6ixgun avatar image
6ixgun asked

Advanced Charging settings for LifePO4

Question for the community . I have been 100% AGM for many years and consider myself an expert at it - but finally decided to convert one of my vans to LifePO4. No regrets so far its amazing but before I make any mistakes I have some questions. For reference , here is my setup and specs:

Victron MPPT 100/30 Solar Charger

Victron Orion TR-Smart DC:DC Charger

Victron Blue Smart IP22 x1 20A (AGM Vehicle Battery Bank 160AH)

Victron Blue Smart IP22 x1 30A (LifePO4 House Battery Bank 200AH)

The LifePO4 Manufacturer of the 200AH Smart Battery specs state :

15V Over Voltage Cutoff

14.6V Absorption

13.8V Float

10.8V Low Voltage Cutoff

I have little experience with LifePo4 - so pardon me if my questions are juvenile or if they cross over into the AGM realm - I am probably overthinking it - but I do need to come up to speed on this quickly because I am more than likely going to have a bunch of these conversions soon and I want to make sure I get it all right on my personal. vehicle before I mess up someone elses.


1> Is it better to not fully charge the battery (i.e. 90% or 95% vs 100%) ?

2> If #1 is yes, 14.6V seems high - wouldn't I be better off charging @ 14.2V ?

3> It appears that "best practice" is to never leave the battery charger on 24/7 (i.e. trickle charging), if that is the case, would it make more sense to disable the float function ? If it cannot be disabled should I set it under 12.8V so it never comes on ?

4> AGM's were set it and forget it I just connected the trickle charger and let them stay on full time - assuming that is not advisable / not possible should I not leave the charger on full time (i.e. vehicle stored / docked) and only energize it just prior to using it to make sure its fully charged prior to a trip ?

5> The battery has a built in BMS - so I assume I really do not need to do much with the charge settings other than getting the voltages right. BUT - I did notice all the Victron charge defaults are 2 hours - should I change that to go by trip current instead to assure a full charge ?

6> Is it possible to use the charger or MPPT in power supply mode and NOT charge the battery ? I assume if one keeps the voltage output of either below 13V the battery will not charge. Is this correct ?

Here is the scenario in which the vehicle is used.

Note that max current draw at any given time is less than 15A, and its not continuous. The only consumers are lighting, Dometic CFX refrigerator, Webasto 2000 ATC heater, and the occasional USB phone , webcam and LTE modem. Nominal currrent is more like 7a.

The vehicle is in covered storage for 1-2 weeks at a time , sometimes more (RV storage facility) AZ shade temps in winter are 40s - 60s, and in summer 80 - 110s

A typical trip is 4-5 days, consuming at night, solar charging during the day. Overnight on a typical day the battery level may drop 15% (AGM). One warmer / sunnier days I have never once run the battery down or had the heater cut off On colder / less sunny days it was not uncommon for the Webasto to cut off due to low voltage from the battery not charging fully during the previous day.

Now that LifePO4's are installed I doubt that will ever be an issue again. I reprogrammed the chargers that chemistry - but I would like to know what are the best practices / best settings on the victron chargers so i can assure safety, proper charge level and battery life.

Any and all suggestions / comments taking into account the info above is welcome !

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

3 Answers
ke3su avatar image
ke3su answered ·

I use LifeBlue batteries. ( out of Yuma, Az) I spoke to Larry about my settings ( one of the owners ) and he's ok with the settings. 425 amp hours ( 3 - 100 and 1 - 125 ) in parallel. Bulk set at 14.8 volts, absorbtion at 14.2 for 2 hours, and float 13.i volts. I live off grid and rarely connect to shore power. 1500 watts of panels - 2 solar controllers - lights, TV refrigerator., additional freezer. Plus what evers needed.. Arizona desert during the winter up on the rim during the summer. I live like on the grid without issue. Batteries and Victron components have not failed me.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

matt1309 avatar image
matt1309 answered ·

Hi @6ixgun

1. I wouldn't stress it too much as the charge curve for LiFePO4 looks like this:

Therefore there's only really additional stress on the battery in the steep parts of the curve (98%+ ish i reckon). Personally I'm super conservative so i charge my batteries just up enough to hit the start of the steep part of the curve to minimise stress on the cells. However high enough so that I'm confident the cells are at 100% (or close to it) so my BMS can balance the cells within the pack. With LiFePO4 it's really hard to judge SoC from voltage unless you're in those steep parts of the curve, so to balances the cells you need them to be in the steep part of the curve. BMS tend to have a balance voltage that is set to balance cells once they hit that voltage, (i set mine just below absorption voltage).

As you can see the amount of capacity I'm losing by being conservative with my voltages is minimal given the steep parts is so close to 100%.

(Per cell i'd say steep part of the curve starts around 3.4-3.45v so if you've got typical 12v pack of 4cells Id say steep part starts around 13.8, this is personally what i set my absorption voltage to, and then i set my float at around 3.375v per cell).

2. 14.2v is 3.55 volts, still well under the thresholds set of LiFePO4 anything under 3.65 is fine, I personally wouldnt go higher than 3.55 though, the capacity you're missing out on is minimal and the cells will be under more stress for going higher. (however still within specs so feel free to push it if capacity is key for you)

3. (tldr not too sure sorry) However I personally have float setup (however a lower voltage compared to the specs you noted). My understanding is if you're not on steep part of the curve battery stresses aren't too much of a concern.

4. (tldr not too sure sorry) I probably wouldn't leave them at float all the time and i think there's guidance on what voltage/SoC to best to store them at, i want to say it's 30-50% soc but cant remember where i've read that so I'm unsure here also.

5-ish. For SoC measuring i use a smart shunt. Measuring SoC based on voltage alone is a pain for LiFePO4 given the flat curve above (ie Voltage at 20% is nearly the same as voltage at 80%). So counting amps in vs amps out is your best bet. And to confirm it's 100% you'll see the voltage start to climb as it enters the steep part of the curve but other than 100% and 0-% it's really had to judge soc from voltage with LiFePO4.

When you say trip current is that the same as tail current? If so I'd just play around with this one. If your BMS let yous see voltage variance per cell in the pack i'd use that as a guide. If your packs tends to be balanced well within 2hr of absorption then i'd reduce it, similarly with tail current. Just see what settings end you up with a balance pack.

6. Unsure how to configure this but I think you're logic is right, ie when my system is in float battery voltage doesnt move but mppt can ramp up/down to cover loads without charging battery.

A note on storage, your winter temps aren't perfect but totally fine for LiFePO4, just got to make sure you're not charging under 32 degrees. I believe discharging is fine (up to negative 20 degrees C not sure what that is in F sorry).

A really good resource for LiFePO4 is offgrid garage on youtube. He'll go in more detail than you'll ever need. He's also living in AUS so be good comparison for your summer temps.

Give me a shout if you need anymore settings happy to share mine (just keep in mind mine are very conservative to what you'll see online)

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

6ixgun avatar image
6ixgun answered ·

Thank you for taking the time to provide these answers - they are VERY helpful ! I think I got it all dialed.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Related Resources

Additional resources still need to be added for this topic