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Home Emergency Power

What happens when the power goes out? This document intends to provide a short introduction to some of your options.

Before we get going I need to remind you that working with electrical equipment and fuel sources is inherently dangerous and should only be undertaken by skilled individuals. Further....

This document and its author are not responsible for, and expressly disclaims all liability for, damages of any kind arising out of use, reference to, or reliance upon any information contained within the document. While the information contained within the document is periodically updated, no guarantee is given that the information provided here is correct, complete, nor up-to-date.

Let's ask a few questions to get the ball rolling...

Question 1: Are your power outages likely to be short (you have reliable power) or long due to hurricanes, snow, or similar circumstances?

Question 2: What do you need to keep running in the event of an outage? for example:

  • Fridge/freezer
  • Lights
  • Sump pump
  • Electric heater
  • Medical equipment
  • Cell phones, etc.

Question 3: What fuel source do you have available? for example:

  • 20lb BBQ propane - this has a very long shelf life and can run a generator for 10 hours. This fuel produces carbon monoxide exhaust gases.

  • Gasoline - this has a limited shelf life (30-60 days) but it can be extended with fuel stabilizer to a maximum of one year. Equipment using gasoline must be run regularly or stored following the manufacturer's recommended procedures to prevent failure. This fuel produces carbon monoxide exhaust gases.

  • Automobile - you have a self-contained generator, electrical system, and fuel! We'll talk about this a little more below.

  • AGM deep cycle battery - this special type of battery has a long shelf life, allows for deep discharge, and produces zero hydrogen when charged with the correct three or four stage charger (slow-charger or fast-charger). The longevity and safety features of an AGM battery are unmatched by car batteries, "maintenance free" batteries, and regular deep cycle batteries.

  • Solar - there are whole home solar solutions available along with battery backup for use during dark hours.

Question 4: How much power do you need?

So... we have a few choices based on the questions! but since this is a "home emergency power" blog post I will assume you have a fridge/freezer you need to run along with some electronics that need charging or maintenance.

When deciding on your home emergency power solution consider the maximum and running electrical load. A typical fridge/freezer or any device with a motor requires a very large surge of power to start the compressor. This surge is indicated on the electrical information label on your device. For example, a fridge/freezer label may indicate 8.5 amps at 115 volts. For this example 8.5A x 115V = 978W. Typically the running watts of a fridge is around 1/5 of that value, e.g. 200W.

So go ahead and check all the devices you wish to run during a power outage. Calculate the maximum watts and approximate the running watts. You can even buy a cheap watt meter to measure running watts for your critical devices - but remember to look at the electrical label for the maximum load details!

For this example let's assume you have a fridge/freezer that requires 978W surge load and 200W running load. You also have a 60W LED TV and 60W light bulb for a total 320W running load and 1100W surge load.

Question 5: How much are you willing to spend?

Now we can choose a power source! You have a few options at different price points but I'm going to narrow it to three of the most common:

  • Portable generators - cheap, plenty of energy, pure sine wave, very loud (lawn mower volume), and uses gasoline/propane. Buy this if you need cheap reliable power and don't mind the noise.

  • Inverter generators - expensive, limited capacity, relatively quiet, and uses gasoline/propane. This is very common for tailgating and camping where low noise is very important.

  • Inverter - inexpensive to moderately expensive but requires a separate power source (automobile or AGM battery) and correctly sized cables (4 gauge for anything longer than 12 inches but less than 48 inches).

Inverters come in two flavors: pure sine wave and modified sine wave. Pure sine wave inverters are preferred due to their similarity with utility provided power. Medical equipment, compact fluorescent lights, and other sensitive equipment require a pure sine wave inverter.

Purchasing a self-contained generator is certainly the easiest solution but comes at a high initial cost and requires maintenance and care. You must use fuel stabilizer to protect your gasoline and run your generator regularly to keep the fuel lines and carburetor functioning. Please follow manufacturer's guidelines to prepare the generator engine for long term storage.

Question 6: Would you like maintenance free power?

If you're still reading... then you're looking for an affordable solution for infrequent power outages and you'd like to avoid the hassle of maintaining a small gas engine. So let's look at inverters, automobiles, and AGM batteries!

Inverters, depending on your needs, can be purchased for as little as $80 for a modified sine wave and $180 for a pure sine wave. Here are three products to consider from reputable manufacturer's:

The modified sine wave inverters are suitable for a fridge/freezer applications but realize a modified sine wave causes your compressor to run warmer than a pure sine wave inverter. For $100-$200 extra you can protect your equipment and have clean power for sensitive electronics.

Carefully check the surge rating of both products against your electrical needs. If you are close to the limit then consider a higher capacity product.

Okay, now we have our inverter we must consider the 12V power source that will drive it. A word of caution:

12V is low voltage but to supply the required power (watts) for residential appliances the amps are VERY HIGH. For example a 200W load requires 20A at 12V. A rule of thumb is to divide the wattage required by ten for the number of DC amps necessary to drive your appliances.

Which leads to another warning:

**Car batteries and AGM batteries can supply hundreds of amps very rapidly. This can and will cause a fire, death, and property damage if handled incorrectly. Keep all cables and equipment out of the reach of children. *** YOU HAVE BEEN WARNED *****

For automotive power source you must consider your car's alternator capacity. Typically it is 80A maximum for a small sedan and 130A for a luxury sedan or heavy duty truck. Here are a few important tips:

  • The vehicle engine must be running with all electrical and electronic accessories switched off.
  • The vehicle should be a minimum of 15 feet from a house to prevent carbon monoxide poisoning.
  • The inverter should be kept out of direct sunlight and kept dry.
  • The cable connections to the car must be of a suitable gauge to prevent overheating (see manufacturer's guidelines).
  • Use no more than 50% of your alternator capacity to prevent overheating and failure of the alternator. e.g. 80A alternator translates to 400W sustained running load.
  • Car batteries produce hydrogen so be extremely careful when connecting the inverter to your car battery terminals. Make sure there's ample ventilation and wait a few minutes after starting the car to avoid sparks igniting hydrogen gas.
  • Do not connect your inverter to the car cigarette lighter, it is only suitable for 100W inverter applications.
  • Do not short the battery terminals; death and property damage will occur.

For non-automotive power you can use a battery... I recommend an AGM battery as it produces no carbon monoxide, it's completely silent, and can be used inside an apartment or other enclosed space. They are not cheap costing $200 for a 80AH capacity... here are some important tips:

  • Store the AGM battery fully charged with nothing connected to it. It should be fine for six weeks between charges (unlike a car battery).
  • You can refresh charge after six weeks without discharging first. Schedule an occasional discharge to 50% to exercise the battery. Be sure to measure the voltage to ensure your battery is still healthy when you do exercise it.
  • You can check the charge of an AGM battery using a cheap digital volt meter. Measure the voltage when there is NO LOAD on the battery (turn the inverter/load off). The voltage must NOT drop below 12.0 volts and is fully charged at 13.0 volts or higher. It is normal to see a lower voltage when the battery is under load.
  • AGM batteries typically do not produce hydrogen unless they are overcharged! so get a quality three or four stage charger (slow-charger or fast-charger) which correctly maintains AGM batteries. Do not cut corners on your charger to save a few dollars!
  • The cable connections to the battery must be of a suitable gauge to prevent overheating and fire (see manufacturer's guidelines). Use no less than six gauge and preferably four gauge, they are sold at Walmart.
  • Use no more than 80% of the battery's rated capacity. For example a 80AH AGM battery can safely discharge 64AH before shortening it's service life. That means an 80AH AGM battery can provide 640W of power for one hour, or 320W for two hours, and 160W for four hours continuously. A volt meter will read 12.0 volts when the battery is at 20% capacity remaining (measure with no load on the battery).
  • Do not short the battery terminals; death and property damage will occur.

Please remember that working with power is dangerous.

Follow all manufacturer instructions to the letter.

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