srschang wrote:
Hey 3 tons, I'm struggling with extended (weeks, months) with my 2 LiFePo4 batteries in my Northstar. I also have small parasitic draws that discharge the batteries over the course of several weeks. And I don't want to disconnect the batteries as my Pioneer stereo takes me 15 minutes with the manual to get demo mode off, dazzling display lights off, all four speakers working..... every time I disconnect it from the batteries.
I currently have a Progressive Dynamics 45A LiFePo4 converter. The problem with the PD LiFePo4 chargers is that they charge at 14.6v - all the time. So if I leave the camper plugged in, it will sit at 14.6v as long as it's plugged in. Bad for LiFePo4 batteries. I found that the WFCO 50A LiFePo4 replacement converter/charger section charges at 14.6v for 4 hours, then drops down to 13.6v as long as the camper stays plugged in. If the camper is unplugged and plugged back in, it will again charge at 14.6v for 4 hours, then drop to 13.6v until the camper is unplugged. Perfect for leaving it plugged in for extended lengths of time. Here's a link to an interview with the CEO of Battle Born batteries. His comments on long term battery storage start at 12:50. Comments specific to longterm float at 13.6 are at 14:30.
https://www.youtube.com/watch?v=ywn-vBjKblI
Scott
Well, since you’ve mentioned that the PD charger stays on indefinitely, I would assume that your camper has access to shore power while it storage...
The problem with most dedicated Li chargers is that there’s no such thing as a ‘one size fits all’ charger algorithm due to a lack of a common convention by the various battery manufactures - thus, the charger guys are left to ‘going it alone’ with their whatever in house LiFePo4 algorithms....The PD unit would be much improved if they’d add a timer, but then the timer would need to be triggered by a reference point... You could always just add a corded timer from a big box store, but would still need a reference point to achieve unattended charging...I agree that theres no point in leaving the charger ON once charging is complete, thus the necessity to determine when the battery is FULLY charged, and BMS balanced...A float mode is inconsequential (i.e. not needed)...
The Victron BMV 712 meter has a genny start signal output that could be repurposed for the charger (say on either the 120v or the 12v sides) but you’d need a relay, and a high amperage relay (say, of up to 1C) can get a bit pricy...
You might consider adding a battery disconnect atop the batt pos post (see my previous..), and then just keep the PD Converter-charger ON when in storage - this should keep the interior lights on and your stereo programming intact...
Without a Li capable meter (like Victron’s or equiv.) you can monitor battery voltage (near the rapid conclusion of ‘upward’ voltage rise) with a VOM to ascertain when the battery has fully charged (resting at 14.4’ish), shortly after which the BMS will begin it’s ‘balancing dance’ evidenced by voltage (and current...) alternatively dipping and recovering - this process might complete itself in say just a few brief minutes...Once voltage finally ‘remains’ stable, this balancing act is complete...
This is the methodology that I use, and for ‘extended long term’ storage I purposefully deplete the battery down to about a 50% state of charge (SOC), then do a disconnect - 50% (approx), a state of ion equilibrium that minimizes the possibility of harmful dendrite formation, and extends battery life...
3 tons
