RE: Stepper Power

Chris,


My real world experience is that with 3 550 in/oz motors running at 5 amps
each from one of Dan's Camtronics controllers I was hooked up to a 24 v
power supply through a 7 amp breaker on the 24 v circuit and I only tripped
the breaker 2 or 3 times and that only occurred when all the motors were not
moving for an extended time. My guess is a 10 amp transformer would be fine
and I am now using a 15 amp unit and it is working just great.


Tim
[Denver, CO]

timg@... <mailto:timg@...>
http://www.ktmarketing.com

> -----Original Message-----
> From: stratton@... [mailto:stratton@...]
> Sent: Thursday, February 24, 2000 10:19 PM
> To: cad_cam_Edm_dro@onelist.com
> Subject: [CAD_CAM_EDM_DRO] Stepper Power
>
>
> From: stratton@...
>
> I've attempted some calculations on the stepper motor vs power supply
> size issue.
>
> I took as an example Microkinetics 34M470, nomivally a 470 oz-in motor
> in a Nema 34 frame. I haven't bought one yet, so I'm working entirely
> off the data on their web site:
>
> http://www.microkinetics.com/34m470.htm
>
> The various wiring voltage/current combinations all indicate that they
> rate this motor for just under 15 watts of I^2R type power.
>
> I looked at their graphs for performance with their various drives,
> and used 7.4 x 10^-4 as the conversion from oz-in-RPM to mechanical
> watts (it seems to be right, can anyone verify?). Their data and my
> calculations give results like this:
>
> 500 ozin 300 rpm = 111 watts
> 100 ozin 2300 RPM = 170 watts
> 125 ozin 2100 RPM = 194 watts (1/4 HP)
>
> These are of course marketing numbers obtained under ideal conditions
> with the best drives they make, and quite possible overheating the
> motors (the were running at 120% of rated current) But needless to
> say, 194 watts is a lot more than 15W (or 21W), and getting this kind
> of performance clearly requires a high voltage supply sized for the
> larger number.
>
> Working backwards, 300 watts (mechanical, winding heat, switching
> losses, etc) at 50 volts requires a supply that can deliver 6 amps. Not
> quite the sum of the rated current for the two windings, but only off
> by a factor of 2 or 3.
>
> It would thus appear that sizing the chopper drive high voltage supply
> current based on the rated motor current results in a large but not
> unreasonable safety margin. Obviously this is bad news cost wise, so
> I'd be thrilled if anyone can poke holes in my logic...
>
> Chris
>