Solar to single cell LFP?

[fireofenergy]

Is there a way to convert the ~15 to 21v from a conventional solar panel to the 3.6v needed to charge a single LFP cell? I tried a adjustable buck converter from China but every time a shadow, it would stop.
I just want to charge a 20Ah prismatic cell with a 30 watt panel to make a portable (and bright) solar LED light.
I understand I will need a simple BMS for overcharge but no balancing since only one cell.

Thanks in advance

 

[Nanren888]

How do you mean

but every time a shadow, it would stop.

..,. you want it to charge when there's no sun?
.

 

[fireofenergy]

Walk in front of it, casting a shadow, no longer worked. I had to unconnect and reconnect to make it work again. Obviously, it's no good if it stops working in sunlight because of any brief shadows.

 

[Bluejets]

Show everthing you have including schematic.
These converters are normally self starting so you have something a-up somewhere or a dodgy converter.

 

[fireofenergy]

This was years ago. I've long since gave up, thinking they all had to have reliable, not solar, power input.
I simply hooked it up and used the voltmeter to adjust output. It's very possible I'm missing something.
It was a cheap deal from ebay, like $1.95 each but I assumed it would work (many sellers selling them and most had good ratings). I believe I used a 10 watt panel in good sunlight (almost .6A)
Now, since larger LFP cells are available for less, I got interested again. Perhaps there's more expensive versions that will work, and handle larger currents.

 

[fireofenergy]

Also, I wonder if it's just better to somehow figure all the parts needed to do it right, however, not sure if I can handle the learning curve. I know ohms law and basic math, but nothing advanced

 

[Bluejets]

The converters are pre-built units so not that difficult.
Battery chargers require some regulation and possibly under/over voltage dropout protection so just a converter on it's own is usually not enough.
You can get help here to some extent BUT first we need to know what gear you have now and exactly what you intend to do.

 

[fireofenergy]

I plan to use a 30 to 100 watt 18v solar panel to charge a single lithium iron phosphate cell of at least 15 to 50Ah, respectively. I also need a protective circuit for the battery cell to prevent overcharge. Since single cell, shouldn't be hard for me to find or be too expensive (no balancing needed).
The load will be no greater than about 1/8th the cell capacity, per hour, or less.
I would use resister, rather than LED driver, since I don't like the rapid flickering, and because the LEDs become very dim, using very little current before the LFP reaches the 2.5 volts (where it's not recommended to continue discharge). If I used driver, the lights would remain bright, then all of a sudden shut off, probably at only 2v (instead of 2.5v) when over discharge protection kicks in. The resistor approach is probably not as efficient, however, after a much longer time period, dim lights provide a better warning than ones that shut off instantly.