DC to DC Charger ?s

[C&G in FL]

My RMD8555 Dometic died last June and I replaced it with a Norcold 12v compressor refrigerator, with which I am most pleased. I have two 100 amp hour Battleborn lithium batteries for a total capacity of 200 amp hours, and one 160 watt solar panel. I am considering installing a DC to DC charger in order to feed the batteries when towing. While I am very familiar with most things electrical, I know nothing about DC to DC chargers.

If there is a forum member who has installed a DC to DC charging system and is willing to PM me detailed how to instructions, I would truly appreciate your insights. The things I need to know are what components are needed and where they should be installed. Recommendations of specific manufacturer part numbers would also be appreciated.

I need to know:

1. How to protect the alternator in my F-150. I am making the assumption that direct connection to the alternator’s output or the F-150’s battery is the starting point.

2. Wire gauge required from the tow vehicle to the trailer and how to get the wire into the trailer. I’m guessing I would have to add some kind of a connector to the front of the trailer and continue running the wire under the trailer to a sealed hole in the floor near the batteries. Would I need to run a ground wire from the tow vehicle also or can I just ground to the trailer’s frame?

3. What components are needed at the battery? Again, I am guessing this is where the actual DC to DC charger should be located. What gauge wire is needed to connect the charger to the battery? And finally, does the DC to DC charger need to be isolated to protect it from damage when connected to shore power when the converter takes over charging the batteries?

Thanks in advance to anyone who can enlighten me.

 

[iamunique127]

Sorry I can't help with your DC-DC questions. I was under the impression the batteries were already charged by the tow vehicle when connected.

 

[MVA]

I installed a DC-DC converter for charging while towing on our 100 Ahr LiFePO4 battery. For the Victron DC-DC models, the main options are bluetooth connectivity and max current. I did not need bluetooth connectivity; once you set the output voltage, I was done. The current output criteria is a more interesting design issue. At one time, ETI was installing 18 amp max Victron bluetooth DC-DC units. The higher current can draw down the input voltage on your TV. I don't have the links, but there are examples on this forum on that occurrence. Hence, on the advice of another forum member, I purchased 9 amp unit.
https://www.amazon.com/gp/product/B07L6H8VKL

It works well, inexpensive, quality made, and I can get more than 50 A-hr in a 6 hour tow day.

YMMV

edit: while this is an isolated unit, I just wired the negative leads together effectively making it a non-isolated unit.

 

[SRS]

Sorry I can't help with your DC-DC questions. I was under the impression the batteries were already charged by the tow vehicle when connected.

That's true. However if you have lithium batteries, they can draw more electricity than your alternator can produce and burn it up. This may depend on the brand and model year of your TV. Lead acid and AGM batteries are not an issue.

 

[dstreight]

Been using a Sterling BB1260 the past 4-years to keep the 7500Wh LFP battery charged while towing (2007 Chevy HD2500 Silverado or a 1999 Toyota LandCruiser; both with stock alternators) and it has worked perfectly. Since the alternators are relatively low amp rated...the most I see coming from the BB1260 is 30-35amps with 25-30amps being typical.

The BB1260 serves as an isolator and it will only flow current if the TV battery is at 13.2v or higher (to protect the TV's battery).

We use the HD2500 most of the time and one of these days I'll get around to installing a higher output (Mechman) alternator to up the current flow to the LFP. But, as it is, it works fine.

 

[CE Vogel]

I suggest this RedArc DC-DC converter: https://www.redarcelectronics.com/us/battery-chargers/trailer-battery-charger
Assuming your tow vehicle already has a charge line through the 7-pin connector, this is easy to install. Find the charge line in your trailer, cut the wire (after disconnecting the batteries and tow vehicle), and wire this in per the instructions. It will protect your tow vehicle from overload by the lithium batteries, boost the tow vehicle voltage to appropriate lithium battery charge voltage, and even disconnects itself when the tow vehicle turns off to prevent starter battery drain. I have a different DC-DC converter from RedArc that also includes a solar MPPT charge controller, and after three years it is still working flawlessly.

 

[alanmalk]

...
I have a different DC-DC converter from RedArc that also includes a solar MPPT charge controller, and after three years it is still working flawlessly.

Its a slow night before Thanksgiving so perhaps I can shed some light.


The magic in MPPT is a DC-DC converter inside. It only flips the input/output voltage/amp equation compared to a vehicle DC-DC converter.


MPPT takes a high voltage-low amps and "converts" it to lower voltage-higher amps, while a DC-DC converter for vehicle charging takes low voltage-high amps and convert it to higher voltage-lower amps. The best part of this magic is that they both do this trick at very high efficiency - meaning no power is wasted in the form of heat. (Well, this is the real world so no, not 100% efficient, but pretty darn close).


Lets take a closer look at MPPT first. Your solar panel could be producing 10 amps (max) at 20 volts. That is 200 watts going into the MPPT controller. But Lithium batteries charge best at 14.5 volts, so coming out of the MPPT controller is 13.79 amps. (Reminder, using the conversion of Voltage x Amps = Watts, and assuming 100% efficiency.) So, 200 watts in, 200 watts out, at just the right voltage. Pretty nice!


And the vehicle DC-DC converter? The same in reverse. Picking the usual alternator voltage of 13.8 V, what does the DC-DC converter need for input amps? If the device in question limits the output amps to 18 A at 14.5 V (= 261 watts), then input amps will be 261/13.8 = 18.91 input amps.


Note, MPPT is primarily controlling the output voltage (amps are constrained by the solar system) while DC-DC converters are controlling both output voltage and output amps. A heavy-duty alternator could produce 200 amps and a bank of parallel batteries (any chemistry) could suck up 200 amps. The converter is in the middle to keep everything in a reasonable balance.


So why do you "need" a DC-DC converter for tow charging? First, the usual 13.8 volts won't completely fill Lithium batteries. (Perhaps to 70-80%?) Second, the long run of wire from alternator to the back seat of an E'21 where the batteries are located is 30-40 feet. That produces a whopping voltage drop, especially in my Tacoma/trailer setup. If I tried to run my fridge on DC while towing, by the end of the day I would have depleted batteries - not charged batteries. (AGM until last year, Lithium would be even worse!) Ouch.


Worrying about Lithiums destroying alternators? Well, my parallel AGM batteries could suck up more amps than 2 Lithiums. (Remember, Lithiums have a BMS that limit charge currents, among other protections.) Saved by that nasty voltage drop! Acting like a heat producing, energy wasting resistor, it keeps too much current from flowing - even if you want it. So, no, a DC-DC converter is not needed to protect an alternator. Possibly, if the Lithiums were just a few feet away from the alternator, like my starter battery (a power hungry size 31 AGM by the way), then perhaps something might be needed between the two. But alternator damage is the least of my worries when towing.


If I were to make the decision to use a DC-DC converter with my fairly new Lithiums, I would put it at the back end of the Tacoma and run a dedicated, heavy gauge feed wire to the unit from the alternator. Then from the unit run the 14.5 volts to the 7 pin connector. Yes, I will still have to live with some voltage drop but probably half as much as previously.


Hope this doesn't put too many people to sleep...

 

[splitting_lanes]

I ran 8 agw wire from the alternator to a power plug connector that’s mounted next to the 7 pin connector in the bed. From there, there’s a second pigtail that’s 8 agw that runs to the dc dc converter.

The main reason I put the second pigtail in was the ground on the 7 pin would fail after a period of time, causing the brakes on the trailer to disconnect. In fact, I believe it was you who answered my wife’s plea for help last year when our brakes kept disconnecting. Small world.

Anyways, if you do route power through the 7 pin, add an additional ground. Or, if you’d like, I’ll look through my parts orders and send you links to everything I used. It works great, I run my fridge on dc, and the dc dc converter has no problems running it and keeping the battery fully charged.

 

[jjdeluca]

I ran 8 agw wire from the alternator to a power plug connector that’s mounted next to the 7 pin connector in the bed. From there, there’s a second pigtail that’s 8 agw that runs to the dc dc converter.

The main reason I put the second pigtail in was the ground on the 7 pin would fail after a period of time, causing the brakes on the trailer to disconnect. In fact, I believe it was you who answered my wife’s plea for help last year when our brakes kept disconnecting. Small world.

Anyways, if you do route power through the 7 pin, add an additional ground. Or, if you’d like, I’ll look through my parts orders and send you links to everything I used. It works great, I run my fridge on dc, and the dc dc converter has no problems running it and keeping the battery fully charged.

I've been following this thread with interest, as I have similar questions to "C&G in FL". So, when you ran the 8 awg wire from the alternator to the new power plug connector in the truck bed, then the 8 awg pigtail to the DC-DC converter in your trailer, am I correct in assuming that you cut the wire to the 7 pin in your truck bed (essentially bypassing the 7 pin)? Thanks,
Jim

 

[John in Santa Cruz]

I installed a Orion TR 12/18 in my Escape 21 after installing 412AH of Lithium.

I discovered with my F250 longbed 4x4 diesel truck, in order for the Orion to deliver about 15 amps or so to the batteries, it was drawing its input power from the vehicle down to like 10 volts due to the 40+ feet of wiring in the truck+trailer combined, and 14V * 15A is 210 watts, 210 watts at 10 volts is 21 amps. thats a vicious cycle. it was more than the truck was happy with. note the voltage AT the truck alternator and batteries remained in the high 13's where it shoudl be.

In order to install the DC DC in the back of my trailer, I had to run a second AWG8 wire from the batteries to the breakaway switch otherwise I wouldn't have emergency braking.

I've switched the Orion off, its not done me any good. my 360W solar is plenty good enough. I too have a Norcold DC compressor fridge, my batteries will run our normal camping load for at least a week and still have 40% capacity left. Yes, 412AH is a lot of battery, its 2 x 206AH SOK's.

 

[splitting_lanes]

I've been following this thread with interest, as I have similar questions to "C&G in FL". So, when you ran the 8 awg wire from the alternator to the new power plug connector in the truck bed, then the 8 awg pigtail to the DC-DC converter in your trailer, am I correct in assuming that you cut the wire to the 7 pin in your truck bed (essentially bypassing the 7 pin)? Thanks,
Jim

Both pigtails have ground and hot, but the secondary pigtails hot only goes to the input of the dc dc converter.

Both grounds go to the frame of the trailer/tow vehicle.

 

[oldwave]

The most effective way to do this is to run dedicated wire, 4 gauge or larger from the battery terminals to an Anderson connector and then install the same gauge directly to the batteries or a bus bar. Victron Orion will give you plenty of adjustment to control when the charger will shut down and wil isolate your batteries from the truck when the truck is off as it has engine charging detection. This will keep the lithium batteries from draining the truck battery if you stay hooked up as the lower resistance lithium batteries will try to charge from your starter battery when the alternator is off. These units can be set as a power supply or battery charger. I’d recommend the iso version and run a dedicated ground along with the hot so won’t disturb and brake connections then
They also have smart alternator versus conventional settings.

 

[rubicon327]

I've been following this thread with interest, as I have similar questions to "C&G in FL". So, when you ran the 8 awg wire from the alternator to the new power plug connector in the truck bed, then the 8 awg pigtail to the DC-DC converter in your trailer, am I correct in assuming that you cut the wire to the 7 pin in your truck bed (essentially bypassing the 7 pin)? Thanks,
Jim

If I understand your question correctly the stock tow vehicle charge line can be disconnected if a dedicated power line is run but this disconnection should take place where the 7-pin umbilical terminates on or in the trailer. I would not modify the tow vehicle wiring. I would keep the 7-pin +12V “hot” just in case you tow another trailer where you might want the charge line active.

 

[Centex]

Please note differences between Victron Orion Chargers and Converters

.... Victron Orion will give you plenty of adjustment to control when the charger will shut down .... They also have smart alternator versus conventional settings.

Folks should take care to note:

These features / capabilities are only found on the Victron Orion-Tr Smart DC-DC Charger units.

They are not found on the Victron Orion-Tr DC-DC Converters such as that linked by MVA in post #3 above which per Victron are not "intended for battery charging" (though they will serve to charge a battery, within certain limits, at a set constant voltage).

There are other differences, such as the converters not offering the capability to 'automatically optimize' LiFePO4 charging.
--------
The converters do offer a more economical solution for providing constant voltage-regulated output when given variable battery voltage levels (buck-boost) when that's one's need (i.e. used in a strictly "power supply" mode). IMO that's their "intended" application.

 

[DougG-ESC]

I put in a redarc BCDC1240D a few years back, and have been very happy with it. A DC-Dc charger works best if it is as close as possible to the trailer batteries, so I mounted mine in the front storage box next to the batteries, I ran 4awg from the truck battery to the rear bumper (with a breaker) and put a flush mount Anderson plug next to the 7 pin on the bumper. I then ran a 6awg pigtail, with an anderson plug, from the trailer batteries, up to the hitch.

 

[MVA]

Folks should take care to note:

These features / capabilities are only found on the Victron Orion-Tr Smart DC-DC Charger units.

They are not found on the Victron Orion-Tr DC-DC Converters such as that linked by MVA in post #3 above which per Victron are not "intended for battery charging" (though they will serve to charge a battery, within certain limits, at a set constant voltage).

There are other differences, such as the converters not offering the capability to 'automatically optimize' LiFePO4 charging.
--------
The converters do offer a more economical solution for providing constant voltage-regulated output when given variable battery voltage levels (buck-boost) when that's one's need (i.e. used in a strictly "power supply" mode). IMO that's their "intended" application.

Good catch. I had installed this based on a recommendation of another forum member. Probably has worked fine due to the low current output (9A). Do you recommend a non-isolated or an isolated DC-DC controller? Since the trailer and TV grounds are connected, the system is operating in a non-isolated condition, either would work.

 

[rubicon327]

Do you recommend a non-isolated or an isolated DC-DC controller? Since the trailer and TV grounds are connected, the system is operating in a non-isolated condition, either would work.

FWIW when I initially hooked up my Victron Orion Tr 12/12-18 Isolated unit with isolated grounds I lost the trailer brakes (and lights I believe). When I bridged the grounds essentially making it a non-isolated unit everything worked fine. Your trailer and tow vehicle frame are one common ground as far as the system is concerned. Save your money and buy a non-isolated unit. I think Escape initially used isolated units but based on how I saw them wired they became non-isolated like mine. I haven’t seen any build picks lately but I wonder if Escape has switched to non-isolated.

 

[MVA]

That's what I figured what would happen since the grounds between the TV and trailer need to be continuous for the trailer to function in tow mode. Thanks for your comment that demonstrated what I thought would happen.

I am still a bit confused on why Victron is stating "not intended for battery charging" on the simpler DC-DC converter. The concern should not be for the battery side of the circuit since a simple constant voltage output to the battery is the same as when the trailer is under shore power and the AC-DC converter is charging the battery under constant voltage. On the input side of the circuit, there could be an issue like John has seen in post #10 where the current draw is high and the input voltage drops to support the output battery current draw. The concern I have with the smart Victron controllers is default LiFePO4 profile is a fixed two hour adsorption profile per their data sheet. It does apparently have some type of TV protection (low voltage?).

For those that have the smart charger, I would be interested how they have programmed it for longer charging periods and how the TV protection works.

 

[Centex]

... I had installed this based on a recommendation of another forum member. Probably has worked fine due to the low current output (9A). Do you recommend a non-isolated or an isolated DC-DC controller? ....

Your Victron converter should serve just fine to add charge to your trailer battery when that battery voltage is below the converter's set output voltage.

Noting that Victron does not offer an Orion Smart Charger in that (9A) output range I have no other suggestion for folks seeking a similarly low output (and corresponding low TV load) unit. Unfortunately, Victron's Smart Chargers cannot be adjusted to limit their current (amp) output / load.

I've not investigated how a unit intended as a low current / higher voltage 'solar controller' might be used in this application though I've read mention that might be possible.

There may be other brands of similarly low-current output / load 'smart' chargers and of course there's the alternatives posted above to improve capabilities for a TV to comfortably support higher-current output / load Victron Smart Chargers if desired.

I happen to be among those who have side-stepped these issues, having foregone TV>trailer battery charging. I disconnected the battery charge line from the TV in my trailer umbilical junction box and just rely on solar and shore-power to maintain my LiFePO4 battery. I realize that may not work for folks who spend lots of time in poor solar-exposure settings absent shore-power, making TV>trailer charging a more urgent priority.

I am using the Victron Orion converters as buck-boost regulators to provide constant DC voltage to my trailer DC distribution panel, but that's a different / off-topic story. It was learning about that application that caused me to gain a better understanding of the differences between Victron's converters and chargers.​

 

[MVA]

Your solution is reasonable. Not to belabor the issue , but I found a Victron Webinar on line:

At about 11:15, the Vicron presenter covers why one needs a current limiter with Li batteries. Good information. In the slide at 12:30, four options are presented to mitigate the concerns including an Orion DC-DC converter. Odd.