Originally Posted by Andrew Leigh

Hi,

I now have my 12V thermosat schematic ready for board design. While thinking about the PCB I got to thinking about the track width. I expect to be switching about 16A through a Mosfet. How does one interface the high current carrying leads with the PCB. I was hoping to use PTR Connectors AK500/2 and /3.

What confuses me is the following;
- theortically I need about 6,5mm², (from wire tables) this translates to a track width of ~ 162mm?
- Why if I need 6.5mm² are the legs on the Mosfet barely 1mm².

Evidently I am missing something here, could someone point me in the right direction?

Cheers
Andrew

hi Andrew,
Look at this pdf, pages 6,7

You can 'beef up' tracks by soldering onto them a heavy gauge tinned copper wire or copper braiding. [recovered from old coaxial cable screening]

Hi Andrew,

keep the traces as short as possible and use flat male connectors (females are crimp connectors as used in car electric)

Here is a picture of one to be soldered onto a PCB.

Boncuk

Hi,

thanks for that, do you know if these connectors are in any Eagle library?

Here is the board, the two T220 packages will stand vertically and the 540 will be heatsinked. Is it OK, the screw connectors I am unhappy with and like the spade terminals.

Cheers
Andrew

Hi Andrew,

as far as I know mounting tabs of that kind are not contained in Eagle.

Standard tabs are 6.3mm. I made a quick library for that one.

Try to get long ends to be bent opposite underneath the PCB for maximum mecanical strength. The females fit very tight and it requires quite some force to separate both parts.

The screw head terminal you used in your design doesn't look like it can stand high current. If neccessary use two mounting pads each for one connection and also use two wires in parallel (total of four)

Regards

Boncuk

P.S. One hint concerning PCB layout: Avoid right angles and route 45 degrees. At T-junctions add manual traces to meet the junction at a 45 degree angle. When done, check if all elements have the same net name. Click "show" and all traces must be highlighted. If not, check for different names and rename the unconnected trace accordingly. Check for air wires after renaming and reroute.

Hi Andrew,

looking much better! You might route the trace from the right bottom connector terminal to the heater connector around the screwhole of the IC.

I zipped the file using 7-zip, but it should open using winzip. Did a double click not unpack the file?

It does on my PC though.

You can download 7-zip free and retry.

Here is what I have done to your design.

The third image is the same design shorted by 10mm.

Regards

Boncuk

The 130W rating is not how much power you can put through the component.

The power the transistor is dissipating is the current, times the voltage across the transistor at the same time (i.e. when it is on.)

When the IRF540 is "on", its resistance is nominally 44mΩ. The power when it is carrying 16A is I^2*R, which is 11.3 watts. (16A * 44mΩ = 0.7V). Yes, 11W will need a lot of heat sink!

Hi,

thanks for that clarification Mr Neary.

I was going to fit a small fan for forced air cooling, something like a 25mm fan. For that matter could even have a 90mm fan cooling the entire enclosure.

Is it better to parallel a couple of devices? They are reasonably cheap in the scheme of things.

As the board is not made I would you mind offering a recommendation as to how you would overcome the problem, it is becoming a little vexing for me.

Thanks
Andrew