Power For Metro Mini

Please tell us which board you are using.
For CircuitPython issues, ask in the Adafruit CircuitPython forum.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Locked
User avatar
Geosciences1
 
Posts: 2
Joined: Thu May 19, 2022 10:40 am

Power For Metro Mini

Post by Geosciences1 »

I will be powering a Metro Mini from a 12 volt battery in the field. I will use either a L4931 (5V) or a 7805 (5V) regulator to supply 5V power to the Metro Mini. From the documentation I need 6v - 16v for Vin on the board. But I have also seen 5V to 16V listed on the bottom of the board. Can I use 5V to power the Metro Mini on the Vin pin, or should I buy the mini usb power adaptor to supply the Metro Mini with 5 volts DC through the USB port. I'm afraid to power the Metro Mini directly with 12 volts at Vin and using the 5V output (150ma max) to power 2 (5v) relays (35ma each) and #254 Miro SD breakout board, #1085 16 Bit ADC board, and #3295 Real Time Clock all on the same circuit from the Metro Mini. Thank you for your help!

User avatar
blnkjns
 
Posts: 963
Joined: Fri Oct 02, 2020 3:33 am

Re: Power For Metro Mini

Post by blnkjns »

7805's are pretty obsolete IMO.
I would get a buck converter, set it to 5V and feed through USB or the 5V pin. These can be set to a range of output voltages, and have like 80-90% efficiency, where a 7805 would just burn 7/12th of the energy. They can do up to 2 Amp.

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Power For Metro Mini

Post by adafruit_support_mike »

If you have the option of using an automotive USB adapter, that will be a good choice. Those are usually well made and reasonably efficient.

User avatar
Geosciences1
 
Posts: 2
Joined: Thu May 19, 2022 10:40 am

Re: Power For Metro Mini

Post by Geosciences1 »

Thank you! The buck converter and automotive USB auto converters are great ideas. I purchased a USB auto converter and found that the current usage for the relays was reduced in half. And it runs very cool. I did purchase an Adafruit UBEC DC/DC step-Down Converter and found that it works very well for the relays. Can I power the Metro Mini directly with Adafruit converter? Would I power it through the micro USB port or can I apply the 5v power to the pin marked USB on the Metro Mini? The DC/DC converter has an output of about 5.25 volts. Is this ok for the Metro Mini though the USB port? What is the maximum voltage allowed on USB port? Thank you, Tom

User avatar
adafruit_support_mike
 
Posts: 67454
Joined: Thu Feb 11, 2010 2:51 pm

Re: Power For Metro Mini

Post by adafruit_support_mike »

Geosciences1 wrote:Can I power the Metro Mini directly with Adafruit converter?
Sure. The UBEC's output is easily smooth enough for a microcontroller.
Geosciences1 wrote:Would I power it through the micro USB port or can I apply the 5v power to the pin marked USB on the Metro Mini?
Connect UBEC power to the 5V pin.

The board has a circuit that selects among USB power, power from the Vin pin (the input to the onboard 5V regulator), and the 5V pin (the output from the 5V regulator), swapping among them as they're connected and disconnected. Connecting an external 5V supply to the 5V pin keeps things working correctly.
Geosciences1 wrote:Is this ok for the Metro Mini though the USB port?
You can do that, but use a cable that plugs into the USB jack.

The idea there is that you have to unplug the 5V power cable to plug in a normal USB cable for programming. Connecting an external 5V power source to the USB pin on the side of the board could cause problems (and possibly damage) with the 5V supply in a computer's USB port.
Geosciences1 wrote:What is the maximum voltage allowed on USB port?
According to the USB spec, it's 5.15V.

We use 5.2V supplies to compensate for voltage loss through the cable, under load, etc. By the time the power actually gets to the ATmega328, it will probably be safely in the 4.85V to 5.15V spec range.

Locked
Please be positive and constructive with your questions and comments.

Return to “Metro, Metro Express, and Grand Central Boards”