Re: DC Motor

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: FIFTYGUY@xxxxxxx 

In a message dated 4/15/06 5:12:29 PM Eastern Daylight Time, 
tesla@xxxxxxxxxx writes:

>What is the max current the motor will draw is the
>question. Tip, there is a lot of high power three phase stuff out there that
>should work fine with single phase. Maybe someone wants to do the ripple
>math and come up with a capacitance recommendation?

    Industrial DC motors are rated for the "form factor" of the 
ripple of the DC they are run off. For a larger fractional horsepower 
motor, there's usually a rating on the nameplate. NEMA codes 
representing the number of "pulses" from a rectified power supply are 
used instead of the true "form factor".

    A battery, DC generator, or 12 pulse/six phase power supply has 
a NEMA code "A".
    A 3-phase, six SCR full converter power supply with a 
mathematical form factor of 1.01 is code "C".
    A 3-phase, three SCR/three diode half converter power supply 
with form factor of 1.05 is code "D".
    A 3-phase, 3-pulse, 1/2 wave power supply with form factor of 
1.20 is code "E".
    A single-phase two SCR/two diode half converter power supply 
with form factor 1.35 is code "K".

    How important is this? Compared to a code "A" power supply, a 
code "C" creates 2% extra heating, code "D" 10%, code "E" 44%, and 
crummy code "K" 82%.

    NEMA designates powers supplies by a long designation, of the type:

    Total pulses per cycle "/" Total controlled pulses per cycle, 
Freewheeling (if a freewheeling diode is used) "-" Nominal AC voltage 
into rectifier (line-to-line) "-" Line frequency "-" External 
inductance to be added in series to armature (in milliHenries).

    So in some instances an external "Load reactor" is part of the 
design, essentially the "filter choke" to smooth ripple.

    Just some things to consider. It pretty much boils down to the 
better filtered the DC is gong into your motor, the happier it will be.

-Phil LaBudde