Heltec T114 solar charge issue

#1

I’m having trouble getting a 3.7v LiPo battery to charge on a solar powered Meshtastic node.
When I replaced the 5W 5v solar panel with an adjustable power supply I discovered the charge rate dropped to almost zero at 5.0 volts input.
The orange LED would light but no useful charging would happen until I raised the voltage to 5.1 volts.
My two RAK nodes don’t appear to have this behavior.

#2

For what it’s worth, the recommended solar panel voltage on other Heltec boards, the CubeCell for example, is 5.5-7V.

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#3

Thanks for the input. The 5W solar panel I’m using is designed for USB voltage (~5.1V).
The LGS4056H datasheets are all in Chinese, so I am unable to look for a modification to the charge controller.

#4

If they are “designed” for USB voltage that means you’ve got something in the way converting the output to 5.1V - usually a small white plastic box with a USB type A. Some surgery will be required to remove it and have a direct connection.

#5

We can’t run a direct connection as there is an upper input limit of 7 volts. Most of these panels can do twice that unregulated.
On the panels I’m using the regulator is in the plastic welded case and I don’t want to lose the water tight integrity.
I’ll probably have to source another unregulated 5W panel and add the buck circuitry or linear regulator.

#6

And you may well be back in the same place with far less efficient as they won’t be able to optimise the voltage / current balance.

Read up on solar - most panels on a multimeter give out much larger than advertised voltages - its the voltage under a load that counts - many of us use off-the-shelf panels that are advertised as 5V, 5.5V or 6V - as long as under reasonable sunshine they can deliver over 4V, the 4056 chip will do fine.

#7

“as long as under reasonable sunshine they can deliver over 4V, the 4056 chip will do fine.”
The delta V will increase as the battery level drops - I’m hoping that I will simply have to live with less than 100% charge.
Time will tell - stay tuned.

#8

Fully charged LiPo to 4.2V = 200 to 300 cycles, NASA charged LiPo to 3.9V = +1000 cycles, YMMV, sure, only 80% capacity but so much longer lifespan - just size up the LiPo a little bit.