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Forum Index : Electronics : Oddball Relay
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew I think this is probably my first time posting to "Electronics". I've been on the 4m for a few years. At any rate, I need to know if anyone can steer me onto a 15-volt d.c. relay. I need it to charge a battery by drawing juice from a capacitor. My idea is, I need a relay, which triggers at something above about 14 volts d.c., so I picked 15. Twenty would even do, but I don't want to get much higher than that (24 volt d.c. relays are available everywhere it seems!). Anyone know where I can buy such a thing? Thanks. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Mac A relay would be very un-reliable in such a circuit. A 24v relay may click in at 15 volts, and may not release until the voltage drops below 8 volts. An identical relay may click in at 18 volts and release at 10 volts. A 24v relay is designed to click in fast at 24 volts, and release at 0 volts. Any voltages in between can give unexpected results. So you need to add a circuit to measure/compare the voltage, and then drive the relay as needed. Typically this is done with a op-amp, like a 741, a couple of resistors or trimpot, and a transistor to drive the relay if the relay coil is of a low resistance. Smaller relays could be driven from the op-amp directly. Google op-amp voltage switch relay Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Glen Hey, thanks. Now all I have to do is find someone, who can tell me what you said. No problem. I'll copy this and email it to my friend, who is an engineer and we'll go from there. The project I'm working on, if it works at all, will be Soooooooooo cool. When it works, I'll post more. Thanks again. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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