Is a DC to CD charger required?

[Big45ACP]

My travel trailer RV is currently running on AGM batteries, but I'm in the process of making the switch to LiFePO4. My truck provides 12v charging through pin 4 of the 7pin trailer plug. My question is, will I need to install a DC-DC charger when making the switch to lithium? There are two concerns that prompt this question. First I've heard that trying to charge from the 12v on pin 4 can overwork and cause early damage to the alternator. Second, the voltage provided by the alternator and starting batteries may not be sufficient to top off the lithium batteries while driving.
The initial conversion will include an Inverter-Charger but no Solar initially. So while I don't immediately need MPPT functionality I'm not opposed to it if something like the Renogy DC2DC with MPPT is the recommendation.

 

[snoobler]

Welcome to the forum.

Your first concern is the greater.

The second is dependent on voltage drop, which may prevent the first concern. The alternator may see 14.4V when the battery is at a much lower voltage due to wiring losses. The alternator would then drop to float and provide little charging current.

The answer then becomes, "it depends".

If you note appropriate behavior after the conversion, a DC-DC isn't necessary. If it is, I wouldn't recommend the Renogy DC-DC w/MPPT as the MPPT is pretty limited. I would get a straight DC-DC (Renogy or Victron Orion) and get a separate MPPT.

 

[Big45ACP]

Welcome to the forum.

Your first concern is the greater.

The second is dependent on voltage drop, which may prevent the first concern. The alternator may see 14.4V when the battery is at a much lower voltage due to wiring losses. The alternator would then drop to float and provide little charging current.

The answer then becomes, "it depends".

If you note appropriate behavior after the conversion, a DC-DC isn't necessary. If it is, I wouldn't recommend the Renogy DC-DC w/MPPT as the MPPT is pretty limited. I would get a straight DC-DC (Renogy or Victron Orion) and get a separate MPPT.

Thanks for the quick reply.
Can you please expand upon your statement, "If you note appropriate behavior after the conversion". What is the appropriate behavior that would mitigate the need for a DC-DC?

 

[snoobler]

Charging not too high or for too long.
Acceptable charge imparted to battery.