How to run Micromod Teensy Processor board on Main Double Board on external power only?

When I connect a 6V external power supply to the V_BATT JST connector with no USB serial cable connected the Teensy will not start because there is no voltage on VIN (LED off). It can’t be reset/rebooted either.

If I now connect the USB cable (with external 6V power still connected at the JST) the VIN LED comes on, and teensy can be reset/rebooted and runs normally.

How can I run the micromod teensy with external power only (i.e. with no USB Serial connection) ?

In other words how to get voltage to VIN without Serial connection? (since the Teensy Processor depends on VIN)

VIN is tied to V_Batt https://cdn.sparkfun.com/assets/7/3/6/d … ematic.pdf

The absolute max for that circuit is 6v and you might be maxing it out, try using a regular 1 cell (4.2v max, 3.7v nominal) lipo and see how that goes

The power schema is described pretty well here

Also: what size is the lipo?

My new Sparkfun LiPo finally arrived, and it powers the boards no problem. The LiPo output voltage was about 3.9V under load, so I also tested using a 4V external power source and it also works fine .

In the meantime I had powered the board up using 5V with this USB-C Breakout and it works fine, although the 5V MEAS point was only 4.5V (on main double) so I upped the power to 5.5V and all works well.

I only just noticed the MEAS cut point on the Teensy processor schematic with this note: “Cut to separate VIN from VUSB to measure current or if using battery or external power”. So I cut it and repeated all the testing above, but it made no difference at all. Maybe that was why 6V input didn’t work? Will test that later.