LoRa 32 V4.2 - battery charge Issue

#1

I’m using a LoRa 32 V4.2 board with an 18650 battery connected to the BAT connector.

Is there an alternative input to the USB-C port that I can use to supply 5V and charge the battery, such as the 5V or Ve pin?

#2

If you check the schematic you will see that the 5V pin connects immediately after the fuse in the USB circuit and so can be used, from a power perspective, just like the USB port (but without the fuse or ESD protection diode).

I have powered my WiFi LoRa 32 boards from both an external 5V supply and a 5V or 6V solar panel connected through the 5V pin. Both will charge the battery. In each case, I include a 1N5819 reverse current protection diode and in the case of the 5V supply, I also include a 0.5 or 1A 6V fuse and RSB6.8S ESD protection diode, the same as is provided by the onboard circuitry for the USB connection.

The Ve pins connect into the power supply system after a 3.3V rectifier, so any input provided there should only be rectified 3.3V.

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#3

The v4 has one on the board after the 5V pin, so that’s sorted!

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#4

But not between the USB input and the 5V input… although I do accept that, while possible, I would be very unlikely to be using either a solar panel or external power source, which in my case is always a an ‘external’ USB connection anyway, at the same time as taking power through the onboard USB socket.

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#5

So many combos, so many ways to releasing the magic smoke.

Been powering a couple of v3’s at the end of a 12V solar system, dropping to 4V with a generic LM2596 buck module before passing it in via the battery connector.

The boards are fine. But the buck module failed after multiple disconnects, most likely due to the inductive spikes in the 5m cable. So I’ll be fitting some suppression, in a trying to prove a negative style result.

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#6

Thanks for your thoughts, @UniquePete and @nmcc!

To be honest, I’ve already been powering Ve with 5V for a while, and the V4.2 board seems to have handled it just fine — at least there’s been no black smoke so far. That was actually based on advice from ChatGPT.

I’ll try feeding 5V into the 5V pin instead and see whether the battery starts charging.

#7

I’m not very experienced at reading electronic schematics, so I’d appreciate a quick sanity check — am I interpreting this correctly?
1. According to the schematic, JP4 pin 2 (VUSB) appears to correspond to the pin labeled “5V” on the board. In the schematic (upper left corner), VUSB looks properly protected.
2. JP4 pins 3 and 4 are labeled Vext (called “Ve” on the board). This pin sits right next to the 5V pin, and that’s where I injected 5V. However, in the schematic I can only find Vext in the 3.3V power path. So now I’m wondering: isn’t Vext actually part of the 5V domain (VDD 5V), or am I misunderstanding how it’s routed?

#8

Surprised this didn’t release any magic smoke - luckily the core components aren’t connected to what is the auxiliary power under programmer control. However I’ve no idea how this managed to power the board - unless it’s blown a path through the voltage regulator to the 5V line.

You can only find Vext in the 3.3V power path … :thinking:

There isn’t a connection in the schematic that links the Vext to 5V apart from where a chip marked CE6260B33M is in the way, has 5V on IN and OUT is Vext. Ms Google provides lots of info on the chip and the 33 bit may be a giveaway.

In summary, 5V in on the 5V pin and you may, with luck, still be able to turn the Vext on & off under program control, which is used to power the OLED.

#9

I’m with @nmcc on that one. I would always have maintained that Vext was ‘output only’ and I cannot for the life of me see how you could power the board through Vext. But this wouldn’t be the first time that some important [with respect to understanding what was going on] ‘detail’ was missing from the Heltec documentation…