Re: [CAD_CAM_EDM_DRO] Re: Need help with servo power supply design

John Rouche wrote:

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...>
>wrote:
>
>
>>In a sense it does, but only for microseconds at a time. It
>>applies the DC supply voltage, for a measured time, first one
>>polarity and then the other. When the motor is not supposed to be
>>moving or generating torque, the + and - polarity balance exactly.
>>That is the same as no voltage across the motor, except for a
>>little heating. This happens 25,000 times a second.
>>
>>
>
>
>Are you saying full voltage is only applied for micro seconds at a
>time? That does not sound right.
>
>

Well, it is applied for as many microseconds as is needed.

>What is the pulse width of the wave and what type of wave form is
>it? I haven't hooked up the O-scope yet, that's next. I thought the
>gecko applied the full 60vdc (we are talkin about a 60vdc supply) to
>the motors for every pulse. Granted the rise and fall of the pulse
>are going to be changing voltages but that is not what we are
>talking about.
>
>

It is a 25 KHz rectangular wave equal to the DC supply voltage, applied
with alternating polarity. At idle, the pulse width is 50%, so it
balances out
to zero. It can go to about 100 % duty cycle, either way, as needed.
If it applied the full power for the entire time of the pulse the motor
would
be running at full power one way or the other. It controls the power to
the motor by making the pulses closer to 50% duty cycle, so the + and minus
parts of the pulse partially (or fully) cancel each other.

>We are talking about the peak voltage of each pulse, no? And if so
>the peak of each pulse is gonna be the input voltage to the gecko
>drive unless the gecko is doing voltage dividing which I didn't
>think it did.
>
>

Yes, it is the full DC supply voltage.

Jon