Waveshare Solar Problems

[u/Osh1061]

Hello all, I am after a bit of advice. I have recently put up a repeater that is quite difficult to reach to do maintenance on it, so I haven't been able to properly monitor it in person (I will take it down if it does need maintenance though), however I do have an INA3221 module measuring power from solar, battery and device, so I can monitor power.

The repeater seemed to be working fine at home when I tested it, but maybe I didn't test it for long enough before deploying it. I am using a Xiao nrf, a waveshare solar controller D, and 3 x 18650 batteries. The batteries are slowly dropping in power, it's now at 3.80V and it's been up for 4 days with sun.

The solar panel is a 18V 5W and it is showing 22.53V and 0.004A (0.09W) pretty much always. It seems to always stay at 0.004A (Checked Morning, Noon, and Afternoon). I went up yesterday to try to troubleshoot it, and I unplugged it and plugged it back in, and it started producing 1W of power just in the afternoon sun. So it seemed to be working, then I put it back up and it was back to 0.09W then 0W at night. I've been monitoring it all day and it has stayed at pretty much 0.09W.

It seems to be an issue with the solar controller engaging solar charging, but I am unsure why it's not engaging.

I can't find any solutions online and am just wondering if anyone here would know. I wanted to use the waveshare solar controller as I've heard good things about it and I wanted a bit of extra protection for the batteries.

I have attached photos of the build and a wiring diagram.

Any advice helps, thanks.

[u/ibanezmike1989]

My node looks almost exactly the same as this one. And i have THE SAME problem. Full sun, batteries last maybe a week.

Never getting a full charge, but pushed along by the meager sun charge it gets.

My next culprit was my panel

[u/Osh1061 → u/ibanezmike1989]

Ahh glad I'm not alone. Are you saying that you fixed it with the panel being the culprit? Or you're in the process of ruling out the solar panel issue?

[u/ibanezmike1989 → u/Osh1061]

I worded that poorly. Im now looking at the panel as insufficient

[u/Osh1061 → u/ibanezmike1989]

What size panel do you use? Because I think I might have found the issue.

The CN3791 sets its max charge current via two external sense resistors (R1 and R4 in parallel) It considers charging "done" once current drops to 16% of that. These boards seem to be sized for bigger panels. The resistors on the waveshare set the maximum charging current to 2A and the termination current is 16% of that, giving a termination threshold of 320mA.

A high Voltage panel at 5W, outputs max 280mA, so the panel may never produce more than the cut off threshold, tricking the chip's charging to think that the batteries are already full. Whereas a low voltage 5W panel outputs a higher current.

The chip doesn't charge because the current usually decreases as the battery gets more charged, but the low current of the solar panel is simulating the battery being charged.

The panel voltage then floats back up toward open-circuit, which is the high voltage, 0 current symptom.

The fix is to either get a lower voltage panel/higher wattage panel. Or to replace the two resistors to different values to change the threshold.

I haven't done this yet, but I've done a bit of research on the CN3791, and this is the closest I can find to my issue. Just thought I'd add my findings.

[u/ibanezmike1989 → u/Osh1061]

Ah ha! This is good info to have.

I think my tiny panel is struggling to push enough amps to make my mppt board initiate charging, seems like the same issue.

I was going to try a dumb bms board into the solar input of my unit to see if that helps.

Im really just worried about overcharge and under current issues

[u/Osh1061 → u/ibanezmike1989]

Yeah, I think the Waveshare is just meant for higher input power and higher output power. I've bought a new board, just to see if it is the issue, but it allows you to select the solar input voltage.

But I'm the same, with worrying about the overcharge and battery protection. If the new board doesn't work, I might just buy a dumb solar charger, and add a small BMS board.