When tinkering with electronics a decent power supply with adjustable voltage and a current limit is usually one of the most important tools. Most of these PSUs are rather clunky and require a connection to the grid. When working in the field this isn't always a handy option.
With this project I built a portable and (optionally) battery powered PSU which can help in a lot of the mentioned cases.It's based around a DPS3005 power supply module, however the concept can easily be adapted for similar modules with higher voltage or current.
- DPS3005 Power Supply Module
- 200W Step Up Module
- 2 x binding posts
- 3-position switch
- DC power socket, 5.5/2.5mm or 5.5/2.1mm, depending on your PSU
- External 24V/>=2.5A power supply or something with similar wattage
- 5V Step Down Module
- 2 x TP4056 LiPo charging module with protection
- 2 x 0505S-1W isolated DC to DC converter (or 1x 0505S-2W)
- 2 x SMD resistor, ~3.9kΩ
- Matching case or access to a 3D-printer
Step 1: Step 1: DPS3005
Let's start off easy: The DPS has 4 connections - input and output. Connect the two output pins to the binding posts. Preferable these should be color coded so you don't reverse polarity when using the supply later on.
DPS modules are buck only and can only output voltages lower than the input voltage. My target was to get at least 24V output. Accorting to the datasheet the required input voltage is around 26V in this case. The maximum for the DPS3005 I used is 40V.
Step 2: Step 2: Step Up Module
Since neither my battery nor the external supply I want to use are in the input range of 26 to 40V I went for a additional boost module. The model I used is labeled as 200W. Real power is dependent on the used input and output voltages, but it should be fine for this purpose.
I suggest to set the output voltage first: Temporarily connect the input to a external supply with <=24V and use the potentiometer to set it at the desired voltage. The minimal input voltage is ~6V. I went with a output of ~26.5V which should be enough to reach my goal but not use more input current than necessary.
When done disconnect the input and connect the output to the DPS module.
Step 3: Step 3: Switch and DC Socket
Next up we finalize the external supply. Connect the negative pin of your DC socket directly to the negative input of the step up module. The positive pin of your DC socket is connected to one of the swtiching pins of your switch. The switched common runs to the step up modules positive input.
The whole contraption should now be usable with an external power supply. I went for a 24V/2.5A brick I also use for my TS100 soldering iron. Since the used step up module has a wide input range everything between ~6V and ~24V should work. When using lower voltages keep in mind the current increases accordingly, so watch your cable sizes and switch ratings.
- Instead of a 3-way-switch you could also use the DC sockets insert detection switch to automatically switch from battery to DC when a external supply is plugged in. I went for the manual way since I always forget to plug the DC supply's primary in first
Step 4: Step 4: Battery Power
When using a battery there are tons of options. A single cell won't work since it's voltage is below the step up modules minimal supply. I went with a 2-cell Li-Po I found in one of my drawers. 18650 or similar would also work. If you intend to use higher currents on the go I would suggest to go for a larger battery and use more cells - a 5S or 6S should would work without modifications to the previous circuit, however you want to go for a BMS/balancer instead of the TP4056-way I used.
Back to wiring: I use a 2-cell battery, however the ubiquitous and cheap TP4056 modules can only handle a single cell. Luckily the battery's balance connector comes in handy here. Connect the common negative of your battery to the negative battery in of your first TP4056. The positive terminals are shorted on the board, so place a wire between B+/Out+ of the same module and Out- of the second TP4056. The common battery positive is connected to the second modules B+. If you do not want to trust the TP4056 integrated protection add a fuse here. The balance connectors center wire to the second connectors B-. You'll now get a protected 7.2V supply between the free output terminals (Module 1 Out- and Module 2 Out+). Do not connect anything to the TP4056s input as this might short your battery!
The negative output is connected to the step up modules negative, the positive to the unused terminal of your switch.
You should now be able to also run your DPS from battery.
- Since there where some discussions: The batteries internal connection between the two cells should IMO not be a problem - when module 2 goes into protection it'll disconnect module 1 positive, as such this one will also trigger and disconnect the main negative terminal.
- The protection will also limit the maximum current/power you can draw from your battery
Step 5: Step 5: Battery Charging 1
Let's have a look at the complicated part. I wanted for the battery to be charged when a DC supply is plugged in. You could get this easier by using a balancer/BMS, but hey, I only got TP4056s in my drawer so let's use them.
First issue: TP4056 is limited to USB, so we need 5V input. To archive this I used a small step down module which I connected to an external supply and trimmed to ~5V first. These modules should easily supply enough power and usually work with up to 30V input, so my 24V supply is OK.
Connect the negative input to the step up converters negative, where we already bundled all other negatives. The positive input is connected to the positive pin of your DC socket, so the module is powered even when the PSU is switched off.
Tipp: The negative output of these step down modules is connected to the negative input, so you can use the common negative even for things operating at 5V.
Step 6: Step 6: Battery Charging 2
So let's connect the 5V to out TP4056 and we're done, right? Well, only if we want to build a happy fireworks. TP4056 connect the input negative (more or less) to the battery negative. If we connect both negatives we effectively short one of the batteries cells. We probably want to avoid this.
To solve this issue I used 0505S-1W, a DC-to-DC converter with isolation. Basically it takes 5V input and gives you 5V output, however the latter has no electrical connection to the input. These modules can output up to 200mA of power, to get a decent current I used two in parallel.
The first TP4056 module uses the system negative anyway, so I connected it directly - negative to the common negative, positive to the 5V output of our step-down-module.
The second one uses to two 0505Ss - connect the isolators input to the step down module and it's output to the second TP4056.
Tipp: There is also a 05050S-2W available, if you buy them new anyway this might be an option
Step 7: Step 7: Battery Charging 3
One final adjustment: Charging current. TP4056 usually charge with up to 1A, our two isolators however can only supply about 400mA, so we need to tell the TP4056 to use a lower current. This is archived by changing a SMD resistor (R3) on the board. I used 3.9kΩ which should get us slightly over 300mA of charging current. Not fast, but hey, it works.
Tipp: Technically only the second 4056 has to be limited. Since charging one cell faster doesn't relly give us any benefit I changed the resistor on both modules.
Step 8: Step 8: Case
There are a lot of things than can be adapted to your needs, so it's best to build your own case. My design can be found on Thingiverse, but it has some flaws. When assembling ensure no metal party touch each other - for me a few tons of tape took care of this. Loose modules where attached with some hot glue, only the battery is kept loose to allow for easy changing.
Step 9: Other Reccources
If you speak german you can also find two videos about this build over on YouTube: