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I've got a setup where I power RPi, 3G dongle from one power source (USB Hub powered from 5V 2A) and a DC Motor HAT and DC Motors (2 small car mirror motors) from a 12V 2A supply. I checked the motors and they work just fine with the 5V supply (although a bit slower but speed is not a priority, I'd even say that if they run slower I'll have more precise control). I was wondering if the connection scheme below is safe.

RPi_3G_MotorHAT_Motor_PowerSupply

If there's too little power I suppose I can switch to more Amps. The purpose of doing that is to get rid of the USB Hub as I'm attempting to miniaturise the solution. Thanks for any advice.

Tom
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  • Yeah that's defiantly too low power, if it works now, you will notice problems when you start loading the Pi cpu up wit code and will see it power off at random, I recommend that you place the do motor hat and the car mirror motor on a separate power supply or upgrade to a power supply that's approx 3-4 amps depending on your motor specifications – Mohammad Ali May 02 '16 at 16:10
  • The slowness of the motors is likely due to a reduction in voltage and not amperage, either way, you will not really be receiving more control as your hat should be pule width modulating the feed to the motors which should give you the most control possible – Mohammad Ali May 02 '16 at 16:11
  • It's still a speculative setup, at the moment it works through a USB Hub and HAT+Motor are on a separate 12V supply. But with the above, if I use the setup shown with a more powerful supply (e.g. 5V 5A) is it considered safe? – Tom May 02 '16 at 16:15
  • It should be, but only you know the ratings of your motors, just do the math for the maximum amperage required, the Pi needs about 1.2 amps, your hat maybe .5 to .25 depending on the model, then your mirror motors could be anywhere between 1-2 amps each so that's approx 4-6 amps so 5 volts 5 amps should be ok. – Mohammad Ali May 02 '16 at 16:17
  • Bear in mind that you can only pump 2.5 amps into the Pi3 polyfuse. If you want more you'll need to power the Pi via the expansion header. – joan May 02 '16 at 16:32
  • Thanks Joan. Do you mean I should power it on pin2 and pin6 as in http://www.modmypi.com/image/data/tutorials/how-to-power-my/4.png and the schematic from my initial question post is still ok? – Tom May 02 '16 at 17:53
  • Powering your Pi from pin 2 and 6 should be ok but I would not recommend it as it does not contain the same protection circuits that usb does, furthermore I believe that you will never hit that 2.5 amp limit because in your schematic in your initial question you show the hat reviving power directly from the power supply and not through the Pi. The 5volt pin on gpio also does not contain a smoothing capacitor and the voltage and short circuit protection features that the usb input offer – Mohammad Ali May 02 '16 at 18:11
  • Yeah not a problem, if your powering the Pi from a bench power supply I'd recommend just striping the USB cable and using that for vcc and ground, by the way in your diagram I do not seem to understand how or why you intend on using micro USB for ground and not data, and why your diagram doesn't have vcc and ground for the 3G stick coming from the Pi and how or why you intended on powering a USB stick directly from a power supply – Mohammad Ali May 03 '16 at 12:34
  • I'm powering it through microUSB as this is the type of socket used in RaspberryPi to feed it with power, its either microUSB or GPIO, with the latter, you said, doesn't have any safety features. 3G is not powered by Raspberry as it doesn't provide enough power, at the moment the two are powered and data exchange is done through an USB Hub. The Hub is relatively large and I'd like to miniaturise the solution so I'm looking for a way to feed the whole setup with a different source of power than the bulky Hub. Intention is to use mains power adapter ( plugged into wall socket), not bench supply – Tom May 03 '16 at 12:46
  • The Pi should be able to power Your USB device if you are using a reliable power source and are powering it through microusb, the Pi should be able to deliver a bit over an amp through the USB port if you use a power supply with An approximately 2.5 amp raiting – Mohammad Ali May 03 '16 at 13:15
  • If you do still have the need to power the 3G stick separately which may need to be done depending on the type of stick, I would recommend that you plug the stick directly into the Pi and then solder to the bottom of the USB port to feed in external power, be aware that it would be logical to make a simple circuit to smoothen out the output as it will be going directly to your USB device and the protection built inside of your hub will no longer be in play, I recommend a simple capacitor and voltage regulator setup – Mohammad Ali May 03 '16 at 13:20
  • Try adding "max_usb_current=1" to your config.txt file to allow the USB ports to draw up to 1.2 amps across USB ports instead of the usual 600 miliamps, see here for reference: http://raspberrypi.stackexchange.com/questions/27708/is-setting-max-usb-current-1-to-give-more-power-to-usb-devices-a-bad-idea the above idea of soldering to bypass power limitations should only apply to the raspberry Pi 2 – Mohammad Ali May 03 '16 at 16:11

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