Powering Moteino via Buck Regulators

[tleavitt]

I have two moteinos out in the field powered by 12v lead acid batteries with solar chargers. For the last several months I have been powering the moteinos by stepping the 12v down to 5v with another MCP1703 in an SOT-223 package, but recently it seems they have degraded to the point where those regulators are no longer supplying a clean 5v causing the regulator on the moteino to either drop out or overheat thus causing the moteino to reset about 1-2 times a second. The moteino does have a pretty good load on it with a RFM69HCW transceiver to power and a 20mA LED on one pin. I know the regulator on the moteino itself is not capable of stepping down much of a voltage differential with the load it has thus the secondary regulator.
I'm guessing the larger MCP1703 has probably gotten heat damage from dropping 7v at a peak of ~200mA, but I'm not sure. Either way, it's making my moteino reset. Because of this I'm looking at replacing the MCP1703 with a buck converter to drop the battery's 12v down to something more suitable for the moteino. I have a couple of questions though, should I continue to regulate down to 5V and feed that to the VIN pin or could I skip the moteinos regulator and buck down to 3.3v directly? Also, does anyone have any recommendations for a buck converter that can handle minimum loads of around 10mA?

[Felix]

I stock these Murata buck regulators for various projects including rectifying from transformers (12VAC and such):
https://lowpowerlab.com/shop/product/133
Haven't tested it in the sun 
They are a nice SIP package and breadboard compatible.

[tleavitt]

I stock these Murata buck regulators for various projects including rectifying from transformers (12VAC and such):
https://lowpowerlab.com/shop/product/133
Haven't tested it in the sun 
They are a nice SIP package and breadboard compatible.

Ill take a look at the datasheet!
The moteinos arent in the sun themselves, they are in junction box to shield them from the elements.
What about bucking directly to 3.3V rather than bucking to ~5V and feeding that to VIN?

[Felix]

Try it.

[tleavitt]

Buck regulators should be here tomorrow. Did some number crunching and decided to just go with 5V regulators and let the moteinos LDO handle the rest. Turns out bucking to 3.3V is only ~1% more efficient than going through the LDO so I didn't see any need to test that for such little returns.

[TomWS]

Buck regulators should be here tomorrow. Did some number crunching and decided to just go with 5V regulators and let the moteinos LDO handle the rest. Turns out bucking to 3.3V is only ~1% more efficient than going through the LDO so I didn't see any need to test that for such little returns.

I'm not sure how you arrive at "only 1% more efficient" but either approach will be significantly more efficient than straight linear conversion from 12V to 3.3V.  However, unless you're running the processor and radio constantly, the LDO is more than capable of managing the load, even with a 12V supply.

[tleavitt]

I'm not sure how you arrive at "only 1% more efficient" but either approach will be significantly more efficient than straight linear conversion from 12V to 3.3V.  However, unless you're running the processor and radio constantly, the LDO is more than capable of managing the load, even with a 12V supply.

Tom, the difference was between a 5V SMPS fed to VIN on the moteino and a 3.3V SMPS fed to the 3V3 pin on the moteino