LiFePO4 Charge Profile

[atatistcheff]

I've built a couple of LiFePO4 batteries over the years but now it seems like the price of the cheap "drop in replacements" has dropped so it's hardly worth making your own anymore. Along that line I'm wondering what the ramifications are for using a Lead Acid charging profile on one of these batteries. This has come up because we just bought a new trailer and I need to come up with a power solution. In my old trailer, I have 2x 200W panels on the roof, Victron charge controller and my CALB battery with a batteryhookup.com BMS. This has worked swimmingly over the years. I disconnected the 12V converter in the trailer and charge the battery exclusively with the solar panels.

Ok now fast forward to today. New trailer, looking at a new Chinese battery. Do I still need to disconnect the converter designed to charge lead acid batteries? Just wondering what the possible negative effects might be.

Thanks!

 

[sunshine_eggo]

Absorption 13.8-14.6 can work.
Float at 13.5 preferred, 13.6 okay, 13.8 absolute upper limit for daily cycling.

13.8V absorption will take 1-2 hours @ 13.8V to fully charge.
14.6V absorption will only take may maybe 15 minutes @ 14.6V to fully charge, BUT cell imbalance may trigger protection at that level.
14.4V absorption will only take a little longer than 14.6V to charge, but it's a little more imbalance-tolerant.

Charges to 14.4-14.6V can be terminated when current drops to 0.05C.

13.8V needs to drop to much lower current... closer to 0.01C.

The issue with mst RV converters are in their high losses due to wiring resistance. The biggest complaint is slow charging and/or under-charging.

A very common algorithm across a couple brands:

Bulk: 14.4-14.6V for 15-120 minutes
Absorption: 13.6-13.8V for 10-24 hours
Float: 13.2V

Some chargers will rebulk periodically.

The chances of damage are negligible.

The chances of undercharge/disappointing performance are significant.

 

[atatistcheff]

According to the manual.

Bulk mode 14.4V for 4 hours or until current draw drops below 5A (whichever comes first)
Absorption mode 13.6V for 48 hours (not clear if there is some other criteria other than the 48 hrs)
Float at 13.2V after that.

I've asked the manuf if float can be disabled. It's likely I'll just disconnect the converter and go with solar only like my last trailer. Just wanted to make sure I wouldn't be damaging anything if I use this converter temporarily. Not going to leave it plugged in when not in use anyway.

Thanks!

 

[sunshine_eggo]

I wouldn't hesitate to use that converter and leave it connected any time you're on shore power.

4 hrs is pretty surprising, but that's excellent.

Still, wiring losses will guarantee that it falls out of bulk well before the battery terminals get anywhere near 14.4V or fully charged unless they're literally right next to each other. 13.6V for 48 hours would top it off. It may require several hours @ 13.6V to get to full charge if that's your goal.

What brand? If it's a WFCO, they're notorious for hitting bulk prematurely, so they're basically a 13.6V charger.

When the manufacturer comes back and tells you that you need to purchase a lithium compatible converter, they are simply trying to extract dollars from you. The only benefit the lithium converters have is they tend to stay at 14.4V for a much longer period to ensure they can fully charge in as little time as possible.

If you find you're on generator power, and you need to charge, I would monitor the converter and power cycle it's AC input to restart the bulk run as needed.

 

[atatistcheff]

Cool thanks, ya it's a WFCO. That charge cycle is what their docs say. The converter is only about 8-10 feet from the battery so it's closer than being back in the middle of the trailer. Thanks for the help, gives me more options.

 

[sunshine_eggo]

Zero chance of it damaging your battery.

Even with only 8-10 feet, high probability it will drop to 13.6V pretty quickly and take forever to charge it, but it's probably better than nothing or spending money on something more expensive/effective.