LiFePO4 battery charging tech article, backup charger

[John E Davies]

For those with a technical interest this is useful. Even if you can’t understand much of it, take away this important fact.

“... it is common to charge a 12 volt a 4-cell series pack with a lead acid battery charger. The maximum voltage of these chargers, whether AC powered, or using a car's alternator, is 14.4 volts. This works fine, but lead acid chargers will lower their voltage to 13.8 volts for the float charge, and so will usually terminate before the LiFe pack is at 100%. For this reason a special LiFe charger is required to reliably get to 100% capacity.”

https://www.powerstream.com/LLLF.htm

So maybe a standard automotive portable lead acid charger of adequate size would be a good thing to have as a backup in case your onboard system becomes inoperative..... it won’t fully charge it, but it will get it most of the way there, about 70%. Or for around $120 you can get a 20 amp Renogy unit  that will eventually get them to 100%.

https://www.amazon.com/Renogy-12V-20A-Alligator-Batteries/dp/B08C2JN76Q

 John Davies

Spokane WA

Edited December 13, 2020 by John E Davies

[Mcb]

Thanks for the info John, I emailed the LifeBlue rep this am asking him for his thoughts on the subject of chargers. If my lead acid battery charger could get the batteries partially charged in a reasonable amount of time I think I’ll stick with that. I’d be looking for something to bail me out of a situation while on the road that I can stow in the truck and hopefully never need.. 

[mossemi]

My backup plan consists of a set of jumper cables.
Mossey

[Overland]

3 hours ago, John E Davies said:

...but lead acid chargers will lower their voltage to 13.8 volts for the float charge, and so will usually terminate before the LiFe pack is at 100%.

Do they mean to say absorption rather than float? Battleborn's recommended float charge is 13.6 volts. 

[carnivore]

Jumper cables or an inexpensive battery charger from Walmart to finish the trip. 

[BackofBeyond]

On the Sprinter forum (few years back) - one system outlined and  used a 2000w inverter, running off the TV system, to power an AC NOCO smart charger. Now - it was all contained within the Sprinter, the inverter wired appropriately - per MB specifications- within about 2' of the Battery/DC buss. The charger was located near the house battery. It worked fine - but- seems a little iffy trying to run an AC circuit between a TV and the RV/battery charger. Properly wire and fused appropriately - perhaps. I'm still in the cheap gen set arena. 

I can see that changing in 3-4 years - given the rate of techno innovation.

RB

 

[mossemi]

1 hour ago, carnivore said:

Jumper cables or an inexpensive battery charger from Walmart to finish the trip. 

The jumper cables were already in my truck so I didn’t have to go to Wally World.

Mossey

[Jim_Oker]

Nice to know. I appears I already have a backup system for shore or generator based charging that isn't to big and not heavy at  all. Thanks  John! Just gotta think through where the clips should  go.

[mjrendon]

John,

Since you are installing an MMPT charge controller, you could disconnect the PVs and plug in the output from a 120V AC to 24V DC converter and have the MMPT controller properly charge your Li batteries.  If you are installing dual controllers (one for roof top PVs and one for external PVs) you could easily use the external PV charge controller connector for this too.  MMPT controllers can handle 100V DC (some 150V) and 120V AC to 24V DC converters for LED drivers or laptops are inexpensive with 10A, 15A or more current (240 to 360watts).

Mike

Edited December 13, 2020 by mjrendon

[NCeagle]

9 hours ago, John E Davies said:

Or for around $120 you can get a 20 amp Renogy unit  that will eventually get them to 100%.

Or for an even better amps to $ deal, for an extra $100 you can triple the amps and get out of an emergency situation with a 15 Amp generator 3x faster (it's $100 off regular price right now).  I have this in my shopping cart but have yet to purchase.  https://www.etrailer.com/p-PD9160ALV.html  Could be mounted in the basement somewhere and connected to batteries or just use alligator clips and make it "portable" (that's what I'm thinking).

[Overland]

 

36 minutes ago, mjrendon said:

Since you are installing an MMPT charge controller, you could disconnect the PVs and plug in the output from a 120V AC to 24V DC converter and have the MMPT controller properly charge your Li batteries. 

Interesting thought. I can’t think why this wouldn’t work. 

Edited December 13, 2020 by Overland

[mjrendon]

$20 for 360 watts (after the original MMPT investment of course)