Do I use a relay, MOSFET, or just a switch? (5VDC 15A load)

Question

I have a 5VDC 15A power supply that will be powering both an Arduino and 288 Addressable LEDs. How do I switch the circuit on and off? First I looked at relays. The only relays that I could find that support a 15A load are ones that use High Voltages around 250V. I think they had a minimum recommended load voltage of 12V. I also looked at mosfets, but I found that many would burn up if I put 15A of current through them.

I have also considered just using a switch, as everything is at the same voltage. In that case, I would need to make sure the switch I use can handle the 15 A of current. Hopefully a switch like that wouldn't be too bulky.

Basically, My load voltage is too low to use a relay, but I'm afraid the current is too high to use a mosfet or normal switch. How should I turn this thing on and off?

Answer 1

You can use a simple p-channel MOSFET as a high-side switch.

^{simulate this circuit – Schematic created using CircuitLab}

The particular part listed above is cheap and has an Rds(on) of less than 2.5m\$\Omega\$ @25°C with 5V drive, so it will drop less than 38mV at 15A, so it will dissipate about 0.8W when hot, requiring a few square cm of copper to run reasonably cool. A slightly more expensive part (still less than $1.50) is more like 2m\$\Omega\$ @25°C so it will run cooler.

Answer 2

You should be able to use a simple relay, like this one:

https://ar.mouser.com/datasheet/2/307/en-g2rl-1670825.pdf

Don’t confuse the coil voltage with the max voltage the relay can handle. The 250V refers to the maximum voltage the relay can switch on/off because of the electric arc that's formed during commutation.

Answer 3

It depends if you are looking to control the system manually (ie flip the switch by hand) or make another electronic system to flip the switch for you. In the latter case, I would look for an automotive N-channel mosfet to install on the low side of your circuitry. The mosfet would also allow you to use a much smaller switch, if you are going for the manual solution.

There are plenty to handle 5V 15A. For instance IRLZ34NPBF (the first to appear in my google search).

A relay would also work, but I would not recommend using one. You should use a mosfet since you are dealing with direct current. Relays are more expensive and less reliable.

Answer 4

Be careful using relays intended for AC loads. These are designed so that any any arcing that occurs as the contacts open is quenched by the AC signal becoming zero 120 times per second.

An automotive relay would be a better choice, although its coil may require 9 V to operate.

Answer 5

So lots of these answers detail very well that you can use a MOSFET or a relay or even a switch. All the mechanical solutions (relay and switch) will have the problem of arcing at these relatively high currents (more on that in a bit).

But they all miss an easier solution. You say these are addressable LEDs. So before you go whacking the power off to a 15A load, first command them off using the arduino (which is presumably generating the commands to the LEDs). Bam. Your load just went from 15amps to like 10mA (arduino current). Now if you want to kill power using an external switch it becomes trivial.

Now as to why the mechanical solutions can potentially have arcing issues: while the system voltage is indeed 5v, the moment you try to pull away the pieces of metal conducting those 5v @ 15amps there is a rather large change in current per unit time. Any inductance in the circuit (either stray or intended) will resist that rapid change in current and cause a voltage spike that will likely arc per V = L*di/dt.

Mechanical switch/relay designers know all this, the plating on the switches and relays are designed to handle this presuming you stay within the DC limits of the switch/relay current. Not doing so will eat away at the lifetime of the switch/relay and would require you re-rate the switch lifetime (re-calculate the expected life of the switch based on the new info). Like somebody else said, automative relays are a great source for higher-current relays, and plenty, plenty of MOSFETs are more than capable of handling 15amps.