Monday, May 3, 2010

Power Management

I was talking to my dad on the phone the other day. His friend had electrical problems. Circuit breakers kept tripping. The 150 amp entrance panel was insufficient for the power being drawn. This is for a double wide trailer occupied by a single retired person.

Now I run my whole 10 room house on less than 30 amps. Most of the time it uses about half that. Currently there are four people living here.

Where does 150 amps go? The first thing my father found was 3 - 30 amp electric heating elements. Those were connected to a 75 amp breaker. When they all came on at once, the breaker would trip. He disconnected one of the elements. The trailer is located in the middle of Florida. Two heating elements were more than enough. Not only was the heat on, the person was running the electric washer and dryer, an electric stove and oven, an electric hair dryer, plus other devices. With all that going, the 150 amp entrance breaker was stressed.

The friend's first response to the problem was to install a larger entrance panel. Dad gently pointed out that by spacing out a few chores, the 150 amp panel is more than sufficient. If the electric heat is on, put off doing the laundry for a couple hours until it warms up outside and the heat goes off. That alone solved the problem. This is central Florida after all. Even if the early morning is in the 40's, but 10 a. m. it could be 70 or 80.

I don't have electric heat, or air conditioning. Those two huge power draws are avoided. However, I do have an electric well pump. That's my main power draw. My inverter is good for about a constant 20 amps. It can surge to three times that for short periods of time -handy when starting motors like a well pump. In the 20 years I've used the inverter, only a couple times did I exceed it's capabilities. Those were in the first years of use. I think I had the well pump going, a coffee maker, the washing machine and tried to power up a big radial arm saw at the same time. The inverter shut down and I got to contemplate my problem in the dark.

So there are two ways of handling power loads. Put in enough capacity for every possible power use at once. (which is how most modern houses are wired) The other option is to plan peak load use so as not to exceed a more moderate power supply.

Alternative energy systems perform much better with the second strategy. Fortunately, most heavy draws are of short duration. Microwaves, toasters, and coffee makers draw significant power, but only for short periods of time. It's not that much of a sacrifice to have to wait a couple minutes before using additional electric devices.

Planning on balancing your loads can save a lot of money on initial alternative energy installation. For example, a 2500 watt inverter is much cheaper than a 10,000 watt inverter. The whole rest of the system would have to be up-sized to match the huge inverter -more batteries and more solar panels or a bigger windmill.

It's not just how much power is used during the course of the day. It's also how much power is used at any given moment.


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