Battery upgrade to DIY LiFePO4 – Introduction and charger

As mentioned before, the lead acid battery of 105Ah and the Xenteq 10A charger are for testing and initial setup only. I was planning on upgrading to Lithium.

During the build, I found there are plenty of options for Lithium. You can get a complete battery, eg a Victron, Liontron, Battleborn, NDS, Wattstunde and a whole bunch of other sellers. Also, there are unknown / lesser known brands, slighly cheaper.
But in all cases: Still pretty expensive, a 100Ah battery easily is around 800 EUR in Europe

I did some calculations, and based on my requirements (beeing able to run offgrid for approx 2 days) I’ve calculated I needed at least 70-80Ah of usable capacity. So with lead-acid, this would mean around 180Ah, since lead acid can’t be discharged <50% without seriously shorten its lifetime.

If I want to run my water heater also, I estimated I need another 35-40Ah / day.
Using the inverter also adds up pretty much, so with 100Ah Lithium I can safely run my refrigerator, lights, fan, but usage of other equipment has to be done carefully and depending on the solar.

So: The bigger: the better. Off course, the drawback is the costs. With 200Ah of usable capacity it would be great, and basicly nothing to be worried about anymore (since the solar will also help, the 315Wp will charge the batteries even in shadown, although very limited. 200Ah = 400Ah lead-acid = way too much weight, so lithium is definitely the way to go.

Also, it would be pretty massive in size. After searching for options, I found there are a bunch of Chinese sellers selling very affordable batteries. Most popular are (as of aug 2020) the EVE 280Ah cells. (There are also 105ah cells available).

These are not Lithium-ion, but are LiFePO4. This is much more suitable for van usage: Safer to use/build and a lot easier: Each cell is 3.2V so you need to wire 4 of them in series. Each cell has 280Ah capacity, so only 4 cells will do.
With Lithium-ion, each cell generally has a much lower capacity so you need to run multiple cells in parallel, and joining these into series to make for the 12V. Also, unlike LiFePO4 which is 3.2V/cell, Lion = 3.7V, so slightly more off 12V (4×3.2 = 12.8V)
And you need to have (or have access to) a spotwelder to create proper connections on Lion-cells….

The LiFePO4 cells however are much easier to use: Just a ‘block’ with M6 inserts, and included busbars to connect them in serie.
And, when sourcing them directly from China, they are much more affordable.
Besides the batteries, you also need a BMS (Battery management system, more on that later)

I only have to replace the charger (Which I was aware of).

Lead-acid batteries require a slightly more advanced charging profile than LiFePO4. A decent lead-acid charger will periodicaly equalize the cells using a higher voltage, primary to remove sulphation on the plates in the battery. However, this voltage is way too much for a Lithium battery, so this will overcharge them!

During initial charge, the charger will start with providing its maximum current (Bulk stage). This continues till the battery voltage reaches the absorbtion voltage. Once the batterie continues to charge, the current drops. If the current is below a certain point (or time, depending on the charger), the battery will hit its float stage, and the charger only provides a lower voltage to maintain this SOC (State of charge). This is 3-phase charging… Fine for lead-acid.
More advanced chargers include more stages, eg equalizing. This can’t be switched of on all chargers, so you have to be carefull when upgrading to Lithium. Also, not all chargers can set to various voltages. ‘Wet’ lead-acid batteries have slightly different voltage requirements eg compared to Calcium-based batteries.

Also, while a lead-acid battery is limited in its charging capacity (generally recommended to have 1/5 C charging rate, so 20A max for a 100Ah battery), LiFePO4 can handle much larger charge currents (and discharge currents as well). So you can charge the battery much faster (although this slightly decreases its life if you charge it really fast).

Anyway: 280Ah with a 10A charger won’t really do, so I needed a bigger charger.

Since I have also DC-DC charging from the alternator (40A) and solar (about 25A max with optimal sun) I didn’t want to spend a whole lot of money on a charger which I’ll probably use occasionally. So: No expensive Victron or so for me 🙂

I only just needed a ‘huge power brick’. So unlike the well known RV charger brands like Renogy, Victron, Ctek and so on, I went to the industrial market: This also uses batteries for various purposes. And as with a lot of stuff: Anything labeled ‘Campervan’ is way overpriced.. (This surely applies to most electrical stuff: Campervan electrics are overpriced, you can get the same quality or better at a marine hardware shop: Boats are using low-voltage system for ages, while campervans are ‘the new kid on the block’ where they can charge you 200%…

So I ended up at https://www.meanwell.com/, a well known brand in power supplies and similar stuff. On their website I found various chargers.
So I found the Meanwell PB-360. This is a very nice, robust charger, aluminium cased, and able to deliver 24A of charging. And its only 3-phase, so will work fine for Lithium. (Note: Not all datasheets of this model include Lithium, but it does work fine, and later datasheets do list it).
It was affordable: 100 euro ($120 or so) and the output voltage can be adjusted to some more conservative settings to increase the life of Lithium even more (more on that later).
Also, the absorbtion stage is not time-based, but current based. So no overcharging, it will go to float automaticly.