Low Voltage DC Power Distribution and Measurement Adapter

Introduction: Low Voltage DC Power Distribution and Measurement Adapter

Some time ago i bought a nice 5V switching mode PSU to have enough power for a raspberry and all stuff in want to connect to it.

In another instructable i wrote some time ago, i showed how i like to wire it up to have safe and durable connections - even for my breadboard setups - and do not actually need to really care about them to much any longer. ( You can find this instructable over here if you are curious. )

Well, i even wanted to have some measuring on how many volts my PSU actually delivers and how many ampere all this stuff consumes. For this purpose, i just bought a cheapo led meter which can measure from 0 to 100 volts and from 0 to 10 ampere. Additionally it needs a power supply which can deliver anything between 4.5 and 30 volts.

I only have to deal with 5 volts from my PSU, but yes, it is capable to deliver really fat 10 ampere..
Luckily, we can power our meter directly from the main PSU, eliminating the need for a extra power source....;)

So the meter perfectly fits to the PSU and the intended job. Lets go on with a nice bill of materials....

Step 1: Stuff Needed for This Project.

Well, it's a relative simple thing to build. All we need is:

  1. A meter which fits your needs.
  2. A prototyping board or other PCB you have at hand.
  3. Some terminals for directly screwing cables in.
  4. Some sockets which fit your wires (and plugs) you want to plug in later.
  5. Maybe a Fuse holder.
  6. Some wire to get all connected together.
  7. Maybe some heat shrink tubing for the power wires to our stuff....

To be exactly, i got virtually everything (except the wires) from aliexpress. I put the links in here for convenience.

  1. A cheapo DC Volt/Amp meter
  2. A Double Side Prototype PCB Tinned
  3. Some 2Pin 5.0mm Straight Pin PCB Screw Terminal Block Connector
  4. And some 2pin 300V 10A 5.08mm pitch Right angle PCB screw terminal block connector

Surely you will need your soldering iron and some solder. And maybe some thick wire to make the connections on the back of the PCB safe and durable even for some more amps. ;)

Step 2: About What We Are Going to Do (Shematics ;) ).

Ok. we have a relative simple task. I want to see how much power my setup draws from the PSU. So we are going to wire up the first two terminals (J1 and J3) simple as pass through connection. Our meter needs it's own power for his task, but fortunately we can simply draw it from the same PSU, so we even wire the next terminal (J2) in parallel to the first ones, as you can see on the breadboard and schematic.

Now, we have our "primary" part perfectly wired up and hopefully safe and insulated where needed. If you are going to create a customized PCB for this, you can simply put some via on there and put another trace on the other side of your PCB, OR even better, use the space to integrate a fuse holder! ;) (actually had none at hand and first thought about putting one on the cable.. well, i will see what i will do later on... ;) )

I just used a simple prototyping PCB and isolated wires for this part.

For the "secondary" part of our board, we can wire up all remaining terminals (J4 to J7) in parallel. As you can see in the schematics, there is not any magic in it, as it is just do conveniently provide more than one connector to get power. ;)

Fortunately, even on my simple quick (and dirty) soldered solution, it was relatively easy to have it safe and isolated. O.k. well, i have to take care about the isolation of the board at all later on, but not right now about the traces and wires on the secondary side.

By the way, i just took the colors from the cables on the meter. Where we have thin Red and Black wire for meter power input and some thicker Red, Black and a Blue wire on the measurement connector.

I don't really know how the meter was designed, but as we just only measure voltage and ampere, we safely can assume that the thick Red and Black wire will feed the power into the meter, whilst only the Blue wire will feed the ground, passed through its shunt, to the device we want to measure.

The reason why we just need these three wires is:

  • To measure voltage, you do not need to pass all wires through your meter but just need to feed in + and -.
  • For ampere measurement you need a shunt in between one of the wires to the device, to measure how much power passes through.

(Yeah for AC amps measurement, there are other methods which do not need to open up a wire.. ;) but we're talking about DC with a cheapo meter here.. )

Step 3: Building It.

Well, there is not so much to say about how to build it.

I assume you are able to solder stuff and put wires onto the back of a PCB.... So that is all you need.

I just show you my version of this build to give you a nice image (pun intended) how to do it. ;)

I marked all contacts which will go to the Red wire on the bottom side of the PCB after i put the screw terminals and connectors in, to have an easy oversight from where i wanna go to where. I did not need to mark the spots for Black and Blue wires because that's really obvious after you have all Red ones done (and keep in mind the split between primary and secondary parts). ;)

For the bigger green connectors, i needed to open up the holes in the PCB (make them a bit wider) because they're having pins which are bit thicker as usual. But, for my purpose, all is going easy. Even if i rip some of the copper/tin pads off on these connections, we will put a lot of solder on it from the bottom side and we will have no problems.

Additionally - and because my solder just got sucked through the holes *MEH* - i took some copper wire and some other wire i had at hand and soldered them straight down on every path between J4, J5, J6 and J7.

Remember, the PSU is rated for 10 Amps, we wanna make sure we can deliver that through our adapter. ;)

Step 4: Wiring the Meter to the New Adapter.

As i already wrote, the meter provides just 5 wires for all operations.

Two thinner wires for powering the meter (and it's LEDs), we will connect it straight to the screw terminal J2.

And three thicker wires to pass through the power connection we want to measure.

The three measurement wires are colored in Red (+5V in our case), Black (GND-In) and Blue (GND-Out).

Yeah i could have used just a five pin or a two and a three pin terminal for this, but i just had only 2 pin ones and i think it makes is a bit cleaner and more obvious what it all in all does if we just give every connection it's own terminal.

O.k., well, there is a little "problem" on the +5V wire, because we need to feed it into the meter (from J3) _AND_ additionally need to pass it to the next terminal (J4), which then distributes it to the remaining connectors, but the meter has no Red wire coming from it.

So just put a short wire in between the +5V pins on J3 and J4. This will even be the very last point where you can put a fuse in between to protect your PSU and meter from any device which draws to much current (except on the power cable itself, for sure). ;)

If you made your own PCB for this adapter, you may have already put a fuse holder in your own schematic i assume. ;)

For the Black and Blue wire, it's just as easy as connecting the Black wire to the GND pin on J3 which feeds the ground from the PSU into the meter and then connecting the Blue wire to the GND pin on J4 for distribution to the remaining connectors.

Well done ... i hope. ;)

Step 5: Wiring Your Brand New Power Connectors for Your Stuff.

Now you can wire up your stuff you want to feed with power from your new adapter.

The wires i connected into these plugs are salvaged from some ATX PSU, they have nice crimped connectors on them which made a really nice and durable contact to the terminals directly on the PSU.

Well, my new connects are some bit smaller, so i needed to squeeze the crimped connector a bit together (it was a small tube anyways so i just compacted it;) ) to be able to screw it in, but all has gone well and fits like gloves. ;)

But, the connectors are even more tight together as on the terminals of the PSU so we have an higher risk of shorting out stuff if we are not careful enough.

To prevent that and make things additionally a bit nicer and giving it a better look, i put some heat shrink tubing on the crimped connectors, so all looks perfectly as it should.... ;)

Step 6: Why? Just Because We Can. ;)

Yeah. You should be already done with all work you need to do for this project. ;)

I made it, as i wrote, to be able to simply look on my brand new meter and see if all is going well and how much power the stuff draws.

Additionally, i got rid of the fixed screwed down connections to the PSU and have now nice connectors which i can unplug on the fly if i need to.. ;) It makes things even a bit cleaner and safer and i can put the PSU in a separate case which is, according to german VDE regulations, importantly needed anyways.

You can see, on the terminals on the PSU there are even the AC mains hot and neutral wires just screwed in, i took care to make it as safe as i could, but it is still exposed mains potential and you absolutely never want to have that in this way any moment longer as really needed for testing purposes......

Remember, depending on the power grid of your country, you will have at least 110 volts and some severe harmful amps on your AC mains. Over here in Germany, we have 230 volts with usually a 16 amps fuse. That's pretty bad to touch with bare skin.

Have fun building it if you need. You surely can choose other Plugs and Sockets which will fit your purpose somewhat better. Maybe you can use barrel type sockets to provide an arduino with power using a simple barrel plug-to-plug cable or other sorts of stuff. (Yeah, you can use this even to power some 12v LED stripes and have a look what it consumes. ;) )

You can even wire more sockets and connectors together on the "distribution end", as long as you keep in mind how much power your PSU can deliver safely and how thick your connection up to the point of splitting out for all connectors need to be.

So long ... and thanks for all the fish. ;)

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