7
\$\begingroup\$

I'm planning a custom power-distribution / fuse-board for in-car application, but that requires carrying high currents (50A+ @12v*) on a PCB trace. Since I'd like to keep the board cost, and physical size down, can anyone suggest efficient (as in easy & inexpensive) methods for creating a power bus on a PCB?

Feed in would be from a chunky copper cable, most likely with a screw-terminal tag on the end.

My thoughts so far:

  • Thick trace with thick coat of solder
  • Same but with some thick copper wire soldered to it
  • Same, but use a single strip of stripboard
  • A length of copper or aluminium, either attached with screws through holes in the trace, or soldered down (obviously not soldering aluminium down!)

These are all OK but require special effort to populate the board, whereas something available off-the-shelf would make life easier.

Edit to add more info: The basic layout will be a bus up the board, with feeds off for each item, each of which may draw <30A (but most of them are <10A), so per-connection there can be a little thermal relief to make life easier.

* = Average of maybe 30-40A if the cooling fan's running and all the lights are on, ~10A if not, potentially 100A max although more headroom is better.

\$\endgroup\$
  • \$\begingroup\$ The fourth option you listed is probably the easiest, but not the cheapest. I don't know how it compares to the custom PCB, so give it a try and ask for prices. I was thinking about something like these threaded copper bars. These are not part of your board, but your board can be attached to them. \$\endgroup\$ – Christoph Mar 4 '13 at 14:50
9
\$\begingroup\$

You might try searching for solderable bus bars. They come in various sizes and shapes. You can solder them down to the PCB, and they provide masses of current carrying capability.

Solderable bus bar

Solderable bus bar

\$\endgroup\$
  • 1
    \$\begingroup\$ The PCB stiffener is almost exactly what I had in mind, thanks very much! \$\endgroup\$ – John U Mar 4 '13 at 16:00
6
\$\begingroup\$

I frequently have currents of that level entering PCBs. I typically use a solderable screw terminal. This, for example, is spec'd for 50A. I've used others rated for as high as 70A, and pushed them past that considerably without problem on a regular basis.

The biggest challenge is often soldering to a PCB designed to handle high currents. Thermal relief is a no-go because the copper needs to be there to handle the current, but then you have to heat up a thick and wide copper plane to get the solder to flow. Proper solder masking and a big iron is a must. We've also used a torch when all else fails.

\$\endgroup\$
  • \$\begingroup\$ I like the terminal strip, neat solution! \$\endgroup\$ – John U Mar 4 '13 at 15:06
  • \$\begingroup\$ Any guidance on currents through PCB tracks as mentioned in my question, EG heavily tinned? \$\endgroup\$ – John U Mar 5 '13 at 13:58
  • \$\begingroup\$ The weight (thickness) and width of the trace are the primary limiting factors. (Other things can matter at high frequencies, and you always have to watch your voltage clearances.) A good calculator is here: circuitcalculator.com/wordpress/2006/01/31/… \$\endgroup\$ – Stephen Collings Mar 5 '13 at 16:58
  • \$\begingroup\$ Also, if you want heavy-copper prototype PCBs, my best luck has been with epec. epectec.com/pcb/index.html \$\endgroup\$ – Stephen Collings Mar 5 '13 at 16:59

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.