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I want to control the power-wire of another 5V powered device (s) using RPi GPIO. Potentially it will 8-10 of such devices, which I want to control. Each device needs 2-5 A (for example, strong LED flashlights). I thought to use an old ATX power supply, but the actual circuit isn't clear at this moment.

I thought to use SN74LS245N and then solid-state relay, but it seems overkill and something much simpler and cheaper could work as well.

All devices will have common ground wire. Therefore some buffer to protect GPIO and MOSFET could work well, I hope.

I will appreciate any ideas!

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This is not strictly a Pi question, however a common solution for Pi users is to use banks of relay modules - these are available in 1, 2, 4 and 8 modules.

These can be controlled by GPIO (before choosing a module check that it can be controlled by 3.3V - some Arduino models will not work with the Pi).

SSR are unsuitable - most are AC only, but generally unsuitable for controlling 5V.

MOSFET are OK, but you need to check that they can be switched fully on by 3.3V. See GPIO_Interface_Circuits

NOTE ATX PSU are a poor choice; they need to be enabled and often perform poorly when lightly/unevenly loaded. The 5V switch-mode supplies designed for LED light strips are a better choice (I actually use one of these to run my Pi).

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  • Thank you for the answer! Is it OK to use MOSFET with SN74LS245N or a similar 3.3 to 5V shift? Could you please provide more information which 5V supplies you use? Can it provide 20A at 5V? – rth Jun 3 '18 at 0:01
  • I have never used SN74LS245N so can't comment, I just pick suitable MOSFET. This is not a shopping site, but you should find hundreds of vendors offering PSU. – Milliways Jun 3 '18 at 0:06
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The Pi is a 3.3v device, not a 5v device. You'll have to take that into account when you are using the GPIO pins.

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To restate the problem, you're trying to control a massive current draw of 5A for 10 devices. That's 5Vx5Ax10 = 250watts. That's more than all the grow lights in my tent, which is powered by mains voltage. You've realized that is beyond standard Pi relays such as AutomationHat, whose 3 relays only support 2A. Your design will need to incorporate considerations for heat dissipation, fuses, etc. With a 250W circuit you could start a fire and burn your house down. Asking us to design a circuit for you is awkward. For such a circuit, the Electronics StackExchange might be more appropriate (e.g., "How do I switch 5V@5A DC with 3.3VDC safely?"). Note that @Milliways has already provided an excellent answer in the context of this forum.

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