Solar Freaks

Attached is an excel document showing the current/voltage curves of the Maxon 118740 under no load.

Two motors were used, a 7 year old 118740, and a new 1 year old 118740.
There are noticeable differences. The idle current draw on the old motor is less than that of the new. Not sure if this is a result of manufacturers changes, or just because of a run-in motor.

I Only tested up to 11 volts. Losses seem to follow a straight line as opposed to an exponential curve.

Like the motors I have tested, the no load current at nominal voltage seems to be significantly lower than that which is stated on the datasheet. The older motor has less then half.

The older motor seems to free spin a little longer as opposed to the new motor. I have a feeling its because the bearings in the new motor are still tight, and the brushes haven't been fully run in yet.

Because the older maxon is 7 years old, i thought about potential magnetic field strength loss. However, when motors lose some magnetic field strength, they tend to draw more current at no load, due to high RPM.

I didnt have a means of accurately testing the RPM on both these motors, but a quick connection to the oscilloscope showed me ripples (due to commutation) with frequencies within 3% of eachother. So i concluded that for a fixed voltage, the RPM of these motors was within 3% of eachother, with the older motor having the slightly higher RPM.

If I were trying to measure RPM I'd put a black or white mark on the shaft, and try to pick that up with an optical sensor. Thanks for the data!

Didn't have an optical sensor setup at hand.
I was going to plot the RPM as well (measured by dividing the commutator ripples shown on the scope, by the number of commutator segments), but couldn't be bothered so late at night, as i ran the tests at 3am.