DC to DC troubleshooting

[Olive2Roam]

So we have had a DC to DC charging system on our LE I for a year now. It worked very well, but has become inconsistent and unreliable. The system was installed by a local inverter service center with a solid reputation. They actually are the supplier for some parts, such as solar panels, to Oliver. The tow vehicle is a 2024 Pathfinder with a "smart" alternator. The charger is a Victron Orion 50 amp. 

Using the Victron app I can see that the voltage on the input side of the charger is sitting between 12.2 and 12.4 volts. Aside from a brief spike on start up to 14.4 or so, it remains there. When driving the voltage remains that low and occasionally jumps to 14.4 or so and occasionally that casues the bulk charging to start. But this lasts only for a short time (seconds) and the voltage drops, and the charging stops.

Bottom line is that the batteries are not being charged. The inverter service center has worked with me to make sure all of the parameters are correct, but there is still something wonky that we can't figure out. Out of curiosity I had the tow vehicle battery tested by a couple of battery shops and all looks good there. 

12.2-12.4 seems very low for the output from the TV battery. In fact, the Victron parameters require 13.3 volts (default) and we have dialed that down to 12. 9. Any thoughts as to why the voltage from the tow vehicle would be that low? Also, does anyone know a DC to DC charging resource/expert that I could connect with to trouble shoot this?

Thanks,

Bob

Edited Thursday at 10:33 PM by Olive2Roam

[jd1923]

18 minutes ago, Olive2Roam said:

12.2-12.4 seems very low for the output from the TV battery.

Yes Bob, this voltage is very low! An automotive LA battery after sitting overnight or sitting for a few days should read 12.5V minimum and more like 12.6V with a newer battery. When towing or at highway speeds, voltage across the battery with the alternator running should produce 13.6V min and more often 13.8V to a max 14.2V.

The term Smart battery bothers me unless it's smart enough to know you have the DC-DC charger attached. Check a Nissan truck forum, search for "alternator" or "towing."

If you have been DC-DC charging adequately for some time and now nothing, you could have blown something in the Nissan alternator. Perhaps it did not have +50A available.

Your DC-DC charger installation is likely fine. Instead of "inverter service" test your alternator or take it to an electrical shop that rebuilds alternators and starters,

Before I installed our Orion 50A charger, I installed a HD alternator rated at 50A greater capacity. Let us know. Best wishes, JD

[Olive2Roam]

2 minutes ago, jd1923 said:

Yes Bob, this voltage is very low! An automotive LA battery after sitting overnight or sitting for a few days should read 12.5V minimum and more like 12.6V with a newer battery. When towing or at highway speeds, voltage across the battery with the alternator running should produce 13.6V min and more often 13.8V to a max 14.2V.

The term Smart battery bothers me unless it's smart enough to know you have the DC-DC charger attached. Check a Nissan truck forum, search for "alternator" or "towing."

If you have been DC-DC charging adequately for some time and now nothing, you could have blown something in the Nissan alternator. Perhaps it did not have +50A available.

Your DC-DC charger installation is likely fine. Instead of "inverter service" test your alternator or take it to an electrical shop that rebuilds alternators and starters,

Before I installed our Orion 50A charger, I installed a HD alternator rated at 50A greater capacity. Let us know. Best wishes, JD

Thanks, JD. This is the best description of the smart alternator that I have found. https://www.thefastreligion.com/mr-smart-alternator-function What I have seen on a couple of other forums (https://www.pathfindertalk.com/threads/disabling-vvcs-voltage-variable-control-system.45074/) is that some choose to disable the variable voltage control system and make the alternator act like they always have and just pump 13.4 V to the battery 100% of the time. 

I will definitely have the alternator looked at. There might be something going on there. 

Thanks for your thoughts. 

[Snackchaser]

Bob, as you already figured out, conventional alternator voltages can’t be applied to a smart alternator. They use a current sensor on the battery’s negative cable that signals the engine computer, which throttles the alternator down once the TV battery is charged.  That saves fuel, and 12.4 V while driving can be perfectly normal.  Based on what you’ve described, there are several possible causes for your problem.

First, I’d verify that the DC-DC charger’s negative cable isn’t connected directly to the TV battery post.  If it is, the Orion’s current bypasses the current sensor, the computer never sees the extra load, and it never raises the alternator voltage… unless for other reasons such as a low TV battery.  Some manufactures specifically say to ground accessories to the body for this reason.  Many vehicles have a ground stud on the far side of the sensor for accessories, otherwise use the chassis ground point where the battery’s negative cable attaches.

Even if it worked before, it could be because the current sensor was seeing other TV loads that caused the alternator to increase voltage, and it wasn’t noticed when it stopped charging.  If the truck can see the charger’s load independently from the truck loads, then the alternator should keep the voltage raised well above all of the thresholds.  So it could have been charging when the truck called higher alternator voltage, but not otherwise.

Second, the Orion’s engine shutdown detection works on voltage.  My abridged explanation is that with the default “smart alternator” settings, it starts charging at 14.0 V.   A smart alternator idling at 12.4 V never gets there, so the Orion thinks the engine is off.  There’s also a separate input voltage lockout setting (default 12.5 V) below which charging stops.  At 12.2 to 12.4 V, you’re under that too.

These thresholds are adjustable in VictronConnect, but there’s a limit.  Set them too low and the Orion can stay on and drain the truck battery when parked.  Every vehicle is different, so some trial and error may be needed.

It sounds like the Nissan system might have some unique quirks, but disabling the voltage control might be extreme.  If fine-tuning doesn’t work, an “engine-running” signal on the Orions Remote L Terminal will force the Orion on.  It’s there for this very reason.  You must leave engine shutdown detection enabled when you do this, so it still turns the charger off when the engine stops.  Victron describes several signal sources and recommends a true engine-running signal over a plain ignition wire.  For your situation, a wire that goes dead with the key off is the best approach.

In a trailer setup, this gets more complicated because it needs a third wire between the truck and trailer.  Fortunately, the +12 V wire in the tow harness should work in most cases.  Check it with a meter.  It must be dead with the key off, and must not be live from the trailer battery with the truck off.  Oliver doesn’t connect this wire on lithium systems so you should be okay.  Ideally, it would also be off with the key on and the engine not running.  Otherwise it could drain the TV battery if key is left on.  This wire is usually capped off near the inverter and it’s typically a #10 or #12 wire.  

Also be aware that undersized cables, poor terminations, and corroded Anderson connectors can cause “additive” voltage drops that only show up when the charger is pulling heavy current.  Corrosion builds over time, which could explain why it worked for a year and then stopped.  This is where the “Input Voltage Lockout” setting comes into play.  It’s set it so that Vlock-out ≤ Vshutdown − Vcable.  The Vcable is the voltage drop in the wiring at full current.  Victron’s manual provides an example voltage drop at 50 amps over a specific length of heavy cable.  It’s a surprisingly high voltage drop, so if you add any additional resistance from undersized wire, corrosion or poor connections, you can add tenths of volts more, and that can push you under the set point where charging stops.

You or your installer can measure your actual Vcable with the Orion running at full current (Turn on Oliver’s air conditioner and use a temporary +12V signal on the remote L trigger).  Confirm its running full amps on the App.  Vcable is the truck battery voltage minus the Orion’s input voltage.  Many people wing this and get lucky, but it can become a latent problem especially with marginal wire sizing.

Another way to get around this it is to de-tune the Orions maximum output amperage.  For example:  I have wiring sized for an old 30 amp charger based on the length of the run.  When I upgraded to a new 50 amp charger, I reduced it’s power output to 30 amps to match wire size, otherwise Vcable could be too high.  Mine actually worked at higher amps, but the wire was getting warm which meant the efficiency was suffering and I was burning more fuel.

Finally, it’s worth load-testing the alternator.  Turn on all the big loads (headlights, rear defrost, blower on high) and check that voltage climbs to around 14 V and holds.  An alternator shop can do a more definitive carbon pile test.  Also do a ripple test, which detects a burned diode that would reduce output.  You can check it yourself with a meter on AC volts, with the loads on. There are YouTube videos showing how.  If the voltage won’t rise even under heavy load, a Nissan dealer can scan for codes to tell whether the problem is the alternator or the current sensor.

Again, it might be true that the Orion has never worked to full capacity and it was just not noticed.  It probably worked periodically over long drives enough to charge a partially drained battery. The Victron has a history function where you can verify its performance over time.  It's a good tool for problems like this.

Anyway, it’s been fun trying to write this out in layman terms.  I hope it helps,
Geoff

[Geronimo John]

14 hours ago, Snackchaser said:

I’d verify that the DC-DC charger’s negative cable isn’t connected directly to the TV battery post.  If it is, the Orion’s current bypasses the current sensor, the computer never sees the extra load, and it never raises the alternator voltage…

Geoff:

Could this be the reason that I don't see a charge rate at via the Ollie's Victron shunt more than 22 amps despite having a 30 amp Orion in play?

GJ

[Snackchaser]

Gj, the short answer is probably not, at least not directly.  The smart alternator issues I described above tend to make the Orion cut in and out.  A steady maximum of 22 A from a 30 A charger likely has a different cause.  However, if your charger’s negative cable goes straight to the battery post and bypasses the current sensor, then it’s worth correcting.

Without a record of the current over time, it’s hard to know what your charger is doing at any given moment.  I’m assuming that the wiring is properly sized for minimum voltage drop, and that the battery was low enough to accept full charge.  A nearly full battery won’t draw as much current and excessive voltage drop can cause other problems with the settings that I touched upon above.

So even without knowing your exact conditions, it sounds like a heat issue. The Orion reduces its output when it gets hot.  I had this with mine.  Even with two cooling fans, my old 30 A ran scary hot at full load (running the trailer air conditioner while driving).  That’s why I upgraded to the 50 A Orion XS, which is far more efficient and makes much less heat.

Here’s the math. Your 30 A Orion is a 360-watt charger at a nominal 12.2 V output  But a lithium battery charges at about 14.2 V.  So 360 W ÷ 14.2 V is only about 25 amps (at 104°F).   Above that temperature, Victron derates it 3% per degree C.  So with the air around the charger at 113°F, you’re down to about 22 A.  See what I mean?

Of course, this is all conjecture.  First, I’d recommend swapping the 30 A for a 50 A and turning its output down to match your cable size and length.  I sold mine on Craigslist to a guy with an Explorer van, where it was better suited.

Second, if you want to see what’s really going on, run a load with engine running above idle, such as a small heater on low through the inverter.  That keeps the Orion working at full output even if the battery is nearly full.  Then put an inexpensive clamp-on DC ammeter on the Orion’s output cable to see the real output.  The shunt only shows the net current in and out of the battery. It can’t separate the charger’s output from trailer loads or solar.

Hope that helps!  Geoff

[Dean and Mary]

2 hours ago, Snackchaser said:

That’s why I upgraded to the 50 A Orion XS, which is far more efficient and makes much less heat.

Thanks, Geoff. I appreciate all the information you've shared. I'm in the process of installing my DC-to-DC charger now, but I haven't begun working on the tow vehicle portion of the project. Your comments about the cabling requirements and the tow vehicle current sensor gave me some useful information to consider before I get started on that part of the install.

I agree that the 50A Orion XS is significantly more efficient than the 30A version. Even with the improved efficiency and reduced heat output, I plan to mount my Victron Orion XS 12/12-50A DC-DC charger on top of Mobile Solar Consulting’s Orion Fan Module, which features temperature-controlled cooling. If you’re not familiar with this option, there are several YouTube videos that demonstrate the noticeable reduction in operating temperatures when using the fan module. For me, the added cooling is inexpensive insurance for a component that will often be operating under heavy load.

Dean

 

Edited 23 hours ago by Dean and Mary
Clarification

[Dean and Mary]

2 hours ago, Snackchaser said:

That’s why I upgraded to the 50 A Orion XS, which is far more efficient and makes much less heat.

Accidental duplication. 

 

Edited 23 hours ago by Dean and Mary
Duplication

[Dean and Mary]

While gathering information for this project, I also discovered that Victron has introduced a new Orion XS 12/12-70A model. It has the same footprint and mounting pattern as the 50A version but adds integrated cooling fans. Victron also slightly increased the terminal size, which should make it much easier to terminate 4 AWG wire. Getting 4 AWG wire into the terminals of the 50A version can be a challenge, so that is a welcome improvement for higher-current installations. It is pricey and I just recently purchased my 50 amp version, so not for me at this time. 

 

[Snackchaser]

6 hours ago, Dean and Mary said:

Mobile Solar Consulting’s Orion Fan Module,

Dean, 

I like that fan, it's a great idea and should greatly help the efficiency!

I noticed that you're going with #4 AWG, which is undersized for 50 amps at the approximate 100’ or more round trip cable run that you will need.  You would be looking at about 1.3V of voltage drop, not including fuses, terminations and Anderson connectors that could add a few tenths more.  #4 AWG is even marginal for a 30 amp charger.  There is a common misnomer that #4 is the correct wire size because the Orion’s terminals are sized for #4.  That’s because most of the installations are in boats, vans and motorhomes with much shorter runs.

There are advocates for using smaller wire, but it’s not the best advice for a number of reasons, particularly if you're watching efficiency.  You should be considering #2 minimum, 1/0 is ideal.  You can terminate the 1/0 cable to a terminal strip on the negative and a fuse block on the positive, then use short #4 jumpers to the Orion.  The jumpers won’t contribute much to the overall voltage drop.

Cheers!  Geoff

[jd1923]

8 hours ago, Snackchaser said:

Here’s the math. Your 30 A Orion is a 360-watt charger at a nominal 12.2 V output  But a lithium battery charges at about 14.2 V.

Again Geoff, thank you so much for providing your electrical expertise and very well written, btw. I've learned a lot in reading your last two posts (reading them twice)!

To extrapolate your math, the 50A Orion is therefore a 600W charger and should produce up to 42A (600/14.2).

+42A output (+/-) is a number I've seen often (Orion on Victron Connect app). I've seen high 30s to low 40s regularly, with a high 40s number a few times. Our Orion is set on the full 50A output setting, wired with 4 AWG (I understand it's on the light side). To date I've counted on the fact that we get +40Ah for every hour towing.

So, I recently have a different kind of issue...
I installed our Orion 50 during March 2025. The TV alternator was also upgraded (output increased by 50A) and we're talking old-school alternator (not Smart). My truck gauges always show readings of 13.8 to 14.2V.

We have traveled (exactly) 100 days in 1 1/2 years (LOL, checked the data) always DC-DC charging, always getting +40A until our last two outings.

We ran a 5-day trip un-plugged needing a bit of A/C. Then we did a 10-day trip no hook-ups. Both trips we hovered around 50-60% SOC most of the time on 900 Ah total, by adding suitcase solar when camped and we ALWAYS have DC-DC cables connected when towing. We move around a lot, so DC-DC is usually all we need. We have rarely needed our suitcase solar since with DC-DC charging. Near the end of both trips we got down below 30% SOC, so I was checking the Victron app while towing which I had not done for awhile.

No longer are we getting a 40A charge, instead recent readings were +29A +/-. I monitored it a few times while towing (didn't think to check history page). When our batteries were very low in SOC% and we needed DC-DC charging the most, it produced less. We used to get +30A sitting at idle, consistently and 40 when towing. Looking back, we only got this low in SOC% because the DC-DC charging was not performing to par!

I thought loose connections or ground (because my installation has a truck frame ground), but I checked all connections and they were tight as when installed.

It will be a while 'til I get to troubleshooting. We're not traveling until Jan. I need to just hook up, run it at idle parked at home and get the clamp ammeter out! It will be easy to read amps on the wiring from TV to TT (is this even a valid test? IDK). Testing ideas appreciated and thanks again. 😎

Edited 17 hours ago by jd1923

[dkeen]

Thanks SnackChaser!  Hopefully this information will help me get my DC to DC charger working properly.  I have been struggling with it since it was installed in May.  I will try grounding to the body first versus to the negative battery cable.  If this does not work, I will try using the 12V+ wire from the 7pin.   

[Dean and Mary]

17 hours ago, Snackchaser said:

Dean, 

I like that fan, it's a great idea and should greatly help the efficiency!

I noticed that you're going with #4 AWG, which is undersized for 50 amps at the approximate 100’ or more round trip cable run that you will need.  You would be looking at about 1.3V of voltage drop, not including fuses, terminations and Anderson connectors that could add a few tenths more.  #4 AWG is even marginal for a 30 amp charger.  There is a common misnomer that #4 is the correct wire size because the Orion’s terminals are sized for #4.  That’s because most of the installations are in boats, vans and motorhomes with much shorter runs.

There are advocates for using smaller wire, but it’s not the best advice for a number of reasons, particularly if you're watching efficiency.  You should be considering #2 minimum, 1/0 is ideal.  You can terminate the 1/0 cable to a terminal strip on the negative and a fuse block on the positive, then use short #4 jumpers to the Orion.  The jumpers won’t contribute much to the overall voltage drop.

Geoff,

Thanks for the detailed feedback. I agree with everything you mentioned in your response. Four-gauge cable is commonly used, even though the voltage-drop calculations and cable-sizing tables show that the loss can be higher than ideal for maximizing the efficiency of the Orion XS.

I think a lot of the recommendations stem from camper van installations where the cable runs are much shorter, as you suggested. Victron generally recommends keeping DC voltage drop below 2.5% to achieve optimal charging performance and efficiency. When I run the numbers, review the voltage-drop tables, or even check with AI tools, the results consistently point to 1/0 cable as the size needed to stay within that guideline for a typical tow vehicle-to-trailer cable run of 80 feet round trip.  

Based on that, it looks like my Orion installation is going to cost more than I originally anticipated, especially considering the current price of quality copper cable. However, I'd rather size the wiring correctly the first time than leave charging performance on the table. I will install individual terminal lugs a few inches before connecting to the Orion and then connect with 4 gauge wire.

Thanks, Dean

Edited 27 minutes ago by Dean and Mary
Clarification

[Snackchaser]

16 hours ago, jd1923 said:

No longer are we getting a 40A charge, instead recent readings were +29A +/-. I monitored it a few times while towing (didn't think to check history page). When our batteries were very low in SOC% and we needed DC-DC charging the most, it produced less. We used to get +30A sitting at idle, consistently and 40 when towing. Looking back, we only got this low in SOC% because the DC-DC charging was not performing to par!

Jd, your math is off a bit. The charger is rated 600W at 12V and 700W at 14V, so 700 ÷ 14.2 is about 49 A.  But that’s only up to 104F, above that it reduces output as it gets hotter.  I assume yours was running pretty hot, since your air conditioner was on.

Clearly heat is a factor, but it doesn’t fully explain why it was dropping down to 29amps.  At 29 amps, the spec would have it at over 150F which is beyond the Orion’s operating limit.  Regardless, you might look into the fan that @Dean and Mary  found.

Voltage drop from cable size and frame resistance doesn’t fully explain it either.  Said in simple terms . .  with the low SOC calling for charge, and only 29amps output, it means the Orion would be receiving under 9V after voltage drop.  Only it would have cut out on low voltage long before that.   

A consistent charge in the low 40s shows the charger is working correctly within the limits you’d expect from cable voltage drop.  Add heat derating and heat-induced resistance, and I’d be okay with those numbers.

If the Orion was really making only 29 amps, it should be confirmed with some more definitive testing.  I’d also look at the alternator. With your conventional alternator, it could be bad diodes, which are replaceable.  They might not show up on the dashboard during light loads, but they cut the alternator’s maximum output.  Look up load and ripple testing; you have the tools and skills for it.

I earlier described some tests to check charger output and total voltage drop.  In your installation using the TV frame as a conductor, it might also be interesting to measure amps at the Orion input at both the positive and negative leads.  Any difference between them would show if there is current bleed-off through the hitch or the tow harness ground.  This would indicate if the frame had any high resistance spots that cause the current to take the path of lessor resistance.

I think you have a good start.  Keep us informed of what you find.  Cheers!  Geoff