Everything You Ever (or never) Wanted to Know about Emergency Power, Lights, and Generators (Part 1)
This entry was posted on December 29, 1995.
Why do we have Power Outages?
Power outages can be caused in numerous ways, including, lightning and wind, tree limbs falling against power lines, overloaded circuits, dig-ins of underground electric tables, and equipment failures. Sometimes, power may be interrupted to rebuild, repair or maintain the electrical system in your area to minimize chances of on unplanned power outage in the future.
Before a power outage occurs, you need to have a few things ready. You will notice that they are the same items you need for just about any emergency. Power companies, like all utility companies, are quick to warn you to be prepared for loss of services for 72 hours.
The Usual List (but many people forget!)
We have a hard time understanding why these items are always in short supply after a power outage. But then again, many people just don't get around to it. Please, get these supplies together. After the windstorm of 1995 (December 12, West Coast USA), you couldn't find a candle, a flashlight, or a set of batteries at a local hardware store if your life depended on it!
- Flashlight with extra batteries
- Candles and matches
- Manual can opener
- Battery powered radio
- Wind up or battery powered clock (we wouldn't want to be late to work, would we?)
One of our local suppliers had a run on emergency supplies when the windstorm of 1995 hit Seattle. He sold several hundred flashlights and battery sets to help restock a local hardware store that ran out. About an hour later, he got another call for several hundred more from the same hardware store! They were selling like hot cakes! There are only so many of these items in any city at any given time. Get yours today while you're thinking about it!
The supplier mentioned above also sold about 1000 road flares to the local power company. You would think that the local power company would be ready for a small disaster like that one, but they weren't!
General Notes about Outages
- Cold weather is especially hard on infants and the elderly. If you lose power in cold weather, dress in several layers of clothing and be sure to wear a hat and a pair of gloves. Keep the heat in.
- Use your hot water sparingly. Your hot water heater will hold its temperature for a day or so, but remember that every drop of hot water that you use is replaced with cold water at the inlet of the heater. If you use a few gallons of hot water, the temperature of the remaining water will decrease because of the cold water that replaces it. If possible, use the hot water from a location that is close to the heater so you don't waste hot water trying to get it to the 3rd floor when the heater is in the basement.
- If possible, keep doors and windows to your house closed. But remember that if you use your fireplace for heat, it will use valuable oxygen in the house, and will require infusions of fresh air from time to time.
- Keep the refrigerator and freezer doors closed as much as possible. We hope you have read the tip that talks about the refrigerator. There are some great tips for keeping stuff cold in a power outage.
- If you have an electric garage door opener, please take a look at it to see how to over-ride the mechanism. You will need to know how to open it!
If You Lose Power
Take a look at other houses in the neighborhood. Do they have power?
Sometimes power will be lost in a very localized area. Often, houses that are served by the same pole mounted power transformer will be dark, while houses next door are fully lit. They might be served by another leg on the local power grid. Your neighbors might be able to provide cold storage for items in your freezer if power is out for extended periods, or you might be able to provide cold storage for someone else in the neighborhood.
Turn off your main circuit breaker.
Know where the main breaker is located in your house. As soon as power is lost, kill the main breaker in your breaker panel. Often times when power is restored, there are several power "spikes" which can damage some of the more sensitive electronic equipment. Most modern equipment employs power supply technology that is less susceptible to these spikes, but older supplies may not fair as well. There are even better reasons to kill power which are discussed below.
Motors draw large amounts of initial start up current. Once a motor starts spinning, the current requirements drop dramatically. The amount of start up current is partly dictated by the start up load on the motor, and the construction of the motor itself.
Let's take a belt driven drill press as an example. If the drill bit speed is set to a slow speed, the chuck reaches its final speed a short time after power is applied to the motor. If the drill speed is set to the high setting, you can hear the drill press "wind up" until the final speed is obtained. The reason is that the drill press belt, pulleys and other mechanics have some resting inertia that the motor must overcome in order to get the works spinning. This resting inertia is larger when the gearing ratio is larger as in this example. If you were to measure the startup current for both cases, you would find a huge increase in start up current when there is more of a load on the motor (more resting inertia).
An example is an 1/8 horse power furnace motor used in many natural gas heaters. The running current is 300 Watts, but the start up current is nearly 500 Watts. That means that you need about 70% more power to start the motor than you need to keep it running once it has been placed into motion. The same holds true for all motors. In some cases you need even more power to start a motor based on the initial load. A good estimate of the initial start current is to double the run current.
Here is a little story to help illustrate the need to turn off your main circuit breaker after power is lost. Let's pretend that I run a toy power station. My station can supply 10 Watts of peak power. I have 6 customers who each use 1 Watt of power. I have a 4 Watt power reserve available for when I get more customers, or when one of my customers buys a new device that requires more power.
Like in the real world, all my customers need power at the same time. They all get up at 6 AM. They all start their toy coffee pot at 7 AM, and they all go to work at 8 AM. Nobody needs my power in the middle of the day, but they all get home at 6 PM and cook dinner in their Betty Crocker ovens. At 7 PM they all turn on their toy televisions to watch re-runs of the Simpsons.
What if the toy coffee pots are run by a toy motor that consumes 1 Watt of power?
Hint: Remember that motors need twice the run power to get started (start up current). If everyone starts their motor powered toy coffee pots at 7 AM, the initial start up current needed by my 6 customers is ... 2 watts (start up) x 6 (customers) = 12 Watts!
Guess what. My toy power station just tripped the circuit breaker, and nobody gets power! One of my customers must turn off the coffee pot! What happens then? Well, if one customer bows out, the remaining power needs are.... 2 Watts (start up) x 5 (customers) = 10 Watts. Now power can be restored. After the motors start running, the current demand returns to one Watt per customer for a total of...1 Watt (running) x 5 (customers) = 5 Watts total. My power station can deliver 10 Watts, so there are now 5 extra Watts available. My last customer can then turn on his/her toy motor powered coffee pot and the new current is....1 Watt (running) x 5 (customers) + 2 Watt (start up) x 1 (customer) which is equal to 7 Watts! Guess what again. Everyone still has power!
I know the example above is a bit silly, but I think it well illustrates the problem. Think about the real life application:
- When power is lost, all the switches in your house (for lights and such) and all the appliances that were on are sitting there ready to consume juice when power returns.
- You might even have turned on more light switches thinking that power was only lost in one room. Did you remember to turn them back off?
- If power is off for some time, the house may cool off, and the furnace thermostat might trigger to start the heater. Remember, power is still off, so the furnace motor will be sitting there ready to consume more start up current.
- The contents of the refrigerator and freezer might have warmed up, so the refrigerator thermostat might also have triggered. The motor will be sitting ready to eat more start up current.
- By this time, the water in the hot water heater might have cooled down enough to cause the water heater thermostat to trigger. The water heater element will be sitting ready to consume more power! Although the heater should keep the water warm for a day or so, we needed to stress the point!
Get the picture? Your house will need much more initial current to get everything going again. Imagine the power demands placed on the equipment at the power company when every customer needs more power than they normally do, and at the same time! Remember that everyone is out of power, and everyone has the same start up power needs! When the main switches at the power company are re-energized, it is highly likely that a breaker will trip, or a power surge (high demand over a short period of time) will cause a spike on the line.
In Part 2 of this series (Power Outages & Generators, Part 2), we review generators in detail. Here are some of the topics discussed:
- Do I need 120 Volt or 240 Volt?
- How much power do I need?
- How much will it cost?
- How do I hook it up?
Some General Notes:
- The smaller the better. Run time is a major concern. If you don't have power in your neighborhood, your local gas station won't either. No power, no way to pump gas at the gas station! The gas supply on hand must last as long as possible.
- All generators manufacturers rate their generators fuel consumption based on running with a load that is 1/2 the rated capacity. It's a bit misleading, but they all do it! Remember the fuel usage numbers shown below are for 1/2 the rated continuous load!
- To get a generator that has 240 Volt output requires an 8 horse power motor in most cases. Try to limit your generator choice to a 5 horse power or smaller which implies a 120 volt only unit.
- Generators with 12 VDC output in addition to 120 VAC cost about $100-$150 more than AC only units. What you are really paying for is an extra set of coils in the generator, and support electronics to rectify and regulate the DC power.
- Quiet is expensive! Loud is cheap!
- Long run time means low power output. High power means short run time!
- 230 volt output means 8 Horse power or larger with most brands, and short run time (small hours per gallon).
Do I Need a Generator?
Evaluate Your Need
The key is to evaluate what you really need to power in an emergency. Take a look at the table we have provided below. A few things should come to mind:
- Your electric range and stove are the largest consumer of your limited emergency resources. Next on the list is Electric heat, the electric hot water heater and the close dryer. All these items require lots of power. Also note that these are the only items in your house that require 230 Volts.
- Most Gas heaters only require 120 Volts to run the blower motor, and control electronics.
- What do you really need to power? All you really need to power is a lamp or two, a TV, or radio, the refrigerator, and a microwave oven. None of these items require a large amount of power, but they do if you want to power all of them at the same time.
Look at the watts needed:
|Lamps (two, 60 Watt bulbs)||120|
+ startup current (+70%)
|Gas furnace blower (1/8 HP)||300|
|Total Watts Needed||2185|
Notice that it looks like the microwave is the largest user of power, but remember that the refrigerator uses about 70% more power on initial start up as discussed above. That means that for a short period of time, the refrigerator uses 425+290 Watts. That's 715 Watts all by itself (at start up). The same is true for the furnace motor which will use 510 Watts at start up.
From the above, notice that you would need a 2200 Watt (3000 Watt peak) generator to be able to run all that stuff! That size generator uses a 5 horse power motor and runs for about an hour on a gallon of gas. Remember that gas will be impossible to get in an emergency! Is it worth using a gallon of gas so all the above items can be used at the same time for an hour?
A better approach would be to use the generator to power just the items you really need on at the same time.
Something to Think About
If you limit the number of items you want powered, you can use a smaller generator. Below are some suggested groups. Assume it is night time and you need a light on.
|Group (including 60W light)||Watts||Reason|
|TV (color) and one light||175||Entertainment/News|
|Refrigerator and one light
(start up current included)
|775||Preventing food spoilage|
|Microwave and one light||710||Cooking/food prep|
|Furnace blower and one light
(start up current included)
From the above, you will see that if you can do without entertainment while you cook dinner, or if you cool down the items in your freezer before you heat the house, you can get away with using a 1000 Watt generator which will run for about 3 hours on a gallon of gas.
It's all a game in tradeoffs!
- 120V or 240V
- Power versus run time
- Generator motor size verses fuel consumption
- Cost versus noise
Wattage Requirements for Household Appliances
Electric heat and hot water are the biggest users of energy. Reducing your dependence on these will enable you to use a smaller generator.
|Gas and Oil Heat Fan||500|
|Hot Water Heater||4,500|
|TV (Black & White)||75|
|Light Bulb (60W)||60|
Another Emergency Power Option
AC to AC Power Converters
These converters provide 120 VAC power from 12 volt DC power found in cars, motor homes and batteries. Smaller units plug into cigarette lighter outlets, and larger units are typically hard wired into a vehicle charging system, or to a battery bank (multiple batteries wired in parallel for higher current capacity).
If these devices are intended to provide emergency power from a battery (or bank of batteries), you must remember that they will draw power out of the battery at a rate that is in proportion to the amount of power required at their output. If power is not added back into the system, they can provide AC power for only a short period of time.
How Power Conversion Works
Assuming that these converters are 100% efficient in converting from DC to AC, they can only produce as much output power as they consume on the input. If you take the example converter above, the rated output is 140 Watts (200 Watts peak). Power is a function of voltage and current given by the equation...
Power = Current x Voltage.
So if we have a load that requires 140 Watts out at 120 volts, the output current is 140W/120V=1.17 Amps. For 140 Watts to be available at the output, and assuming we convert 100% of the input power to output power (in actuality, most units are only 90% efficient), that means we need...140W/12V=11.7 Amps from the 12 volt DC source!
If you have ever left your headlights on in your car, you know that your battery will die by the end of the day. Your head lamps require about 10 Amps. I hope you see that powering 120 volt items from a battery using a power converter is impractical for more than a few hours unless additional power is put back into the battery. Lots of power can be put back into a battery from the charging system of a car, but a car engine, with its hundred+ horse power, is a bit over kill for charging batteries!
Another solution to providing a large amount of DC power to the converter would be to use an alternator from a car, and a small gas powered motor. This combination can deliver over 780 watts (with a 65 amp alternator).
Other Notes about Converting Power
There are really only a few devices in the world that require 120 Volts AC. Most of them are motors, heating coils etc.! They have been designed to run on that power for a variety of reasons that we will not go into here. Just about everything else on the planet converts the 120 Volts internally to what ever the electronics need! Take your computer as an example. You put 120 Volts in, but inside the computer, you will only find DC voltages like + 5, 12 and -5, -12 (3.3 with some fast processors). The point is that just about everything in the world plays the power conversion game and most items waste power in the form of heat just converting it all!
The key is to use a device that is intended to run on the power source you have, or plan to have. If you plan to power a TV on batteries like D cells, or your car battery, then buy one that holds D cells, or has a 12 volt cigarette lighter input. You can still run it on wall current (when local power is available) with the adapter that comes with it, but if you need to run it off battery, you can!
For the Consumer
When you buy a new item, think about whether you want to use it in an emergency. If so, try to find a version of the item that supports several power sources.