PCB Cu Oz rating and A capacity?

[bob332]

hello.

i build and fly multi-rotor radio controlled copters. currently have been flying the 4 rotor versions and when building a power distribution pcb, a friend and i came up w/ a design and we milled it out. total size is less than 2" x 2" w/ trace cutouts as we are just using 1 side of a 2oz pcb. nobody can give me a max amount of A for the traces and i am wondering if there is a formula to figure out what the pcb trace can handle w/out an additional Cu wire soldered onto the traces. i have attached a pic of the current power distribution board, not fully finished, just has the connectors that go to the electronic speed controls which feed the motors. i need to solder on the main power feed that will connect to a battery that is 12.6V max and can burst upto ~50A. for size reference, the distance between the traces is .060 (1/16")

a friend of mine is currently flying this same board w/ no beefing of the traces and is pulling at least 20-30A if not more w/ no issues, but we don't want to burn through a trace because these quads don't glide, they just drop and weighing 2#s or so, don't want that to happen.

**broken link removed**

tia,
bob

 

[Roff]

Google "PCB trace width calculator". Here is one, but there are others. I didn't check to see if they all agree.

 

[bob332]

thanks, am i correct that 2oz pcb = .0025 Cu thickness?

 

[Roff]

PCB Copper Thickness
I used to know this stuff. I hope these guys are correct!

 

[bob332]

thank u sir

 

[ronv]

Here is a neat calculator.
PCB Via Current | PCB Trace Width | Differential Pair Calculator | PCB Impedance
Look at conductor properties for fused current.

 

[bob332]

thanks, will give it a try. guess i have been searching the wrong terms...glad you guys got me squared away, thanks

 

[bob332]

Here is a neat calculator.
PCB Via Current | PCB Trace Width | Differential Pair Calculator | PCB Impedance
Look at conductor properties for fused current.

while using that tool, for the length and width of trace, do i just do either - or +, or both? if both, ~46A is claimed that the pcb can support and this would support the fact that my friend is flying w/ motors that pull ~10A/ea or so at their higher levels. looks like i will look for some 4 or 6oz pcb for future boards though for larger quads and a bit of headroom. used 122F ambient w/ a 90F temp rise, if i lower the temp rise to 45F, then it drops down to ~33A. what is a acceptable temp rise?

please educate, thx
bob

 

[ronv]

FR4 is ok to over 120C.
I think for your purpose you just need the length of a single trace.
If your concerned, just tin them up with some solder.

 

[bob332]

if i do the lower left trace, it is approx .250" wide by 1.6" long by 2oz pcb material. that gives me 17.25A, so would that be the rating for the whole board? or would that double because there is another trace on the upper right carrying the same current? or would i multiply by 4 since the internal traces would carry current too? my main reasons for asking is because if at all possible, would like not to beef it up w/ solder/copper since the lighter the quads are, the longer they can fly, more they can lift and the more responsive they are.

although the quads have an extreme power to weight ratio the way i build them, if possible losing an ounce here and there would be nice

tia,
bob

 

[ronv]

If I understand correctly.. The weakest trace should be your guide. If it is double sided and those holes are vias or both sides are used for the same trace the current will be higher just like you doubled the trace width and kept the length the same.

 

[bob332]

the board is single sided, so then i should go off that if that single trace can handle ~17.25A, so if i connect 2 motors to that trace, i should just make sure they run less than 8.5A continuous?

 

[ronv]

Correct; however, when I ran it it came out almost 26 amps.

 

[bob332]

Correct; however, when I ran it it came out almost 26 amps.

even better was plated trace selected? w/ a 2oz board? wonder what the difference you used was...i had 50C ambient and 50C rise as being ok. using the saturnpcb program?

 

[ronv]

Ahh. I had 20C ambient and 100C rise... Unplated.