Odd power issue

[vunderbob]

I have a weather observatory I homebrewed using an Uno, Sparkfun Wifi shield, and Switchdoc Labs Weather Board. It's powered by a 12v 1a wall wart, with no custom modifications.

The problem is that when I try to run from just the wall wart, all looks good for about a minute, then over about a 15 sec timeframe, the visible LEDs fade as though there is not enough supplied current.

This condition DOES NOT happen when the USB programming tether is plugged in additionally, running from USB solely, or I am running from an external battery via USB.

The observatory should be drawings about 300 mA, well within the 1A capacity of the wall wart. I have extra Unos and warts, this happens for new and old parts.

Any ideas on what is happening?

[JBBOP]

I'd love to see the schematics.

[J-M-L]

The max current you can push through your board depends on the heat dissipation in the voltage regulator you have. (it's thermally limited, meaning that as you draw power, the regulator will heat up and when it overheats, it will shut down temporarily)

if you provide 12V to your UNO, it must burn the unused power ➜ (12V - 5.7V) x current
how much current do you consume on the UNO?

[dlloyd]

Uh-oh ... might be an unregulated 12V wal wart which would output 16V no-load causing thermal shutdown. Got a multimeter and/or link to your wal wart?

[vunderbob]

I don't have a schematic for this iteration because the Wifi shield encaspulates the ESP I use. I originally had a breadboard set up to handle a -01s.

Enclosed are a couple of closeups of my hardware.

Uno with Wifi shield and screw terminals.

[vunderbob]

Weather board...

[vunderbob]

Here is the label on the critter.

[jremington]

Almost certainly, the regulator is overheating and shutting down.

Power the project with a regulated 5V supply, via the "5V" pins.

[vunderbob]

The thing is the wall wart is not the final supply I intend to use. The observatory will be in a remote location in my yard, and will be run from a 6V solar charged AGM battery (and the Wifi).

I have a bitty cooling fan I can set up to blow air under the shield, so I'll try that.

[ShermanP]

The power options that work all bypass the Uno's 5V regulator. The one option that doesn't work goes through the regulator. The most likely explanation is that the great amount of heat dissipated by the drop from 12V to 5V, at high current, is causing the regulator to overheat, and it probably has a thermal shutdown function that reduces output current when it gets hot. If that's the problem, then you would need to use a much lower voltage brick, such as 7V, or use a 5V brick which would connect directly to the 5V pin of the Uno. I don't think a fan is going to do much good.

[vunderbob]

The wall wart I am using at the moment is what I have on hand, not my final design. That will be a 6V AGM battery connected to a solar charger. I have a new desktop supply that has selectable output voltage on order to use at my desk; 6 or 7.5V is my intended setting.

[J-M-L]

Explore a lower voltage and see what happens

[madmark2150]

The onboard voltage reg is overheating. Reduce your supply voltage to 9 or less or connect hard +5 to the +5 pin directly.

[vunderbob]

I have a dual set buck converter on order for my final install, as well as a settable wall wart for use on my development desk.