I am working on a project for school and i am in the process of designing a printed circuit board. I am wanting to read the current through a rather large wire, 2 gauge, with a honeywell CSNX25 sensor. The current through the wire should be less than 15A. This sensor is made to measure current up to 56 amps. I was just curious if my PCB designs are correct. It looks like I need traces of 100mils, 0.1inch, to carry this current. This is assuming I have a pcb made with 4oz/in copper.

I am designing this PCB in eagle, and I'm having trouble working with such large traces.

I guess I am just wondering if I am missing something, I feel like 4 oz copper is very thick. Is it just this hard to work with high current and PCBs?

Thanks,

Nate

 

4oz copper is quite thick, as is 2 gauge wire. Is the increased cost justified vs. 2oz or even 1oz? Note that's it's ok to have significant temperature rise so long as you don't have nearby temperature-dependent processes (electrolytic caps, poorly designed BJT circuits, regulators with temperature cut-off, oscillators).

 

15A isn't that huge of a load (look at size of conductor inside 20A Auto Fuse), those currents and more flow in audio amplifier PC Boards using around 0.25" traces on 2oz copper from what I've seen. The traces do turn into fuses when a MOSFET fails short, but that isn't common.

If you create the trace and it gets warm try soldering a wire down along the trace, I've seen that done in commercial apps, apparently cheaper than redesigning all the PCBoards that were etched.

 

How are you connecting the primary pins together? If you are connecting all three pins on each side together (0.1 in. spacing between them), getting a trace of 100 mils or 200 mils should not be a problem for a school project. Do you have other constraints?

 

Well I was originally wanting to hook it up with 2 primary turns because most of my current will be below 12A. I'm actually measuring the current being provided from an AIR Breeze wind generator. Which will only put out 160W at 28MPH.
We are using 2 gauge wire because of the voltage drop over the long distance with smaller wire.

160W/13V= 12.3A
I am also wanting to read current going to a load, which can be up to 30A. For this I would be connecting all of the primary pins together.

I have looked at other hall effect current sensors, that do not require current running through a board. Many of them do not have large enough holes to run a large wire through and the ones that do do not read small amounts of current.

 

Would it be possible to run traces on both sides of the board for added material?

 

Yes, but pay attention to what that does to your ground return path. Interruptions in high current returns cause floating ground voltages and noise. In my unprofessional opinion I would solder some 10 gauge wire to high current traces, as thatoneguy said, to keep costs down.

 

This calculation is for a 0.300" track 6 inches long:

Estimated max. current (based on IPC-D-275)
Outer layer: 12 A
Inner layer: 8 A


"inner layer" means the same track in a multilayer board. This is a single layer board using 2oz. Switching to 4oz copper makes an outer layer track 0.3" capable of 30A.

This calc doesn't take into consideration tinning or adding something like 3M 1187 copper sheet, or wire to "beef up" that single area of the board.

--ETA: Info is from MiscEl

At the same time, now that I know the app, why not use an off board sense resistor of 0.1 Ohms, and work with that voltage?

 

I would suggest mounting the sensor component on the PCB so that it's near an edge, and have traces as short and wide as possible that go straight to holes in the board, where you would have lugs that bring the current in/out via cables. By "wide" I mean big areas of copper, an inch across if you can manage it. Maybe there's some reason you need to have the high current travel a significant distance across the board, but if you don't have to do it, don't.