Re: [CAD_CAM_EDM_DRO] re: e-stop sceme

zbushz wrote:

>This is my problem. I have two power supplies . One is 50 vdc the
>other os 70vdc. The first is 120vac the second is 240vac. I keep
>thinking that I should be able to cut the DC to the geckos by
>switching them off when they enter the driver box. I am thinking DC
>solinoid on the + side of DC in. That way whatever power supply I use
>the current gets cut when the e-stop is executed. All the other
>solutions I have seen call for cuting the ac to the power supply and
>draining the capacitors. Graingers has 100 amp DC power solinoids for
>$40.00. I think the problem may be with the generated current from the
>motors stopping. Is this way off the mark, or an idea that could work?
>
>

You can't do this that simply. First, when the large capacitors in the
power
supply are connected to the modest capacitors in the Gecko drives, the
current
will be WAY above 100 Amps. It could be 1000 to 10,000 Amps, depending on
wire size and length. This will quickly destroy even a 100 Amp contactor.

Secondly, if the motors are moving at a high speed, disconnecting the drives
from the cap bank gives no place for any generated voltages from them to
go to. This may or may not be a problem, partly depending on the motor's
inductance and resistance. So, what you want is an energy drain system.
I have a design that solves both of these problems, although Mariss does
not think highly of it for his drives. See the 2nd schematic at
http://jelinux.pico-systems.com/EMC.html for my charge/drain circuit.

Mariss put a circuit on the list's file section at
<http://f6.grp.yahoofs.com/v1/cM42P0obWOdVSvjJ5q_Q3dsYNwqNjfjymfznMUu0IYCPKjNPZ7Zdn-ctBPTtL-0q_HAwWFl_1yc6ASrs/A%20Servo%20E-Stop%20Circuit.pdf>
which is a bit simpler, and does the same job. Because the main cap bank is
discharged, it may take a little longer to stop the whole system.
This circuit will work with stepper drives, as well.

Jon