Feb 142019

This is my battery backup project. I have a natural gas steam boiler that I want to be able to operate and produce heat in case of a power outage in winter. The boiler has an electronic ignition. There is also an automatic water feeder. I am not aware of any other electrical loads (I disabled flue damper because its micro-switch is not working reliably).

Here are the obvious advantages of a battery backup: it’s located indoors, does not emit any fumes and works silently. A disadvantage of course is once the battery runs flat you need to find a way of recharging it. This can be tough during a widespread blackout.

First, for easy connection of a backup power source I did some re-wiring around my furnace. I had to break the connection between the AC line and the master switch and install an additional electrical box with changeover switch and inlet as shown in the diagram. Note that I run only electrically “hot” wire through the switches;  the neutral is continuous. To use the system during a power outage I need to flip the changeover switch to isolate the rest of the house (and utility lines). Then I plug an extension cord from an inverter into the inlet.

Diagram of battery backup connection
Here is how my system looks like. In the I’ll describe in detail all the parts (including battery, charger and inverter).

Picture of inlet and changeover switch