Portable Solar Generator for electric fence

The clock is ticking for me to get my new DC electric fence operational.

Solar powered electric fences are perfect for this, butI can not find a single DIY application of anyone using 18650s.

All I can find are references using 12V lead acid deep cycle that say stay away fromautomotive batteries.

Typical usage on these would be2ah/day, although I would like to leave extra capacity in the solar generatorto run a 12V work light.

My reason for lithium is I have plenty of power-tool & laptopcells & this would help reduce weight. (I need this to be portable)

As a general rule, you need 10 watts of power for each Joule of your fence energizer.

I also see a number of 2J systems running on 30W panels. (extra 10 J for safety factor)

I have also readthese same energizerscan draw 200 milli amperes per hour which calculates out to 100 amp deep cycle battery running for 10 days without sun.

Before I jump into my build, I wanted to confirm if there is any reason an 3S 10P18650 pack could not be used for an 1J electric fence.

I could swap these out fairly easy if the panels are not getting sun for a week.

The one issue could just be the temperature in winter time not being recommended for lithium applications.

If needed I could use a deep cycle for just the winter months.

There are plenty of portable solar generators that run a MPT-7210A at24V (6s) then step down to 12V with a buck converter. If I am working with 12V, energizer & work-lights,I would assume I can stay with the 3S10P, but I am still looking for a 3S solar charge controller for lithium as the ones for lead acid will provide a full charge reducing the life of the cells.

A single 18650 is considered charged at 4.2v and flat at 3 volts
3s would give a range of 3*3v to 3*4.2v
Ie 9v to 12.6v
You would need equipment that works in that range.
What voltages does the equipment you have work at?

Instead of going with 18650 (that is, Lithium Cobalt cells), I'd recommend to go with LiFePO4's (which also come in 18650 format, but more common in others). Then use 4s on those and be a direct replacement for the lead acid. No need worry about voltages. And they can handle a charge better from solar using the existing setup.

All my cells are from reclaimed laptop or powertools so I do not have any LiFePO4's.

Several of the energizers are designated as

Input voltage:
Nominal 12.7vDC (Max 20v)
At 11.5 V a low battery light comes on.
At 11V the energizer shuts off to protect the battery.

Others designate a low cutoff range of 11.8/11.2 While others list 11.4/10.8 .

So it seems the battery would never hit the 9V lower limit.

Then go 4s.

3.0 * 4 = 12.0V
2.7 * 4 = 10.8V

4.2 * 4 = 16.8V
4.0 * 4 = 16.0V

You have a bit more flexibility with the 4s over the 3s.