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