Re: [CAD_CAM_EDM_DRO] Sizing a power supply

Jon: There are no series(current limiting)resistors and I was running10
volts supply. The heat sinks were busy also. I put a fan on them. My
goal is to get chopper drives. I got outbid on 3 of those OEM650x
drivers on ebay 3-4 weeks ago. That wasn't you was it? I will probably
try to convert an oatley drive to chopper. I bought an extra for parts.
I have one really big stepper that I will put on my knee feed that will
use all of that 14A. For now I am just testing with one of the
Compumotors on the knee.(Bridgeport J). It goes up and down but not very
fast. I adjusted the supply voltage up a couple of volts while running
and the motor liked that a lot. A chopper would really wake it up.

Jon Elson wrote:

>
>
> "Carey L. Culpepper" wrote:
>
> > I am in the middle of that myself. I was just reading the section on
>
> > power supplies on the gecko site when your e-mail came in. I saw
> some
> > information there that was very confusing to me. On my Bridgeport
> > conversion I have 6 wire nema 42 Compumoters. They are supposed to
> be
> > rated at 5A/phase. I am (for now) using the Oatley kit drivers rated
>
> > at
> > 100V and 14A. Just for grins I decided to hook my digital meter in
> > series with the power supply to the driver.I am running the six wire
>
> > motors in series with the center wire unused. While running, the
> > motor/driver drew about3.8A. But when holding(not turning) it drew
> > 10A.
> > You have the 5A/phase times two phases ,I guess.
>
> I take it the Oatley drivers are not the chopping type? Are there
> series resistors to
> limit motor current? What power supply voltage are you giving it?
>
> This is the expected behavior of the R-L type drivers, which use a
> huge
> power resistor
> in series with the power input to the driver (or motor) to limit the
> current when idling.
> When the motor is moving, the inductance of the windings limits
> current
> (and speed).
>
> A chopping-type driver limits current by turning the input power off
> when the current
> limit is reached. This has the advantage of not dissipating the
> difference between
> winding and supply voltage, but accomplishing this by varying the duty
>
> cycle.
> This has the effect of lowering input current by the factor of the
> duty
> cycle.
> Assuming just one winding for now, if it has a rated current of 5
> amps,
> and the
> resistance of the winding plus the driver transistor is such that it
> drops 5 volts,
> but you have a 50 Volt power supply, then the duty cycle would be 10%
> to
>
> accomplish the voltage drop. But, the current drops to 10%, also!
> So,
> the
> current draw from the power supply would be 0.5 A, while 5 amps
> recirculates
> through the motor winding!
> The second advantage is that without the power resistor in series, the
>
> winding current
> can be increased faster.
>
> Finally, the current draw on most chopping-type drivers INCREASES when
>
> the
> motor is moving, as energy is thrown away when the magnetic field in
> each
> winding has to be dumped as the motor is stepped.
>
> Jon
>
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