Portable AC Inverter Project |
Overview
This is a simple project to build a portable 12 VDC to 120 VAC inverter. Unlike similar projects, this one was designed to be quite rugged. The only real major modification, was removing the front panel LEDs and outlets from the commercial AC inverter and moving them to the new front panel. Other features include rubber washers and sealant around any holes to make the final package fairly water resistant. An optional AC line filter should be added to the inverter's output if the intended operational area will be swamped with RF energy.
Pictures & Construction

Project overview. You'll need a standard, high amp-hour, 12 volt gel cell battery (and charger). A commercial DC-to-AC inverter. The one shown above is a Schumacher Electric PI-400. The label says "400 Watt" for the output power, but the actual output can only handle around 2 Amps (240 Watts) continuous. You'll also need some L-brackets for mounting and securing the battery, some assorted hardware, an optional banana jack output to supply a good source of +12 VDC, and a cheap digital multimeter to mount inside the box. The meter is a very handy addition for verifying battery integrity or for monitoring the inverter's AC voltage output. As always, everything is mounted inside an old ammo box. The four rubber feet mount to the bottom of the box.

The L-brackets are arranged as seen above. This will secure the battery to the side of the ammo box, yet still allow its removal. The blue pad is from an old can cooler. It's there to absorb any shocks.
On the front panel, you can see the power switch, the +12 VDC output banana jack, and also a single AC outlet. Secure the outlet against the ammo box by using a piece of art foam with a hole cut in it. The ferrite beads on the AC outlet's leads are to supress any induced electromagnetic interference. The banana jack output taps the battery's voltage directly. Place a 0.1 µF capacitor across the banana jacks for RF bypass.

Take apart the AC inverter and remove the internal AC outlets and power switch.

Internal view. The power switch wires are on the left (red circles). The AC inverter will always be on, so connect these two wires together. The three wires for the 120 VAC output are on the right (red circles).

The three wires for the AC output (hot, neutral, ground) are then mounted to little stand-offs. This allows easy access to them for tapping off additional outputs or for monitoring with the voltage meter. Also note that the power and overload LEDs from the inverter's front panel have had extension wires added to them.

Start to mount everything as shown. The large RED wire coming from the battery is the POSITIVE. This should be at least 12 or 14 gauge wiring, same with the battery's NEGATIVE.
The POSTIVE wire from the battery passes through a power switch on the front panel. The AC inverter has an internal fuse, but make sure you can get at it when you mount the inverter.

Alternate view with more wiring added. Add heatshrink tubing to the L-brackets to protect the battery.

Optional internal multimeter. It is a Cen-Tech model from Harbor Freight Tools (#90899). Mounting hardware is on the right.

Drill two holes off to the side of the meter as shown. These are for mounting the meter to the inside of the ammo box.

Mount the meter as so. Cut the meter's leads down to only a few inches and add some alligator clips. This will make it very easy to measure the battery (or inverter) voltage.