I always thought that would be too small of a battery and not enough solar power?
I currently have a Heltec 32 V3 that is plugged into a security camera solar panel with a cold weather 18650. Has been running non stop since December. Itās in Router mode and I can send reboot commands to it if things get a little strange. At one point the battery finally died (5 days snow covered panel). I think it was -22F. After the sun came out again 5 days later it kicked back on as the solar panel only will output 5v if it can hold it consistently for 10 seconds or so it seems. This kicked the unit back on and has been running since. So maybe one of those panels would be good to use on a RAK4631? I have a wisblock setup with the unify case I have been testing and it seems as long as the panel gets direct sunlight for 4 hours a day it will maintain in router mode with sending node info and environmental telemetry every hour from the BME680. Which is nice for case temperature monitoring and if something let the magic smoke out and it happens to report the air resistance will skyrocket. Iāve got this sitting next to my weather station that collects solar radiation per square meter. Iāll send the snapshot of this if anyone is curious what kind of consistent sunlight is needed to keep these things up and running with the small panel in the unify enclosure with a 3000mah lipo.
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Correct, Iām not using as a permanent router setup. Using as a base station mounted on a tripod or tree with a telescopic pole when camping, hiking, hunting, etc. When there is no cell/mobile coverage. The unit will charge in the full sun, Australian weather generally favoring solar power.
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I had the same problem with the RAK and the T-Beams.
Iām put a voltage supervisor to monitor the battery. When it dropped below a predetermined voltage (in my case 5.75VDC (Iām using a 6 colt motorcycle battery)) it would disconnect the battery and remain that way until it rose above a certain voltage (ie the solar panel charged the battery, in my case that is 6.25VDC (fully charged battery is 7.2VDC)) and then do a power up. Has never failed to bring the node back up.
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I have a question in regard to RAK4631 on solar. Iāve been running one on a 5V 150mA and it barely keeps it going. We had a bad July which killed it. Iām ordering a slightly larger 250mA panelā¦butā¦I came across a comment where somebody stated that they think the panel needs a blocking diode. Has anybody looked at this? I may delve deeper and see if I can determine leakage (somehow).
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Hello John,
do you have some new information for us, about that problem?
tnx
You need to have the right rise in order or an nrf chip to start back up. This is the way the nrf52 works. Running batteries flat is a really bad idea, much better off sizing up your panel.
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Iām looking into this in other ways-like a plugin board that cuts out at 2.5v and comes back instantly to present a rise time to the NRF thats livable.
Is it thought the slow solar rise time is causing the POR not to fire? That seems to be the general consense based on my reading so far.
This hardly ever happens unless you are using a real small panel, pretty much a non issue at this point.
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Let me see if my rigs do this again - I am using 2 60ma panels in parallel for a 120ma panel throw weight.
My battery has a 2.4V overdischarge protection board - I wonder if its possible to have a shutdown occur on the CPU at 2.3V so it always triggers that board and then when solar comes back it might boot properly.
A workaround that will certainly work is to route the battery power through a normally closed relay that regularly cuts the power, like every morning at 3:00 - this can be achieved by an RTC chip like the PCF85263A from NXP which has programmable alarms. Restarting every night like that of course might incur a bit more power consumption. But once a week would be enough, since if the battery has been all emptied it makes sense to give it some time to recharge.
Another possibility is:
Using some discrete logic to check whether the RAK module is in reset and if it is trigger a power cycle using an LDR connected to a Schmitt-Trigger which trips every morning when the sun comes out, especially if it comes out in force.
EDIT1:
Ackshually, my ideas are really retarded, user āDrumā up there had the correct idea. Although, i wouldnāt know how to implement it without adding my own solar charger IC.
EDIT2:
I figured it out! This C12 here is connected to the ENABLE pin on U3 which generates the 3.3v rail from the VBUS. BTW, there is not even a solar charger IC on the baseboard, there are only schottky diodes from VUSB, VSolar and some other power input going to VBUS. So all thatās needed is a comparator that pulls down that pin. I will come up with something like that.
EDIT3:
source: RAK19007 WisBlock Base Board 2nd Gen Datasheet | RAKwireless Documentation Center
EDIT4:
So, no, itās not that easy: VBAT also goes directly to the RAK4631 module, not just the regulated 3.3v.
EDIT5:
New idea! And I think this one will work: I can put a voltage monitor on the solar-panel input. This way when the sun rises the input voltage will be held back until it is not - and then it rises suddenly, causing a clean reset and causes the RAK4631 to start up. Ha, I really think this is it!
EDIT6:
See, I am actually measuring stuff, not just guessing:
EDIT7:
This should work and is fairly easy to build:
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Solar panel max voltage question. The RAK module requires a 5v panel, however the max voltage these panels can be higher. Iāve just received some larger panels to keep the node alive (hopefully) in the darker days. In full sun Iāve measured over 6v, even on the smaller panels. I think this is normal but just checking its ok for the RAK4631?
you can count the cells in the solar panel.
Rak Wireless sells and uses 10-cell Panels for these devices.
so maybe 11-cell would still be ok, if not too much current.
but dont use 12+ cell devices.
The current RAK19007 base board can handle 6v, whereas the previous EOL RAK5005-O can only handle 5v max.
Thanks, Iāll check my base model. The ones on the mountains have panels that can touch 6v and havenāt blown up so hereās hoping.
I did the PCB design for my idea undervoltage lockout circuit from further up the thread.
Now, i just have to build and test it.
If it works then this would enable solar repeaters with just a single pouch cell, that might go offline for some days during the very darkest weeks of the year and then spring back into action as soon as the sun comes back.
PS: this really would not have been necessary if the guys at RAK had done a better job with the RAK19007.
Eventually there will need to be a dedicated RAK4630 based solar router board that implements this silly workaround.
EDIT1: it is actually happening:
next up soldering and testingā¦
EDIT2:
All soldered up and testing now. ATM it is wired up with a purposely undersized battery so testing takes less time.
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Are you charging via usb or the dedicated solar port? Im wondering if there are any downsides to using solar on the usb eg solar getting less than 3.3v or leaking at night??
I did implement your idea, because I had time. I used a voltage supervisor chip connected to an n-channel FET wich is acting as a low side switch. It is in test now.
BTW,
I found a very significant design fault in the RAK19007. They connected the p-channel high-side switch the wrong way. If they really made the board according to the published schematic this means that we always loose 0.6 volts of battery power. I will check later, maybe they just drew the schematic wrong.
EDIT: I was just plain wrong, see post below by @DirkH.
As long as VBUS_D is low the p-channel MOSFET will turn on an the voltage drop is Rdson x I.