How to use relay switch

V+ goes through the relay, into the collector of the darlington pair inside the driver, then down to ground. A second V+ connection to pin 10 acts as a 'flywheel' diode to stop back-emf.

Connect GND to ground (anywhere), one of the outputs to the relay, and the other side of the relay to +12V.

The logic '1' signal is enough to power the base of the darlington pair to turn it on/off. It needs no power supply of its own.

Here is the circuit built on breadboard. The connectors along the top are:

• Black: Common ground
• Yellow: +5V
• Blue: +3.3V
• Green: +12V
• Red: -12V

The Solid State Relay linked in the question will not work for loads which could operate in either direction. For such purposes, search for SSRs specified for bidirectional DC or AC/DC loads (as distinct from just DC, AC or AC/Zero-crossing types).

While narrowing down to a specific such part will involve price, availability, voltage, package, size and perhaps other considerations, here are a few examples to illustrate that such relays do exist. Note how they are specified, to help extend the search for the ideal part:

• Tyco MS14 SSR Solid State Relay with Bi-Directional Output
  • Notice that the V_load pin is indicated with a +/- in the diagrams:
• From the same family as the CPC1709 SSR in the question, IXYS CPC1909 would work, with the constraint that its maximum rated current is 6.5 Amperes, just at the limit for the application in question. Hence, it is inadvisable to use this part.
  • Notice how the relay's switching portion is indicated in the diagram, with two FETs as opposed to the single FET in the CPC1709:

Unfortunately Digikey does not seem to carry any bidirectional load SSRs specified for greater than 6.5 Amperes, so the search needs to continue elsewhere.

Alternatively, consider limiting the current across each SSR to below the maximum load current rating of the part.