How much mercury is in mercury relays?

Probably true. But it is encapsulated in glass. You have probably already seen:

They seem to operate just like the older thermostats. Arcing of the contacts will vaporize some of the mercury, but it is recovered when the switch cools.

Paul

Right. But I want to know how much of it is there. I bought a cabinet with contents, with big mercury relays. When I shake them, I feek a significant "heft" of liquid inside.

Ignoramus29535 fired this volley in news:mu-dnQXeg7QULkXPnZ2dnUVZ snipped-for-privacy@giganews.com:

Ig, at 7.6g/cc, it would take 33cc of mercury to make up 251g.

That's a half-pound! (which ain't a huge volume. I've got a 1lb bottle of Hg that's only the size of a small pill vial).

I've have a lot of different single-pole mercury tilt switches, with the biggest one rated at 30A. It doesn't have more than about 2cc of the metal in it.

Think about it... 11cc per pole is 2-1/4 teaspoonsful per pole. (Although you probably think 'naturally' in metric volumes, some of us have to translate to Imperial to 'get it'.) That seems like a great deal.

Now... if they were 100A switches/relays, I could see maybe having that much in them, just to increase the contact area, so they don't get hot.

But that sounds like too much for 35A jobs.

Lloyd

Read the Wiki more carefully. The coin shown floating on mercury has a density of 7.6g/cc, mercury's is 13.534. jsw

"Jim Wilkins" fired this volley in news:lbb7nt$1au$1 @dont-email.me:

Correct! That would make it something over a teaspoonful per contact. Still a lot, but about half of what I wrote.

LLoyd

You piqued mine, too.

I like their wording. "contains about 251.6 grams." Since when does "about" go down to tenths of grams?

Mercury is exceedingly dense and heavy at 13534 kg/m3, but ~9oz does seem overly much for a small, single-pole relay. (I wonder if it's a weight v. volume mismatch I'm experiencing. I believe so.)

So 252 grams would be roughly 0.64 fluid ounces. OK, that works for me. That crap IS dense!

I will try to open one up and see. I will do it outdoors

The EPA goons are likely on their way to your house as I type this...

On 1/17/2014 9:19 AM, Larry Jaques wrote: ...

...

Yes, it's 20% more dense than Pb -- 13.6 vs 11.3 gm/cm^3

Just shake it! You can probably feel the mercury sloshing around in there. Yes, the huge old mercury contactors had an amazing amount of the stuff in them.

Jon

I think more mercury would be required if the switch was activiated many times per minute, at the rated amperage. Much more vapour would be produced during the time of contact arcing.

Paul

Paul, I believe that this is what these switches are for, for very frequent switching.

They are also used in explosion proof applications where a contact arcing in a normal relay could be an ignition source.

Best Regards Tom.

"azotic" fired this volley in news:lbcc1r$9al$1 @speranza.aioe.org:

Really? I'd like to know more about that. Any citations?

Lloyd

Read it in a manufactures literature many years ago. Don't remember who, might have been magnacraft.

Best Regards Tom.

As a kid, I used to reclaim Mercury from such relays, and remember that Mercury is quite dense compared to a similar volume of steel. Have you ever lifted a bottle filled with it?

This site:

says: "The density of mercury = 13534 kg/m^3 or 13.534 gram/cubic centimeter"

so that would be 18.546 cc, or a cube (if you froze it) 2.64 cm on a side (a bit over an inch). That is fairly close to my experience. So an 80 Amp three pole would probably be on the order of 1,694 gm (making perhaps unjustified assumptions on the needed increase in size), or about 3/4 of a pound.

The relay needs quite a bit of mercury to handle the current, since *it* is the conductor, and if you have too little of it, it will vaporize (and possibly shatter the container if it is an all-glass one (some are, some are not.) Mercury wetted reed relays, in contrast, use a tiny drop, which simply wets both contacts, and make a clean connection quickly when it closes, and does not suffer from contact bounce.

Sort of somewhere between those two are the old home thermostats, which used a small ball of it rolling around in a glass tube to short the contacts when it tilts one direction, and open them in the other direction. (The rolling mass of mercury also adds a bit of hysteresis to the operation of the switch -- something which I had not realized until I started typing this. :-)

Enjoy, DoN.

"DoN. Nichols" fired this volley in news: snipped-for-privacy@Katana.d-and-d.com:

A quart glass milk bottle of it in the 1960s -- Yes, it's heavy!

I still have a 1lb bottle (a mere 'vial', and shy a few grams) of chemically-pure mercury which I use in tiny quantities for compounding experiments (not electrical purposes).

Lloyd

The standard remedy for spilled mercury when I was in high school was flowers of sulfur, which is finely divided elemental sulfur. This combines with the mercury to yield the sulfide, which is the ore.

The EPA is nutso about mercury. I handled a lot of it when I was in my teens. Nothing bad happened.

Joe Gwinn

Really old DEC computers used them. I guess the problem was the possibility of the turn-on surge welding the contacts of traditional contactors, and the mercury contactors were pretty immune to that. This was in the PDP-8 days of the 1960's.

Jon