Power for Mega256

Hello all. This is probably a simple one but I just can’t find something suitable.

I’m currently moving to the next step of my prototype and ideally want to power it all from one source (a 230v plug from mains).

The power setup will be as follows:

  • 230VAC in
  • Splits to
    —24VDC power supply which provide power to the LED tapes I’m controlling.
    — 2 x 230VAC relay power outputs.

Currently I’m powering the Arduino with a separate 7.5v power adaptor plug.

I’m looking for a small board/supply I can fit in the box that can provide 7.5v 2a supply for the Arduino from either the 230VAC supply (preferred) or 24VDC supply.

Requirements are as small as possible and the least heat generated as possible (I know it’s not going to be eliminated completely)

I’m based in the UK if that makes any difference.

Electrical safety is probably what makes those mains voltage to DC voltage 'converters' bulky.

If you have a 24 DC power source, then just look for DC to DC buck (step down) converter power supply boards.

You mentioned 'as small as possible' - which is sort of open ended. It's best to provide some rough dimension details.

Thanks Southpark.

Yes that was my thoughts exactly. I will have a look around but I was struggling to find 24v to 7.5v step downs. They were all 12->7.5 or 5. I’ll keep looking.

As far as size is concerned I don’t have the final enclosure yet so I have some flexibility. But just as small as they come would be useful. The 300W 24v power supply I have is already bulky enough.

You are better off if you can find a stepdown (DC DC converter) to 5V. Then connect the DC DC converter to the 5V pin. That bypasses the weak on board 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. Powering through the 5V pin with a DC DC converter means that the rated current of the DC DC converter is available on the 5V line.

reptileelectronics:
Thanks Southpark.

Yes that was my thoughts exactly. I will have a look around but I was struggling to find 24v to 7.5v step downs. They were all 12->7.5 or 5. I’ll keep looking.

Surely the universally available cheap adjustable LM2596 modules will do this easily?

reptileelectronics:
Thanks Southpark.

Yes that was my thoughts exactly. I will have a look around but I was struggling to find 24v to 7.5v step downs. They were all 12->7.5 or 5. I’ll keep looking.

If your goal is to minimise heat 7.5V is a bad idea anyway. The board has a linear regulator which will waste a significant portion of the supplied power and this is converted to heat in your enclosure (though it should be noted the total power draw of the Arduino is likely much less than your switchmode 24VDC will dissipate anyway).

With the Mega2560 running a simple LED blink script I measured 85.3mA at 7.5VDC (0.64W). At 5VDC it used only 78.5mA (0.39W).

Here's a couple of 24/5VDC options I found in the UK (not specifically endorsing these products, just the cheapest ones I found with a quick search)