Real world experience here. Mike's solution is good and used by folks I know to have higher charge rates. But I use a Victron DC/DC 12/12-9 converter ($63) that charges at 9 amps through the 7-pin connector. No need to rewire or use separate charging wire to the trailer. I checked to make sure my tow vehicle (4Runner) had 12 ga wire with 10 amp fuse from the factory. I routinely charge at 9 amps while driving (monitored via bluetooth), which I can combine with solar while driving, topping off the batteries nicely. This setup definitely won't fully charge depleted batteries, but has been adequate for us for years to avoid using the generator.
Great info as always, Mike. While I don't have a lithium battery set up, I do have a question about sufficient charging of my deep cycle lead acid batter running my 12 v refrigerator while towing. Charging is does not seem sufficient to recharge the 2 6V batteries. After towing 4+ hours, I've actually depleted them by about 5% after starting out with full power on shore power. Need new batteries or refrigerator drain is too much for a alternator charging system?? Thanks!!
I believe most 7 way power connectors provide 30 amps of power to the trailer for whatever you want to connect it to. I hook mine to a 20amp DC to DC charger which recharges my 400 ah Lithium set up just fine while traveling. They make larger capacity DC to DC chargers (40 amp, 60 amp) but then you do need a larger size conductor with fusing from the engine battery to the trailer.
Note that not all 7-way plugs are connected to 10-gauge conductors and a 30-amp fuse. Some use 12-gauge wire rated for 20-amps. And to be safe at 30-amps the contacts must be perfectly clean and unoxidized.
Also, be aware that the voltage drop over an extra 20+ feet of copper wire can create a substantial voltage drop that reduce SoC level. That’s why it’s best to mount the DC-DC converter in the trailer near the batteries. The DC-DC charger can then make up for any voltage drop.
Last spring I installed a Redarc 50 amp DC to DC charger in my F350 diesel that we have a large truck camper on. We're fulltimers & we use a lot of electricity, & I have a large solar array on the roof, but it's not reliable enough to fully recharge our 736AH of lithium as we travel. So, if you're travelling most days, DC to DC chargers are the greatest rving accessory to come along in recent years. I no longer have "battery capacity" anxiety. We typically use 150-200 AH a day & driving a few hours the next day fully makes it up as it recharges along with the solar. We rarely stay in rv parks. These are one of the best investments you can make in your rv lifestyle if you're spending a fair amount of time on the road & like to boondock.
Mike, My AGM house batteries are charged by the alternator through relays in my battery control center on my 1999 Fleetwood Bounder. If I switch to lithium batteries will I need to add a DC to DC charger to the alternator and bypass the battery control center? These relays allow both the house and chassis batteries to charge while driving down the road and while plugged in to shore power, and to combine both battery banks so the coach will start in a low battery situation.
Real world experience here. Mike's solution is good and used by folks I know to have higher charge rates. But I use a Victron DC/DC 12/12-9 converter ($63) that charges at 9 amps through the 7-pin connector. No need to rewire or use separate charging wire to the trailer. I checked to make sure my tow vehicle (4Runner) had 12 ga wire with 10 amp fuse from the factory. I routinely charge at 9 amps while driving (monitored via bluetooth), which I can combine with solar while driving, topping off the batteries nicely. This setup definitely won't fully charge depleted batteries, but has been adequate for us for years to avoid using the generator.
If you are willing to charge with only 20A, Renogy makes a DC to DC Charger for just over $100.
https://a.co/d/6I0zXMu
Great info as always, Mike. While I don't have a lithium battery set up, I do have a question about sufficient charging of my deep cycle lead acid batter running my 12 v refrigerator while towing. Charging is does not seem sufficient to recharge the 2 6V batteries. After towing 4+ hours, I've actually depleted them by about 5% after starting out with full power on shore power. Need new batteries or refrigerator drain is too much for a alternator charging system?? Thanks!!
I believe most 7 way power connectors provide 30 amps of power to the trailer for whatever you want to connect it to. I hook mine to a 20amp DC to DC charger which recharges my 400 ah Lithium set up just fine while traveling. They make larger capacity DC to DC chargers (40 amp, 60 amp) but then you do need a larger size conductor with fusing from the engine battery to the trailer.
Note that not all 7-way plugs are connected to 10-gauge conductors and a 30-amp fuse. Some use 12-gauge wire rated for 20-amps. And to be safe at 30-amps the contacts must be perfectly clean and unoxidized.
Also, be aware that the voltage drop over an extra 20+ feet of copper wire can create a substantial voltage drop that reduce SoC level. That’s why it’s best to mount the DC-DC converter in the trailer near the batteries. The DC-DC charger can then make up for any voltage drop.
Last spring I installed a Redarc 50 amp DC to DC charger in my F350 diesel that we have a large truck camper on. We're fulltimers & we use a lot of electricity, & I have a large solar array on the roof, but it's not reliable enough to fully recharge our 736AH of lithium as we travel. So, if you're travelling most days, DC to DC chargers are the greatest rving accessory to come along in recent years. I no longer have "battery capacity" anxiety. We typically use 150-200 AH a day & driving a few hours the next day fully makes it up as it recharges along with the solar. We rarely stay in rv parks. These are one of the best investments you can make in your rv lifestyle if you're spending a fair amount of time on the road & like to boondock.
Mike, My AGM house batteries are charged by the alternator through relays in my battery control center on my 1999 Fleetwood Bounder. If I switch to lithium batteries will I need to add a DC to DC charger to the alternator and bypass the battery control center? These relays allow both the house and chassis batteries to charge while driving down the road and while plugged in to shore power, and to combine both battery banks so the coach will start in a low battery situation.