Paralleling for increased power output.

We all know of the little Honda Inverter Generators. These very fuel thrifty, quiet, and reliable generators come in 1000, 2000 and 3000 Watt capacities. They are very quiet, the typical open frame generator sounds more like a lawn mower but with the quiet Hondas you can stand over one and have a normal conversation. Honda reliability is well known, many of the home center generators use Honda engines then save on the rest of the components. The only downside is cost. The little Hondas cost 3-5 times more than the home center open frame generators but their other features more than make up for it.

There are other inverter generators by other manufactures such as Yamaha and Robin Subaru. I have no experience other generators so this article is only about the Honda eu2000i. As far as I know what I am writing about also applies to the other Honda inverter generators. There are some Asian knockoffs but I am afraid they are in the realm of "you get what you pay for."

From what I have seen the eu2000i is the most popular. Its 47 pound weight makes it easy to move around and 2000 Watts is enough to charge batteries and run most things on the RV. Sometimes 2000 Watts is just not enough. In particular 2000 Watts is usually not enough to start the typical RV air conditioner even with a soft start kit installed. That is where another feature of the Honda comes into play. Two of the Inverter generators can be connected in parallel to double the power available.

Honda sells a parallel kit for around $300. Others are available for around $200 and I have heard of some for less than $100. I built mine for less than $30 in less than a half an hour. One advantage of building your own is that you can easily add features.

To start this project make a visit to your favorite hardware store and collect the following parts:

1. 6+ ft of 12 ga. Extension cord cable. I like high visibility yellow to make it easier to see.
2. 2 20 Amp plugs. 15 Amp plugs will also work but the 20 Amp make it more difficult to use the combiner outside its intended purpose. You could also use spring loaded banana plugs, more on this later.
3. 30 Amp RV plug with cover plate. This combiner is to connect two inverter generators in parallel for a 120 Volt 30 Amp system only. As far as I know there is no way to connect the generators in series to make a 220 Volt 50 Amp connection.
4. Plastic electrical junction box big enough for the RV plug.

You may want to add other things such as a 20 duplex plug and a circuit breaker but after you have read this those things should be easy to add if wanted.

A brief explanation of the Honda operation. The engine drives a three phase alternator. Alternator output is fed to the inverter where it is rectified to DC then inverted to pure sine wave 60 Hz AC. If the generator is set to eco mode, engine speed is regulated according to power demand. Engine speed has no affect on the output 60Hz. The engines are connected together with the combiner kit, one engine started then the other. The second engine uses the input from the first to set its own AC in phase. Do not connect the combiner with both engines running.

Build the combiner. Wiring is dead simple, green to green, white to white, black to black. Start by cutting th cord in half. Strip back the outer insulation on all four ends then strip about a half inch or so from all the inner wires. Start by connecting the plugs to one end of the two lengths of cord. The back of the plugs will have a green, silver, and copper screws. Green wire to the green , white wire to the silver, and black to the copper. Connect the back covers and that is done.

There is an important note here. Using the plugs described above leaves a safety hazard. If for some reason a cord comes unplugged from one generator the other is still putting voltage to the plug. Should someone touch it they could get a nasty even fatal shock. An alternative is to find banana plugs with spring loaded shrouds. The hot ends are then covered when unplugged. One problem is that the banana jacks on the eu2000i do not route power through the internal circuit breaker. You could add circuit breakers to the box but that is an added level of complexity and expense. One source for the plugs is http://www.mcminone.com.

Next thread the other ends of the cords into both sides of the box. Be sure to use strain reliefs and leave several inches hanging out of the box. Connect the wires to the RV socket, it will have the same color code as the plugs. You will have to twist the ends of the wires together, green to green, white to white, black to black. Get a good tight twist to fit into the screw connectors of the RV socket. Push the wires back, screw the socket to the box, and put the cover in place. Now it is ready to use.

Hardware store combiner for Honda eu2000i generators.

To use the combiner, be sure both generators are off then connect everything. It does not matter which side of the duplex socket you use. Start one generator then the other. They should be in sync. I have run the air conditioner with both units of eco throttle with no problems except running out of gas in the middle of a sweltering Houston, Texas night.

Honda eu2000i generators running in parallel.

With the above setup I can enjoy an evening and a full nights sleep in the most sweltering of nights with the air conditioner running or just run one to top off the batteries run the microwave.