A BIG HELLO! and welcome to Mixed Outputs first instructable.

As most of my project involve electronics of some sort, having a good power supply is essential to be able to meet the demand of different power requirements. So I built me a bench-top power supply from an old ATX power supply Unit (PSU) that worked (and still works) great. However I've recently noticed some limitations with having a full fledged bench top PSU.

Whenever I wanted to build or test something on the go I still had to resort to poor battery hacks and random power adapters that in best case worked poorly or worst case fried or didn't fit my project. And since my PSU was way to clumsy to carry around in my man-purse or pocket I realized that I needed to build me a mini power supply unit (mPSU), kind of a travel power pack for your on the go power needs.

The requirements I had for this mPSU was that it had to be able to output adjustable voltage, a fair amount of current, be small and handy to carry around, be battery operated for total mobility and as a bonus I added a 5V USB output to be able to use this to power usb stuff or use as a power bank when needed. So in this Instructable I'll show how I achieved this with cheap components from ebay and some random stuff I had laying around.

This instructable requires some soldering and understanding of simple schematics.

So lets do this already...

Step 1: Stuff You'll Need

Note! an instruction video of this project is featured on the last page!

For this little project you'll need the following parts:

one or several 18650 Batteries https://goo.gl/g4st2v

18560 Battery charger https://goo.gl/eM1s9S

5V USB DC-DC step up converter https://goo.gl/Kp3J2R

3.3V - 30V DC-DC step up converter https://goo.gl/pC88HU

3 wire voltage meter https://goo.gl/GRJwrC

a power switch https://goo.gl/NReccY

an on-on switch https://goo.gl/aoNbNP

a 100k potentiometer https://goo.gl/QbPJZB https://goo.gl/2hGMCu

also a case for all this would be recomended

Step 2: Modify and Plan

The first thing you want to do is to replace that trimpot on the DC-DC step-up converter for the potentiometer extended on some wires. If you solder it directly on the board then that could limit your options of placement depending on what case you use.

If you're only using one battery then you may skip this nest step. If you're however using two or more batteries you want to configure them in parallel. To do that solder both/all battery plus poles together and both/all negative poles together. The reason for using two batteries for me was that two batteries will give you a longer runtime than one and since I could fit two in my case, that's what I went with.

Of course the charge time for using multiple batteries will be longer than using only one battery but that's something I could live with. According to the instruction video I connected everything after the switch, but that is a slightly wrong connection. I actually connected the charger directly to the battery bypassing the switch. That way there is no need to turn on the mPSU to charge the battery(ies).

Step 3: Build

So the next step is to connect the battery charger boards "bat-" to battery - and "bat+" to battery + ...kind of obvious I know :-). Now we add a power switch to the negative pole of the battery.

After that we connect the main board which is the 3-30V boost converter. This is connected; input plus to battery positive and input minus to the power switch. Also connect the 5V usb converter in parallel with the 3-30V boost board. Now connect the output of the boost board to a suitable output connection. I used JST connectors, that way I can make different types of connectors that are easy to plug in and out.

Now connect the voltage meter to the negative line (after the power switch) and the positive to the middle pin of the second switch. And the other pins to the positive output from the battery and positive output from lead. This connection setup will give you the possibility to check the battery status by the flick of the switch.

Tip! Use a springy switch here that returns to its default position when released so that you don't accidentally leave it on the battery check side thinking your mPSU is outputting 3.7V while in fact it might be set to something totally different.

Step 4: Package

Finally find a suitable case for the setup and place the different knobs and switches appropriately.

Some final notes. I recommend building this thing quite robust if you plan to use it as a travel mate. It's been far more useful than I anticipated and sometimes use it instead of my main supply due to the fact that it's just easier to set up and use. This thing also seconds as an excellent fan controller for when I'm soldering stuff. The only downside is the lack of proper current control and there are boards out there that offers that but they are usually slightly bigger and you'll need a second display for the amps for that to be useful which wouldn't fit in my case so I skipped them.