[DisasterRadio] Battery Charging

[John Fitz]

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/integrated-power-stage/buck-converter/part/PAM2305

-Fitz
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