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Old 18th February 2009, 09:52 PM   #11
jaycee is offline jaycee  United Kingdom
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Quote:
Originally posted by Bonsai

don't use atmel . . . . they may not be around in 6 months time.
What makes you say that? Their MPU's are certainly superior to the PIC junk that Microchip offer!
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Old 18th February 2009, 10:21 PM   #12
fotios is offline fotios  Greece
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Quote:
Originally posted by jwb
In a latching relay the contact itself is a permanent magnet.

Quote:
Originally posted by SQLGuy
Correct. And it's not the contacts themselves that are magnetic anyway. The contacts are carried on metal strips which are themselve attached to a steel plate. It is this plate that is spring-loaded and actuated by the electromagnetic pole piece of the relay.

Better relays sometimes even have gold plated silver contacts (certainly non-magnetic).
In a common type relay (non latching) there is not the same effect?
If you consider that your remark it is right and that it does make sense, then it is better to inform about this mistake mr. Nelson Pass because in his X0.2 preamplifier he uses Panasonic DS2E latching relays. From there it comes my proposition.
I don't know who are you dear friends from USA. Maybe you are designers of relays. Me, in Greece, by no way

Greetings
Fotios
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Old 18th February 2009, 10:41 PM   #13
SQLGuy is offline SQLGuy  United States
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I'll have to take a look at how those latching relays are constructed. I can't think off-hand of why the contacts themselves would need to be magnetic... and I can certainly think of reasons why you wouldn't want them to be.

What I have generally seen for relays set up to latch is that you use one contact to close a circuit to power the coil itself. So, in this case, you're using a normal relay that will latch itself closed once initially triggered, and remain closed until power is removed.
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Old 18th February 2009, 10:52 PM   #14
fotios is offline fotios  Greece
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Quote:
Originally posted by SQLGuy
Better relays sometimes even have gold plated silver contacts (certainly non-magnetic).
Are you sure that are non-magnetic? If yes, then jwb may be informed about this from the datasheet of Panasonic and Omron for their latching type relays:

1) Panasonic DS2E contact material: Gold-clad Silver

2) Omron G6AK234 contact type: Bifurcated crossbar AgPd (Au-clad)

3) Omron G6AK274 contact type: Bifurcated crossbar Ag (Au-clad)

Notes:
Ag = chemical symbol of Silver
Pd = chemical symbol of Paladium
Au = chemical symbol of Gold

Greetings
Fotios
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Old 18th February 2009, 11:02 PM   #15
jwb is offline jwb  United States
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That's interesting information, thanks. I actually can't find the specification for the contact plating on the G6K type relay in the data sheet, although I do see it in the G5A datasheet.

Update: the contact material is listed in the euro market datasheet but not in the usa market. Weird.
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Old 18th February 2009, 11:03 PM   #16
fotios is offline fotios  Greece
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Quote:
Originally posted by SQLGuy
... and I can certainly think of reasons why you wouldn't want them to be.
Sorry, but i can't understand why you said that.

Fotios
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Old 18th February 2009, 11:46 PM   #17
jwb is offline jwb  United States
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What about the Axicom FP2 latching relay? It has better specs than the Omron or Panasonic and costs much less. Frankly I am suspicious of its low price, but it has Au-clad AgNi contacts, rated for 100 million operations, lower rated contact resistance, and has a 100 times lower minimum permissible load (100µV vs. 10mV) and only costs $2.15

http://ecommas.tycoelectronics.com/c...08-98005_E.pdf
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Old 18th February 2009, 11:51 PM   #18
fotios is offline fotios  Greece
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Quote:
Originally posted by SQLGuy
What I have generally seen for relays set up to latch is that you use one contact to close a circuit to power the coil itself. So, in this case, you're using a normal relay that will latch itself closed once initially triggered, and remain closed until power is removed.
Latching type relays, apparted from:
1) One or two coils which push or pull a clear mechanical latching armature.
2) A mechanical latching armature, which push the contacts to close or open.
3) A set of 2 or 4 contacts in form either SPDT or DPDT.
The operation of latching relays it is similar with flip-flops. For this reason some times called also bistable. In the type of single coil, the same coil is used to close or open the contacts simply by inverting its polarity. In the type of two coils, the one is used to close the contacts and the other to open the contacts.
The trick of latching is found inside the mechanical armature. It is executed from a smart mechanism which apparted from a ratchet and a cam.
In industrial applications, these relays called Power Saving Relays instead latching, because they haven't the need of continuous supply of coil to keep closed the contacts. For this it cares the smart mechanical armature. In some cases the latching armature is apparted from a spring or a magnet, according to the demand exists.

Fotios
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Old 19th February 2009, 12:09 AM   #19
fotios is offline fotios  Greece
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Quote:
Originally posted by jwb
What about the Axicom FP2 latching relay? It has better specs than the Omron or Panasonic and costs much less. Frankly I am suspicious of its low price, but it has Au-clad AgNi contacts, rated for 100 million operations, lower rated contact resistance, and has a 100 times lower minimum permissible load (100µV vs. 10mV) and only costs $2.15

http://ecommas.tycoelectronics.com/c...08-98005_E.pdf
I think the difference is found in the contact alloy? I am not sure. Panasonic and Omron offer contacts which can carry 3A continuous current instead Axicom reffers 2A. The rest specs are almost the same. The issue is the reliability in practice and not in papers. This depends on the manufacturer trustability. If i was in your place, maybe Omron because are less expensive from Panasonic and a little most expensive from Axicom.

Fotios
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Old 19th February 2009, 01:57 AM   #20
SQLGuy is offline SQLGuy  United States
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Quote:
Originally posted by fotios


Sorry, but i can't understand why you said that.

Fotios
Magnetic contacts would, in most cases, be non-stainless ferrous metals. That means they would be prone to oxidation, especially if being repeatedly heated, cooled, and exposed to arcs.

Also, magentic materials lose magnetism when heated. High current relay contacts that rely on the magnetism of the contacts themselves might become bad connections under high current.
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