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

Very encouraging that all of your strategies are things that I had considered as possibilities, so at least I know that I am not totally lost here. I actually already purchased a second 7 ohm resistor, which I eventually blew, but also ordered a 10 ohm along with it just in case. I was also thinking of pairing a big contactor to my ES Relay to carry the Cap dump load. Just have to source one that is suitable. For right now, I am temporarily using a standard 100 watt light bulb, placed in a socket on top of my enclosure in plain view, as my dump resistor. It reads about 12 ohms, and also gives me a visual indication of what is happening during bleed time, and an instant warning if the contacts are welded. If contacts are welded, the light bulb stays on, and I know to cut the power right away. This prevents me from eating $13 resistors (with shipping) while I isolate the problem.
If the shop light "blink" from inrush current is not indicating a larger problem, then I won't worry about it. It does not cause any other electrical problems, and I don't blow any fuses or breakers.
What do you think about the idea of using a condenser (capacitor) immediately in front of the relay contacts, to soften the "hit" that they see from the current inrush, and reduce the initial arc jumpover on contact close? Kind of like what auto manufacturers used to always do with points style ignitions to keep from buring the contacts on breaker points. Do you think that this might be an effective means to preserve the contacts? Thanks!

Dan.

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--- In CAD_CAM_EDM_DRO@yahoogroups.com, David Speck <Dave@...> wrote:
>
> KZF,
>
> It sounds like you should have a higher resistance value for the dump
> resistor. It might take a bit longer for the voltage to drop, but a
> higher value would limit the peak current through the dump contacts.
>
> It wouldn't hurt to use a higher rated contactor for the dump relay,
> either. The larger the contact area, the less likely they are to weld
> with a current pulse.
>
> If you can find a big double pole relay for the dump circuit, then you
> can split the current between the two contact sets.
> It may also be advisable to use a power thermistor or a power resistor
> bypassed by a short delay cutout relay to limit the inrush current to
> your supply. That saves me from blowing breakers with my big VFD
> circuits, and should stop you from dimming your shop lights at system
> turn-on.
>
> Dave
>