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I need to be able to switch up to 100 amp @ 48v DC with a Raspberry Pi.

I came across this video which is what I am trying to emulate: https://www.youtube.com/watch?v=dhIbZa6yg5k

at 1:15 in the video it shows how they have the mosfet connected to 2 busbars to control the current flowing through both sides of it. This is what I need with the added twist of having logic level voltage to be able to control the mosfet.

Here is a quick and dirty schematic I came up with that I would like to know if this is the correct way to go about this:

enter image description here

The 10 V on the logic level switch will come from a voltage regulator connected to the main 48 V battery (same batter that that SCC connects to).

My biggest concern here is how to attach the high current mosfet to the bus bars just like in that video posted above (shown at 1:15).

Any advice on this would be greatly appreciated!

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  • \$\begingroup\$ What you included is not a proper schematic. Include a proper schematic, one that looks like this example: electronicshub.org/wp-content/uploads/2019/03/… Also include links to the datasheets of the components that you intend to use. A more general remark: if you want to switch a 100 A line and have to ASK if what you're doing is correct then in my opinion you lack the experience. It is very likely that you will be destroying some components in the proces. \$\endgroup\$ Mar 19 at 9:05
  • \$\begingroup\$ #NomNomCameron, Your video is educational for MOSFET newbies like me. Passing 380A through the little power MOSFET guy with 8 so thin legs and seeing the copper wires glowing red hot is indeed eye opening. Good luck to your huge current switching project. Cheers. \$\endgroup\$
    – tlfong01
    Mar 19 at 9:09
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That's not a mosfet on a PCB.
That a mosfet bodged on some copper plates bolted to a pcb to demonstrate the low Rdson of the thing. They also bring it right up to max Tjunction with 200A.
enter image description here

Normally with these currents you're looking at SEMIPACK or similar which is meant for this. Browse the power modules from IXYS or SEMIKRON and find a suitable module for your use. Over a standard PCB 100 Amps is an expensive challenge.
enter image description here

Also note that you may have to take switching noise into account where a raspberry pi may function unexpectedly.

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  • \$\begingroup\$ I wasn't aware that transistors came in such a package, this definitely looks like a much better approach to what I need. Thank you so much! \$\endgroup\$ Mar 19 at 15:56
  • \$\begingroup\$ Also, the specsheet for one of the power modules I found shows that the terminal screws is only 4mm wide. That doesn't seem to provide space for a big enough lug still to handle 100 amps or more? \$\endgroup\$ Mar 19 at 21:41
  • \$\begingroup\$ @NomNomCameron There are more sizes of those modules. Eg: semitrans 2 has M6. However, those little flaps over the thread insert is where the current goes, so good contact with the lugs. You can also find suitable SSR, it has the gate driver built-in. These do not. \$\endgroup\$
    – Jeroen3
    Mar 20 at 16:05
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how to attach the high current mosfet to the bus bars

Hot plate.

enter image description here

It would probably be a good idea to stick a thermocouple on it to measure the temperature.

Surgeon general warning: do not cook with lead.

Note IRFU7540 in your schematic is not the proper MOSFET for the job. You need one with tiny RdsON, that can take the current both through the chip and source leads, in a package without bondwires. The NXP video uses a LFPAK FET which has a clever source leads arrangements and no bondwires.

But you should really use a package with bolts, as Jeroen says.

Since it's a NMOS you need to drive the gate above the +48V supply, so you need a boosted supply voltage. Your choice, canned isolated DC-DC, charge pump...

It should be able to switch off very fast in case there is a short, because if there is a short, current will rise to many thousands of amps, and during switch-off the FET will have the full VxI dissipation (ie, 48V x thousands of amps) so you don't have much time before it blows.

Ideally you want to exploit the wiring inductance to limit the rate of rise of current during a short, so the entire overcurrent protection chain, from current measurement device, comparator, etc, has to react extremely quickly. If you got 100nH of total inductance in your wiring, in 200ns on a short the current will only rise by 96 Amps. So if you have a very fast protection circuit you can turn off the FET before current rises to dangerous levels. On the other hand if your protection circuit takes 2µs to react, by then current will have reached a thousand amps, and FET turn-off losses will thus be 100x more.

If you use software to implement your short circuit protection, you will find bits of MOSFET embedded in the ceiling when it blows. It has to be hardware, it has to be fast and foolproof, and it has to work even if the CPU and all peripherals are frozen by the debugger.

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  • \$\begingroup\$ I don't see why this gets a downvote. The hot plate idea is both funny and practical. \$\endgroup\$ Mar 19 at 9:29
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    \$\begingroup\$ Who knows. I'm more worried about the choice of FET by the OP though. In fact there is no need for hotplate with this FET: it will reach solder melting temperature on its own with 100 Amps. \$\endgroup\$
    – bobflux
    Mar 19 at 9:35
  • \$\begingroup\$ The mosfet being on a "hotplate" makes sense to me haha. What would be an appropriate use of small mosfets that are rated for such high amperage? I never could understand that since the leads on a mosfet are so small? @bobflux \$\endgroup\$ Mar 19 at 15:59
  • \$\begingroup\$ The hot plate is to heat the big copper bus bar to soldering temperature in a cheap and controlled way (unlike a blowtorch). A soldering iron will probably just warm up the copper bar slightly. And the tiny MOSFET video... I believe they did it just for bragging rights. Although lower resistance in the leadframe of the FET leads to lower losses, which is always nice for a DC-DC powering a PC CPU that gobbles up 100 amps at 1V... \$\endgroup\$
    – bobflux
    Mar 19 at 16:33
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Solid state relays is what I would use to switch the 48V@100A

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