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Basic Electronics » Relay ratings

December 24, 2010
by Hexorg
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Hello friends, so I'm trying to control my room-light (110VAC) with the nerdkit... I found a relay online that had a coil voltage of 5V and a power rating of

"NO: 10A 250VAC | 10A 120VAC
 NC: 6A  250VAC | 10A 24VDC"

Sounds great, so I bought 5 of them (were cheap, like 80 cents), and 5 diodes to work as a fly-wheels. The package came today and this relays are too small for my expectations - 15x15x18 milimeters. Like I said, I plan to power just a household light-bulb (maybe 120W max). Will it be safe to try send that power through this relay, or should I look for something different?

December 24, 2010
by mongo
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Relay contacts are deceptively small for their purpose. In most cases, an overloaded relay will burn out the little wire or pivot on the armature before the contacts go. The voltage ratings are mostly for arc suppression, regarding contact "break", not contact "make".

That does not mean that the relay will last long under these conditions, it just means that it can handle it for a time.

A 120V 100 Watt lamp will draw just under one amp and is quite safe at that level.

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