Re: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim

Mariss
Hot is to hot on a 23 motor?
Jim

----- Original Message -----
From: Mariss Freimanis <geckohall@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Monday, June 12, 2000 6:14 PM
Subject: [CAD_CAM_EDM_DRO] Re: Gecko and Anaheim


> > Mariss;
> >
> > I have 42's rated at 10A, 80V and 1125 in.lb. Can a triple stack
> 34 equal
> > this (and possibly offer greater acceleration due to lower
> inertia)? And
> > (here's the kicker) is such a motor less expensive than the 42?
> This sounds
> > interesting.
> >
> > Doug Harrison
>
> Doug,
>
> Winding inductance and power supply voltage determine motor output
> power. The relationship is:
>
> P = V / square root of L
>
> Where L is motor inductance and V is power supply voltage.
>
> If you don't mind me being a little technical, here's what comes
into
> consideration. First, a step motor is a constant power motor. If you
> double its speed, then torque is cut by half. From the equation, if
> you want to double power then you must A; double the power supply
> voltage or B; cut inductance by 4. You can do this by going from
> series (or full-winding) to parallel (or half-winding).
>
> There is a limit to this however. While power increases
> proportionally with supply voltage, iron losses (hysteresis and eddy
> currents) increase more rapidly. An empirical determined limit is
> your supply voltage should not exceed 20 to 25 times the motor's
> rated voltage. Beyond that the motor will be too hot because of iron
> losses.
>
> Detent torque is always present and subtracts from the motor's
output
> power. If you double motor speed, you double the power necessary to
> overcome detent torque, which subtracts from what the motor could
> have put out.
>
> Now to bring this all together. Size 42 motors I'm sure you have
> noticed have much higher detent torque than size 34 or 23 motors.
> This is the reason why size 42 motors run out of steam before the
> smaller motors do. Second, for the same amperage, a size 42 motor
has
> much higher inductance and rated voltage than a 34 motor. That means
> they come into their own at much higher supply voltages; 160 to 200
> VDC. To get the maximum power from a 7A, 80V drive, pick a 7 Amp, 4
> volt motor. This will be either a 4 stack 34 or a single stack 42.
> For peak power, gear the motor to run just past the speed where the
> drive ceases chopping (i.e. current limiting).
>
> Hope that helps; and yes, 34 size motors are much cheaper.
>
> Mariss
>
>
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