Solar Charging a Lithium Iron Phosphate Battery

Hi All,
This is not a typical TacomaWorld question, but I trust the expertise out there when it comes to the science and mechanics behind solar charging.

I'm going to be in a VERY remote part of Washington and will need to charge some 11.1Ah lithium batteries (lithium iron phosphate/ LFP) to run some equipment. I do not want to bring 8 to 10 batteries on my back, especially if they are dead-weight after discharge. I'd like to charge them via PV panels and a solar controller, so I'm looking for input on the components needed. I have done this before with lead-acid batteries and a Sun Saver solar charger, but charging LFP batteries is new to me.

I'll be backpacking all the gear around and will hopefully have a decent "base" in the back-country. I'm looking into getting a Jackery or Goal Zero and panels for our "front-country" cabin or boat location.... but the 8-day backpacking trips will need a way to recharge

Battery link here:
https://store.smith-root.com/collections/electrofishing/products/24v-11-1ah-lithium-battery

 

Great question! I've been transitioning to LiPo also due to weight and capacity/capability. I'm curious about solar charging also....Waiting on the EE's to respond!

 

If you are able to charge these with a PV and solar controller, how many batteries would you bring with and charge at a single time?

That link to the battery product doesn't have much for tech details. You'd probably want to contact the vendor and get specs like charge rate so you can match it to whatever solar components you pair it with.

 

I have a divorced 300watt PV charging system for a Battleborn LiFePO4 battery in my truck all running through a Solar Controller and Amplifier. I don't know the specs on your specific battery or the chemical design, but Lithium batteries come in various designs for specific utilization. The branded, Goal Zero type setups, are convenient but very expensive and you are paying a LOT for their mental math into the setup. For a manpack lithium setup, I think your biggest concern is going to be temp control during charging without any Battery Management System. The lithium will typically charge off any PV setup just the same as any lead-acid or Absorged Glass Mat battery. The LiFePO4 like a steeper charge rate than typical Lead-Acid, but ambient temperature makes a huge difference. This is why all those nice Lithium cordless tool batters and jumpstarters should be removed from cold garages in the winter time, because they don't maintain any sort of interal BMS setup which will siginificantly stunt their capacity.

If your batteries have an internal BMS then carry on. Just setup your Solar Controller for the same chemical charge rate as an AGM if it does not have a LiFePO4 or any simliar Lithium chemistry option.

This site has a ton of great resources and ideas, mostly larger than what you need, but the concept remains the same.

https://www.mobile-solarpower.com/

 

Search for small solar controllers, there are a number of them out there. Be aware the LiFe batteries have a unique charging cycle, so be sure the controller is compatible. Am assuming you'll be hiking in the summer with good sun access. If you have all day to charge the battery then a 1 amp panel will work for you, 1A for 11Hrs = 11 AHrs. 14V at 1A = 14Watts. Double that for good measure and figure a 25-30W panel will get you what you need.

 

As long as you have a compatible charge controller that can be configured for your battery, LiFePO4 is going to do way better with solar/ opportunistic charging than most lead acid batteries (unless you're talking about Lead Carbon, then they're more similar)

The biggest thing about lithium in general vs lead acid is that lead acid charge current acceptance tapers quite a bit starting around 85% state of charge and most chargers are designed to sense that and adjust voltage accordingly. Lithium doesn't taper in the same way so in some cases a lead acid charger will shut off the charging too early on a lithium and in others it will be the opposite.

There are also automatic equalize functions in chargers designed for lead acid that you'll want to disable for lithium because it's not needed.

You have to remember now you have a computer on both ends (battery and charger) so they have to play well together.

That said, lithium is becoming so popular most new solar controllers will have some type of lithium charge profile.

 

The vendor is very cautious to encourage solar charging of their products, and the only other person they know that's done it before is my old colleague... working with her now to get specs from the lead-acid setup we used in Yosemite. I'm in touch with vendor now for charge rate, but the "UBC" charger they use is pretty sophisticated at applying different charging input.

I can either carry 8 to 10 batteries for the entire 8 day trip, or figure out solar and carry 3 batteries and rotate them as needed. We will have several of these stints over the summer/fall with a few days in between each stint to recharge and resupply.

 

I think its just a matter of defining your power and charging requirements, then finding the hardware to meet that.

I've been looking at building a power supply for a kayak race and looking really heavily at the stuff from powerwerx. I've been pleased with what I've bought from them in the past, and they also build cables to order for reasonable prices.

https://powerwerx.com/solar-portable-power

 

I missed the link you posted the first time. Looking at the battery and the recommendation about only using their charger I would guess the BMS in this battery is very basic if it's there at all. It may rely on the charger to protect the battery which would not be good. I'd try to find something that is a little more universally compatible.

Over charging or under charging a lithium ion battery is a good way to create a whole lot of smoke and heat.

 

BMS is maintained by their UBC-style controller (The UBC-24 features a fully automatic, three stage charge sequence with an electronically timed routine and a desulfation mode). I've used a Jackery and the UBC charger to charge batteries during car-camping trips, and can see the output fluctuate during the charge cycle. Looking into the weight of PV panels needed, and the fact that I'll be in the PNW with trees, shade, clouds, and fog, I may just pony up and carry more batteries, but set up a proper charging station at our remote resupply station on the off days.