Re: [CAD_CAM_EDM_DRO] servos,geckos,and power supplies

docholliday01201 wrote:

> My question is; if I am to use these motors to drive the
> axes, and I anticipate a maximum current per axes of approximately 10
> to 15 amperes, and anticipate using gecko drivers, where can I find a
> transformer with sufficient output current to feed three of these
> drivers. I realize that this question may have some inherent
> problems. I had anticipated that a worst-case scenario would be all
> three axes drawing 15 amps of current simultaneously. This would
> create a circumstance of 40 to 60 volts flowing at 45amps of current,
> for power output of nearly 3hp. The difficulty is finding a
> transformer capable of flowing that level of secondary current. Now
> what I am wondering is how much output current is necessary at the
> transformer assuming an output voltage of approximately 50 volts AC
> (run through a rectifier with DC output slightly higher) given the
> current draw of these motors. And based on that necessary current
> and voltage, does anybody know all the place that sells transformers
> like this relatively inexpensively. Obviously the large capacitor
> and rectifiers I will self assemble.

Note that the 45 Amps will be only momentary, and very worst-case.
If you apply this much power (about 1 Hp per axis) for more than
an instant, the machine will probably flip over. So, the capacitor bank
will do most of the hard work, and the transformer will only be overloaded
for a tiny instant. Remember that there will be a big surge every time
you turn the power supply on, too, and the transformer will survive
that.

Note also that a PWM driver only draws an input current equal to the
output current when the output voltage is equal to input. At other
times, the input draw is less. The motors only accept full voltage
when they are turning rapidly, the applied voltage is roughly proportional
to RPM (with a small allowance for resistance).

Make sure the motor's magnets will not be damaged by 15 Amps, or you
may ruin the motor.

> And by the way while were on the subject of CNC machining,
> I've asked this question before but I forgot the correct answer; I
> had had numerous problems with EMC running apart up until about the
> third to the last line of G. code, and then the program discovering a
> minor syntax error, and locking up. Is there any rapid and the easy
> way to verify a part program before running it. Specifically is the
> back plot feature capable of performing this function. And it's all
> what is the procedure to run back plot under EMC.

EMC has a verify mode, the interpreter runs through all the code
but causes no motion. It is a pull-down menu on the screen in
TkEMC, I think verify is the name of it. If an error is found, it stops
on that line, with a dialogue box reporting the problem.


Jon