Re: [CAD_CAM_EDM_DRO] Re: tachogenerator

bondeoca wrote:

>
> Yes Jon there are two sets of brushes parallel to each other,and
> on the same commutator.The two brushes at 0 degrees are wired
> together,and so are the other two 180 degrees apart.
> I checked the ohm meter on it, @ the 200 scale it reads 0.02.
> I checked a couple of treadmill motors I have here .002 and .003.
> Quite a difference.
>

2 brushes on the same commutator slug? Hmm, maybe to eliminate brush noise?
Your meter readings are 20 Ohms on the tach, and 2-3 Ohms on the
treadmill motors?
Yeah, that sounds about right. Well, with 20 Ohms on the tach at 100 V,
you can only get 5 A at stall, and the power dissipation would be 500
W. So, it wouldn't last more than a few seconds like that. Assuming it
could stand 50 W of dissipation, then the current limit would have to be
1.5 A.
So, maybe it could actually deliver a little power to the shaft. At 1.5
A, you'd drop 30 V in the resistance, leaving 70 V to drive the motor.
70 * 1.5 = 105 W output. I think the real killer would be the awful
speed drop under load, as soon as it started to cut, the speed would sag
horribly.

Jon