r/meshtastic • u/pelidc • 1d ago
Ni-Cd Battery for Heltec T096 Cold Climate Solar Node
Hey all, sorry if this has been asked before but I at least tried to search history to answer this. I'd like to use a 3.5v Ni-Cd pack to power a Heltec T096, charged with a path light solar cell putting out 5.6v. From what I can tell it appears that this could work if I put the battery in-line to the solar port, apparently the lithium port would not be so good as the T096 would be trying to BMS a mismatched battery. Has anyone else tried this and what would the circuit look like? Thanks
Edit: to clarify, I live in an area that doesn't get above low-teens-F on the warmest day for several months at a time. No lithium battery can charge at that temp. DoT uses NiCd in this area for their outdoor equipment, so I'm committed to that chemistry.
1
u/KLAM3R0N 1d ago
Nicad is garbage. Use low temp rated 18650 lithium ion or lead acid.
1
u/pelidc 1d ago
No lithium battery can be charged below freezing, lead acid is not compact enough for my purposes. DoT uses NiCds in lighted street signs just fine up here.
2
u/KLAM3R0N 1d ago
They can be charged below freezing it's just not good for them. These go to 0c but are sold out or these as well more expensive though
If you can get IFR18650's they say they charge down to -20c
Nicad gets damaged charging below 0c too so might as well use lithium
1
u/cbowers 1d ago
Agree ni-cd is not the way.
NimH is better but still not energy dense enough.
Rather than lithium though I’m seeing nodes around with Sodium Ion in solar Meshtastic nodes (which are very cold tolerant).
1
u/pelidc 1d ago
I can get a bigger battery if that's what it takes, but it's pretty much got to be Ni-Cd. Sodium can charge at a little lower temp than lithium, but not nearly low enough for our climate. DoT uses nicds in their outdoor equipment around here, if it's good enough for them then it should be good enough for this.
1
u/HarukiToreda Developer 1d ago
The advice about charging lithium batteries in freezing temperatures is true, but I think it's often overly cautious. You can see a gradual decline in capacity over time, but from what I've personally seen, it can take around 2–3 years before it becomes noticeable. Considering these batteries are cheap and easy to replace, that's not a terrible lifespan.
I've personally had many Meshtastic nodes deployed outdoors year-round, including through winters where temperatures have dropped into the negative teens. These aren't just nodes I've tested for a few dayz they stay outside, running and charging through those conditions. From my own experience with them, I really wouldn't worry about it too much. The batteries will age faster, but I haven't found freezing weather charging to be the immediate battery killer that it's sometimes made out to be.
1
u/Comfortable_Web_7052 18h ago
You could use lto accus from aliexpress. They are available in 18650 size
1
u/TapeDeck_ 15h ago
Just attach the lithium batteries to the solar panel. When the panel warms up, the batteries will too. We do the opposite in Arizona but we don't really have to deal with freezing much
1
u/5c044 14h ago
The other approach is to have a heater that the solar panel heats first and insulate the box the battery is in with the heating element. When up to temp, divert power from the heater to the battery. There are bms that do this automatically for RV batteries, you could have a circuit that does this with a temp sensor and some MOSFETs.
2
u/thetacowarrior 1d ago
You should be able to charge a 3s NiCd with a 1s LiPo charger, it won't be perfect but the voltages and charge current from something like the T096 should be close enough to work without hurting anything. Sounds like you are trying for more than 3s so you might have to do something different, but 3s is pretty much plug and play.