Sunday, October 23, 2011

DiaMag8 Test Platform

Finally got the DiaMag8 Test Platform running, despite some problems that are still giving me some trouble.  Namely the power supply, and regulation were plaguing me all week.  Then when I finally got to spin it up the epoxy on the rotor failed, and caused the magnets to crash into the stator.  Here is the video of the test.
The inside diameter of the rotor magnets and the outside diameter of the rotor body are the same diameter.  This means there is only  a very thin layer of epoxy holding them together.  The centrifugal forces on the magnets cause them to pull away from the rotor body.  When I spin the rotor up to 5000 RPM the forces on the magnets were enough to cause the epoxy to fail, and the magnet popped off of the rotor, and hit the stator.

I did, however, have a little time to run a test, which turned out good.  The alternator develops about 15.5 Volts open circuit.  I am using a 12 Volt 7 Amp hour battery to drive the motor.  So its a fixed speed for now.  I hooked up the output of the alternator to a 1 to 10 transformer.  The open circuit voltage coming out of the transformer is 151 volts.  Then the voltage drops to around 71 Volts when it is loaded with a 10 Watt, 120 Volt light bulb.  This test only lasted a few seconds before the rotor lost one of its magnets.
Earlier in the week I had built a speed controller board to vary the speed of the motor.  It is a Voltage regulator with a power transistor to allow me to use a potentiometer to change the voltage applied to the motor.  Here is the schematic.
I am planning to use a bank of D size batteries to be my power source.  I have had these batteries and battery holder for years, and used them for many other projects.  So I had some dead batteries, and some weak batteries that contributed to my troubles.  Then when I had those problems solved, I found that the D cell batteries really don't have enough current to get the motor going when I use the speed control board.
So, I wound up using a sealed lead acid battery which develops more current, but is probably still deficient for running the motor.  With just a few minutes of testing the battery Voltage was starting to droop.  I think I am going to have to get a bench top power supply, so I don't have the current deficiency problems.
So, despite a menagerie of problems, I think this test went well.  I need to get my rotor problems worked out, then I can start doing some current and power measurements and figure out what the DiaMag8 alternator is capable of doing.

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