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Given a hybrid DC relay, I've been wondering if contact erosion is occurring (albeit at a slower rate), or if the design eliminates this entirely.

(Assume that there is no snubber or other contact protection)

I'm presuming that there is erosion for the following reasons:

According to my old H W. Ott book ("Noise Reduction Techniques in Electronic Systems" Ch.7), there are minimum voltages (9 to 20 V) and currents (10s to 100s of mA) where contact arcing will occur. With a hybrid relay, once the the solid-state switch (or relay) turns on, the EMR contacts stay below the voltage minimum due to the low voltage drop of the device. However, once the EMR is closed (or opened) the contact current minimums (e. g., rated > 1 Amp) will be exceeded. The reason? The contact's inductance in conjunction with the contact bounce during closure (opening?) will resulting in arcing once the current flow exceeds the minimum rating.

So it suggest to me that there is contact erosion (albeit much less than a standard EMR).

Is this correct, or am I missing something?

  • I'd say that it's probably a lower rate, Photonicinduction managed to get contacts to spark at a low voltage with his 50,000A transformer https://www.youtube.com/watch?v=uXEPy6Za6cI, I'm not sure how many volts a white-hot screwdriver is. – Jasen Слава Україні Feb 04 '20 at 03:35
  • I checked my own design (I've been using it for more than two years now) a few months ago and there was no noticeable wear on the EMR contacts. I don't use an SSR, but rather I use a custom design of my own with two SCRs per SSR-equivalent used for a 40A 220 VAC stove switch system. I avoided massive heat sinks, nicely. The EMR is a CNCJ JQX-40F. (I have a bunch of "new in-box" to compare against.) Looks okay, so far. So it's at least "lower rate." If I were to hazard a guess, I'd say it reduces the wear to below 1% of just an EMR alone, or less. So I feel it's often worth the effort. – jonk Feb 04 '20 at 07:02
  • Per this [TE app note](https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3236_AppNote&DocType=CS&DocLang=EN), the minimum arcing currents for Silver, Gold, Palladium, and Platinum is 380, 430, & 500 milliamps, respectively. For copper, 430 milliamps. Arcing occurs if either min voltage or current is exceeded. So per my 3rd grade arithmetic, 50 kAmps > 430 mA. Per the second answer, it sounds safe to go with this assumption. I'm designing power switch that needs high reliability due to a remote location that is inaccessible seven months of the year. – User Hostile Feb 05 '20 at 03:16

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