Portable Adjustable Mini Powersupply




About: I'll post various projects, builds and creation using all kinds of materials and techniques.

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...

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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/QbPJZBhttps://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.

Step 5: Instruction Video of the Whole Thing

Now go out and enjoy your new source of power!

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    86 Discussions


    1 year ago

    I really liked the ability to check 'Battery Voltage'. Because that is a valuable information & foreshadows any explosion :0


    2 years ago

    soo cool device! i love how to put useful things in a minimal place as you can , and this have all of that, congratulations !!!

    best regards from mexico


    3 years ago

    There is big need for more like this only will mains input and up to 60 Volts output. We have one but it weighs 20 lbs for 6 amps at 48V, a common voltage. good going!


    3 years ago

    You should really use protected 18650 cells for this. The unprotected cells are meant to be used in a battery pack with external protection circuitry.

    15 replies

    Reply 3 years ago

    technically you can get away with un protected cells if you cover the ends really well and use a better charging circuit that has built in over discharge, over charge and short circuit protection. like this one



    Reply 3 years ago

    Nowhere in that link does it say that this circuit has any over discharge protection. I would not use this board.


    Reply 3 years ago

    the link i shared is a different listing
    but same chip from previous listing i bought from which ended but did
    list all the features and ive used them before and they do feature
    discharge protection. Great scott on youtube has used these aswell. i
    have linked the charger chip data sheet below for reference


    Mixed Outputrocketman221

    Reply 3 years ago

    The battery charger has overcharge protection built in so the only concern is over discharge hence why I added the switch to be able to see the current voltage of the battery. Imo that is sufficient if you know that 3.7 means the battery is discharged.

    ac-dcMixed Output

    Reply 3 years ago

    1) No, 3.7V is not the right cutoff voltage to use for Li-Ion cells. On the contrary that is only the nominal (average) voltage over its discharge curve so you are getting at most, half the capacity out of the cells.

    2) It's never a good design to have to monitor something and manually cut it off to avoid damage, particularly damage that could result in a fire later on.

    Practically every other battery chemistry is safer to use if you don't want to follow the requirements for Li-Ion cells!

    Mixed Outputac-dc

    Reply 3 years ago

    1: I didn't mean that 3.7 was the cut off just that it should be considered as discharged. I know the cut-off can go <3V but that is not what I aim to reach especially If I can easily charge it. And also having lower charge in the battery will affect the output performance.

    2: Well of course it's not but then again this is not a commercially manufactured product. I somewhat feel that following and using diy builds should always be done with common sense and one should realize that not everything is gonna be 100% fool proof.

    pfeerickMixed Output

    Reply 3 years ago

    Nice project. You could improve the battery safety aspect by using one of the TP4056 charger boards with built in battery discharge / short protection - such as 181577935056 on eBay.


    Reply 3 years ago

    That one has a protection voltage of 2.5V. Is that really safe? THAT low?


    Reply 3 years ago

    It is actually 2.4v if you check the datasheet for the DW01 one lithium cell battery protection IC that is used on these boards. It controls a mosfet (8205A) which allows it to disconnect a unprotected cell from the load. 2.4v under load is perfectly fine. The battery will float back up to near 3.0v once the load has been removed. And the protection IC will reconnect the battery to the load once it goes above 3.0v. It also protects the battery against short circuits, overcurrent, and over charge (which shouldn't happen since these boards have a TP4056 dedicated lithium charge controller. Boards like the one I and boyrock375 linked are the upgraded boards that have a TP4056 charge IC, DW01 protection IC and 8205A mosfet switch. Boards like 291688004833 and 272010768765 (eBay ID) are simply charger modules and have no protection at all. Just look for the longer board / three IC packages / input and output connectors for the battery if your looking at the pictures to tell them apart.


    Reply 3 years ago

    Technically 2.5V is the lowest you can go, but I wouldn't go any lower than 3v. When the batteries get that low, there isn't very much energy left in them anyways.


    Reply 3 years ago

    How do you know if they're protected or not, If you salvage them from somewhere?

    Shorct circuit them and see if there's a spark? ;)


    Reply 3 years ago

    If you salvage them from a battery pack, they are unprotected.
    You can buy protected cells online (watch out for cheap ones, they lie about the capacity).
    They should have something like "protection circuit" or "discharge protection" printed on the label.
    They are about 2mm longer because they have a circuit board in the negative end of the cell and the positive end sticks out so they fit in a battery holder.
    If you short circuit lithium cell, you could weld the wire to it and start a fire or possibly cause the cell to explode.


    Reply 3 years ago

    By checking the capacity and stuff like that (GreatScott has a YouTube video on the, I think)

    Probably also by weight

    I believe 18650's are 2000, 2200, 26000mah only. Many eBay sellers sell them as 6000mahs, Which means they're fake...