVIEW that lets you pick a series of points and draws a red line between them. Make that line across one pole in your model. Now hit the "integral" button, and the normal flux across that line is calculated for you! Flux is the crucial number that can be compared from model to model. Flux makes volts.
While you have the line drawn, you can also use it to make a graph of the flux across all of the teeth - a nice pretty picture.
Overall, the thicker magnets should give you more Total flux than a thinner magnet, by penetrating more saturation into the stator. They "should", but maybe the model will tell you the difference is small. Once current flows in wires, the reverse flux will cancel out the magnet flux. Saturation gives you a margin before that reverse flux takes over.
One more thing: I carefully modeled my Toshiba conversion in FEMM, tried different magnet combinations, selected the best for flux and $, and used a bit of info from a college textbook to figure out how much power to expect. When the conversion was done, I followed it up with performance tests on a lathe. Comparing the power prediction with the power actually obtained, I learned several things:
-college was a waste of time
-theory and experiment never agree
-I shoulda known better
I don't think FEMM is a waste of time: just be aware of its limitations. The Toshi became really hot in the lathe tests, so the room-temperature model is wrong on that count alone.
Have fun!
