DC to DC charger - Montana Owners Club

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.

rames14 · 03-30-2021, 08:45 AM

We have an appointment with Future Sales to install the Li-BIM charger. Since we have the Super Solar on our new unit, it also comes with soft start on both AC’s. A friend has this system and is seeing 50 amp charging while driving. Good luck with your new system. Are you adding more panels on your roof down the road?

Daryles · 03-30-2021, 10:14 AM

Yes I will be adding more solar panels. With the pre installed solar wiring (10 gauge, how lame) i can go up to 30A. The next 200W panel will go parallel to the existing two panels. This will give me 20vdc at 27A.
I will need to install an additional roof to basement 4 gauge cable to handle any future expansion.

hemiallen · 03-30-2021, 10:43 AM

Thank you Daryl.
Very informative post, and good timing for me. Bad news for me is I didn't check the dual alternators option on my trucks build sheet, so all I have is a 180A single. Curious what that equates to for supplying the dc-dc charger?

Thank you

Allen

Daryles · 03-30-2021, 01:26 PM

Allen,
You can check with your trucks manufacturer for output capacity. Or find out the make/model alternator and go directly to their webpage and get the specs.
You can get smaller DC-DC chargers, say a 30A (same output you would get with a RV ready generator, 30A). Your alternator should be able to manage that easily.
When running the 60A DC-DC charger while the truck is idling, I plan on putting a fan blowing on the alternator to help with cooling. When testing it I checked both alternators with a laser thermometer. One was 88°F the other 128°F. Air temperature was 54°F. So I'm guessing the hi temp one was the one doing all the work.
That test was only 15 minutes.

hemiallen · 03-30-2021, 01:39 PM

Thanks again.
Good plan on the fans for cooling while camp-recharging dc-dc. So I need to check Mfg ( probably dodge) to see if it actually puts out a max of 180 Amps, sorry if I got that wrong. And you are just powering from one battery's terminals vs direct from the Alternator, I assume? That's how I wired the 2 1/0 cables feeding my rear winch power, hoping if I go this route just using it for power. I also assume oversizing the renology for me ( 30a vs 60a) isn't detrimental with my 180A alternator, just more expensive, or could it possibly overload the Alternator?

Are these the same type fans you mentioned to help the RV fridge?

Thank you Daryl

Daryles · 03-30-2021, 02:44 PM

Yes, the DC-DC charger is wired into the left truck battery through a 90A circuit breaker. The 70A circuit breaker goes between the charger and the RV batteries. This is in accordance with the installation instructions for the charger.
If you already have 1/0 wiring feeding a winch on the back of your truck, you are 1/2 way there.
Be careful of the charger you use. Verify your alternator can handle it.

https://m.youtube.com/watch?v=jgoIocPgOug

To help cool the alternator when parked and idling with the DC-DC charger running I used a regular 120vac fan plugged into the trucks receptacle. Truck has its own 480W inverter.

kowbra · 03-31-2021, 07:28 AM

Great writeup, @Daryles !

Thanks for the detailed explanation,

Brad

PNW Fireguy · 03-31-2021, 08:37 AM

Quote:

Originally Posted by Daryles

Yes I will be adding more solar panels. With the pre installed solar wiring (10 gauge, how lame) i can go up to 30A. The next 200W panel will go parallel to the existing two panels. This will give me 20vdc at 27A.
I will need to install an additional roof to basement 4 gauge cable to handle any future expansion.

Not to hijack your thread but why not add panels with bypass diodes in series and keep the 10 gauge wiring while boosting your voltage on the PV run to negate any drop. We are now planning to run our PV array at 150vdc, voltage drop will be a neglible figure. On the positive side (no pun intended) our array will harvest sooner and later within the day due to the increased voltage. The bypass diodes shunt any shaded panels within the array.

jetskier · 03-31-2021, 10:34 AM

I agree. Don't do parallel exclusively. Here's a sample of the output on my setup with six panels (two parallel strings of 3 panels in series). I'd run it at full series, but it would exceed the 150V input on my controller (Victron 150/85). I've seen 80V in some situations as it's tracking. It has never exceeded 17amps so the 10awg is fine. Not to mention at a higher voltage, the voltage drop is lower than at 18-24V. I do have awg4 from the controller to the batteries. I have a total of 1175W solar panels on the roof. This screenshot was the peak output at midday taken last Friday.

rames14 · 03-31-2021, 10:56 AM

So that I’m reading correctly, you’re putting 68 amps back into your battery? We get our new 3230CK in two weeks. I have a lot to learn. I currently have a Bogart meter with no solar. This will be a learning curve.

jetskier · 03-31-2021, 11:10 AM

Quote:

Originally Posted by rames14

So that I’m reading correctly, you’re putting 68 amps back into your battery?

Yes, that is correct. If I run my generator at the same time, my inverter/charger adds another 115-120A . I've seen 180-190a charging my battery shunt at midday. It's below the charge limit of 200A (0.5C) of my 400AH bank.

PNW Fireguy · 03-31-2021, 12:22 PM

We had to go with 250/60 smart after taking into account temp correction.
Prior to migrating from our old system we routinely got 70A going into our bank.

Daryles · 03-31-2021, 03:34 PM

Yes, I agree on the 3 series/ 2 parallel configuration when I add more panels.
I wish I had a table showing the Victron 100/30 MPPT conversion of input voltage/current to output voltage/current.
It would greatly help in deciding which way to go with the wiring rather than trial and error.
Here's a good article on mixing panels, more so for the math involved really.
https://solarpanelsvenue.com/mixing-solar-panels/

jetskier · 03-31-2021, 03:41 PM

Quote:

Originally Posted by Daryles

Yes, I agree on the 3 series/ 2 parallel configuration when I add more panels.
I wish I had a table showing the Victron 100/30 MPPT conversion of input voltage/current to output voltage/current.
It would greatly help in deciding which way to go with the wiring rather than trial and error.
Here's a good article on mixing panels, more so for the math involved really.
https://solarpanelsvenue.com/mixing-solar-panels/

Keep in mind, the 100/30 is limited to 440W of solar w/ 12V battery config. The 100 is the open circuit voltage of the PV side and the 30 is the rated charge current on the battery side.

https://www.victronenergy.com/upload...-100-50-EN.pdf

jbeletti · 04-05-2021, 09:11 AM

@Daryles - this is a worthy project for those who need it.

Before I took delivery of my F150, I drew up the plan and drop-shipped the parts to my truck upfitter and had them install the charging infrastructure on it, then I installed the Victron 30A DC-DC charger in the RV and made the interconnection. Love it!

In the future, I'd like to increase that charge to 60A or so but will do so when I upgrade the truck or upgrade the alternator in my F150.

Pics: https://beletti.smugmug.com/RV/2020-...ries/i-Hb87n8w

Arkventurer · 04-18-2021, 05:59 PM

Daryles

Do you have any pictures of where you mounted the circuit breaker under the hood? I bought the Renogy 40 amp dc dc charger and a 200 amp relay. I have an F250 with the 6.7l and dual alternators. I want to be able switch the dc dc charger at the truck so I intend to use the relay attached to a switch. My issue is where to mount the relay and breaker in the engine compartment? There doesn’t seem to be much room...

Thanks

Daryles · 04-19-2021, 08:52 AM

Arkventurer, here you go
I used the left side battery. There is some space near the brake booster.
I don't understand the 200A relay?
To turn on the charger only requires 12vdc present at the charger terminal from the source battery, 12vdc present at the charger terminal from the RV battery, then a 12vdc "on" signal. Some people have wired the 12vdc "on" signal to the trailer marker lights. Then you can turn it on/off from the truck using the lights switch.
You have a circuit breaker at each side so you can control power to it.

carlrx7 · 04-20-2021, 08:38 PM

I was getting ready to do this install with the same 60A DC-DC charger. But then I decided i wanted to be able to charge a 24 or 48v battery bank with the truck as well (dual 220A alts) The cost of SCC's when in the 1.6K/2k Solar at 12v is a hard pill to swallow.

I decided to go a slightly more flexible route. I grabbed a 2k watt (4K Max)pure sine inverter off Aliexpress and plan mount it behind the rear seats of the truck. I will run 2ga 105c wire to the inverter/through a 200A CB, directly to battery. Then install a covered 120V/15A receptacle (weather resistant) in the bed near the trailer 7-way. Using a 25 ft/15A 10 gauge extension cord, i'll connect the inverter to the bedplug, then snake it through the rv pinbox and down into the trailer and wire to the gen/prepped box.

My current 12v lithium battery will be charged by the factory converter (50As observed) with 700 watts and power the Fridge with 300 watts for the fridge. Should be no problem with the 2K inverter without the fan spinning up to max.

Later down the road, the truck inverter will power a 24/48v multiplus to charge the bank.

hemiallen · 04-20-2021, 09:01 PM

That's a new one , so the trucks batteries will run the inverter, you'll feed power while driving through the Gen prep's box and use the RV converter to charge your batteries. Seems less potential to cause harm to the truck's recharge system.
Is this the inverter you purchased
https://www.aliexpress.com/item/4000...8%2315607%2378

Will what you purchased max the converter-charger's charging rate?

Hope it works good for you, changing to 120v seems like a good option.

Allen

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