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

Ahh, Haah: From your description of arcing conditions, I think that I know what is happening now. Although my relay is rated at 15 amps, I bet that I am killing the contacts with a "break" arc. When I push the "reset" button I have probably already charged the power supply by the time the relay opens the contacts for the load dump resistor, arcing the life out of the contacts and eventually welding them closed. This would all make sense, as the load dump resistor has blown both times while the machine was powered up, not immediately after an E-stop. I had to cut the power to stop the load dump resistor from smoking. Sounds like it is impossible to have a substantial arc on initial close (make). I do have some big monster open frame relays lying around, and will probably try one of those. At least I will be able to directly observe any arcing that takes place during break. Thanks,

Dan.
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--- In CAD_CAM_EDM_DRO@yahoogroups.com, David Speck <Dave@...> wrote:
>
> Dan,
>
> TBQH, I'm not sure how this would be beneficial for you.
>
> However, at 60 volts, there will be no appreciable arcing on contact
> "make" of the dump circuit. There may be some arcing at the contact if
> it bounces, but a well designed and spec'd relay, in conjunction with a
> proper dump resistor should prevent any arcing.
>
> Relay contacts routinely arc upon release if they are carrying
> appreciable current.