12V 1.5A output AC adapter drives my BrickPi 3 crazy


#1

Hi there, I am using a I am using an AC adapter w/ 12V 1.5A output. When I run the motor scripts, the motors run crazily fast and then the RasPi is rebooted. Is the power adapter the issue here? Any requirement on the adpater?


#2

Alright, now I see the battery pack actually offers 9V output. Probably that is the reason? But still I am a bit puzzled because 8 AA should provide 1.5*8 = 12V. Did I miss anything?


#4

The power supply should be nominally 9v, but 7.5-12v is typically okay. However, if you’re running motors, a 1.5A power supply probably isn’t adequate. It sounds like your power supply is being overloaded and causing a power reset. As a general rule, try using a power supply rated for at least 1A plus at least 1A per motor. If you are going to run two motors, try using a 3A power supply.

Please ensure you are using a regulated power supply with a DC output (center-positive).

The BrickPi3 is perfectly fine running at 12v (don’t exceed 14v), but Lego motors are designed for a nominal voltage of 9v. Since Lego motors have built-in over-current protection to prevent them from burning out, they seem to do okay at up to 12v (although 9v is recommended).

Lego mindstorms motors could draw up to around 2A each for a short time, and their current draw will depend on the running conditions (voltage, power %, mechanical load, etc.). See here for details regarding Lego motor voltage and current.


#5

Hi Matt, thanks for the feedback. You mean the adapter reset the power supply to protect itself? But why the motors spin much faster compared to when I powered it with the battery pack plus 8 AA batteries?


#6

Yes, my guess is that the adapter either resets to protect itself, or it goes into brown-out and trips (pretty much the same thing).

As far as running faster with the power adapter, assuming your code and power settings are the same, it would be because of a voltage difference. It could be your “12v” power supply is actually higher than 12v, or perhaps your batteries aren’t 1.5v (maybe they are dead or 1.2v rechargeable).

Again, make sure you are using a regulated power supply, not just a transformer with a DC output. A 12v 1.5A transformer might put out 18v with no load, 14v with 1A load, and 10v with 2A load. That would not be suitable for the BrickPi3. A regulated power supply will put out 12v from no load all the way up to the rated current, and is suitable for the BrickPi3 (as long as the available current is sufficient for the requirements of the BrickPi3 and motors).