Montana Owners Club - Keystone Montana 5th Wheel Forum - View Single Post

Daryles · 03-30-2021, 07:21 AM

I just finished installing a Renogy 60A DC-DC charger in my 5th wheel.
The purpose of this is to be able to charge your RV batteries from your truck "safely" whether parked or driving. The 7 way cable from the truck to the RV does provide some charging. The most I have measured is about 7A. It would take all day and then some to recharge your batteries if they were low.
This gives you alternatives if you dont want to haul a generator on a short boondocking trip BUT you want backups to your solar power system (400W and expanding) if you have cloudy days.
By "safely" charging, I mean without draining the truck batteries to where you cannot start the truck AND where you dont fry your alternators. I have lithium batteries and when drained they can pull 100A charging.
Look up the YouTube video on burning out an alternator when charging a lithium battery.
In an emergency you CAN just use jumper cables from the truck to the RV to recharge them. Just ask the people in Texas who went through that record breaking deep freeze without shore power or a generator. They used their trucks and jumper cables to keep their RV batteries charged so they could run their furnaces.
Anyway the details...
I have an F350 Super Duty with dual 200A alternators and dual batteries. So the truck is more than capable of handling the load.
In the RV, 552Ah of lithium batteries and 400W of solar panels and a Victron 100/30 Smart Solar MPPT. I also kept the original 100Ah FLA battery as a backup. I have a 250A three way switch to control what is connected.

FYI, DC-DC chargers can come in two forms.
Isolated: you run + & - cables from the source battery to the charger then run + & - cables from the charger to the RV battery.
This installation I believe is best if you have separate source and RV vehicles.
Non-isolated: you run a + cable from the source battery to the charger then a + cable from the charger to the RV battery. A single - cable goes from the charger to the chassis. This installation I believe is best suited for a boat, class A, B, or C RV where all components share the same chassis.

The Renogy charger I chose is an Isolated version. Running copper wire has less losses than using the chassis. The steel frame is 33% less conductive than copper.

RV work.
I loosened the vinyl cover under the overhang covering the pin box by removing the 4 screws next to the pin box. I put the vinyl siding "J" channel face to face to make a conduit. Then I pushed the 4 gauge wire through the J channel. I did this so if I needed to add any future wiring I already had a conduit from the pin box to the battery compartment. I pushed a yard stick carefully between the vinyl and the insulation then turn it vertical to open a gap. I sharpened one end of the J channel and carefully pushed it through the gap between the vinyl and the insulation to the battery compartment.
I made these cables (+ and -) long enough (8' pin box to Anderson plug end, 17' total) to be able to reach the truck plug in from either side if the truck was parallel parked beside the RV.
I mounted the charger and 70A circuit breaker. All my equipment is mounted labeling upside down. This is due to the cooling fans of the equipment. I did not want them blowing hot air into each other. In this position the hot air is blowing away from each other. Other considerations was the position of the inverter 120vac outlets.

Truck work.
Routed the cables, installed the 90A circuit breaker. Put anti chaff cable wrap where necessary and secured all the cabling tight.
In the truck bed I used a PVC valve gromet in the truck bed sidewall hole as a gromet to prevent wire chaffing. Pay close attention to what goes on first when assembling the Anderson connectors. Slide weather boot onto cables, crimp on connector contacts, insert contacts into Anderson connectors.
I am fortunate the guys at my local auto parts store have giant cable crimpers (like bolt cutters). Once I had the cables pulled through the truck and secured and the RV cables cut to the lenght I wanted, I removed the cables from the RV and I drove to the auto parts store with all the cables. Once there the guys crimped all the connectors on the ends of the cables in the truck and for the RV cables. I had to grind down the sides of the Anderson contacts because when they crimped them onto the 4 gauge cable it flattened them a bit so they were too fat to go into the connectors easily. After grinding them down a tiny bit they fit comfortablely.
Took everything home and put the RV cables through the J channel conduit, assembled the Anderson connectors and connected the other end to the charger.
The charger requires a 12vdc on signal. I just put a wire with a switch from the charger to the 12vdc buss bar.
Testing...
Connected the truck to the RV via the Anderson connectors, started the truck, closed the circuit breakers in the truck and RV. Turned on the switch and "voila"!!
Green light on the charger.
I had already ran down my batteries to 40% (13vdc in my case). My Victron BMV-712 battery monitor measured 54A input current into my batteries. I think that’s pretty good for a 60A DC-DC charger. The battery state of charge (SOC) was up to 45% in 15 minutes. Truck was at idle speed.

When we left the house a few days later on our latest road trip, the RV batteries were at 39%. I decided to see how much they would charge with the tow cable + 400W solar panels. After 5 hours of travel time batteries were at 43%. Cloudy day. We had 1 hour to go before our overnight stop. I plugged in the Anderson connectors and turned on the DC-DC charger. It read 57A charging on my BMV. When we reached our overnight stop an hour later the batteries were 100%. Im really happy with that. The real test will be in a few days. We will be in the OBX boondocking for 5 days. No generator. Just solar and the DC-DC charger.

Parts
Renogy 60A DC to DC charger
Anderson 175A connectors
Anderson
SB175 Environmental Boot with Cover, Source Side
SB175 Environmental Boot with Cover, Load Side
(Anderson products from Powerwerx)
90' 4 gauge copper welders cable (flexible)
4 gauge copper lugs
Buss 90A circuit breaker
Buss 70A circuit breaker
12vdc switch, lighted
Scrap vinyl siding "J" channel

DC-DC charger, Isolated vs Non-isolated operation
https://alenconsystems.com/learning/new-current-war-isolated-vs-non-isolated-dcdc-converter/

Another aspect of this is being able to run one air conditioning (A/C) unit while driving.
You install a SoftStartRv (Mike Sokol has talked about this)
https://www.rvtravel.com/rv-electricity-softstartrv-hrdl-testing/
If you don't already have a transfer switch installed, wire one A/C unit to a transfer switch where you can run it from your inverter while driving. Your DC-DC charger will keep the batteries topped off while driving. You arrive at your destination with the RV already cooled down.

03-30-2021, 07:21 AM	#1
Daryles Montana Master Join Date: May 2019 Location: Alton Posts: 2,707 M.O.C. #24086	DC to DC charger I just finished installing a Renogy 60A DC-DC charger in my 5th wheel. The purpose of this is to be able to charge your RV batteries from your truck "safely" whether parked or driving. The 7 way cable from the truck to the RV does provide some charging. The most I have measured is about 7A. It would take all day and then some to recharge your batteries if they were low. This gives you alternatives if you dont want to haul a generator on a short boondocking trip BUT you want backups to your solar power system (400W and expanding) if you have cloudy days. By "safely" charging, I mean without draining the truck batteries to where you cannot start the truck AND where you dont fry your alternators. I have lithium batteries and when drained they can pull 100A charging. Look up the YouTube video on burning out an alternator when charging a lithium battery. In an emergency you CAN just use jumper cables from the truck to the RV to recharge them. Just ask the people in Texas who went through that record breaking deep freeze without shore power or a generator. They used their trucks and jumper cables to keep their RV batteries charged so they could run their furnaces. Anyway the details... I have an F350 Super Duty with dual 200A alternators and dual batteries. So the truck is more than capable of handling the load. In the RV, 552Ah of lithium batteries and 400W of solar panels and a Victron 100/30 Smart Solar MPPT. I also kept the original 100Ah FLA battery as a backup. I have a 250A three way switch to control what is connected. FYI, DC-DC chargers can come in two forms. Isolated: you run + & - cables from the source battery to the charger then run + & - cables from the charger to the RV battery. This installation I believe is best if you have separate source and RV vehicles. Non-isolated: you run a + cable from the source battery to the charger then a + cable from the charger to the RV battery. A single - cable goes from the charger to the chassis. This installation I believe is best suited for a boat, class A, B, or C RV where all components share the same chassis. The Renogy charger I chose is an Isolated version. Running copper wire has less losses than using the chassis. The steel frame is 33% less conductive than copper. RV work. I loosened the vinyl cover under the overhang covering the pin box by removing the 4 screws next to the pin box. I put the vinyl siding "J" channel face to face to make a conduit. Then I pushed the 4 gauge wire through the J channel. I did this so if I needed to add any future wiring I already had a conduit from the pin box to the battery compartment. I pushed a yard stick carefully between the vinyl and the insulation then turn it vertical to open a gap. I sharpened one end of the J channel and carefully pushed it through the gap between the vinyl and the insulation to the battery compartment. I made these cables (+ and -) long enough (8' pin box to Anderson plug end, 17' total) to be able to reach the truck plug in from either side if the truck was parallel parked beside the RV. I mounted the charger and 70A circuit breaker. All my equipment is mounted labeling upside down. This is due to the cooling fans of the equipment. I did not want them blowing hot air into each other. In this position the hot air is blowing away from each other. Other considerations was the position of the inverter 120vac outlets. Truck work. Routed the cables, installed the 90A circuit breaker. Put anti chaff cable wrap where necessary and secured all the cabling tight. In the truck bed I used a PVC valve gromet in the truck bed sidewall hole as a gromet to prevent wire chaffing. Pay close attention to what goes on first when assembling the Anderson connectors. Slide weather boot onto cables, crimp on connector contacts, insert contacts into Anderson connectors. I am fortunate the guys at my local auto parts store have giant cable crimpers (like bolt cutters). Once I had the cables pulled through the truck and secured and the RV cables cut to the lenght I wanted, I removed the cables from the RV and I drove to the auto parts store with all the cables. Once there the guys crimped all the connectors on the ends of the cables in the truck and for the RV cables. I had to grind down the sides of the Anderson contacts because when they crimped them onto the 4 gauge cable it flattened them a bit so they were too fat to go into the connectors easily. After grinding them down a tiny bit they fit comfortablely. Took everything home and put the RV cables through the J channel conduit, assembled the Anderson connectors and connected the other end to the charger. The charger requires a 12vdc on signal. I just put a wire with a switch from the charger to the 12vdc buss bar. Testing... Connected the truck to the RV via the Anderson connectors, started the truck, closed the circuit breakers in the truck and RV. Turned on the switch and "voila"!! Green light on the charger. I had already ran down my batteries to 40% (13vdc in my case). My Victron BMV-712 battery monitor measured 54A input current into my batteries. I think that’s pretty good for a 60A DC-DC charger. The battery state of charge (SOC) was up to 45% in 15 minutes. Truck was at idle speed. When we left the house a few days later on our latest road trip, the RV batteries were at 39%. I decided to see how much they would charge with the tow cable + 400W solar panels. After 5 hours of travel time batteries were at 43%. Cloudy day. We had 1 hour to go before our overnight stop. I plugged in the Anderson connectors and turned on the DC-DC charger. It read 57A charging on my BMV. When we reached our overnight stop an hour later the batteries were 100%. Im really happy with that. The real test will be in a few days. We will be in the OBX boondocking for 5 days. No generator. Just solar and the DC-DC charger. Parts Renogy 60A DC to DC charger Anderson 175A connectors Anderson SB175 Environmental Boot with Cover, Source Side SB175 Environmental Boot with Cover, Load Side (Anderson products from Powerwerx) 90' 4 gauge copper welders cable (flexible) 4 gauge copper lugs Buss 90A circuit breaker Buss 70A circuit breaker 12vdc switch, lighted Scrap vinyl siding "J" channel DC-DC charger, Isolated vs Non-isolated operation https://alenconsystems.com/learning/new-current-war-isolated-vs-non-isolated-dcdc-converter/ Another aspect of this is being able to run one air conditioning (A/C) unit while driving. You install a SoftStartRv (Mike Sokol has talked about this) https://www.rvtravel.com/rv-electricity-softstartrv-hrdl-testing/ If you don't already have a transfer switch installed, wire one A/C unit to a transfer switch where you can run it from your inverter while driving. Your DC-DC charger will keep the batteries topped off while driving. You arrive at your destination with the RV already cooled down.