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Home Power #29

June / lulu 1992

battery charger; this feature comes in very handy when exceptionally heavy demands are made on the system. By simply plugging the inverter into a portable generator (via a separate cord to its input side), full power can be restored to the batteries in under two hours. There's no need to take the cart apart or attach jumper cables.

Safety

Safety in the system is controlled by a 200 Ampere DC-rated circuit breaker between the batteries and the inverter. These two are connected by a pair of 2/0 cables with color coded ends. Don't skimp on any of these components because the Trace inverter is capable of drawing 160 Amperes in normal use; some may say even this amount of protection is inadequate. Consult your favorite electrician and get his opinion before you decide to build a similar unit. It's important that we keep alternative power as free from accidents as possible.

Inside the cart, the batteries are seperated by a wall. Batteries give off hydrogen and oxygen when charging, and should be partitioned from anything that could ignite this gas. For that same reason, the end of the cart that contains the batteries is not closed. This allows the gas to dissipate into the air. The batteries are secured inside the cart and cannot fall out the open end. The cable between the controller and the panels is connected with a twist lock plug. This allows me to use these panels in other projects and also ensures that anyone unfamiliar with the system keeps the polarity right if the panels are disconnected.

Loads

Although this is meant to be a portable unit, the power cart serves double duty. During the winter this system powers the tools in my shop. There is a separate system for the lights, which are 12 Volt.

The largest load I have is a 1 1/2 h.p. table saw, which the inverter has no problem running. Other tools it runs include a miter saw,13 amperes ac; shop vac, 7.5 amps; a small 1 1/2 h.p. compressor, and a 12 amp router. These are the large loads. Numerous hand tools, jig saws, sanders, grinders, plate joiners, and so on are used as well. The only problem load is a small chainsaw sharpener. For some reason, this small tool won't run to full speed on an inverter. In all fairness to Trace, the sharpener won't run right on our Heart inverter either.

Drawbacks

Now, I should give you the down side of this system. Although the inverter is capable of handling large loads such as a saw, two people cannot use power at the same time - at least not the larger loads. Most inverters will not be hurt by this type of overload. As part of their protection, they will shut down until the overload is corrected, but this can create a dangerous situation. If someone is using a tool and does not switch it off after an overload, the tool will have full power when the power comes back on, possibly catching the user unaware. The habit of one person at a time using power soon becomes routine.

The Trace people recommend that their inverter be placed in an environment suitable to the finest stereo equipment. This inverter has been in places I wouldn't even leave a Walkman, but it has held up admirably. Other inverters on the market, some of which are more sealed to the elements, and some with less features, should be considered by those with different needs.

My design is by no means perfect. I had doubts, especially about the batteries. The lack of battery capacity is a drawback, but the ability of this type of battery to be quickly discharged without damage allows it to work. If I were to start fresh, nickel-cadmium batteries would be my first choice. The ability of the new fiber-plate nicads to stand up to more abuse really makes them more desirable. However, on a low budget, this power cart has certainly proved adequate for my needs.

Below: The PowerCart's innards. Photo by William Raynes.

Below: The PowerCart's innards. Photo by William Raynes.

So far we've had ample power for our usual crew of three, but found when the crew grew larger, we had to use the generator more often. With a larger crew and shorter days of winter, the three panels could not keep up with the demand for power. Still, even having to run the generator to recharge the batteries once or twice a day, we're keeping the noise and air pollution down to a new low for us - a welcome relief.

Conclusion

I wanted to write this article to show another way to use alternative power. We all know how well it works in our homes, but it should not be confined to that job alone. The more we can expand the ways we use alternative energy, the more people will be exposed to the viability of photovoltaics and aspects of renewable energy. When I first designed the portable power cart, the people I asked for advice in making it work told me it wouldn't. Notwithstanding that type of stumbling block, I hope people continue to find new ways to apply alternative energies to their everyday lives.

The future holds more refinements for my system. As money allows, I will improve it. If you depend on a brain-scrambling, noisy generator for remote projects, I hope this gives you a "quiet" alternative.

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Author: William Raynes, Great Spruce Head Island, Sunset, ME 04683

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