Will a link to the chart do?
http://www.fieldlines.com/images/scimages/13340/30V.jpg
Not sure what you mean by efficiency.
Need to test input power vs output power. Prony brakes, etc.
I always found they need to spin faster to make 12V, than the RPM they turn themselves while running on 12V.
Some people say they may make more voltage turning one way than the other. My drill press only spins one direction.
Your findings seem kind of drastic for a 30 though. I didn't think they were that far apart.
This 30 wouldn't happen to be from ebay's 'fuzzy logic', the sticker has square corners, and the shaft end is drilled and tapped?
Or possibly came from an ebay guy in SC with military logos all over his listings, who is no longer a registered user?
On a good note, the 13V mark is about right for a decent Ametek, 13V at about 375RMP. A little high, but could be worse.
Something else can make them turn slower with 12V too. Gunky grease in the bearings, possibly something related to the brushes, etc. Remember, that is an old motor.
I found running them with 12V for a few hours, or a couple days, picks up the speed.
It also lowers the current required from the battery.
I measure the amps from the battery, then again in a few hours. If the amps drop, then the motor is sort of freeing up. I keep it going until the amps don't change.
I expect that will get your chart to match up a little better. But in a bad way because the Blue line will move closer to the Purple line.
G-
