It is always good to have some sort of backup power for emergencies. The means to charge cellphones, tablets, laptops, and run lights, TV, and radios is a great asset in an emergency.
I am going to show you how to make a backup power box out of off the shelf equipment. Zero skill is required to do this project. All you need is the parts and a place (i used a storage crate) to put them.
Step 1: Parts Required
Most of these parts can be found in the local hardware store, automotive department, or auto parts store.
12 volt battery.
The bigger the better. Find a place that sells remanufactured batteries with a warranty to save up to 60% on price.
400 watt power inverter.
You can buy a bigger one but the more wattage you demand the faster the battery will run down. Can be purchased for under $50
Powered USB hub.
Use a hub that gets its own power from an outlet. This will let you use it to charge usb devices without hooking it up to a computer for power. I used a 15 port hub i had in the parts pile.
A standard drop light with a CFL bulb is great. You can buy LED drop lights too. Don't use incandescent bulbs because they draw too many watts and will run the battery down fast.
12 volt power outlet with battery connectors.
Very handy to run 12v items directly from the battery.
Get an extra USB cable for your devices and put it in the box. You can use the 12v power outlet and your phone's car charger to charge the phone directly off the battery.
Extension cords and adapters
Keep a 12ft extension cord in the box. Pick up a 1 to 3 adapter for the cord to run the power where you need it.
Float charger / Battery maintainer.
To keep the battery fully charged while you have power. A float charger or battery maintainer is used to keep 12 volt batteries charged up while they are not in use. This also extends battery life.
- Jumper Cables. For charging the battery off the car.
- Solar Panel with charge controller. This is a big help when power is out for days.
Step 2: Some Basic Battery Knowledge
The battery, inverter, and power port connector are 12 volt DC. The battery has positive and negative posts
The negative post will be marked with a - symbol or NEG abbreviation or Ground. The terminals are usually colored black.
The positive post will be marked with a + symbol or POS abbreviation. The terminals are usually colored red,
When you hook the inverter to the battery you hook positive to positive and the negative to negative. red to red. black to black.
DO NOT REVERSE THE POLARITY. This will cause your electronic device, inverter, etc to blow a fuse or burn out. Be careful and make sure you hook everything up correctly.
Step 3: Selecting Your Battery.
The battery is the biggest investment in the whole project and you need a large battery to provide a long term amount of power. Look around for a place that sells reconditioned, remanufactured or used batteries a good battery shop will sell you a reconditioned battery with a warranty for less than half the price a new one at the parts store.
Some of the best batteries you can get cheap are deep cycle batteries. Deep cycle batteries are used on things trolling motors and motorhomes to provide a continuous steady flow of power. One 12v deep cycle battery will work very well.
Standard automotive batteries are very cheap when purchased used or remanufactured. Car batteries are built for providing a lot of current for a short time (to start a car) but can be easily used for our project. Consider buying two car batteries of the same shape/size. you can link them together and increase the storage capacity.
Sealed Lead Acid Batteries or gel cells.
IF you can find a 50+ amp hour SLA or a 73 amp hour gel cell (like i am using) these batteries are great and perfect for the project. You want at least 50 amp hours of storage capacity.
Step 4: Power Inverters and Power Usage.
Power inverters are great for the car or camping. They let you run 120 volt AC home electronics anywhere. You can get inverters that can run 60 watts to 10,000+ watts of AC electronics. The more wattage you want to use the bigger the battery bank you need to feed it. I am using a 400 watt inverter in this project. In reality this 400 watt inverter can safely run about 250 to 300 watts of AC power continuously without the fear of overheating it or burning it up. If you keep your power usage below 150 watts the battery will last a long time.
When the voltage on the battery gets too low you will get a warning beep from most inverters. The inverter will shut off after the battery hits the cut off voltage. This insures that the battery is not completely drained and can be recharged again.
Look at some of the appliances in your home and see how many watts they consume. You will notice not many things can be run on a 400 watt inverter. With 400 watts you can power a small TV, cellphone/laptop/tablet chargers, laptop chargers, am/fm radios, lamps, non DVR satellite boxes, non DVR cable boxes, and many other small appliances.
If you want to run refrigerators, heaters, coffee pots, desktop computers, and other high wattage appliances you will need to get a much more powerful inverter and about 10 batteries to last 24 hours.
Keeping it small is a good idea. If you use a tablet instead of the tv you save on power. If you use a wood stove or fireplace you don't need a heater. If you have a BBQ outside you can cook food.
Step 5: Accessories.
These are the things you should have in the box at all times. When the power goes out you have it all in one place.
Cell phone, tablet, laptop chargers.
Pick up some cheap cell phone charging cables for your brand of devices. If you can find a cheap car charger cable put it in the box too. Dollar store is a good place to get cheap.
USB all the things!
Most devices charge off of USB. There are 2 ways of charging USB devices in this setup. The powered hub can be used with the inverter turned on or the 12v power port can be connected to the battery to run a USB car charger.
Extension cords and adapters.
I have this power box in my workroom. When the power goes out i run my extension cord into my living room to hook up my devices. It is always good to have at least one extension cord in the crate.
Step 6: Charging Your Power Box and Keeping It Ready to Use.
Keeping your battery topped off and ready to go at all times is as easy as hooking up a float charger. You can get a basic float charger at the hardware store that plugs into the wall to provide a tiny amount of power to the battery without overcharging it. Classic car collectors and motorcycle owners use them on their cars to keep the battery charged up on vehicles that see little use.
Charging your battery after a power outage with a float charger or battery maintainer will take a very long time. If you have a standard automotive battery charger you can charge it up with that. When charged up just put it back on the float charger so it is ready to use next time the power goes out.
If the power has been out for a while and you need to charge up there are a few ways to get it done.
If your neighbor has a generator running ask if they can charge it up for you with a standard car battery charger.
Go somewhere there is power and charge it up with the car battery charger
Invest in a 100 watt solar panel and charge controller. Works if the sun is out.
***not too safe but i t has helped me in a pinch***
Hook the battery up to your car with jumper cables. Just like you were jump starting a car. Run the engine and let the vehicle's alternator charge up the battery for an hour. Keep watch on the temperature of the batteries, jump cables, and engine temp. If the batteries or the jump cables heat up to the point that you cannot touch them stop immediately.
Step 7: Advanced Charging With Solar
Solar is a great way to charge your battery in sunny locations. In a previous Instructable i made a battery charger out of an AC to 14.4v DC wall wart power supply and a solar charge controller.
Using this setup i can connect either the power supply or a solar panel into the barrel connector powering the controller. Using a 45 watt solar panel i can charge my battery box to full from 50% on a sunny day. Depending on how much solar power and sun you can get and keeping an eye on power consumption you can have a continuous supply of power.
Link to charging instructable: Solar controller dual power.
Step 8: Conclusion and Video
I hope i made this instructable helps out. There are zero tools required and parts are easy to find. This power box has a wide variety of uses.
Recharging cordless tools on the jobsite
Use the drop light as a lantern while camping. Saves on fuel/propane.
Take it to the lake to charge phones and MP3 players. Use it to power some speakers!
Make a car/truck mounted version to run equipment without running the engine.
Jump start your car with it.
Run an electric trolling motor with it
Keep it in your basement during tornado season
Use it to power lights in a barn
Recharge RC drone and RC car batteries on site.
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