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Shall We Make Our Own Electricity?

April 14, 2012

So it’s nearing the end of tax season.  Hopefully everyone reading this is getting a refund this year.  If so, try to save your money for a rainy day.  If you have the ability to put the money towards preparations for things that life throws your way (beyond savings), you might want to consider investing in a portable generator…

WARNING:  This post is written by Kristina’s husband.  I’m a professional geek (a real rocket scientist) but fairly down-to-earth outside of work…at least I think so.  Hopefully I can keep this post from being too much like a sophomore thermodynamics textbook.

What’s a generator?

A generator is an integrated device that typically has a gasoline engine and converts the rotational motion of the engine into electricity. Of course, there are other types of generators but they’re out of our price range (steam generators, nuclear generators, etc)…in fact, the Mars Rover I work on has a radioisotope generator that converts heat from nuclear material into electricity (for more on Curiosity, see this website or video).  The ones we’re talking about here are “portable” generators that can be wheeled to wherever you need electricity.

Why would I consider owning one?

Generators are useful in a variety of circumstances…not all of which will be applicable to you:

Power Outage:  this is obviously the main reason to consider having a generator. Late last year, there was a wind storm in Southern California that knocked down thousands of trees (literally) and left many without power for as long as two weeks!  Kristina and I had been collecting grass fed beef from the Farmer’s Market as it would go on sale and we were not thrilled at the thought of losing the contents of our refrigerator and freezer to a power outage.  Additionally, we have a tankless water heater which requires electricity to operate.  (Read…  Kristina was NOT happy at the thought of taking a cold shower!!!)  Even though our house has solar panels, they are tied to the electrical grid so when the power is out in the neighborhood, the inverter on our solar system cuts the power so that technicians working on the power lines won’t get electrocuted by the power generated by our house!  In a power outage, the generator can be connected to your freezer, refrigerator, tankless water heater, and cell phone chargers. I’m not advocating using it to power your TV, video games, lights, etc…there is something special about sitting as a family playing board games by candlelight around the fireplace during a power outage!

Working in the yard: depending on the size of your yard, having portable electricity can be handy!

Parties in the park:  if you’ve got a big event in a park, a generator can be used to power whatever you need.  One of the bands Kristina and I are in recently played a wedding reception held in a grove of stately oak trees at a winery in the Malibu Hills. This beautiful event wouldn’t have been possible without generators.  Check this out…isn’t it pretty?

Camping:  Some people have to have their electricity while camping and many campgrounds allow generators during certain hours. Since we camp to enjoy the quiet of our surroundings, we don’t camp with a generator…but it is popular and many do.  I’ve even seen pictures of people who bring a generator to power the portable air conditioner they put in their tent…seriously.

Photo Credit

How do I pick which generator?

Picking a generator is primarily about sizing. I will try my best not to go into total “geek” mode here. The size of a generator is typically measured in units of power (watts).  The things that get hooked to a generator are called loads. Each load draws power and the amount of power is expressed as the current draw (in amps) times the voltage (110 volts) for common house plugs. So, power=current x voltage. If you have a 2200 watt generator, it is capable of supplying power to a combined load of 20 amps (2200W = 20A x 110V).

So in the simplest terms, look at the labels or owners manuals for the things you would want to power with your generator and add up the current draws, sometimes referred to as “max current.”  The concept of max current leads me to another point, things that have moving parts or motors, like refrigerators, need more power when they start than they do when running continuously. If the generator cannot handle the start-up current, it won’t work…the circuit breaker will likely pop before the refrigerator gets going. For refrigerators, if there is no maximum current mentioned on the label, the rule of thumb is 2-3 times the regular current draw.  For the new, high efficiency refrigerators, it can be A LOT higher. When we bought our generator, during the power outage resulting from the previously mentioned wind storm, I used 3x the refrigerator current to size our new generator. We brought the generator home, plugged it into the refrigerator and “pop!”…the generator’s circuit breaker tripped and all power was cut off.  I checked for proper grounding and all the usual things an engineer would do when faced with a situation like this…My calculations said this should be the right size, but it wasn’t working.  It worked with all of our other appliances combined, but wouldn’t work with the fridge by itself!  Come to find out, our fridge can pull up to 9x its running current when starting up!  So, we returned the generator and moved up to a significantly larger size (5000 watts and capable of 6250 watts of starting power). The larger generator has no problem with the refrigerator, freezer, water heater, and cell phone chargers!

Here’s an example of how to size your generator:

Refrigerator= 9A (this is 3A times 3 for startup)
Freezer= 4.5A (1.5 A times 3…it also has a motor in it)
Cell Phone Chargers= 2A combined (to charge multiple devices)
Margin= (I’d add 10-20% here..but I’m a conservative engineer)

TOTAL LOAD = 15.5 amps + 20% = 18.6 amps (in this case, the typical 20A, also known as 2200W, generator will work great).

I can hear Kristina in my head…”put away the plastic pocket protector, Jordan.  You’re not describing a deployment mechanism for a robotic arm on Mars!”. Sorry for the extra geekiness of this portion of the post!

Don’t forget you’ll need a gas container and you’ll want to fill it with gas and store it in the garage!  When we had that wind storm, the power was out and the local gas stations quickly ran out of gas.  It was very surprising and a wee bit unsettling!

What if I have a question?

Leave a comment and we’ll give you the answer or at least point you in the right direction!

(This post is linked to Frugally Sustainable and Little Farm in the Big City.)

4 Comments leave one →
  1. April 15, 2012 9:35 pm

    Good info! i’m sure my geeky hubby and you could talk about this stuff all day. 😉 thanks for the post! btw, did you work on the latest rover for mars? just curious…

  2. rocketscientist1 permalink*
    April 16, 2012 6:57 am

    Talking all day about geek stuff sounds fun! I’m game! The answer to your question is “yes.” I’ve been working on the Mars Science Laboratory Project (Curiosity Rover) for about 6 years. The spacecraft is currently about half way to Mars and we land on August 5th at 10:32pm PT!


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