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Old 09-14-2021, 02:18 PM   #1
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Options for LIFePO4 Charging in Fifth Wheel

Based on the feedback from the troubleshooting I did on my existing inverter, I'm about 95% sure it's toast and I will likely replace it along with my single FLA Group 24 battery over the off season. Currently running the stock WFCO 9855 deck mount converter/charger.

Intending to do 2X100ah Lithium batteries and a DC-DC charger to protect the truck's alternator. I need to power a residential fridge (best estimate is 67amp @12V starting, and 16amp @12V running plus inverter losses) plus a CPAP for occasional one night boondocking, plus running the fridge while traveling. Figuring a 2000W pure sine inverter will handle the CPAP and fridge for AC needs. Also typical 12V loads like the lights.

That leaves "regular" charging while on shore power to figure out.
Possibilities I'm considering:

1. Inverter/charger (since I need a new inverter anyway)
-unhook the charge lead from existing WFCO converter

2. Replace WFCO converter with a lithium compatible (WFCO or Progressive Dynamics) converter/charger

3. Keep the existing converter/charger and run its 12V charging output straight to the DC-DC charger, using it to modulate charging for the batteries on shore power or when truck is running
-from a "number of components" perspective, this seems elegantly simple, but no idea if it's feasible and/or efficient. I assume I'd need a way to switch between alternator power from the truck and the charging current from the converter/charger?

Interested in thoughts/feedback about the various options (or any others) as I'm sure they each have pros and cons--including stuff I'm not even aware of I'm sure.
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Old 09-14-2021, 02:29 PM   #2
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Unless you've made a typo and meant a 2000W PSW inverter instead of 200W I think you're asking for trouble. The start up of 66A at 12V will result in a momentary 804W load on the inverter, way over your 200W spec. I'm thinking that 200W is a little light for any kind of typical load as your refrigerator alone will consume 192W. I think you should rethink your inverter wattage or maybe fix the typo. Good luck.
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Old 09-14-2021, 02:31 PM   #3
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I’m very happy with our Xantrex XC2000w inverter charger. $700 on Amazon. It will charge my LiFePo4 at 80 amps, so I can go from 30% to 100% in less than 2 hours, either on generator or shore power. It’s also has 3000w surge and, we can run our microwave on it if we turn off all other loads. I didn’t like that standby mode uses a fair amount of power, so I installed an inverter disconnect when installing the Xantrex. Also like the Bluetooth, but don’t like that Bluetooth disconnects and has to be manually reconnected when phone goes out of range. For the past year, it’s been pretty bulletproof, and is a good match for battery bank of 150-250ah. For more than 250ah, they have a 3,000w model. Like that it also negates the need for a transfer switch and stand alone charger.

Wiring can be a challenge but not insurmountable. I chose to keep it close to dc loads, so dc wiring was easy. But for the ac side, I had to route a heavy cable through the floor of pass thru and toward the rear, and the up under the kitchen sink to connect to the breaker panel.
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Old 09-14-2021, 02:38 PM   #4
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Quote:
Originally Posted by arcaguy View Post
Unless you've made a typo and meant a 2000W PSW inverter instead of 200W I think you're asking for trouble. The start up of 66A at 12V will result in a momentary 804W load on the inverter, way over your 200W spec. I'm thinking that 200W is a little light for any kind of typical load as your refrigerator alone will consume 192W. I think you should rethink your inverter wattage or maybe fix the typo. Good luck.
Typo Corrected! The current inverter is a 1000W WFCO unit from the factory. It's an early 2019 build, but I just bought the trailer. No idea if the inverter ever actually ran this fridge. Certainly doesn't now...

Figured upgrading to a 2000W unit would be a safe bet for the fridge, and give me some space for the CPAP.
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Old 09-14-2021, 02:45 PM   #5
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I use cpap. The XC2000 handles that and all other loads easily. Although, I have since added a dc adapter for cpap which reduces battery usage somewhat. I also have a compressor fridge, but it’s 12v.
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Old 09-14-2021, 02:52 PM   #6
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I use cpap. The XC2000 handles that and all other loads easily. Although, I have since added a dc adapter for cpap which reduces battery usage somewhat. I also have a compressor fridge, but it’s 12v.
I've also considered a DC power supply for the CPAP. It seems a little silly to take a battery, invert it to AC current, plug in a CPAP, then let it convert it back to DC!
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Old 09-15-2021, 05:29 PM   #7
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Currently running the stock WFCO 9855 deck mount converter/charger.
Intending to do 2X100ah Lithium batteries
DC-DC charger to protect the truck's alternator.
residential fridge (best estimate is 67amp @12V starting, and 16amp @12V running
CPAP for occasional one night boondocking, plus running the fridge while traveling. Figuring a 2000W pure sine inverter will handle the CPAP and fridge for AC needs. Also typical 12V loads like the lights.


A 1000 watt inverter is probably enough. It most likely can sustain 50% over current for the brief time the compressor is starting. You can add a 120 volt branch to the inverter output to power the CPAP. Don't try to power the whole 120 house system.

Use short oversize 12 volt supply wire to keep line loss for starting low.

A 2000 watt inverter will need about 170 amps 12 volts to deliver 2000 watts. Check lithium battery capacity. Lead acid would require at least 400 amp hour deep draw.

That leaves "regular" charging while on shore power to figure out.
Possibilities I'm considering:

1. Inverter/charger (since I need a new inverter anyway)
-unhook the charge lead from existing WFCO converter


You probably don't need a new inverter. But, splurge, get an inverter/charger/converter with transfer switch built in.

Keep in mind the charge lead on the WFCO also back-feeds the house 12 volt fuse panel from the batteries. Just disconnect the 120 volt input to the
WFCO.

2. Replace WFCO converter with a lithium compatible (WFCO or Progressive Dynamics) converter/charger

The WFCO lithium charger may drop in replace your current charger. Check it out.

3. Keep the existing converter/charger and run its 12V charging output straight to the DC-DC charger, using it to modulate charging for the batteries on shore power or when truck is running
-from a "number of components" perspective, this seems elegantly simple, but no idea if it's feasible and/or efficient. I assume I'd need a way to switch between alternator power from the truck and the charging current from the converter/charger?


This off the wall method may take some significant design skills. You usually want heavy short 12 volt wire with few connectors for charging and inverting.

I wish you good luck and happy trails ahead!
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