Creating boards with high wattage output?

[Anonymous]

Basic question from a beginner: My 1st board design will require outputs of 500mA using 24VAC inputs as a power source. There are no micro voltage power supplies (or chips) onboard, just 24VAC relays, LEDs, etc. It's a boiler control, so it's externally powered by a 50VA standard transformer for HVAC. That said, how do I insure that my "wire gauges" (circuit paths) can handle the proper load wattage for my components, which are also standard HVAC industry zone valves with a rated load of .32A at 24VAC? In other words, given that I am powering external valves which pull much higher amps than a standard IC, how can I make a board with enough metal in the circuit to handle those loads? If I were to increase this load, how would I compensate on the board?

[crrrack]

Hi Scott,

The tracks on your PCB will have - like every conductor - a certain amount of resistance, which will vary depending on the cross-section of the track, which is affected by the thickness of the copper, and the width of the track as drawn by you. This resistance will cause there to be a voltage drop in the signal (can be calculated with Ohms law), with some power being dissipated as heat. If too much heat is generated, bad things will happen, so you'll need to make your tracks wide enough, and/or use thicker copper on your board to stay within a safe range for your application.

There are a number of calculators available online that will tell you how wide your tracks need to be for a give current to stay within a specified temperature rise. Here's one of the first ones that came up on a Google search:

https://www.4pcb.com/trace-width-calculator.html

500mA is not a lot of current so you shouldn't have trouble designing a board to handle that. It's always a good idea to design for a higher amperage load than you think you need, and to include a fuse in your design for safety. If you end up needing wider traces than seem practical, consider using thicker copper on your board. Don't forget that your ground traces need to carry as much current as the high voltage ones.

[one-of-the-robs]

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@Anonymous wrote:

 standard HVAC industry zone valves with a rated load of .32A at 24VAC?

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When I first saw that I thought "wow, over thirty Amps" but on closer inspection, there appears to be a dot there?

As @crrrack said, there are plenty of track width calculators on the web, most of which follow the IEE standards (which are usually fairly conservative). If you need to carry a lot of current, you need wide tracks, thicker copper (2oz boards are available), or you could put a solder mask / solder paste trace along the track to build up with solder (doesn't conduct as well as copper but can easily be built up thick). However, if you're down below 1A then you're not dealing with big currents. Even Veroboard, at 80mil width, can do a couple of Amps quite happily despite all the perforations.

[Anonymous]

Hi

I have been using a book titled "Printed Circuit Design" by Gerald Ginsberg for years. Its actually still available in hardcover on Amazon. The book was published just in the days of CADs beginnings so it does have outdated stuff but I only use the suggested mapping suggestions in parts placement, lead bend info and other stuff that applies today.

There are curves in it that tell the whole story on track info from board trace "weight" in ounces to mils calculations to curves showing safe currents to expected temperatures rises.

The curves come from an older IPC standard (949) but power is power. 

For .32 amps, go up a bit for surges with valve coils...use 1 amp, not a big deal. 1 amp for a 10 degree C track rise requires about 15 mils of cross sectional area for the track. For a 1 ounce board (pretty standard) , that equates to a .015 to .020 wide track which should be very comfortable with that .32 amp (320 ma) load.

Good luck....

Jay

[jjm17XBGQ]

 ... which pull much higher amps than a standard IC, how can I make a board with enough metal in the circuit to handle those loads?

- Define your requirements in copper width, via and drill size

- Make a net class with this values and name it maybe "500mA_max" 

- Set the net in the schematic to this class  (change class command or in net properties)

Other way round is to define the values in the drc minimums. But then you can't set smaller traces without errors and the "intention" for what the net is for get's lost.