DiaMag8 Test Platform

The balance of the rotor was just the start of the engineering challenges associated with the DiaMag8 Alternator.  This is the first compound rotor that I have put in one of my alternators.  The others have been monolithic magnets with high mechanical tolerances, and were well balanced because of that.  DiaMag8's rotor is a aluminum core piece, with 8 arc segment magnets glued to its periphery.

There was a good chance for an imbalance, and it happened.  The imbalance wasn't very noticeable at 1400 RPM, but at 30,000 RPM it sure was.  So I endeavored to find a way to balance the rotor.  I made a static balancing jig, but found the imbalance was too subtle to find with the static balance jig.  I don't have a spin balancer, that would be nice.  So, I had to resort to trial and error adjustments.  I looked at the rotor very carefully, and tried to ferret out where the machining imbalances were, and then correct them.  This worked surprisingly well, and I was able to balance the rotor enough to run it at 30,000 RPM.  Then I noticed another problem.  The rotor expands at high speed.  This rotor's core is aluminum, much more stretchy than neodymium.  So, when the rotor is turning at high speed it stretches and there is rotor to stator contact.  Shards of aluminum stator material come flying out of the alternator at 30,000 RPM...

So, the Ryobi drill is too slow, the Dremel tool is too fast, uulgh...  OK, I could get a variable speed Dremel tool, $70, or I can scratch up some stuff around the shop and make a variable speed alternator test jig.  Admittedly I did have to buy some parts, but a lot of this stuff was in inventory, like the motor...

The motor is about 20 watts, and I can push it upwards.  The name plate RPM is 2350, and that can also be pushed up to 3600 with more voltage.  The plate there does have markings on it, they are just hard to see.  In order to make to alternator tester flexible it needs to be variable speed, so I am using a voltage regulator to vary the battery voltage.  Then we also need variable power, so I'll add a current regulator.  Also need some mechanical flexibility, so we're going to use a belt drive system with many different size pulleys.  What is on there now is about a 1 to 2.3 ratio...

I made cutouts in the motor mounting plate for the motor, alternator, electronic controls, and mounting holes.  There is a need to align the pulleys, and also we'll need to make belt tension adjustments.  The motor mounts flush to the plate while the DiaMag8 alternator is mounted mid-plate to align the pulleys.  I'll make some right angle brackets with wood to mount the motor mount plate on a platform.

I am in the middle of this build right now, and will keep this post updated until the alternator test platform is finished.  A couple more shop days will get it running...