[sdiy] OT: 48v psu for dc motor

[Seb Francis]

Hi Julian,

I don't have any specific experience in this area, but I would say that 
this is quite a lot of current and you really need an efficient PSU.  So 
switch-mode rather than linear (and definitely easy to buy off the shelf 
rather than design your own).  Probably there exist some special switch 
mode PSUs that can output PWM DC directly.  But I reckon you would be 
fine just to use a normal one with external PWM switching circuitry.  
You could always stick a parallel capacitor followed by a series 
inductor to soften the edges (although this will loose you some 
efficiency).  But I'd just try it direct first and see if it works.  
It's not like you need ultra-clean DC to drive a motor.

I'm not sure if the motor control kit you mention is necessary though .. 
maybe whatever you use to control the CNC machine will be able to output 
PWM signal directly (most uProcessors can for example).  So then you 
only need to add a suitable power MOSFET on the end.  If you want the 
possibility to run the motor in reverse then you would need to use an 
H-bridge or Full-bridge driver (plenty of ICs around that will give you 
this, just add suitable PWM control from a PIC or something).

Seb



Julian wrote:
> Im building a CNC machine here (for synth use, amoungs other things : 
> ) and the spindle will be driven by a small DC motor.
>
> I have the motor, and the spec sheet for it, but no power supply.
>
> The spec sheet lists the following -
>
> Stall Current (amps) : 3.1
> Peak Current (amps) : 24.5
> Max Voltage (VDC) : 48
>
> In order to control the speed of the motor,  i was going to go for one 
> of these kits to vary the ammount of time the supply is connected to 
> the motor -
>
> http://www.quasarelectronics.com/3067.htm
>
> But, yes, my knowlege of higher ampage / voltage power supplies is 
> next to nothing.
>
> For example, i could probably pick up a switchmode psu off ebay for 
> very little, but would the PWM of the speed controller interfear with 
> the switchmodes regulating capability?
>
> And if i want to build a torroidal/rectifier/capacitor combination, im 
> unsure of the exact details values anyhow!
>
> So, yep, im stuck.  And whenever i try and google myself an answer, i 
> get stuck reading about low ampage 48v phantom power units.
>
> I know its not really synth talk, but i figured the chances of someone 
> here not knowing the answer would be pretty slim : )
>
> Cheers,
> Julian
>
>
>
>