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I got my hands on a Gigo microbit robotics set. It uses a control box to house the microbit. As you can see from the control box specs, it uses 6 AA batteries, but it can also use an external micro-usb power source of no more than DC 5V/2A. I'm not sure how to power the 2 motors (part 63 and 64) that it contains, a dc motor named C-50X PLANETARY GEARBOX (DDM) and a servo motor named C-180 SERVO MOTOR (METAL GEAR). There are no specs for these motors. I'm assuming they work with 5V since that's what the external power interface is using. I prefer not to use batteries, so I tried to use a USB 3.0 PC port with the external micro-usb interface and the motors are working. Do I risk damaging the port, microbit or the motors this way?

Wizard
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  • If you don't know, yes there is always a risk of damage of you connect two unknown things together. I am surprised how people connect random hobbyist things to their expensive computers without hesitation, possibly blowing up the USB port, or in worst case, bricking the whole computer. USB 3 ports are rated for 900mA max only, unless they are special. – Justme Feb 25 '24 at 08:36
  • @Justme, no, USB3 ports are rated for 900mA minimum, not maximum. On a desktop PC one should expect to have at least 2-2.5A from a USB port even in STANDBY mode. And if you try to take more, the port power will be simply shut down, either by electronic high-switch means, or by a simple polyfuse. For polyfuse reference, see https://electronics.stackexchange.com/a/510842/117785 – Ale..chenski Feb 25 '24 at 21:19
  • @Ale..chenski I don't think so. The USB standard says no USB3 device shall consume more than 900mA, they cannot even request more - via USB. Yes, ports with Battery Charging specs exist, but that is unrelated to USB as a data port. Hard to have at least 2 or 2.5A as you can't find many Type-A USB3 connectors rated for more than 1.8A. And there is no guarantee your power supply 5V standby supply is rated for that much, and no guarantee your motherboard contains a polyfuse or overcurrent protected load switch, and won't blow up if you try to draw 2-3 amps without any negotiation. – Justme Feb 26 '24 at 09:54
  • @Justme, the situation has been explained maybe a dozen times. There are "device side" specifications, and "host side" specifications. See https://electronics.stackexchange.com/a/424074/117785 https://electronics.stackexchange.com/a/361929/117785 https://electronics.stackexchange.com/a/419323/117785 – Ale..chenski Feb 26 '24 at 19:32
  • @Ale..chenski No there are no such thing as separate specs. A USB2 port is required to source at least 500mA, or 100mA for a low-power port. There is no guarantee you can get more than 500mA, just at least 500mA. The limit required for protection from short circuits and malfunctioning devices is 5A Connector rating requirement is 1.5A. The fact that you can draw any more than what the specs allow is pure convenience for users to prevent nuisance trips, when you e.g. put two 900mA USB3 devices onto a USB3 hub, which could total up to 2A, exceeding most connector ratings. – Justme Feb 26 '24 at 20:07
  • I would suggest to take measurements of power consumption of your entire robotics setup before worrying. Use a device something like this, https://www.amazon.com/YOJOCK-Multimeter-Detector-Volmeter-Capacity/dp/B0B96X5Z1S – Ale..chenski Feb 27 '24 at 03:06
  • @Ale..chenski, I used a similar one https://www.amazon.com/Current-Voltage-Multimeter-Digital-Detector/dp/B0CP66VDWH While the motor was running at half speed with no load, it showed 0.08A. But, it won't show me startup current because it happens too fast. Is the one you posted able to measure every sudden change? Or maybe I can manually stall the motor for 5 seconds to measure it or do I risk burning it? – Wizard Feb 27 '24 at 09:09
  • @Wizard, yes, you need to apply mechanical load, not to stall maybe, and check the consumption. So far the 80mA number does not look any alarming. And again, it is a toy, and it should be safe. – Ale..chenski Feb 27 '24 at 15:52
  • @Ale..chenski, I measured the motor with half speed and the maximum load I'd use and it showed 0.15A. I grabbed the shaft for 2 seconds to stall it and it showed 0.51A. So, I think my USB 3.0 port can handle the specific motor. – Wizard Mar 01 '24 at 13:52
  • @Wizard, good. You can provide this as your own answer to your own question. – Ale..chenski Mar 02 '24 at 04:26

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I measured the motor with the speed and the maximum load I'd use and it showed 0.15A. I grabbed the shaft for 2 seconds to stall it and it showed 0.51A. So, I think my USB 3.0 port can handle the specific motor.

Wizard
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