Building the Ultimate Universal Power Supply

Almost every consumer electronic product runs on either 5 volts (USB) or 12 volts. These include cell phones, radios, walkie-talkies, flashlights, Ipods, mp3 players, laptop computers, battery chargers, cameras, drones, gps, etc. Most every item uses a "charger" to convert household power (117 volts AC here in the U.S.) to either 5 volts, 12 volts or rarely a custom voltage for a specialized piece of equipment. Many of these chargers also have the capability of charging a product off a 12 volt auto cigarette lighter socket.

Many of these chargers are built in mass production and very cheaply. They are low cost and efficient in some ways but many don't have the power to charge more than one, or various units. They are also "noisy" meaning they radiate RF switching noise that can interfere with some radios from the AM band, short wave, ham band, to the FM band. There may be times you may need to charge an item from solar or wind power or some other form of energy too.

In disaster or emergency conditions it may be necessary to power and charge multiple loads from a variable voltage such as a solar panel. A power supply must be able to regulate the output to a constant voltage. Modern regulators are highly efficient and are referred to as a switching supply. A regulator that steps a voltage down from a higher voltage to a lower voltage is commonly referred to as a "buck" supply. A regulator that steps the voltage up from a lower voltage is called a "boost" supply. Some that will do both are called a "buck-boost" supply.

Dimensions 1" x 2"

There are many variations of these and can be purchased very cheap on Ebay, typically from less than a dollar to about US$3.00. Of course higher power ones will cost a bit more. Be aware that some of the specifications need to be scrutinized and deciphered. Some specs may never be achieved so you will need to confirm them before using. One main feature of these supplies is that the output voltage is adjustable. The small brass screwdriver adjustment on the square blue component is the adjustment.

In designing your power supply you will need to know what your power source is and how much output voltage it may vary, and what your load conditions are.

I stumbled upon a few police automobile laptop power supplies for my UUPS with these specs:

Typical power in, 12.6 volts, minimum power in 7 volts, maximum in 17 volts.

Output power, 19 volts to charge and run a police laptop.

The specifications were to provide 19 volts even if the input power dipped to as low as 7 volts when starting the vehicle. This was an important requirement.

In reverse engineering the unit I found it had a powerful boost supply to take any voltage from 7 to 18 volts up to around 27 volts @ 6 amps output. Then there was a buck supply to take the 27 volts down to 19 volts @ 6 amps (with sufficient headroom) for the laptop load. I was able to add a few more buck supplies inside the housing to provide two isolated 5 volt USB outputs and two isolated 12.6 volt 6 amp cigarette lighter socket charging ports for universal loads. Ample noise filtering in the housing made this an ideal Ultimate Universal power supply.

In designing your own, the heart of the supply will be the boost supply. This will take the 8 to 16 volts in, up to 24 or so volts. From there you can put any number of buck supplies to achieve your desired source.

What makes this unit particularly valuable is that you can hook a 12 volt solar panel, preferably around 100 watts to your UUPS since 12 volt solar panels will reach 21 volts output with no load and under full sunlight and typical load the panel voltage supplies 16 or so volts.

There are a couple of rules you should be aware of.

You can't get something for nothing. A 15 volt 4 amp supply into a boost switching supply cannot provide 30 volts at 4 amps. Typically it will be about 2 amps or less output. Why? Do the math: 15 X 4 = 60 or 60 watts into boost supply. 30 X 4 = 120 watts. You cannot create power. Thus the output will be 30 X 2 = 60 watts. But there is some loss in the boost circuit, maybe 10% or slightly better so the output will be 54 watts or 1.8 amps @ 30 volts. If the 30 volt load exceeds the 1.8 amps and the boost supply is capable of higher current, you will supply the higher current but the 4 amp supply current will proportionally increase.


2022 Rick C. Ver 0.13 Mar 31, 2022