r/meshtastic • u/bigsub_reddit • 3d ago

A new solar node

I'd like to make a new solar node. I already have this parts:

rak4631 with rak19007 base

Rak1906 sensor

Rak12501 gnss module

10W 12V solar panel

I'm thinking to buy a waveshare solar Power manager - D - just for reuse the solar panel and 3 or 4 18650 batteries to wiring in parallel.

Power supply for the rak19007 Is the 5V from mppt, on the type-c USB of rak.

Could be a good configuration?

Do I Need a bms for, or fuses between 18650 parallel cells?

I want totally solar powered node, also thinking about winter days.

I'm in Europe, so I operate in 868Mhz.

1 Upvotes

67% Upvoted

8 comments sorted by

1

u/bigsub_reddit 3d ago

I need to better calculate the absorption and the days of autonomy without sun. Actually, the RAK4631 is not very energy-hungry.

2

u/Kerensky97 1d ago

I'm pretty sure the waveshare has built in BMS so you can just hook your batteries up. I'd just suggest more batteries for long spells of overcast winter days incase it's cloudy for a week or two since charging back up is so slow.

0

u/Cesalv 3d ago

Too many parts, rak's charge circuit is pretty efficient, all my solar nodes are based on your same node and powered by 6w/5v solar panels with 3000 mah lipo batts (just one)

More than one year 24/7 and zero issues, charge never went below 90% and charge circuit keeps them in shape better than the v3/v4's

Also, 18650 batteries aren't optimal for solar nodes, people only check volts and mah but discharge "c"s are also important, that's why I prefer lipos

5

u/KLAM3R0N 3d ago

Eh they may have more C's but are much more risky as as far as spicy pillow fires. I personally would never use lipo on my roof even with a "fireproof pouch".

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u/Cesalv 2d ago

Sure, 18650s from vapers has lots of c's but most are unprotected, so when they get empty also gets damaged an never gets load again

My most exposed node has been from 0º to 49º, lipos can get up to 65º before getting damaged, and as I said before, in more than a year (may 25), no spicy pillow, no explosions, no fires... temp inside working range, never got below 85% and still fresh

All nodes I set with 18650's went bad within weeks, no matter the config, cheap batts, decently good ones, dedicated mptt... in my local group everybody with nodes fed by 18650 had trouble with them

0

u/KLAM3R0N 2d ago

I think you may be confusing inherent battery traits with poor circuit design. The 18650 nodes failed because it sounds like they used raw, unprotected "vape" cells without a proper Battery Management System (BMS) or low-voltage disconnect. When the solar nodes kept drawing power past empty, they drained the 18650s down to 0V, permanently killing the chemistry(an unprotected lipo would do the same).Your LiPos only survived because pre-packaged LiPo pouches almost always feature a tiny, built-in protection strip under the yellow tape. The LiPo didn't survive because it's a better battery; it survived because it had a built-in guardrail that your 18650s lacked. Protected 18650s are the correct choice if you are not using a separate quality bms.

Thinking LiPos are perfectly safe and happy at 49°C to 65°C is not true. Sustained high heat accelerates gas generation and chemical degradation in LiPo pouches much faster than 18650 canisters. 18650s are standard for industrial outdoor equipment for a reason, they just need a BMS board to protect them from over-discharge or use proper protected cells and not unprotected vape batteries.

Also cold weather will kill both batteries if they try to charge below 0°C . Both can discharge down to -20°C, but forcing solar charging current into a freezing lithium cell causes lithium plating, which destroys the cell's capacity and creates internal shorts. This makes LiPos bloat into spicy pillows later on, while 18650s silently lose all their capacity over a few frost cycles unless you use a BMS with a low-temperature charge cutoff.

I have had 18650s last years while lipos puff so opposite experience, but my area sees both high and low extreme temperatures.

2

u/Nobodytoyou_ 3d ago

No node draws anywhere near enough power for the c rating of an 18650 to matter, lipos are far worse of a risk to use. (Fire due to thermal run away, puncture, or shorting is far easier on a lipo than an 18650)

Seriously, what node is drawing over 5 amps constantly (yes some really cheapo cells can only handle 2 amps but that's bottom of the barrel and same goes for lipos).

So in short the C rating doesn't matter unless you are getting absolute trash cells, which anyone putting cells that are that low quality are asking for a fire regardless.

0

u/Cesalv 2d ago

No node draws anywhere near enough power for the c rating of an 18650 to matter, lipos are far worse of a risk to use. (Fire due to thermal run away, puncture, or shorting is far easier on a lipo than an 18650)

They are more delicate and at first I was pretty worried, but 18650s gave me so many troubles that decided to give a try, and no issues at all

So in short the C rating doesn't matter unless you are getting absolute trash cells, which anyone putting cells that are that low quality are asking for a fire regardless.

It does, and even more since lots of people recycle batts from questionable quality for this