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I would like to connect two external 2.5 HDDs a Pi 4. Can the Pi 4 power two of them at once?

This is the model I have in mind: WD 2TB Elements

Pierre Spring
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1 Answers1

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Not without voiding your warranty. An RPi4 can deliver a maximum of 1.2 A to all the USB ports together. This is done to protect the USB-C connector which is rated for 3A maximum.

The disks you have in mind consume up to 1 A each. Without touching to the Pi, you'll need to use a powered USB hub or a bigger-capacity single disk. If you don't care about the warranty of your Raspberry and you're powering it externally, you can bypass the current limitation by connecting the 5V GPIO pin to the Ubat pin of USB directly (check out the semi-translucent copper wire):

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P.S. A small 5V capacitor between the USB 5V and nearby GND (I used 300 uF between the same point where the wire arrives, and one of the 4 bigger solder joins) greatly improves the stability of the USB w.r.t hot-plugging new devices. Otherwise hot-plugging a second HDD may produce a voltage dip which reboots the HDD that was already connected.

Dmitry Grigoryev
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    I have connected, at the same time, a WDElements 2TB disk, and a similar Toshiba Canvio 1TB device to an RP4, and it won't boot properly. The initial current surge for spinup for these is around 900 - 1000 mA, each, even though the steady current might be lower. Either one alone is fine. – Michael Harvey Sep 27 '19 at 23:29
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    @MichaelHarvey Spin-up current is indeed one of the highest peaks in a drive's power consumption, but it's not the only one. Running find /media/pi/drive > /dev/null on a partition with a lot of folders and files will also get you near the max current, because you'll have the head servo running all the time in addition to the spin drive. – Dmitry Grigoryev Sep 28 '19 at 05:31
  • is there any way to do this without a soldering iron? – Rebroad Jan 17 '20 at 15:38
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    @Rebroad You could plug a jumper wire on the 5V pin and an unused USB cable in one of the ports, then twist the 5V line with the jumper wire. But trust me, you will want to solder it. Get the cheapest iron for $10 if you're getting it for a single use, or just borrow one. – Dmitry Grigoryev Jan 18 '20 at 13:44
  • @DmitryGrigoryev Is this safe to do? Also in the long run? – Miguel Stevens Dec 23 '20 at 10:15
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    @MiguelStevens I did this more than a year ago and the Pi still runs fine. Obviously, it's not safe in the sense that connecting a defective USB device will let the Pi to dump excessive current into it, however, I have some over-current protection in the power supply. – Dmitry Grigoryev Dec 24 '20 at 14:44
  • @DmitryGrigoryev thanks! I can't find any reading material about this, could you explain what happens here? When the 5V is connected to that Ubat pin, does it from then on allow unlimited current to flow to the usb ports? – Miguel Stevens Dec 25 '20 at 09:33
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    @MiguelStevens No, I don't have any reading material, and yes, a wire allows unlimited current to flow to the USB ports, which (the current) otherwise would have to go though the current limiting chip enforcing the 1.2A limit. – Dmitry Grigoryev Dec 25 '20 at 21:52
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    @DmitryGrigoryev It worked! This is pretty amazing, there's a lot of people that have tried connecting 2 hard drives to a Rpi, I don't think many people know about this trick. – Miguel Stevens Jan 08 '21 at 09:47
  • @DmitryGrigoryev how exactly did you power this Pi. I soldered the wire, and have tried powering over USB, but there is still not enough power for a second drive. I have tried over GPIO but the Pi won't boot when a hard drive is connected – Mike Apr 13 '21 at 08:02
  • @Mike I power mine "externally" (meaning using the GPIO 5V pin), using a 4A power supply and the thickest wire I could fit in the GPIO (18AWG). I can plug 2 HDDs and a smartphone into the Pi simultaneously, although if the smartphone charge level is low I sometimes get the lightning bolt. The mod doesn't create extra power, it just distributes it to USB without the 1.2A limit. If you get the lightning bolt after the mod, or the Pi won't boot, it probably means your supply is too weak. – Dmitry Grigoryev Apr 14 '21 at 07:53
  • @DmitryGrigoryev great information, thanks, so I tried to power mine into the GPIO from the 3A 'official' raspberry pi plug, where can I get a 4A PSU to try? I guess it would need to be 5.1V 4A....and the wire you have added passes that power directly to the USB socket. Is that correct? Do I need to use the same GPIO pin that is soldered to the USB ports? (PIN2) – Mike Apr 15 '21 at 08:42