Re: [CAD_CAM_EDM_DRO] Re: [DIY-CNC] need transmission ideas / advice re: gantry

The overheating is more possible than you think!

For example, your motor is rated at 130V DC 18.5A 6000RPM.
At 24v, you should get 1107RPM. IIRC the fan's cooling capacity is the
square of the RPM, so it's like 3% effective, so basically nothing.

Now there's two losses here, one is core loss which is complicated to
calculate but DC I^2*R wire losses are not.
You might load the motor down at 18.5A at 1107 RPM. That's "legal" and
only consumes 444W. This will produce torque comparable to the torque
at full load at 6000 RPM.
The I^2*R losses are now exactly the same as the 130V full-power case,
BUT the cooling is reduced to nothing (or maybe I was wrong on the
squared basis, maybe it's just linear- in which case we have 18% fan
cooling power).

So, you have a serious cooling problem! It "might" overheat in a minute
or two, it's hard to say. Depends on how much extra cooling that motor
had. Probably ok.

The treadmill motors usually have a fan on the pulley output+flywheel.
In fact you may not even have one at all, some surplus mfgs don't ship
the heavy flywheel. In which case you don't even have the fan in the
first place.

The 24v scooter motor makes much more sense.

Danny

gcode fi (hanermo) wrote:

> Good points.
>
> Summary;
> - The speed does not matter. 1 minute is good, 2 minutes are ok.
> - Motor overheating is unlikely, as long as the motor load is not large
> than 1.5 Hp. Motors are rated for continuous duty at 90v, no fan, 1.5
> Hp, in an enclosure..
> - I will do about 25 lifts / day total. The use is thus very intermittent.
> - Inverters are a problem because they are very expensive in the sizes
> needed (her in Spain)
>