Triggering 10A Relays - Best Practices Requested

everest

My applications needs to be able to trigger a 10A relay. My current solution is to use a Darlington transistor array to trigger a small 5v relay. . .which then triggers the 10A relay. This is to keep the current draw on my Stamp pins to a minimum. . .plus they can't trigger the 5v relay anyways, they don't produce enough current.

Is this approach the best way to do this? It seems a bit overly complex to me. Any best practice recommendations?

-Jeff

Post Edited (everest) : 6/18/2009 10:18:22 PM GMT

Joms

Depending on what you are controlling maybe a SSR (solid state relay) would work for this application.· You can get SSR's that will control up to 50Amps.· They have a built in opto-isolator, which means it can be connected directly to a stamp pin.· Small, nice little package keeps is simple and clean.· However, depending on how many you need, cost might be a factor...

everest

I only need 5. . but still, I want to keep the costs down per unit as much as possible. . .

xanatos

SS relays are definitely the way to go, if you can. Sometimes you can't, for a variety of reasons. I am currently designing a system that has the same requirements you are stating... Oddly enough, I only need 5 relays as well! But the folks in charge have specified that the big contactors must run 24v AC, and there's some wiring code that prevents AC and DC wiring from running in the same conduit, so I am stuck with a setup just like you specify -a transistor driving a small relay, which provides 24 vac circuit path to the bigger relay, which runs the contactor. Seems convoluted to me, but that's what wiring codes can do to you!

erco

Surely 10A is your relay's contact rating, not coil current rating.·A 5V coil·probably draws no more than 200 mA·and·your Stamp·can trigger it easily using ONE (not an array) of most any small switching transistor, even a generic 2N2222. You won't need any intermediate relay.

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·"If you build it, they will come."

everest

Yes, I'm using an NTE46 and it's working flawlessly on my BoE board with my Stamp2. . .my Stamp2p-40 is a whole different story. I just fried one of the pins (I'm assuming) running exactly the same circuit that my Stamp2 is not running along happily, snapping my 10A relay back and forth. I'm utterly disappointed in this Professional Development Board and Stamp2P-40. I'm sure I'm doing something wrong but I don't understand why a circuit that runs perfectly on a Stamp2 would kill the chip with the Stamp2p-40. . .this makes no sense to me. [noparse]:([/noparse]

-Jeff

pwillard

Good question: Since the SX48 can SINK an SOURCE twice the current at the I/O pins that the STAMP2 does... it makes no sense to me either.

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There's nothing like a new idea and a warm soldering iron.

Phil Pilgrim (PhiPi)

Jeff seems to have started two different threads on the same topic. Let's tie them together. Here is the other thread:

····http://forums.parallax.com/showthread.php?p=816702

-Phil