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Electronics Forum / Basics / July 2006Why polairity on a DC relay?
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: http://rocky.digikey.com/WebLib/Aromat/Web%20Data/TK%20Series.pdf (Digikey # 255-1028-5) > 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: > http://rocky.digikey.com/WebLib/Aromat/Web%20Data/TK%20Series.pdf > (Digikey # 255-1028-5) 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 http://www.leachintl2.com/english/english2/vol6/ and Priniciples of Electromechanical Relay Operation, Ch. 3.25 http://www.leachintl2.com/english/english2/vol6/properties/00034.html Remember -- it's not a bug, it's a feature. Good luck Chris ah-hah thx >> Why does this 5V relay have a polarity marked on the coil? It does not >> seem [quoted text clipped - 24 lines] > Good luck > Chris see http://booksbybibin.14.forumer.com/viewtopic.php?t=33 > ah-hah > thx [quoted text clipped - 27 lines] > > Good luck > > Chris > 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: > http://rocky.digikey.com/WebLib/Aromat/Web%20Data/TK%20Series.pdf > (Digikey # 255-1028-5) as soon as you use a latching relay you need a polarity indication. but it saves the manufacturer money if the use the same marking on relays and if the user remembers pin 1 is + on all relays. rw -- > 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: > http://rocky.digikey.com/WebLib/Aromat/Web%20Data/TK%20Series.pdf > (Digikey # 255-1028-5) maybe there's a permanent magnet in there,  SignatureBye. Jasen |
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