Why does this 5V relay have a polarity marked on the coil? It does not seem to have a built-in diode. See bottom of page 2 of the spec sheet:
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(Digikey # 255-1028-5)
- posted
17 years ago
Why polairity on a DC relay?
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- posted
17 years ago
Hi, Joe. The short answer is, there's a tiny permanent magnet in there.
Look at the data sheet. This relay will reliably switch with 140mW of power. How can you get enough force to pull in a magnet with only
140mW? You use a magnet to help.The difficulty is, if you apply DC in the wrong direction, it will repel instead of attract.
Here's a few links:
Engineer's Relay Handbook, 5th edition excerpts
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and Priniciples of Electromechanical Relay Operation, Ch. 3.25
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Remember -- it's not a bug, it's a feature.
Good luck Chris
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17 years ago
ah-hah thx
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17 years ago
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17 years ago
maybe there's a permanent magnet in there,
-- Bye. Jasen