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Old 01-03-2011, 01:52 PM   #1
terrazza
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Default 2PDT mech relay that is normally closed?

Looking for one in the 5 amp+ range... Ideas where to look?

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Old 01-03-2011, 02:38 PM   #2
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Ebay has a bunch of them....

http://shop.ebay.com/?_from=R40&_trk...All-Categories

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Old 01-03-2011, 04:42 PM   #3
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Just to clarify what I think you're confused about. A double throw mechanical relay is typically "normally" in one of the throw positions so one side is NC and the other is NO. I guess if you're thinking about standalone selector switches that have an OFF center position, it would be easy to mistake a relay for having it also.

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Old 01-04-2011, 05:43 AM   #4
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Quote:
Originally Posted by Bobby_M View Post
Just to clarify what I think you're confused about. A double throw mechanical relay is typically "normally" in one of the throw positions so one side is NC and the other is NO. I guess if you're thinking about standalone selector switches that have an OFF center position, it would be easy to mistake a relay for having it also.
Still don't get it....
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Old 01-04-2011, 12:37 PM   #5
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A 2 pole double throw relay has 2 circuits built in, and 6 contacts (Plus 2 for the coil)

If you look at it like a 2PDT switch where the contacts are aligned like the number 6 side of dice, the center 2 contacts (Middle dots on the dice) are common. The top contacts are normally open, and the bottom contacts are normally closed, all of the time.

When you energize the coil in the relay, it breaks the normally closed contacts and makes the normally open contacts.

So in other words, by definition all 2PDT relays are normally closed AND normally open. It's just a matter of which contacts you connect to your circuit.

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Old 01-04-2011, 02:31 PM   #6
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You can see the two "common" connections on the left. They are connected to the two Normally Closed contacts on the right. When the coil is energized, they both "throw" over to the Normally Open contacts. There is never any connection between the two "poles" or circuits but that dotted line indicates that both throws are coupled physically.
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Old 01-04-2011, 02:50 PM   #7
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Thanks Bobby!
A picture is worth 115 words!

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Originally Posted by Ecnerwal View Post
What does the primary pressure gauge on the tank tell us? That's right, the temperature. Put it on a scale if you want to know how much is in it...
Put some duct tape over the gauge - Or better yet - Replace the high pressure gauge with a plug - High pressure gauges are useless!
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Old 01-05-2011, 03:53 AM   #8
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mouser

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