Battery charging concern and rating of converter

[48Rob]

My current camper 12 Volt system consists of a lead acid battery on the tongue, and a WFCO converter inside. The wire from the battery to the converter is AWG 10 and also carries current from the tow vehicle when connected.

My new power source will be a 440 AH 12 Volt LFP bank inside the camper.

I wish to do away with the tongue battery, and repurpose the main charging/supply wire to feed the power jack and break away switch, by removing that #10 wire that currently feeds the fuse panel, and using it as a branch circuit. It is currently protected by a 40 Amp fuse in the panel, but will be reduced to a 30 Amp.

The new battery bank will have new 50 Amp wire that feeds the converter as I have a 40 Amp charger. The converter will then need a 50 Amp fuse.

Doing this will then feed those tongue mounted devices from the fuse box. However, the incoming power feed from the tow vehicle also connects to the auto circuit breaker on the tongue.

Am I safe to back feed that incoming power to my new LFP battery bank through the old wire (which is rated for 30 Amps) to the fuse panel, or do I need to run the tow vehicle charging wire to my battery bank bus bar? I am aware that the voltage from the tow vehicle isn’t going to do much for my higher voltage LFPs. I may at some point add a DC-DC charger, but I believe for it to be effective, I would need to run much heavier cable from the tow vehicle battery all the way back to my new battery bank?

I also will be adding solar, so it is possible that the SCC could be putting out up to 80 Amps at the same time the charger (shore power) is running.

Am I correct in believing I need to up my wire capacity to account for that, or make sure they both never run at the same time?

Next is the converter. It is a WFCO WF-8955PEC, which is rated at 55 Amps. I plan to disconnect the converter transformer, so that all power is fed from my battery bank, even when connected to shore power.

Our camping consists of off grid for multiple days until the battery bank, assisted by solar, is mostly depleted, then connecting to grid for a night to recharge.

I could switch out the circuit board so it would produce the higher charging voltage needed, but it still isn’t a very good charger, compared to my stand alone, and is another expense that seems unnecessary?

The converter at least at first glance appears defective, as it is sometimes putting out 13.68 Volts and other times putting out 17.47 Volts, which may be why it was regularly cooking the previous owner’s lead acid battery on the tongue.

 

[Reed Cole]

I would figure out what's going on with that converter before you use it to charge your new LiFePO4 battery. Most LiFePO4 batteries have a maximum recommended charge rate of .5C, or half the capacity of the battery, which would be 220 amps in your case, so you should be fine charging at 80+55, 135A, or ~.3C.

Not quite able to follow everything without a diagram, but generally speaking you should be fine connecting any 12v circuits in parallel as long as the wires are properly sized and the voltages and currents are within the tolerable ranges for your equipment.

 

[TacomaJoe]

Without the wiring diagram I'm not totally sure what you're doing but I have the basics. You mention converter and charger, do you have a new charger? I'm picturing a battery bank with the SCC and crarger near by, with a feed to the WFCO panel. The old wire from the tongue will move to a fuse on the panel.

It is OK to have the 12V from the TV feeding the system, as noted the 12V stuff just gets paralleled fine.

One caution is placing any battery disconnect. You can't disconnect the WFCO because of the circuit that feeds your breakaway brake system.

 

[48Rob]

Reed,

Thank you for your thoughts.

I have attached a drawing that may help.

I do not intend to use the converter to charge my new LFP battery bank. I have a stand alone charger.
I will be using the WFCO simply as an AC-DC breaker/fuse panel.

 

[48Rob]

Without the wiring diagram I'm not totally sure what you're doing but I have the basics. You mention converter and charger, do you have a new charger? I'm picturing a battery bank with the SCC and crarger near by, with a feed to the WFCO panel. The old wire from the tongue will move to a fuse on the panel.

It is OK to have the 12V from the TV feeding the system, as noted the 12V stuff just gets paralleled fine.

One caution is placing any battery disconnect. You can't disconnect the WFCO because of the circuit that feeds your breakaway brake system.

Joe,

Thanks for your reply.

Your are correct with your understanding. I do have a new charger. I will have to think of a way to create a failsafe for the breakaway as I do have a system disconnect switch.
Maybe a very small LFP on the tongue.

My lack of understanding is with the amperage coming from my battery bank, going to the fuse box. I understand that the wire from my battery bank to the fuse box needs to be rated for the current it is able to carry, and that I need to choose that cable size based on my anticipated maximum use.
However, if I plan on charging currents of 40 Amps + 80 Amps (120 Amps total) am I pushing too many amps into the converter/breaker box which is rated at 55 Amps?
I think I need a better understanding of the ratings? The converter outputs 55 Amps as a battery charger, so that must be how the box is rated?
The Amps coming from my battery bank can easily go higher than 55 if I have multiple draws. The converter/fuse panel, DC side has a 40 Amp main fuse. Am I looking at it all wrong?

 

[time2roll]

The WFCO dc distribution panel should have a stack of small fuses and a set of larger main fuses in parallel. I believe the board will be printed with the max fuse rating for these positions. Good chance there is a pair of 30 or 40 amp fuses for the main giving at least 60 to 80 amps feed through.

 

[48Rob]

Time,

Thank you.

I hadn't thought to look on the circuit board.
It states "Maximum current 150 Amps"
Currently has 2-40 Amp fuses.

 

[TacomaJoe]

The charging currents from your SCC and charger to the battery don't use the wires to the WFCO. The wires to the WFCO need to handle the fuse panel load which is probably less than 30A, unless you deploy the slide, the awning and run the water pump at the same time the furnace is running. The fuse panel will only pull what it needs as it needs it, no matter what your chargers are doing.

If your batteries don't have bluetooth, I would suggest adding a shunt monitor to your system.

My current setup has a 100Ah sitting on the tongue to run the jack and brakes. I have a switch in the line to my main bank so I can keep the tongue system isolated or tie it in with the rest of the batteries. Being isolated, I could run my old FLA out on the tongue as well.

 

[48Rob]

Thank you Joe.

I do have a shunt/monitor, it isn't visible in the photo as it is inside the camper. Good tip though!
In addition to having "better" batteries than the lead acid that was on the tongue, I am trying to shave off unneeded weight. The battery on the tongue is very heavy.
Do you have Lithium as your main bank, and lead acid on the tongue? If so, doesn't your Lithium charger overcharge the tongue battery, or do you charge it separately?
I'm thinking maybe a 10 or 12 Amp hour scooter battery for the breakaway switch, which would be "charged" by the tow vehicle, and or a small charger maintainer from grid.