How do they charge huge LiFEPO4 batteries?

[mcarthur]

So the usual advice I’ve heard is that your charger should be about 1/10th the size of this battery - so a 600ah 12v battery should have a 60a charger. Is it the same for LiFEPO4 chemistry? If so, I see people using 5,10, even 60+ kWh battery packs (like for the electric boats) - how the heck do they charge them?! I’ve seen 70amp, 48v chargers (victron Quattro, 3.5kW or so), but even that wouldn’t be enough!

[mbartosch]

The charging current is (almost) irrelevant with a LiFePO4 battery.
You can charge a 100 kWh battery with a 10A charger. It just takes a long time.
You could also charge the same 100 kWh 48 V LiFePO4 battery with 6000 A (and be done in 20 min).
This property is one of the primary benefits of this chemistry.

[mcarthur]

Thanks - that's what I had hoped. I thought that the 10-20% sizing was more related to the lead acid/AGM which have the need for bulk-absorption-float phases.

[Pyxis156]

Originally Posted by mcarthur

So the usual advice I’ve heard is that your charger should be about 1/10th the size of this battery - so a 600ah 12v battery should have a 60a charger. Is it the same for LiFEPO4 chemistry?

We have a 1080Ah @ 24V LiFePO4 battery bank that we charge using two 150A @ 24V alternators run off our engine. Cruising at 2000RPM we get about 315A out of the alternators and can go from empty (20-30% SOC) to full (95-98% SOC) in about 3 hours. So in our case our charging is about 1/3 our battery capacity. Has worked great for the five years we have had the batteries.

[more]

Originally Posted by mcarthur

So the usual advice I’ve heard is that your charger should be about 1/10th the size of this battery - so a 600ah 12v battery should have a 60a charger. Is it the same for LiFEPO4 chemistry? If so, I see people using 5,10, even 60+ kWh battery packs (like for the electric boats) - how the heck do they charge them?! I’ve seen 70amp, 48v chargers (victron Quattro, 3.5kW or so), but even that wouldn’t be enough!

if you have 60+ kWh battery packs go in the marina 1 time /1 day in 3 months and full charge battery, and you.

[codingparadox]

30kWh 48V (600Ah) battery pack here. Two of the 5kVA Quattros mean that, plugged into shore power or on the generator, it charges at a real world ~120A. The 5kVA says 70A charging is possible, but it blocks at at pulling 4000 watts, which is less than 70A after efficiency losses, unfortunately. So 120 Amps = 4 hours from 20%->100%. With the 2000W of solar going or the alternators helping out, faster than that.

[mcarthur]

Wow codingparadox, thanks! Sounds like you've done what we want to do using a similar boat to our 50' powercat - lots of solar, 5kVA Quattros, and 48V batteries. I'll PM you with some questions if that's ok...

[codingparadox]

All written up:
https://www.highwind.fun/2021/04/16/...-power-system/

But feel free to PM questions too! (or better yet post them on the blog post!)

[mcarthur]

Woohoo - bedtime reading tonight! Lol

[tanglewood]

LFP charge rates shouldn’t exceed about C/4 to C/2, ie a 4 hr to 2 hr recharge time. That’s within the recommended rage for most vendors. Charge rate could be much higher, but you start getting into battery heating issues.

Charge rates can be slower without penalty.

I’ve got 1600Ah and a theoretical max charge rate of 600A.