Arduino Pro Mini 12V to RAW and additional 5V power supply

Projects General Guidance
1

I am new in Arduino.
I am developping a project with Arduino Pro Mini.
I read that Vcc max output to power the 5V peripherals is limited to 200mmA.
This is not enough for my project.
I plan to power Arduino through RAW pin from a 12V external PSU.
I thought I might add a DC-DC converter from 12V to 5 to have more power for my project,
Now actually I will have 3 power supplies. The 12V, the Vcc output of Arduino and the +5V output from the DC-DC converter.
I suppose we will have common ground to all three power supplies.
Is this possible?

For example I want to power an SSR module (which draws 120mA and drains Arduino).
Is it possible to connect the supply line (+5V) on the module from the outut of the DC-DC converter and have the signal coming out from the arduino directly?

2

Even 200mA may be too much. The linear regulator on a Pro Mini can overheat easily.

If you have a 12V to 5V "buck" converter, you don't need to use the Vin pin on the Pro Mini. Power the Arduino directly using the 5V pin.
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You must have a common ground!

That sounds strange. SSR should not draw much current at all. Please post a link to that. A mechanical relay might draw that much.

3

Thanks!

As much as I understand, by powering Arduino from the "buck" converter I can use the same source of power for the peripherals too. If I understood correctly, this will solve all my power issues by solving a suitable "buck" converter.

I was just a little supsicious, if voltage quality from the "buck" converter is according to the specifications of a stabilized voltage needed for the Vin.

I have Relay (for regulating a DC fan at 12V) and an SSR for a thermal load at 220V.

Maybe you are correct. The stated load consumption of 120mA at the SSR module specs was referring a consumption of the output load.

4

You would not connect the buck converter to Vin. You would connect it to the 5V pin.

You cannot "regulate" a fan with a relay, if you mean control the fan speed.

A 12V fan can be controlled with a MOSFET, including its speed. This will require almost zero current at 5V. Maybe you don't need the buck converter after all. If the Pro Mini powers only the SSR and a MOSFET, the built-in linear regulator should be ok.

5

Most likely better than using "Vin", certainly because of the lack of heatsinking on the on-board regulator.

The "take-home message" is - just forget that the "Vin" pin - or the "barrel jack" on a UNO - even exists. :grin:

6

for the FAN, no, I will not regulate speed. Just on-off.

7

My mistake. Vin is not present on mini pro. I meant Vcc.

I suppose @PaulRB that by 5V pin you also mean the Vcc.

8

Even so, using a MOSFET will require far less current from the 5V supply than a relay. A relay will consume perhaps 50~100mA for the whole time that the relay is as activated. A MOSFET will require practically zero current, making powering the Arduino with 12V to its Vin pin a possibility, provided nothing else is drawing more than a few mA from the 5V pin.

If you must use a relay, use a 12V relay, not a 5V relay. 12V relays can be activated by a 5V signal from the Arduino, but draw current directly from the 12V supply to power their coils.

9


"Vin" (UNO, Nano) = "Raw"
"5V" (UNO, Nano) = "Vcc"

"Raw" pin = mostly useless. Do not use it, forget it ever existed. :roll_eyes:

10

ok!

Thank you all very very much!

11

No.
If you drain 200ma from an arduino pin, you can damage it.
see the recommendation table. (For all arduino with ATMEGA328).

ArduinoPinCurrentLimits
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