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I am currently working on a project where 2 batteries powers multiple components on a board. A raspberry pi, 2 thrusters and a winch. Each device is powered via the battery and a buck converter. The main issue is that the thrusters and the winch cannot run at the same time because they will overdraw the battery. Changing the battery is unfortunately not an option. This also has to be implemented in the hardware and not the software. Here are the numbers. The winch runs on 12v and can pull up to 20amps (but most likely will not). 2 thrusters run at 18.5v and can also pull up to 20amps each (again will not reach this). There are 2 18.5v batteries with a draw limit of 20amps each. The batteries are fused for worst case scenario. How can I switch the power from one device to another using the raspberry pi. Originally, I was thinking a relay however I have not been able to find a relay that can handle about 50amps to be safe, and have a control voltage of 3.3v (rpi gpio). I know there has to be other options however I cannot find any through my own research. enter image description here

Here is the current model of the PCB I have now. (Feel free to rip it apart, This is my first time doing this and I don't necessarily know everything) The red circles indicate the two paths, the green circle indicates the power supply. Essentially I need a single pole double throw switch that can be controlled by a raspberry pi. Any ideas would be amazing. Thank you.

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  • \$\begingroup\$ Do you need to switch on/off a 20A load, or can you adjust the load to 0 before switching the relay? \$\endgroup\$
    – Jack B
    Commented Nov 18, 2019 at 19:35
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    \$\begingroup\$ "This also has to be implemented in the hardware and not the software...How can I switch the power from one device to another using the raspberry pi" the Pi is controlled by software, so this appears to be an impossible requirement. \$\endgroup\$
    – Bruce Abbott
    Commented Nov 18, 2019 at 19:38
  • \$\begingroup\$ @BruceAbbott you are not wrong. To clarify, the winch and thrusters are already being controlled by the raspberry pi so what I was trying to say is that the solution cannot be to program the thrusters and winch to never work simultaneously. \$\endgroup\$
    – Nick Alfano
    Commented Nov 18, 2019 at 19:56
  • \$\begingroup\$ "the solution cannot be to program the thrusters and winch to never work simultaneously." - Why not? \$\endgroup\$
    – Bruce Abbott
    Commented Nov 18, 2019 at 20:03
  • \$\begingroup\$ @BruceAbbott the project is a senior design project. These were the sponsors requirements. \$\endgroup\$
    – Nick Alfano
    Commented Nov 18, 2019 at 20:05

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You could possibly get away with using a high power, super low Rdson MOSFET as a low-side switch (N-FETs have generally lower Rdson than P-FETs) for each device. If you get a MOSFET that has an RDSon of 4mOhm you'd have 1.6W dissipation on the FET at 20A. You could use the battery voltage to drive the MOSFET gates with either a gate driver IC, level translator, or inverting MOSFET (Something like a 2n7002 in common source configuration) to change the 3.3V control signal to a suitable gate drive level for that high of a current. Something like the Infineon BSZ009NE2LS5ATMA1 (1mOhm Rdson at 4.5V Vgs).

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