Hi I'm Sam
I was involved in the now defunct http://www.bristolwireless.net/about-us/ for about 10 years, more recently I helped start The Things network in Bristol. I was thinking about hacking together one of these: https://github.com/dmahony/Lora-Chat-Device
When I found your project :) I'm curious how you're handling routing?
Could the Mesh datagram protocol from Serval be any use to you?
https://github.com/servalproject/serval-dna/blob/development/doc/Mesh-Datag…
Or is it too heavyweight for the LORA side?
I also read on your mailing list that you've had a few boards made up, would you consider shipping a couple to the UK?
Thanks
Sam
Hi All,
I've been thinking a bit about solar charging and have come up with a few
options.
First, this is a pretty good application note laying out the basics of
Maximum Power Point Tracking for solar panels:
http://www.microchip.com/wwwAppNotes/AppNotes.aspx?appnote=en561417
Also, this is a good overview of charging Li-Ion batteries in general:
http://sound.whsites.net/articles/lithium-charging.htm
Here are some ideas with pros/cons and approximate costs at 1000 and 10
quantities.
1. Use reputable MPPT ICs
BQ24650 ($2 @1k, $4 @10)
http://www.ti.com/product/BQ24650
LT3652 ($3 @1k, $4 @10)
http://www.linear.com/product/LT3652
LTC4121 ($3 @1k, $4 @10)
http://www.linear.com/product/LTC4121
Pros:
High Efficiency
Excellent Documentation and Support
Available at all major parts distributors
Wide input voltage range
Reliability/long part lifetime
Cons:
Cost
2. Use Chinese brand MPPT ICs
CN3791 (maybe $0.35 @ 1k, $0.68 @10)
http://www.consonance-elec.com/seriesCN3791-E.html
Pros:
Wide Input Voltage Range
Decent Datasheet
tons of working modules available from Ebay/Aliexpress
Cons:
Less Efficient (I believe they use fractional open voltage MPPT)
Not widely available from US parts distributors
Unknown Quality/Reliability (probably good though)
3. Use Name Brand Li-Ion Charging IC
MCP73831 ($0.40 @1k, $0.50 @10)
Pros:
Simple/Compact
Widely Available
Reliable
Cons:
Low Input Voltage Range
Bad Efficiency (No MPPT built in)
4. Use Chinese Ultra Low Cost Charging IC
JZ4054 ($0.06 @1k, $0.10 @10)
http://www.szjingzhong.com/enproduct_show.html?id=26
Pros:
Lowest cost IC for charging Li-Ion batteries
Same footprint as MCP73831
Reliable in my experience
Cons:
Poor Documentation (No English)
Not Available from US Distributors
Low Input Voltage Range
Bad Efficiency (No MPPT built in)
5. Bootleg MPPT onto option 3 or 4
This is an idea I have, not 100% sure that it will work, but its worth
experimenting. The Wemos chip would monitor the Solar Cell voltage and
adjust the charger current with PWM to maintain the maximum power point.
Here's the basic circuit:
[image: Inline image 1]
Pros:
Lower Cost (only requires a few extra components)
Decent Efficiency
Cons:
Requires Wemos control (maybe updating once a second)
Complexity
time to test and implement
Also, I recommend this chip for buck controverting (stepping down the Li-po
voltage to 3.3V):
PAM2305 ($20 @1k, $0.40 @10)
https://www.diodes.com/products/power-management/dc-dc-converters/integrate…
-Fitz
