Prepackaged Normally-Closed DC Relay switched w/3vdc?

Projects
1

I really like the PowerSwitch Tail for AC loads because it is a packaged unit. Quick, easy, safe, looks good. And switched with 3vdc.

http://www.powerswitchtail.com/Pages/default.aspx

Problem is I need a Normally-Closed DC Relay switched with 3vdc, rated for say 5 amps and 18volts. Enough to drive a fluid circulator pump by a small solar panel. Ideally it would also be a clean packaged unit suitable for a mechanical room.

Anyone know of options?

2

It’s not housed, but something like this would work fine:

http://www.ebay.com/itm/Two-Relay-Module-Board-8051-AVR-PIC-Project-5V-/130668495468?pt=LH_DefaultDomain_0&hash=item1e6c73026c

You’d hook the VDD to 5v and the imp IO pin directly to the control input. This control input is connected to the gate of a 2N7000 FET (if his schematic is to be believed) and this device has a maximum Vgs(th) of 3v - ie the imp is guaranteed to be able to control this no problem.

3

If you look at the schematic for Sparkfun’s COM-11041 (there are several other similar examples), you can see the circuit is pretty simple. A couple of resistors, a transistor, a diode and the relay. You could fairly easily get a small breadboard and make the same circuit only using the NC contacts in lieu of the NO.

Here’s something I found on eBay:
http://www.ebay.com/itm/5V-2-Channel-Relay-Module-for-Arduino-PIC-ARM-DSP-AVR-Electronic-Raspberry-pi-/110954333883?_trksid=p2054897.l5669
Here’s a similar:

I believe the only “trick” with these may be needing to change the series resistor on the opto-coupler input to allow the 3.3v from the imp to turn it on.

4

Thanks @Hugo and @ctmorrisonhvacsp. I really appreciate the help.

I just got done with my first few days of playing with relays (for the first time) of various types from various manufactures and must admit I learned a LOT!

Thanks again for the time you took to help me along.