I was wondering something about the PCBs in motor controllers, especially those around 70-180A or so. How do they route all that current on the PCB? Like the trace width calulators seems to say you need an 8cm wide trace, and that's when you have 6oz copper.

Like those TO-247, Super 247 TO-220 packages seem like they are meant to be mounted on a PCB. But at the same time some of them are rated past 100A.

Thanks.

 

You generally don't run PCB traces for currents that high, you place the component as close as possible to a terminal block and use real wire. Just because it's mounted on a PCB doesn't mean it needs PCB traces to connect it to things.

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That's what I was thinking but to connect to the terminal block and the component lead it still has to pass through the PCB doesn't it? Even if it's the smallest trace? UNless you are talking about getting really long terminal block leads and soldering them directly to each other.

 

I don't know, I've never really seen the inside of a motor controller built to handle that much current. They probably skip PCB traces and do the linking with large pieces of copper jumper wire. A hole can be easily made to fit both the lead of the part and one end of the jumper. Any leads on the PCB carrying that much current are going get off the PCB as soon as possible and keep the leads and short as possible until you can get it to really high gauge wire. Most really high powered devices like that often have simple screw terminals on them as PCB leads are pretty pointless.

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I was thinking about buying strips of copper bar from the hardware store and maybe screwing them down to the PCB and having the leads go through those and solder it to those isntead. Can you solder pure copper with regular electronics soldeirng?

 

You can solder to pure copper with electronics solder, so long as your iron is powerful enough. . . take into account that it's a much larger piece of copper you have to heat. I have soldered wire to copper plate about 1/2 mm thick using a 30W iron.

Oh, just a thought. . . If you're soldering components to copper plate, I would 'tin' the plate first so you're less likely to overheat the component

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'Intellectuals solve problems. . . Geniuses prevent them.' . . . Albert Einstein

 

You can try to headsink the component lead as you solder it.

 

Here's a picture of a motor controller I have been using for several years. It runs on 12V at well over 100A when under load. I used 4oz copper and kept everything short. The FET drains are soldered flat on the board, and the board is on a heatsink. I have had no problems with that arrangement for intermittant duty. As pointed out above, the full capability of the MOSFET may be limited by the lead size of inexpensicve packages, such as TO-220 or DPak, and one would have to go to a more expensive package to get screw terminals.

Let me add that for even greater power in an earlier design, I cut traces from 0.025 inch copper plate, which was obtained from the local hobby shop. The traces essentially duplicated the PC traces in outline and were attached to a heatsink with a thermally conductive adhesive and insulated screws. Heavier copper than that is much more difficult to work and to solder. I have not compared the two designs for maximum current capacity. I have added a picture of the board made in that way. The thicker copper conductor is shown in the closs-up.

Attached Images

	Power board 1.jpg (51.7 KB, 19 views)
	Power brd original1reduced.jpg (38.8 KB, 16 views)