I have not seen your setup, but I got some similar effects in two different experiments before. Today, my digital multi-meter blew up simply because of this reason.
Originally posted by DavidE
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Sparking of the commutator inside the hobby motor can make your meter erratic. If you want to rule this possibility out buy a simple panel meter or analogue gauge and place it in parallel with your digital meter. If you still get erratic readings you could be onto something. Or if your DC motor is brushless then this is a different story. Remember a commutator is like a simple switch, in a way it is similar to the single relay circuit shown recently by Imhotep. So the make and breaks of the commutator inside the hobby motor causes the inductive spike, in this case it doesnt have anywhere to go, its not directed anywhere upon coil collapse. You will probably find that your meters continue to become more erratic the more you try to measure this type of electricity, I have about 8 cheap DVMs sitting here which all do the same thing.


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