What should I use for a power switch on a high current device?

Electronics
1

Depending on my approach, there are 3 ratings I could go with:

  • 30A (at 24V) - if I put the switch between the regulator output and device
  • 72A (at 10V) - if I put the switch between the regulator input and batteries
  • 100A - max current the battery back and BMS support for continuous drain
    (Those are the max it could use, not what I would be consistently drawing.)
    Ideally, I’d prefer going with 100A just so I know I know the BMS will cut power before the switch breaks.

The 3 options I see are a mechanical switch, a MOSFET (or other type of transistor), and a relay.
Mechanical switch sounds like the simplest option. But I can’t find any rated for that much current that aren’t giant.
I’m thinking a MOSFET or relay are the better choice, because then I could cheaply change the type of physical switch I’m using. Also I’m debating using 2 momentary switches that both need to be pressed as a sort of failsafe, and that sounds harder to do with a physical switch.

This is just going to be an on/off switch. So switching speed isn’t important. The main thing I care about is that it doesn’t leak much power when off or waste power when off. Ideally, I want something that wouldn’t need active cooling. But I’m not sure if that’s feasible when working with that much current.

I’m going to be powering this with 4 LiFePO4 batteries in series. The pack will have 10V-14.6V over the course of its life. Each battery has a 105Ah capacity. So the whole pack will have 1344Wh of power.

Anyone have advice on a switch/chip that sounds good for this?
Sorry if this is a bit rambly. Since I’m not sure how to make a decision on this, I’m just trying to give all the info that could be relevant.

2

Also, I’m not sure if I could use the BMS for this. I don’t get the one I ordered until tomorrow.
It’s a “smart” one. Maybe I could use an arduino to tell it shut off over UART.
But that would require either bypassing the BMS to power the arduino or adding a second, small battery for the arduino.

3

Look into contactors, they’re like relays but designed to safely disconnect higher voltages and higher currents. There are some types of relays and contactors that are no power required to stay in a state but only power required to move into that state (so power to turn on, then no power required, then power to turn off, then no power required etc). Have a look at Latching Relays and Contactors.

2 Likes
4

This post read like coming into the middle of a conversation. What is the application? What are you trying to accomplish?

5

I guess there’s a bit of a story to this:
I’m trying to make a powerful handheld fan. That has basically split into 2 projects now:
Make a powerful practical handheld fan.
Make the most comically big and powerful fan that I can technically hold with my hands.
This switch would be for the second one. Since my goal is “as over the top as I can get”, I was wanting to get a switch that could handle anything my batteries could output.

6

Thank you! I haven’t heard of those before, they sound perfect for this case!

7

Of course! That’s what DMS is for.