Introduction: Small Emergency Power System

We’ve all had our power go out, grab the flashlight or radio,discover the batteries are dead and run to the battery drawer to find that its empty or we have the wrong size. Usually, the worst case scenario is that we have to sit in the dark for a couple hours until the power comes back on. But, if an outage lasts for a week or more, most of us would be in trouble, especially with our reliance on cell phones and computers for communication. And, with a major disaster or a cyberattack on the grid it is a very real possibility that we could lose power for an extended period of time.

I’d like to show you a couple options you can use to provide yourself with a small backup power system to keep you out of the dark and talking.

Step 1: First System

A couple years ago, my daughter bought me this Whistler Jump and Go emergency jump starter kit. It cost about $80 and came with a 12 volt battery pack with 3000 milliamps, a little pair of jumper cables, a 14 volt wall charger and a car charger. It charges through a 3.5/1.3mm jack. It has a built in flashlight and a female USB port. There are a lot of these outfits for sale and many users say they can jump their car battery with them. I have never tried to use mine to start a vehicle as I drive a truck with a big V8 and I doubt this will start the engine if my battery is very low. However, it makes a great little backup power supply. I have used the flashlite a couple times and I use the USB outlet to charge my phone and watch all the time.

This worked good for USB powered stuff, but I wanted something I could charge/power a variety of devices with, I also wanted a larger capacity and to be able to charge the batteries without mains power. And, I wanted to do it cheap! So, with these criteria I set about to make a mini power system that you can build easily and cheaply and will be really handy when your power goes out or for camping and other outdoor activities.

It would help to have some experience in electricity, but if you can tell a ‘plus’ from a ‘minus’ and ‘red’ from ‘black’ you’ll get along fine. Also, I soldered all the connections, but if you can’t solder, there are ways to do most everything here without soldering. It just won’t be as neat. It’s hard to show these mods in photos and will look like a snake’s nest so I will try to provide a diagram as well as a pic.

Step 2: The Heart

To increase the storage capacity, I bought a little 12 volt Sealed Lead Acid battery. It is 5 Amp Hours (5000 mAh) and cost $13 on Ebay. It measures about 3.5 x 2.5 x 4 inches and weighs a couple pounds probably. It can easily power some LED lights or a radio and, with an inverter, power a laptop for a little while. And, of course, charge my phone quite a few times.

Step 3: Battery Mod

To make the battery a little easier to use, I built this setup on a piece of circuit board and velcroed it on the new battery. It (along with the voltage converter in the next step) enables me to get three different voltages from the battery simultaneously. With the exception of the mini voltmeter ($2 on Ebay) which I can use to check the battery status, this is all stuff I had. But, if you bought it all, it would be just a few bucks.

The momentary switch turns the voltmeter on and the LM7805 regulates the USB port to 5 volts just like on the Whistler. The only thing this doesn’t have that the commercial one does is a built in flashlight, but there are plenty of cheap little USB lights that will work. I built a cable with a 5.5mm male BC on one end and an EC-5 connector on the other so I could use the jumper cables from the Whistler with this battery if I want.

Note: I printed the white box for the voltmeter.

Step 4: The Brain

The battery is the heart of the system, but this little fella is the brain. It is a DC to DC Step Down Buck Converter I bought on Amazon for $12. They can be bought without the case and display for as little as $3, depending on
features. It has a big name, but all it does is to allow you to manually adjust an input voltage (from 4 to 40 volts) down to what your device or battery requires.

This one has a 7 segment led display to show you the input, output voltage, current and power. It also came with a nice acrylic enclosure. The inputs go in on the left and the outputs are on the right – watch the polarity. It also has a female USB on the output side. This is important if your battery pack does not have a regulated 5 volt USB. But, be careful as it is not regulated and outputs whatever you have it set at.

The left button turns the display on and off and the right button scrolls through the options. The two little blue boxes in back are potentiometers that control the output voltage and current. The right one controls current and the left one controls voltage. You turn the screw on top counterclockwise to lower and clockwise to raise the voltage or current.

Note: I printed two posts and expoxied them on the potentiometer screws so I don’t have to use a screwdriver to adjust the voltage. I had to drill out the holes in the enclosure to make them fit.

Step 5: Typical Use

This first diagram shows the typical use of the SLA battery to power a device requiring less than the full 12 volts from the battery. To use the jump starter battery rather than the SLA battery (second diagram), you would need to use a cable with a female EC-5 to female barrel connector cable attached to the jumper cable connection.

Step 6: Solar Charging

To charge the system without mains power, I bought two 9 volt, 500 mA solar panels on Ebay for $20. I wired them in series with a diode to prevent reverse flow and a 5.5mm female Barrel Connector. There are many options for connectors, but I decided to go with Barrel Connectors throughout my system to prevent the possibility of reversing polarity somewhere and I used female connectors on the ‘hot’ side to shield the current better. I bought 5 pair of 5.5mm mated Barrel Connectors with wires for $4.50 on Ebay and they can be just wired together and you can use wirenuts if you can’t solder.

Note: I first tried to use two 12 volt panels in parallel, but they didnt have enough push to charge the SLA so I had to trade for the 9 volt panels in series and the use the Buck converter to step down the input voltage to 14-15 volts.

Step 7: Solar Charging Setup

Here is a diagram of the whole solar charging setup. It’s a little bit overkill as I have inserted a cigarette lighter male/female set in the middle, but I did so to be able to use the car charger from the jump starter and to make it more versatile.

You can see how you can charge or power a variety of things. For example, if you want to charge two AAs, just set the Buck Converter to output 2.6-2.8 volts. You can buy a variety of battery holders with snap connectors on Ebay or an electronic supplier.

Step 8: Using the Wall Charger

Both the wall charger and the car charger for the Whistler came with a 3.5/1.3 mm male Barrel Connector, but I wanted everything to use 5.5mm, so I replaced the ends of both wires with the 5.5mm male connectors. This necessitated buying a 5.5mm female to male 3.5/1.3mm adapter to use to charge the Whistler battery pack.

I also got a female to female 5.5mm adapter so I can use the wall charger in conjunction with the Buck Converter to power/charge anything less than 14 volts with mains power. If I am charging either 12 volt battery, the Buck Converter is not necessary.

Step 9: Using an Inverter

To power or charge a laptop or tablet or other similar device you will need to use an inverter. The one shown here provides 150 watts and is big enough for this small system. It cost $10 on good ol’ Ebay.

If you build this all from scratch and don’t have a jump starter outfit for parts, the costs would be (approx.):

Battery $13

Solar panel $20

Mini voltmeter $2

Wall charger $3-20 (13-15 volts) Note: You can use an old computer supply which is usually around 19 volts, if you put the buck converter in series to keep the voltage and current down so you don’t damage the battery.

Buck converter $12

Usb light $5

Wire, connectors, bits and pieces ~$20-25

Total cost around $75- $90, which is close to the cheaper jump starter outfits, however, this system provides significantly more options for use.

Step 10: Final

Here’s our little battery all dressed up and ready to:

- Charge/power almost any of your USB electronic devices

- Charge all your household batteries three ways – battery, solar, mains power

- Charge/power anything requiring 12 volts DC or less with battery, solar or mains power

- Power (for a limited time) 110 volt AC devices and appliances

- Jump your car battery

- And, it can do several of these jobs at the same time!!

I hope this gives you some ideas on how to build yourself a backup power system and plan for the unexpected.