Re: [CAD_CAM_EDM_DRO] Re: Spindle motors

At 08:55 AM 8/29/2007, you wrote:

>This interesting but something in my engineer mind says to ask some
>basic questions. Since 1 HP is 746 watts and the voltage is 30 to
>40 volts to get the RPM the current has to be like 15 to 20 Amps at
>that voltage! That is a sizable power supply.

Yes, it is a big supply. I saw controllers up to 300 Amperes, that
is significant overkill.

>I suspect those motors are not designed to run continuously given
>their application of running off batteries. I would also question
>the lifespan in hours. RC stuff is designed for a different duty
>cycle than running 8 hours a day.

I suspect that ANYTHING running 60,000 RPM would have a longevity issue.

>As discussed I think heat removal will be a problem.

I suspect that you are right, that was why I suggested a ducted fan to cool it.

>The controllers are pretty neat but not
>real cheap considering you would need to front end them with a DC
>supply of 40V at 20A (based on the specs). At that point it would
>probably be cheaper to build in a voltage regulator on the supply
>(even a simple phase control of the transformer primary).

You need high frequency three phase power to run the motors.

>I guess we won't know until someone can play with one and get some
>test results. I'm not sure how they do the HP ratings (even on the
>standard routers) unless it takes in to account RPM and inertia. If
>you look at the ratings of a 2hP full sized router that runs on
>120VAC it should pull more current running than it does....If you
>try to ask the vendors how that rating is measured they give you
>blank stares.

Actually, I got a "Well, that is the peak HP output for 1 second
max." The next question was how the router passes UL at that level,
it doesn't. To get the power in takes a special cord.

>Not trying to be negative but just working through the physics!

Hardly negative to ask good questions. I freely admit that I don't
know everything, I am learning too.


David G. LeVine
Nashua, NH 03060