Automatic Transfer Switch



Here in hurricane prone Florida, the chances are better than average we will have power outages.  These can last seconds, to weeks, depending on the situation.  The worst one I experienced was in 2004.  Two back to back hurricanes trashed the power grid.  The area was without power for 18 days.  This was my incentive to add solar panels, and a battery bank.

Solar is fantastic when the sun is shining.  Just prior to the storm, during, and for a day or two afterwards, it tends to be rather cloudy.  Not much energy being collected by the panels.  As a backup, I've added an outlet on the side of the house to connect our generator.  Details on that project here

Since my inverter is only 120VAC, I can't easily use a big commercial transfer switch. Instead, I used a 120VAC transfer switch that's often found on an RV.  It's limited to 30 Amps, which is more than enough for my application.  My generator is rated at 20 Amps.

I have portions of my house running exclusively from the inverter - off the grid.  I've connected the inverter output to one of the inputs on the transfer switch.  The other input on the transfer switch is connected to the generator power inlet box.  When the generator is connected, the loads automatically switch over to generator power.  When the generator is disconnected, the loads transfer back to the inverter.  Very simple.


I didn't care for the large decal on the cover.  If the box was in a hidden location, I wouldn't worry about it.  But it's going to be visible.  The adhesive was softened with a heat gun.

The residual adhesive was removed with some Goo Gone.

The transfer switch enclosure was mounted to my Alt-Power board in the garage.

I wired it as shown in the diagram on the left.  Where it says "Powercord", I connected the inverter.  Where it says "Generator", that's what was connected.  This transfer switch features a 30 second delay, which can be bypassed.  The intent is to connect the generator, fire it up, and have 30 seconds for the generator power to stabilize before the transfer occurs.

All wired up.

I decided to add an LED on the inverter and generator inputs.  A quick visual indication that power is available from that source.

Labeled, ready for use.

Here's the generator power input.





Last updated 11/07/15    All rights reserved.