Moteino M0 - Remove charge controller?

[adam.g]

Hi there,

I was curious, would it be possible to remove the MCP73831 charge controller on the Moteino M0 in order to allow a higher voltage battery to power the board? I don't actually have a need for the charge controller and was hoping to be able to use a 7.4V or 11.1V battery. The MCP1703 LDO can handle 2.7 to 16.0 V, but the charge controller tops out at 6V. Looking at the schematic it appears that I'd also need to disconnect the voltage divider on A5 so as to not expose the pin to greater than 3.3V (I imagine I could make it a 1M/10M ratio to keep the voltage within range).

Would appreciate any feedback!

Cheers,
Adam

[Felix]

Yup, if you are brave enough to try this, go ahead, it should work.
The only reason for the 6V max input is the charger MCP73831.
In fact if you're careful, you could just lift the VBAT leg from the trace on the board, and leave the rest of the charger in place - this still assumes VUSB never exceeds 6V (USB power).
Then VBAT only goes to the LDO and you're OK. The VMON divider should also be changed as you already noticed.



Someone else asked about this, and maybe a jumper would help for this purpose but the only room for that would be on the bottom, not sure I want to route VBAT through 2 extra vias.

[adam.g]

Thanks Felix!

I just picked up a hot air rework station and have been having fun removing surface mount components from the various damaged components I had laying around.

Could you tell me the size of the SMT resistors on the Moteino M0 (e.g. 0603/0805)?

Cheers,
Adam

[Felix]

All resistors are 0603.

As a good practice with hot air - you need to protect the connectors/button/LEDs and non serviced components in general with a piece of sheet metal - I like soda can aluminum since it's easily bendable and has enough thermal mass. Tinfoil as a last resort. Stencil scraps also work well.
This is to draw heat away and prevent them from melting.

[mantonakakis]

Yup, if you are brave enough to try this, go ahead, it should work.
The only reason for the 6V max input is the charger MCP73831.
In fact if you're careful, you could just lift the VBAT leg from the trace on the board, and leave the rest of the charger in place - this still assumes VUSB never exceeds 6V (USB power).
Then VBAT only goes to the LDO and you're OK. The VMON divider should also be changed as you already noticed.



Someone else asked about this, and maybe a jumper would help for this purpose but the only room for that would be on the bottom, not sure I want to route VBAT through 2 extra vias.

I'm been having some issue with this - is Q1 able to handle ~12V? Sometimes it works when I use ~12v to battery JST with the charge controller disabled by cutting the trace to pin 3 of the MCP73831, but other times Q1 ends up getting fried and shorts from drain to gate (or VBAT to VUSB). Something else could be going on I suppose, but I wasn't able to find any info on Q1.

[Felix]

Unfortunately I just cant process all the mods that people have in mind. The board is designed to take a 3.7V lipo.
I cant really predict how things will fail and how to fix, undo, properly mod, etc, when higher VINs are connected when 6V max is expected on on the VIN pin.
There is the schematic for reference and any mods and hacks, cut traces and things like that are not endorsed or supported. You might render the board useless.

As a rule of thumb, it is very uncommon and not recommended to supply low power electronics from anything over 5-6V or so. 9V batteries are small capacity and will waste lots of that energy when fed into an LDO, 12v, 15v, 24v situations should be regulated with an external efficient DC/DC regulator, rather than try to feed that into a small linear regulator that is most efficient at around 4V anyway.

[mantonakakis]

I understand, in my situation I'm hoping to use a 3.6v lithium thionyl chloride battery that will also power another peripheral. It's for outdoor usage, so temperatures may drop significantly and battery voltage may drop significantly below 3.3v (and the peripheral requires 4.5v for its power supply circuitry). So a single cell won't do it, and 2 cells will bring me to 7.2v nominal, so a little too high for the charge circuit on Moteino M0.

I wasn't able to find any specs on Q1, hence the question. Since my last post, I realized a 2-cell setup would work. I also may have shorted or miswired something - it was a little strange the way it failed (it was working pretty well for a little while, then after one of the power cycles *poof* I saw current increase drastically and after that Q1 was broken).

Also since the last post I did a little more experimenting and removed Q1, and put the battery straight to the LDO, and it's working well now - I did have to add a switch to the Schottky jumper pads to be able to power via USB for flashing new code (not brave enough to try simultaneously connecting USB and battery).