DC-DC Charger

PixandMsBee

We will be towing a 2022 T@B 320-S Boondock with a current model Subaru Outback that I installed the 4-pin wiring harness on. The dealer has since installed the plug that “upgrades” it to a 7-pin.

I will be switching out the AGM battery to lithium as soon as the battery arrives which could be another month or so. The Lithium battery is 100AH but may upgrade to a 2nd one in the future.

I have heard that there can be problems with the tow vehicles electrical system, in particular the alternator when towing the trailer as the “charging profile” is different for the lithium battery compared to the tow vehicle lead acid battery.

My trailer dealer does not know anything about lithium batteries. I know some have discussed using  a DC-DC converter in their tow vehicle and would appreciate hearing from anyone knowledgeable on the subject.

Picking up my trailer next week, any information is greatly appreciated!

Dutch061

Sent you a very detailed PM.

Brad

VictoriaP

I’m aware of one Tab owner towing with an Outback XT (an Onyx, if I recall) who added 200 ah of lithium to their 320 and did not bother with a DC-DC. No issues charging or with the alternator so far. They do have an isolator inline on the 7 pin, so the trailer does not draw power when the ignition is off.

What I have not found anywhere on the ‘net or in person is anyone who has added a DC-DC to a gen6 Outback XT. I search every month or so, and I’ve asked a few people I’ve encountered using these as tow vehicles. Haven’t found anyone yet who has tried it, and also haven’t found anyone willing to install one. (The install is too far out of my comfort zone, I couldn’t pick an alternator out of a lineup, and wouldn’t know where to start.) What I *have* gotten is plenty of conflicting advice, usually from electrical engineers…about half saying it’s a non issue with a small lithium battery bank of 100-200 ah, and the other half saying OMG, you MUST use a DC-DC with lithium or you’ll eventually kill your alternator.

This issue has kept me from upgrading to lithium. To me, it’s one thing to kill a battery (even a lithium)…whatever, I’ve owned 4 Subarus, that happens every couple of years like clockwork. LOL  It’s another to fry the alternator on a fairly new car, and so far, I’m not comfortable with the risk of adding lithium without that DC-DC protection.

PixandMsBee

VictoriaP said:

I’m aware of one Tab owner towing with an Outback XT (an Onyx, if I recall) who added 200 ah of lithium to their 320 and did not bother with a DC-DC. No issues charging or with the alternator so far. They do have an isolator inline on the 7 pin, so the trailer does not draw power when the ignition is off.

What I have not found anywhere on the ‘net or in person is anyone who has added a DC-DC to a gen6 Outback XT. I search every month or so, and I’ve asked a few people I’ve encountered using these as tow vehicles. Haven’t found anyone yet who has tried it, and also haven’t found anyone willing to install one. (The install is too far out of my comfort zone, I couldn’t pick an alternator out of a lineup, and wouldn’t know where to start.) What I *have* gotten is plenty of conflicting advice, usually from electrical engineers…about half saying it’s a non issue with a small lithium battery bank of 100-200 ah, and the other half saying OMG, you MUST use a DC-DC with lithium or you’ll eventually kill your alternator.

This issue has kept me from upgrading to lithium. To me, it’s one thing to kill a battery (even a lithium)…whatever, I’ve owned 4 Subarus, that happens every couple of years like clockwork. LOL  It’s another to fry the alternator on a fairly new car, and so far, I’m not comfortable with the risk of adding lithium without that DC-DC protection.

All good points! I have a lead acid battery to use until the lithium arrives which I hope is sometime in May. All the dealer did was run a light 2-strand wire directly from the battery to the 7-pin plug that also uses the very light gauge 4-pin plug.  Hard to sort it all out!

Dutch061

@VictoriaP, there is a lot of conflicting information and opinions regarding the necessity to use a DC-to-DC Charge Controller when you upgrade to Lithium. Even Battleborn says that they may or may not be necessary depending on the vehicle, wire size, etc.

What I have found is the following.

1. A DC-to-DC Charge Controller can act as a relay, preventing the tow vehicle battery from being drained.
2. A DC-to-DC Charge Controller will limit the amperage that can be used to charge the battery bank, providing alternator protection.
3. A DC-to-DC Charge Controller will boost the voltage to provide the correct charging voltage to a lithium battery bank.
4. A Victron DC-to-DC Charge Controller can be configured to use with a Smart Alternator. Other brands-models may be able to do the same.

Most of the time the gauge (size) of wiring between the 7-pin connector and the voltage source will prevent excess amperage that could damage an alternator. Even so, the difference in voltage from what the alternator produces and what Lithium batteries require will prevent them from ever truly being charged. 

In the case of my 2021 F-250 truck, by installing a DC-to-DC Charge Controller I was able to go from 2 to 4 amps of charging rate to 18 Amps at 14.6 volts. Which is exactly what was expected based on the components I chose.

Bottom line as I have mentioned many times, the benefit of Lithium batteries only applies to those who boondock. If you spend the majority of your time plugged into shore power, it makes zero sense to spend the money.

Brad

VictoriaP

Dutch061 said:

Bottom line as I have mentioned many times, the benefit of Lithium batteries only applies to those who boondock. If you spend the majority of your time plugged into shore power, it makes zero sense to spend the money.

Brad

@Dutch061 Yeah, this is where my issue comes in. When I bought the Tab, getting sites in my region with full hookups or even just electric & water was difficult. But once the pandemic hit and RV sales went from already crazy to ballistic, it went from difficult to downright impossible to get those sites even on weekdays without reservations made 6-9 months out. I am not that sort of person, I’m lucky if I know what I’m doing next week! So I’ve gone from being a shore power type to wanting to boondock, in a rig that currently isn’t well suited to that (no permanently mounted solar yet, and a single 12v 105 ah AGM), and in a region where solar collection isn’t as dependable as some. I’ve gotten as far as adding a SmartShunt to the battery and will be tracking usage as well as seeing exactly what charge the alternator provides on an upcoming trip that includes three days off grid.

Like most modern vehicles, the 6th generation Subaru Outback is heavily computerized and has a smart alternator, which is why I suspect installing a DC-DC charger is likely the smartest move even if the jury is still out on whether one is absolutely necessary.

Dutch061

I believe to get the "desired charging rate" if you upgrade to Lithium, it will be a necessity. I too was on the fence and convinced I could get by without but realized after I finally got my 2021 truck (that took 6 months) that if I wanted to gain any battery amp hours while driving that it would be a necessity.

Unfortunately, I have learned many lessons (spelled $$$) along the way in this journey. But overall, it has been a great education in all aspects; plus, I have some real-world experience that I can share with others to help guide them. 

Brad

Verna

“ We will be towing a 2022 T@B 320-S Boondock with a current model Subaru Outback that I installed the 4-pin wiring harness on. The dealer has since installed the plug that “upgrades” it to a 7-pin.”

If I am understanding this statement correctly, your Subaru Outback only has 4 pin wiring, which gives you lights on your T@B (brake lights, turn signals, running lights). If the dealer did not add wiring to the Subaru’s 7-pin “upgrade”, then your Subaru Outback will not be charging your T@B battery. There must be a wire added that goes to your battery or fuse box to be able to charge your T@B’s battery. 

VictoriaP

Good catch, @Verna, I missed that! And I should know better, since it’s very rare for a Subaru dealer to actually upgrade the Outback hitch wiring to 7 pin. I actually had a sales guy try to tell me “there’s a $20 adapter that you can plug in for that”…um, NO. Most owners either DIY the install or take their Outbacks elsewhere to have the 7 pin wiring added.

Horigan

I just went through a DC DC charger installation on my boat.  @Dutch061, gives sound advice.  I would go with the Victron Orion Smart 12V 18amp DC DC charger, not the 30 amp.  Your alternator will be able to handle the 18 amp load and the Victron has a good smart alternator function to work with modern cars.  Just make sure the TV charging wires to the 7-pin are sufficient gauge for the amps drawn (12 awg).

PixandMsBee

Verna said:

“ We will be towing a 2022 T@B 320-S Boondock with a current model Subaru Outback that I installed the 4-pin wiring harness on. The dealer has since installed the plug that “upgrades” it to a 7-pin.”

If I am understanding this statement correctly, your Subaru Outback only has 4 pin wiring, which gives you lights on your T@B (brake lights, turn signals, running lights). If the dealer did not add wiring to the Subaru’s 7-pin “upgrade”, then your Subaru Outback will not be charging your T@B battery. There must be a wire added that goes to your battery or fuse box to be able to charge your T@B’s battery. 

If I have misunderstood your “upgrade to a 7-pin” I apologize. 

I did not have the Subaru Dealer do any of the work on my Outback, all they are good at is over charging and under delivering.

I ordered this hitch and had a body shop install it:
2022 Subaru Outback Wagon Trailer Hitch - Draw-Tite (etrailer.com)

There is not a ready made 7-pin harness for any Subaru's, I ordered this and installed it myself:
 CURT Manufacturing 56040 Vehicle-Side Custom 4-Pin Trailer Wiring Harness for Select Subaru Forester, Outback, Sport, XV Cross Trek, Wiring - Amazon Canada

The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada

and this:
Curt 58000 Easy Mount Electrical Bracket for 2" Receiver Tube, Wiring - Amazon Canada

Now to my question:  Do I need to have a DC-DC Charger to keep from damaging my new 2020 Subaru's Smart Alternator like this :
Victron Energy Orion-Tr 12/12-18A (220W) Isolated DC-DC Converter : Amazon.ca: Electronics

Dutch061

I don't believe that you will damage the alternator with a Standard Lead Acid (SLA) battery or an Absorbent Glass Mat (AGM) battery. The amperage will be regulated by the size of wiring that was installed or the circuit protection (fuse or circuit breaker) that was installed with the auxiliary wiring. Plus, the resistance of either the SLA or AGM chemistry will closely match the OEM battery in your Subaru. 

However, when you upgrade to a Lithium Battery it will become a must in order to boost the voltage to the required level to charge Lithium. In addition, due to the very low resistance in Lithium, there is a potential (based on wire size, length, etc.) to draw more amperage than your tow vehicle is "comfortable with" (IE blown fuse or tripped circuit breaker up to damage or life shortening of components). A DC-to-DC Charge Controller will limit this to a "comfortable level" (IE fuse or circuit breaker protection and damage prevention).

Brad

Horigan

With Lithium, it's key you get the DC to DC charger at the correct amp rating, like the 18 amp Victron unit noted above.  That will draw close to 18 amps from your alternator, which it should easily handle.  

N7SHG_Ham

@PixandMsBee, you said:

The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada

Was there additional wiring connected to those bare wires to run up to your battery? If not, you don't have any active charge line yet. Note the part about some manual wiring required.

Verna

@PixandMsBee, in reference to this part of your post:

“The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada”

The DC-DC Charger will not work without the charging wiring from your Subaru’s battery or fuse box.

See the last sentence from the post above here from @N7SHG_Ham. 

CharlieRN

Dutch061 said:

I don't believe that you will damage the alternator with a Standard Lead Acid (SLA) battery or an Absorbent Glass Mat (AGM) battery. The amperage will be regulated by the size of wiring that was installed or the circuit protection (fuse or circuit breaker) that was installed with the auxiliary wiring. Plus, the resistance of either the SLA or AGM chemistry will closely match the OEM battery in your Subaru. 

However, when you upgrade to a Lithium Battery it will become a must in order to boost the voltage to the required level to charge Lithium. In addition, due to the very low resistance in Lithium, there is a potential (based on wire size, length, etc.) to draw more amperage than your tow vehicle is "comfortable with" (IE blown fuse or tripped circuit breaker up to damage or life shortening of components). A DC-to-DC Charge Controller will limit this to a "comfortable level" (IE fuse or circuit breaker protection and damage prevention).

Brad

I am far from an expert on LFP batteries and their interaction with the electrical system of the TV, but have gotten quite an education from the techs at Batttle Born, and from the videos posted on trustworthy sites like Solar Solutions and DIY Solar Power. Here's a thumbnail sketch of what I've learned:

• The charging profile of LiFePO4 batteries is quite different than for lead-acid batteries, and very different from that of the starter battery on your TV.
• The alternator and its voltage regulation system is calibrated for starter batteries, and is not really appropriate for deep discharge and/or Li batteries.
• Lithium batteries have a large appetite for current (as distinct from the voltage of the charging profile) and this is what can potentially damage your alternator.
• The anemic wiring of the charging circuit of a typical 7-pole harness usually, but not always, limits the amount of current from the alternator to the house battery bank. This is why the TV alternator is not often damaged when charging LiFePO4 batteries.
  
• Even if the output of the TV alternator is sufficient to provide adequate current to charge an LFP house battery(ies), it is unlikely to to charge it/them fully (a side note, unless your camper's charge controller has a setting for lithium batteries, it too will not charge to 100%.)
• While from a functional standpoint it's not a big deal to have a less than fully charged battery, LiFePO4 batteries (at least those from Battle Born) require an occasional topping to 100% to allow their battery management system to stay properly calibrated.
• The use of a DC-DC charger will address the issues outlined above and help prevent damage to the TV charging system.

As I stated, I'm not an expert, and what I've written is only a summary of my takeaways of the information I've found on this subject. I know that there are quite a few folks on this forum who are experts however, aid will hopefully chime in to correct anything that incorrect. 

Dutch061

@CharlieRN, I think you have a great set of bullet points, and I would agree with all of them.

Brad

PixandMsBee

N7SHG_Ham said:

@PixandMsBee, you said:

The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada

Was there additional wiring connected to those bare wires to run up to your battery? If not, you don't have any active charge line yet. Note the part about some manual wiring required.

Yes, they ran two wires, one each from the positive and negative posts from the battery.

PixandMsBee

Verna said:

@PixandMsBee, in reference to this part of your post:

“The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada”

The DC-DC Charger will not work without the charging wiring from your Subaru’s battery or fuse box.

See the last sentence from the post above here from @N7SHG_Ham. 

Verna said:

@PixandMsBee, in reference to this part of your post:

“The Nucamp dealer used this to "convert the 4-Pin to 7-Pin:
Curt Manufacturing 57672 4 Way Flat To Both 7 Way Round And 4 Way Flat Adaptor, Electrical Accessories - Amazon Canada”

The DC-DC Charger will not work without the charging wiring from your Subaru’s battery or fuse box.

See the last sentence from the post above here from @N7SHG_Ham. 

Yes, they ran two wires, one each from the positive and negative posts from the battery.