Re: E-stop relay welds contacts for load dump resistor

Funny that you mention the issue with the "Reset" button. I retrofitted a Mill/Drill about 4 years ago, using many of the same parts and methods that I am now using on the Bridgeport, and yes, I smoked the small reset button after a few weeks. Put a much larger one on, and it has been OK since 2006, but I agree that it will eventually fail as well.
My dump to ground circuit is: + Terminal on power supply Cap---> 7 ohm resistor---> NC contacts on relay---> Ground buss bar. When the relay de-energizes, the Capacitor then has a path to ground, of course, to bleed off it's charge.
I just glanced at your link quickly, and it looks like a better idea for dumping load. Is there a schematic on your site on how to hook it up to my existing E-stop circuit? Also, does my idea about using a condenser before the relay contacts have any merit, or does this type of arc control scheme not apply here? Thanks again for all the help.

Dan.
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--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@...> wrote:

> This is why I now use an electronic control for this purpose. It ramps
> up the voltage to the servo drives rather than trying to apply it
> instantly. The main capacitor bank stays charged all the time.
>
> Most relays are not rated to break DC, and may not be able to carry the
> HUGE inrush surges the supply takes.
> Where do you have this relay connected? Mariss' circuit doesn't look
> really well thought-out. The N.O. start
> button will have to carry the full surge when pushed, until the relay
> pulls in. Most pushbuttons are not designed to carry several hundred
> amp surges. I'm surprised that the button wasn;t the first thing to go,
> but it will not last long.
>
> Anyway, you need relay contacts that are rated to break 9 A at 60 V DC,
> but you will have a real hard time finding an affordable one. A
> double-break contactor would be the best choice, and will probably last
> a while.
>
> I make a device for this purpose, that goes between the DC supply and
> the servo amps.
> http://pico-systems.com/oscrc4/catalog/product_info.php?cPath=3&products_id=28
> It is controlled by a 5 V logic signal that is grounded to power up the
> amps. A solid state
> relay can be used to switch it on and off. When the control input is
> not grounded, then
> the power is cut and the braking resistor is connected.
>
> Jon
>