Introduction: Portable Adjustable Mini Powersupply

Picture of Portable Adjustable Mini Powersupply

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

Picture of 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

18560 Battery charger

5V USB DC-DC step up converter

3.3V - 30V DC-DC step up converter

3 wire voltage meter

a power switch

an on-on switch

a 100k potentiometer

also a case for all this would be recomended

Step 2: Modify and Plan

Picture of 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

Picture of 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

Picture of 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!




: D

newbeatle (author)2017-01-13

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

KDDSearch (author)2016-04-09

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!

rocketman221 (author)2016-03-08

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.

boyrock375 (author)rocketman2212016-03-13

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

PaulC21 (author)boyrock3752016-04-07

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

boyrock375 (author)PaulC212016-04-09

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

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-dc (author)Mixed Output2016-03-11

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 Output (author)ac-dc2016-03-11

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.

pfeerick (author)Mixed Output2016-03-11

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.

PaulC21 (author)pfeerick2016-04-07

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

pfeerick (author)PaulC212016-04-07

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.

rocketman221 (author)PaulC212016-04-07

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.

sukhbir singh (author)ac-dc2016-03-13

You are right sir.

Yonatan24 (author)rocketman2212016-03-09

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? ;)

rocketman221 (author)Yonatan242016-03-09

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.

billbillt (author)rocketman2212016-03-10

How can you tell a good battery from a fraud??..

Yonatan24 (author)billbillt2016-03-10

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...

billbillt (author)Yonatan242016-03-10

Is there a way to tell before buying??.. Once a bad battery is bought, it is a lot of trouble to return them to China.. If possible..

gtoal (author)billbillt2016-03-25

If it's coming from China, just assume it's fake.

Yonatan24 (author)gtoal2016-03-25

With batteries, You're probably almost right

ac-dc (author)billbillt2016-03-11

1) Research the brand prior to purchase, NOT from customer reviews at the point of sale as those may be fake but rather at website forums from reputable long time members, especially flashlight oriented forums for 18650 cells, like at or

2) Choose major battery manufacturer brands. Sanyo, LG, Samsung, etc. Nothing that has "fire" in the name for example.

3) There are quality cells with 3000mAh or more from brands like Panasonic, but not from generics and certainly anything at this point in time that's rated for 3600mAh or more without qualification/datasheet-proof, is a fraud.

4) Check the seller reputation for supplying accurate specs and genuine, NEW products. Some sellers may pull old cells out of laptops then have new shrink wrap put on so you are buying something with 3/4ths of its lifespan gone already.

5) There should be no need to return anything to China. If you receive junk because you didn't research it, suffer the loss as it shouldn't have cost much for that junk, less cost than the value of your time and return shipping because you definitely should not buy a large quantity at first of an unknown brand or from a seller with unknown legitimate reputation.

If you receive counterfeit merchandise, ask for a refund without having to bother with returning the counterfeit merchandise or that the seller pay for shipping. A reputable seller will not argue about this as they do not want the bad customer reviews/reputation about selling counterfeit merchandise.

In short, do not buy something unless you already know what you're getting. Low price might be tempting but if the lifespan is lower and the capacity too, it really wasn't a bargain, especially if you're building a project around it like this instructable does, opposed to just tossing a budget cell in a cheap generic flashlight where the value of time and total money spent was minimal.

Even then, I urge people not to support fraud by not allowing sellers of misrepresented (capacity or brand) products to get away with it, not to take the gamble to make a purchase at all. Don't pay them then expect them to make things right later as in the best case it becomes too much of a hassle for you.

Batteries are a commodity item, to get a decent one you should pay for brand, then capacity in that brand, keeping in mind that high capacity cells often only achieve that significant difference at a relatively low discharge rate - which should be easy to see in their datasheet.

Other people have suggested weight. It is true that most low capacity cells weigh less, but a seller might (knowingly or in ignorance) pass along specs that list the wrong weight, and weight won't tell you if they pulled a used battery out of an old laptop pack and put new shrink wrap on it! The group that does this to old batteries may even be distanced a bit from the seller so the seller can legitimately claim no knowledge that this is what happened, but back to my notion of commodity items that I mentioned above.

If it's a decent, fresh cell with good life and capacity, it won't have a price substantially below that of major brands from reputable sellers, although "sometimes" if you buy direct from a Chinese merchant you do get a little price break due to Chinese subsidized shipping discounts but with that, the risk of dealing with a merchant not bought by foreign country laws and unrealistic to return most merchandise to.

Note that instead of asking here you could have just done this research yourself, too.

pollux64 (author)ac-dc2016-03-19

Thanks ac-dc, that's the best advice to handle possible rip-offs from ebay etc. First you investigate well and place your order, but you never let them get away with fraud: fraud should never be profitable. So I keep the fraudulent merchandise and get a refund. That's my compensation for losing time with those sellers. I then look for another reliable-looking seller, and order again.

User1 (author)ac-dc2016-03-16

Thanks for the info ac-dc. I'm kinda in this spot now where I want to start playing around with these 18650 sized batteries. I'm thinking about just going to electronics recyclers and asking for some packs.

Thanks again.

billbillt (author)ac-dc2016-03-11

"Note that instead of asking here you could have just done this research yourself, too.

Certainly I can search for myself!.. I didn't realize it was such a long process to select a "good " battery.. Thanks for you help anyway!...

Yonatan24 (author)billbillt2016-03-10

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...

Sir not 26000 but 2600mah by mistake u added extra 0

Yonatan24 (author)sukhbir singh 2016-03-13

Oops, My mistake

I wish it was 26,000... ;)

devwatts5 (author)Yonatan242016-03-11

Its best to salvage them from laptop batteries!

billbillt (author)devwatts52016-03-11

Thanks for the tip!..

devwatts5 (author)billbillt2016-03-11

Yeah,Laptop batteries have more than 2000mah most commonly

Yonatan24 (author)billbillt2016-03-11

I haven't Googled it, But if you do, You'll probably see a couple articles on that. Probably by the price, I think 18650's should be pretty expensive: They probably shouldn't cost a dollar

HerbertD1 (author)billbillt2016-03-10

By weight.

HerbertD1 (author)rocketman2212016-03-10

I Accidentally shorted some used 18650, with wires like his only the wires will burn their Insulation. Maybe because even "the best" of a used package have a too high inner resistance. Not that hot wires in your pocket are a good thing.

The only fires i found on Youtube were made by forceful overcharging. The real problem is overdischarge by not shutting the device totally off. For that you really need a protection circuit. such things you can salvage from used cellphone batteries(the bigger the better). Here in Germany we have boxes for used batteries in every market, i search them regularly. You only must test them for polarity and function, maybe a smartphone battery will deliver more than the 1.4Amps of a little cellphone one before shutting of.

ac-dc (author)HerbertD12016-03-11

Fires happen in random cell phones and laptops just from slight manufacturer errors, manufacturers with years of experience, quality cells, and engineer oversight. It definitely does not require deliberate overcharging to result in fire.

Cellphone protection circuits are often not reasonable to harvest for reuse. They are fragile and the parameters for current are wrong for larger 18650 cells. There's really no reason to do it when batteries with protection circuits built on are available or more user friendly and appropriate to the application, circuits can also be bought separately.

HoldOnTight (author)rocketman2212016-03-13

coulda, woulda, shoulda... His batteries were virtually free, so he who has the gold makes the rules. Maybe your advice is best directed to the audience and not the author! My guess is he plans to spend his gold on something he considers more important.

kart15 (author)2016-04-05


tutdude98 (author)2016-03-13

You should put them in series
It would draw a lot less current from batteries and you could add cheap li-ion buzzer alarm that would alarm you
But then you would need another charger to charge second battery
I really like how you repurpused case (i cant find cheap ones that are not plastic :P)

Lashway (author)tutdude982016-03-28

I was going to reply that this would obviously halve the available current, limiting what can be done with it, but then I looked into the battery and saw that one can provide ~20A continuously with a max of ~30A. I now agree with you, I'd much rather double the available voltage and keep the current as is.

gtoal (author)2016-03-25

These battery packs used by cyclists could make a good starting point for a version of this project:

Jonathanrjpereira (author)2016-03-16

Nice Instructable.

Ayush Sharma (author)2016-03-15

Thank You for Sharing! I Really Liked the Simpleness and Use of Cheap Module to make a Great Mini Power Supply. Featured on my Website too.

ljhopkins (author)2016-03-08

where did you get this case?

Jean0x7BE (author)ljhopkins2016-03-14

Seems like the box of an older "Music Angel" portable speaker system.

Mixed Output (author)ljhopkins2016-03-08

The case is from an old portable speaker that was broken, so i got it for free. But of course you could use any kind of container as long as everything fits inside tight and snug.

I have built several of these in plastic cases, I take them along in our Motorhome while we travel, they do come in handy, I also picked up several power banks for charging our nooks, and cell phones when there is no shore power to hook up to. My favorite is built in a rather large case and hosts six 18650's in battery holders, a step down converter, as well as an amp/volt meter and a 30 watt LED light mounted in a vehicle type mount. Makes a SUPER flashlight, and you can unplug the light, and plug in any device with a standard 2.1 mm power plug, with a small screwdriver, you can set the power to the needed voltage and use it to power laptops etc. The idea of changing out the small variable resister with a pot makes a lot of sense, I may make that change on mine as well.

lhj734017 (author)2016-03-14

never mind, I see you already did

lhj734017 (author)2016-03-14

could you please post a schematic? it would be easier to follow than directions

Dan39 (author)2016-03-13

it would be a huge help if you could give links or part numbers to buy the parts. it always seems half the battle for me is finding the parts. i often spend the majority of time on a project just looking for parts online...

About This Instructable




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