Low voltage cut off

[DaveInDenver]

You'd probably need surface traces that are 75 mil wide, 5 mil thick (or ~400 mil, i.e. 1/2 an inch, at 2 mil thick), and internal traces that are like 900 mil wide, 1 mil thick. We'll typically use planes for anything over a couple of amps (and you are looking at 8.5A). But doing PCBs in your kitchen is a lot less flexible than the multilayer stuff we do, so you'd just have to lay it out carefully to group high current stuff and not end up with necked down sections of copper. Your limitation doing boards yourself is how thick the copper on photo-sensitive boards might be. I dunno what the thickest you can find is, but I'm guessing it's not more than 1 or 2 mil.

 

[nvprospector]

Just woke up - work graves.

The PCB in the previous post will handle up to 20A of current in it current setup. 12v X 20A = 240w. Since you want to be pushing 60A plus, 700w/12v = 58.3A, don't use traces but use copper planes and minimize the distance that the current must flow through. Two or three layers of 2oz copper can easily handle 100A. You just need to make sure you have the same number of layers for the return path as well.

The other option is to use bus bar with a tin or soldermask. If say running 100A use 12 gage solid copper wire and jump the bus bars. Here is a image of where it would look like. This is a H-Bridge contrlor but will give you a idea on wire traces.

View attachment 11900

If I am pushing high current and I am etching my PCB I will use a 4oz copper at 0.025 which will handle 1000w and higher. Then I make the power and ground planes as large as possible and soldermask the trace. To show what I mean but the copper here is a H-Bridge that I use that is 12v @ 100A 1200w using only PCB traces.

View attachment 11899

Mainly what I trying to say is keep everything short. Resistance is dependent on the length of the conductor. A few mils between where your high current trace ends and the pad begins will have a extreamly low resistance, even if it is small compared to the power trace.

 

[nvprospector]

Opps, Just realized that you said 70w. Then in that case just use the power and ground trace size on the previous messages PCB as a reference for the route you wish to go.

 

[cruiseroutfit]

A link that might come in handy: http://max8888.orcon.net.nz/pcbs.htm
(Firefox stopped some sort of pop-up though, no idea what it was.)

Great link