I've looked for solutions and cannot find anything that's clear to me that accomplishes what we need.
- 12V furnace 8A load (fan)
- 120V to 12V adjustable power supply
- 12V backup battery bank
The goal is to switch the furnace from the power supply 12V output to the battery bank when the power goes out (that is, no power from the power supply.)
I've set up relays to handle this switch over but they're not rated for continuous duty so they are getting hotter than I am comfortable with (just 15A BOSCH SPDT relays.)
All circuits are 12V, maximum 10A (furnace fan takes ~8A). I also have a low voltage disconnect between the battery bank and 'switching circuit' to prevent complete drainage of the batteries.
If I could find a continuous duty DPDT 12V relay or a DPDT SSR I'd have it sorted, but no luck (at least not at reasonable prices.)
What are your recommendations? Should I enlist a microcontroller (Arduino?) running off the battery bank that powers an SSR when the power supply has power feeding that power to the furnace, and when the power goes out it triggers a second SSR connecting the battery bank to the furnace?
Something like this would work, but I cannot find the right relays.
Even an SSR-based setup. I wish I could find NC SSRs for SSR1.