backchannel: converter charging your RV batteries with Tito

from this blog post

> Single stage converter/chargers can shorten the lifespan of your batteries by overcharging them.

Probably not.  Most old-school single-stage converters kill batteries by undercharging them with too low a voltage. They were typically set up to hold Vfloat, let’s say in the mid-13s.  Let’s review what “Vfloat charging” can do:

  • it can hold a previously-charged bank at 100% state of charge (SoC) as long as shore power remains avaialble. That’s their job.

  • it _can’t _fully charge cycled batteries to battery manufacturer specs because there is no Absorption phase.

> Newer converter/chargers have multi-stage charging capability and are recommended for modern RV deep cycle batteries.

Not sure what a “modern RV deep cycle battery” is, since lead-acid has been around for a century.

Also not sure what the author thinks multistage chargers do after charging (hint:  they hold Vfloat).

> Many can even be programmed to the exact manufacturer recommended charge settings.

Mandatory, IMO.

> There are even models that support the unique requirements of lithium deep cycle batteries.

Lithium is not magic and does not have unique requirements, other than not charging below freezing.  The aforementioned configurability is sufficient.

Lead-acid batteries (flooded or AGM) require a four-stage charging cycle.

AGM and mobile FLA do not required the 4th stage, Equalization.  EQ is for FLA batteries that sit stationary on float.   EQ your AGM if you want to buy a new set of AGM (lifeline excepted).

.> Each stage has specific voltage and current profiles designed to get the battery safely to a full-charge without overcharging it

I don’t know of any converter that has current profiles other than their max output.  This makes sizing the converter to the bank important.

> Single stage chargers simply push a fixed voltage into the battery at all times


> This often causes these problems: They do not supply sufficient charge voltage during charging which may tripple the charge time or prevent your batteries from reaching a full charge

Tripling wouldn’t be such a bad thing, since the RV is sitting on shore power. 24 hours a day.  The inability to charge completely is a problem.

> When batteries are fully charged, they keep pushing a higher voltage into the batteries which can cause overcharging, buid up of heat and gas, and a significant reduction in lifespan.

It’s just floating, the way the multistage chargers do it.  If you want a converter with a lower Vfloat for some reason then buy one.

The primary advantage of the new unit is the smart battery charging feature. When the batteries are low, the charger kicks into bulk charge mode (around 14.4 volts) and gradually decreases the voltage as the battery reaches a full charge.

No, the converter holds Vabs until Absorption is done, then it holds Vfloat indefinitely.   This stuff is covered in the owner’s manual, or can be directly observed on the battery monitor.

> When connected to shore power, my batteries were able to reach a full charge within 2-3 hours.

Deep-cycled lead acid batteries cannot be fully charged in 2-3 hours.  The Absorption phase alone typically takes 4+ hours.   It is possible to charge lightly cycled lead batts in 2-3 hours, particularly if they weren’t discharged for too long.

Non-boondocking RV folks tend to run  off the house batteries only when between hookups (moving from campground to campground).

After upgrading my batteries to LiFePO4 lithium batteries, I needed to also upgrade my charger. The one I installed was the Progressive Dynamics [PD4655LIV]( model designed for lithium batteries

Somewhat perversely, the old single-stage converter would have been just fine for charging Lithium.    LFP is fully charged at 13.8v.