Heltec V3 LoRa 32 trying to power with 9V battery

#1

I purchased 2 Heltec V3 LoRa 32. I have successfully installed the software and uploaded a basic Arduino program. When powered with the computer USB everything works fine.

I tried to build a voltage regulator circuit where I use a rechargeable 9V battery as the input power. The circuit looks like the following:
Circuit%201

The diagram above is found here:
https://electronics.stackexchange.com/questions/148340/how-to-protect-lm317-from-output-short

The completed circuit I built outputs 3.7V. When connected to the circuit through the battery connector the Heltec display keeps blinking and the program does not load. If I go back to using the computer USB the program loads again, no problem.

Maybe there is something in the circuitry that doesn’t like this type of power source? The blinking display is the only clue I have. Any troubleshooting ideas would be appreciated.

#2

A rechargeable 9V PP3 style battery has very little capacity compared with almost anything else, even most coin cells. In theory they can deliver 300mA as a normal peak but in practise they just aren’t designed for this sort of application - you’d probably run the battery down in just a few hours.

And the LM317 is not particularly efficient either and only needs the diodes if it’s being protected against larger output voltages &/or larger capacitors than normal use.

The V3’s have a battery charger circuit on them - why not use a LiPo and charge them via USB?

The board also has a voltage regulator on-board that can cope, in theory, with up to 8V - so even 3 x AAA rechargeable would power the board on the 5V pin, better with 4 of them - and give you about twice the runtime. AA’s would give you about 5-7x more. YMMV!

#3

I lowered the circuit voltage to 3.35 V. Before powering it “on” I placed a meter in series with the positive output to check the amp draw. When it is powered on it draws a maximum of 100 mA.

When powered from this circuit all the Heltec does is blink the display with the words “Heltec” showing. The amps drop a little while it blinks.

This whole point of powering the Heltec this way is because I do not have the recommended rechargeable battery. In the meantime, I wanted to get away from the USB and set at least one of them in a seperate location while continuing to experiment. The parts to build this little circuit were already at hand.

I am missing something obvious? It is a two wire battery connector. The Heltec shouldn’t care what the source of the power is as long as it is usable - right?

#4

Found what I was missing - these darn things are sensitive to the power source:

I will not waste anymore time with homemade power supplies for the Heltecs.