Powering the Ultimaker by just the 19V main supply.

[Daid 287]

Now that I have an SD card option, with LCD panel I'm looking into just powering the whole machine from the wall connection.

Now, with 1.5.6 electronics, you have the ARD_PWR jumper which powers the Arduino from the 19V wall supply. But I have 1.5.4 electronics, so I would need to fix that myself. And I see two posibilities. I can connect the "Vin" pin to the 19V main supply, which is within the 6-20V supply range for the Arduino. However, Arduino does not recommend to power it above 12V. So I can also connect it to the 12V regulated power used for the fan. But then we have a regulator regulating a regulator, which sounds like a bad idea.

Next, when making this VIN connection, we have the "fan powered by USB" problem. And general machine power by USB, which I never really liked. Which I think that can be solved by removing the MOSFET T1 from the Arduino Mega2560 Rev3.

As anyone attempted anything like this?

[jelleatprotospace 0]

Why would making 5V from 12V be a problem? So why would it be a problem when linear regulators are used? A simple connection from the 12V regulator output to Vin on the main board suffices.

No fans turning when you connect the USB, nor is it trying to power a 40Watt machine from a 2.5Watt connection.

[Daid 287]

Well, I connected the 19V to the Vin a few days back, and that seems to work fine. The problem with connecting to the 12V side of the linear regulator is that the regulators are not designed for that, and you leak 5V to the 12V fan, which might turn then.

I've moved my machine and I'm now unable to test with USB right now. (but the noise is gone from my living room )

[jelleatprotospace 0]

19V may heat up the regulator a little too much, as it needs to dissipate 14V*0.xxx (arduino current), which will quickly approach >1Watt. If you connect to the 12V output, the load will be spread over two regulators, with the largest load (the 7812) getting some cooling air from the fan (if you trim the airduct)

I do not understand 'leaking 5V to the 12V fan'. Does a voltage on the output side turn up at the input side of the regulator when it is not powered? And how much current will it pass then?

[Daid 287]

The 5V USB leaks to the Vin when you only have USB connected. That's the "leak" I mention.

The Arduino Mega uses about 60mA, so it's burning about 0.84W, I haven't looked into the terminal specs of the regulator chip to see what's possible.