RV Upgrade to Lifepo4 12v from Trojan 6v

29 Foot Trailer with 2x 6v Trojan T105s to 4x 12v Lifepo4 batteries with built-in BMS (Think Battleborn/Lion with BMS) most of the time charged by 400w solar.​

question #1.
I have been doing a ton of reading about switching battery chemistry and most people point to needing to upgrade the alternator and shore power charger (Inteli power 9100 with the wizard, add on) to ones that are compatible with Lifepo4 but I am seeing differing opinions with some people saying that I don't HAVE to update the shore charger as it will work ok charging the new Lifepo4 batteries is this ok? I have solar for the main charging duties as we boondock most of the time from Victron so I can update those charging profiles.

question #2
I know that I "should" disable the Tow vehicle's alternator charging via the 7pin plug until I can get a DC/DC converter or a LifePO4 compatible alternator. but again whats the recommendations here?
The shore power charger I believe puts out LESS than Lifepo4 would like so is charging at a lower voltage a bad thing?
The alternator could put out more voltage I think so that may be not good.
Thanks

dpackham said:

29 Foot Trailer with 2x 6v Trojan T105s to 4x 12v Lifepo4 batteries with built-in BMS (Think Battleborn/Lion with BMS) most of the time charged by 400w solar.​

question #1.
I have been doing a ton of reading about switching battery chemistry and most people point to needing to upgrade the alternator and shore power charger (Inteli power 9100 with the wizard, add on) to ones that are compatible with Lifepo4 but I am seeing differing opinions with some people saying that I don't HAVE to update the shore charger as it will work ok charging the new Lifepo4 batteries is this ok? I have solar for the main charging duties as we boondock most of the time from Victron so I can update those charging profiles.

Click to expand...

Devil is in the details, what converter do you have?
The best solution is an inverter charger but often a simple converter can be made to work fine.

dpackham said:

question #2
I know that I "should" disable the Tow vehicle's alternator charging via the 7pin plug until I can get a DC/DC converter or a LifePO4 compatible alternator. but again whats the recommendations here?
The shore power charger I believe puts out LESS than Lifepo4 would like so is charging at a lower voltage a bad thing?
The alternator could put out more voltage I think so that may be not good.
Thanks

Click to expand...

If you leave the tow vehicles charge pin connected the alternator can expose the LFP batteries to voltage stress.
That means holding them above full resting voltage beyond the time required to charge the battery.
Its added stress on the batteries but its not sudden death.
What voltage does your alternator produce?

smoothJoey said:

Devil is in the details, what converter do you have?
The best solution is an inverter charger but often a simple converter can be made to work fine.

If you leave the tow vehicles charge pin connected the alternator can expose the LFP batteries to voltage stress.
That means holding them above full resting voltage beyond the time required to charge the battery.
Its added stress on the batteries but its not sudden death.
What voltage does your alternator produce?

Click to expand...

Inteli power 9100. it's the original lead battery charger. I know that I don't need the wizard so I can disconnect it and leave the charger in NORMAL mode at 13.6v

BOOST Mode 14.4 Volts – Rapidly brings the RV battery up to 90% of full charge.
NORMAL Mode 13.6 Volts – Safely completes the charge.
STORAGE Mode 13.2 Volts – Maintains charge with minimal gassing or water loss.
EQUALIZATION Mode 14.4 Volts – Every 21 hours for a period of 15 minutes prevents battery stratification & sulfation – the leading cause of battery failure.

The Chevy alternator "should be" 12-14.5v

I also understand that LifePO4 should have 14.6v to charge normally and the Solar I have and use 95% of the time will provide that. the main question is.. will lower voltages from the shore power hurt the batteries? I understand that the alternator should be updated or disconnected.

dpackham said:

Inteli power 9100. it's the original lead battery charger. I know that I don't need the wizard so I can disconnect it and leave the charger in NORMAL mode at 13.6v

BOOST Mode 14.4 Volts – Rapidly brings the RV battery up to 90% of full charge.
NORMAL Mode 13.6 Volts – Safely completes the charge.
STORAGE Mode 13.2 Volts – Maintains charge with minimal gassing or water loss.
EQUALIZATION Mode 14.4 Volts – Every 21 hours for a period of 15 minutes prevents battery stratification & sulfation – the leading cause of battery failure.

The Chevy alternator "should be" 12-14.5v

I also understand that LifePO4 should have 14.6v to charge normally and the Solar I have and use 95% of the time will provide that. the main question is.. will lower voltages from the shore power hurt the batteries? I understand that the alternator should be updated or disconnected.

Click to expand...

LifePO4 = LFP
Lets call it LFP because its easier to type.
Its not necessary to charge an LFP batttery to 14.6 volts to get it full.
13.8 volts or above will do it.
From memory he boost mode on those batteries those battteries is 4 hours max so its not a big deal.
13.6 is 3.4 volts per cell with is an acceptable level to float the batteries.
I prefer 13.4 but would not lose sleep over 13.6 especially since its your secondary charge source.

If it were me I would have a look inside the converter and see if there is a trim tab to lower the voltage a tad.

Will you be adding an inverter?
If yes then you need to change the wiring to the converter to avoid a power loop between the inverter and converter.
The best and easiest solution is to disable the converter and use an inverter/charger.
An inverter charger also includes an automatic transfer switch.

smoothJoey said:

LifePO4 = LFP
Lets call it LFP because its easier to type.
Its not necessary to charge an LFP batttery to 14.6 volts to get it full.
13.8 volts or above will do it.
From memory he boost mode on those batteries those battteries is 4 hours max so its not a big deal.
13.6 is 3.4 volts per cell with is an acceptable level to float the batteries.
I prefer 13.4 but would not lose sleep over 13.6 especially since its your secondary charge source.

If it were me I would have a look inside the converter and see if there is a trim tab to lower the voltage a tad.

Click to expand...

I'll look into this and changing to 13.4v

smoothJoey said:

Will you be adding an inverter?
If yes then you need to change the wiring to the converter to avoid a power loop between the inverter and converter.
The best and easiest solution is to disable the converter and use an inverter/charger.
An inverter charger also includes an automatic transfer switch.

Click to expand...

I will not. we don't use much AC power when boondocking and when we need to microwave something to start the generator

dpackham said:

question #2
I know that I "should" disable the Tow vehicle's alternator charging via the 7pin plug until I can get a DC/DC converter or a LifePO4 compatible alternator. but again whats the recommendations here?

Click to expand...

If you disconnect the 12 volt charge from the 7-pin then you have also disconnected the trailer breakaway system from power. That's bad.

If you put a DC-DC charger in the circuit you have also disconnected the trailer breakaway system from power. The DC-DC charger is a one-way circuit, it won't allow power to flow backwards.

What I did is disconnect the power coming from the 7-pin circuit at the main distribution panel inside the trailer. My LiFePO4 system gets no charge at all from the tow vehicle. I then left a small 12 volt battery on the tongue of the trailer. This battery gets a charge from the 7-pin circuit and also powers the trailer breakaway system.

An alternative to what I did is to install a DC-DC charger and then run an additional line from the LiFePO4 battery back to the trailer breakaway system. You'll have to isolate the trailer breakaway system from everything else, otherwise it's a loop.