0
\$\begingroup\$

I'm in the napkin-sketch phase of a project that will be ~100 custom devices in a big mesh.

Each device is an ATMega328P on a custom PCB with 16-40 'mini' neopixels.

I plan to power the whole installation with something like this 5V, 10A supply (keeping my use of the neos subtle) or possibly a 20A supply if I need to, say, run the neos a bit brighter.

What I'd like to do is distribute the power through each board to the next, so that the whole installation has one connection to the power supply, rather than one per board.

My thought is to have two JST connectors on each PCB, one for +5VDC in, the other for +5VDC 'thru' to the next board.

Is this possible/dumb? This is more power than I'm used to, but I don't think it's so much power that I'd need bus bars, solder islands or a ridiculous (4+ oz) pour on the PCB. I'm thinking just a gigantic (~1.5cm) trace from the "in" connector to the "thru" one (and placing them close to each other).

\$\endgroup\$
7
  • 2
    \$\begingroup\$ It sounds like you mean in parallel rather than in series. What's the maximum current requirement for each board? \$\endgroup\$ – Colin May 15 '18 at 14:53
  • \$\begingroup\$ Yeah, what you're describing is parallel, not series. That should work fine, if you're not carrying too much current. Make sure you use wire and connectors rated for the current you need, though! \$\endgroup\$ – Hearth May 15 '18 at 14:54
  • \$\begingroup\$ Have you done some calculations on it? \$\endgroup\$ – pipe May 15 '18 at 15:05
  • \$\begingroup\$ @pipe I've calculated what's described above. Anything else I should run the numbers on specifically? \$\endgroup\$ – buildsucceeded May 15 '18 at 15:55
  • \$\begingroup\$ @buildsucceeded I was mostly curious about your 1.5 cm trace, if you reached that by calculating voltage drop/heat. \$\endgroup\$ – pipe May 15 '18 at 17:08
2
\$\begingroup\$

I wouldn't string that many loads (boards) in series and expect good performance. Mainly, I'd be concerned about noise and voltage drop.

One alternative is to supply ~6V instead of 5V and on each board include a Low Dropout (LDO) regulator to obtain the 5V needed to run the board. And if you have the room, you could use 24V as your main supply and install a small SMPS at each board to provide the 5V; this way you would be connecting and routing 1/5 the current as you would by supplying 5V.

Also, I would try to avoid passing the power supply through the foil but use vertical PCB mount bussbars to route current across the board.

Ten-amp connectors shouldn't be a problem unless you have extreme size restrictions. Multiple pins can be paralleled to increase the ampacity. Twenty amps might be more of a challenge.

\$\endgroup\$
1
  • \$\begingroup\$ Good suggestion. Also consider combining some of the answers, and have 5 modules that have a local power supply to 20 units (for example) from a higher voltage supply. \$\endgroup\$ – awjlogan May 15 '18 at 16:13
1
\$\begingroup\$

Obviously, at least one connection in the mesh will have to be able to handle the full 10A (or 20A?). This includes both the physical connector and the traces on the board.

If the boards are identical, then they ALL need to be able to handle that current, which means that they'll all have to have a fairly beefy connector and heavy traces.

It might make more sense to provide each board with four connectors (N, S, E, W), and then feed power along one edge or two opposite edges of the mesh. Then each connector only needs to handle about \$\frac{1}{\sqrt{N}}\$ of the total current.

\$\endgroup\$
3
  • \$\begingroup\$ It's probably better to use some sort of spliced wire for power, with low-current power taps coming off for each device, and a high-current wire to power them all. I'm not aware of any easy way to make cables like that, though there probably is one. \$\endgroup\$ – Hearth May 15 '18 at 15:03
  • 1
    \$\begingroup\$ It is kind of an annoying problem @Felthry you either have a big wire spliced multiple times to tap to each device or you buckle up and create 99 interconnected wires. Advantage of doing a single spliced wire is that you can reduce the connector size on the PCB itself (thus probably reducing the cost). They are more labor intensive tho and are less flexible to a change in length or any kind of resizing. In all cases, wire management is the art of not creating a freaking mess. \$\endgroup\$ – Simon Marcoux May 15 '18 at 15:07
  • 1
    \$\begingroup\$ @Felthry using a Posi-Tap or something similar is probably one way to do it. \$\endgroup\$ – Arsenal May 15 '18 at 15:28
1
\$\begingroup\$

Instead of connecting 100 boards in series, make a backplane PCB or series of PCBs to distribute the power. You can have a single heavy duty connector and branch out the power.

\$\endgroup\$
2
  • \$\begingroup\$ This might be the way to go, could you possibly edit your answer to link to an example backplane PCB or a resource about their design? \$\endgroup\$ – buildsucceeded May 15 '18 at 20:11
  • 1
    \$\begingroup\$ @buildsucceeded At the most basic level it's just a long single-sided PCB with copper pour carrying the current and connectors at regular interwals you can use to attach the actual PCBs. Since the current per connector is rather low, you can use e.g. a regular 2.54mm pin header. To provide branching, you could use one PCB out of which the branches fork in E pattern. You can put e.g. extra screw connectors on the PCB bar so you have a single PCB that can be populated in two different configurations. \$\endgroup\$ – Barleyman May 16 '18 at 8:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.