Connecting Victron DC-DC Charger

[jnm30327]

As part of a lithium upgrade, I bought a Victron 12|12 30 Isolated DC-DC Charger. This is the story of the difficulties and issues I had connecting it to my TV which is a 2018 Toyota Tundra 4WD Limited.

1. At first, I thought I would connect the charger wire in the 7 way cable to the input of the Charger. The fuse on the TV was 40 amps for the charger wire and the wiring 10 AWG. I thought this was worth a shot since there was only a max of 30 amps going to the charger.. When I did this with the batteries at a low charge (~50%), the DC-DC Charger went into bulk charge mode trying to pull the rated 30 Amps. The measured voltage at the Charger input dropped to 5 volts which was under the input voltage cutout. Obviously, this was not going to work.

2. Next, I installed a 4 AWG wire fused at 60 amps to an Anderson connector at the rear of the TV. I followed the Victron recommendation for fuse size but went one side larger, 4 AWG rather than 6 AWG, on the wire size. Importantly, only the positive lead went all the way to the TV battery. The ground wire was grounded into the truck body near the rear of the TV. On the trailer side, I connected a 4/2 Cable to the unused 4 AWG cables that previously had gone from the old trailer battery to the original inverter which had been removed. I no longer needed the old inverter as I had installed a Victron Multiplus II to fill the charger and inverter roles. With the truck idling and a slightly depleted battery, the voltage at the Charger input was 11.2-11.7 volts. The TV battery with engine running was 13.5 volts. So, I had 1.8+ volts drop in the system. This bothered me a little as the numbers for voltage drop for 4 AWG over 30 feet with 30 amps should have been more like 0.6 volts. I was perplexed but thought it would work OK. I lowered the settings on the Charger to stay operating at this lower voltage. Incidentally, the 13.5 volts indicated the TV had a “smart alternator” which operates at a lower voltage than older alternators.

We took a weekend trip. At the start of the trip, the lithium trailer batteries were fully charged. There was no load on the charger, and all seemed well. On the return after 3 nights of dry camping, the batteries were at 60%. When we left the campground, the charger was pulling 30 amps. As we descended the mountain we were on, the TV was mostly idling and braking was applied by the TV brakes, trailer brakes, and use of a lower gear. About 5 minutes in, I got an alarming message on the TV console – “Trailer disconnected”. This meant the trailer brakes were no longer operating. The message stayed on for a few seconds and then disappeared. This message reappeared briefly and repeatedly all the way down the mountain. I realized that the TV trailer brake controller was reading a low voltage and issuing the alarm. The on-off nature of the problem indicated that the charger was disconnecting on a voltage lower than the setpoint I had created and then reconnecting for a brief period when the input voltage rebounded with the absence of the charger current draw. Of course, the trailer was never actually disconnected. At the bottom of the hill, I pulled over and disconnected the charger cable. We went the rest of the way home in peace and with operational trailer brakes.

3. At this point, I concluded that the remaining voltage drop had to be in the ground circuit to the TV battery which was going through the TV chassis. I returned to the shop where the battery cable has been installed and asked them to install a ground wire from the connector on the rear of the TV to the TV battery. Incidentally, I had this done at a shop whose main business was installing high end car stereo systems. They did a good job on both visits. After this additional wiring, the voltage at the charger input with truck idling was 12.7-12.9 volts which was close to the calculated drop.

4. One other issue was probably peculiar to the 2018 Tundra. In researching this, I discovered a Toyota Technical Service Bulletin (TSB) that was issued for early 2018 Tundras to address the “trailer disconnected” message. (One of the anecdotes in the Tundra forum was from an Airstream owner!) The TSB lowered the voltage at which the “trailer disconnected” message appeared. Whether merely adding the additional ground cable alone would have fixed the problem, I do not know, I added the ground cable and applied the TSB at the same time.

5. Result, after expenditure of worry and time, is that everything is now working OK. I still had to lower the “engine off” and “input cutoff” settings for the charger slightly, but that is the only adjustment I made to the default settings.

6. Lessons:

a. 7 way cable is simply not big enough and also not grounded back to the
TV battery.
b. A separate 4 AWG wire is adequate if grounded properly.
c. There is at least 1.5 volts of voltage drop in the circuit through the steel chassis of the TV.
d. I think the isolated Charger is helpful in this situation where separate ground wiring is applied. I could be wrong about this as both the Airstream and the TV are chassis grounded, but I was glad I had this clear isolation when I ran into problems.

Hope this experience is helpful. Let me know of any comments or questions.

[J-Dog]

Thanks for this information. I was contemplating just running my ground through the frame but will now run the negative all the way to the back of the truck now.

[ejs5405]

Originally Posted by jnm30327

As part of a lithium upgrade, I bought a Victron 12|12 30 Isolated DC-DC Charger. This is the story of the difficulties and issues I had connecting it to my TV which is a 2018 Toyota Tundra 4WD Limited.



1.At first, I thought I would connect the charger wire in the 7 way cable to the input of the Charger. The fuse on the TV was 40 amps for the charger wire and the wiring 10 AWG. I thought this was worth a shot since there was only a max of 30 amps going to the charger.. When I did this with the batteries at a low charge (~50%), the DC-DC Charger went into bulk charge mode trying to pull the rated 30 Amps. The measured voltage at the Charger input dropped to 5 volts which was under the input voltage cutout. Obviously, this was not going to work.



2.Next, I installed a 4 AWG wire fused at 60 amps to an Anderson connector at the rear of the TV. I followed the Victron recommendation for fuse size but went one side larger, 4 AWG rather than 6 AWG, on the wire size. Importantly, only the positive lead went all the way to the TV battery. The ground wire was grounded into the truck body near the rear of the TV. On the trailer side, I connected a 4/2 Cable to the unused 4 AWG cables that previously had gone from the old trailer battery to the original inverter which had been removed. I no longer needed the old inverter as I had installed a Victron Multiplus II to fill the charger and inverter roles. With the truck idling and a slightly depleted battery, the voltage at the Charger input was 11.2-11.7 volts. The TV battery with engine running was 13.5 volts. So, I had 1.8+ volts drop in the system. This bothered me a little as the numbers for voltage drop for 4 AWG over 30 feet with 30 amps should have been more like 0.6 volts. I was perplexed but thought it would work OK. I lowered the settings on the Charger to stay operating at this lower voltage. Incidentally, the 13.5 volts indicated the TV had a “smart alternator” which operates at a lower voltage than older alternators.



We took a weekend trip. At the start of the trip, the lithium trailer batteries were fully charged. There was no load on the charger, and all seemed well. On the return after 3 nights of dry camping, the batteries were at 60%. When we left the campground, the charger was pulling 30 amps. As we descended the mountain we were on, the TV was mostly idling and braking was applied by the TV brakes, trailer brakes, and use of a lower gear. About 5 minutes in, I got an alarming message on the TV console – “Trailer disconnected”. This meant the trailer brakes were no longer operating. The message stayed on for a few seconds and then disappeared. This message reappeared briefly and repeatedly all the way down the mountain. I realized that the TV trailer brake controller was reading a low voltage and issuing the alarm. The on-off nature of the problem indicated that the charger was disconnecting on a voltage lower than the setpoint I had created and then reconnecting for a brief period when the input voltage rebounded with the absence of the charger current draw. Of course, the trailer was never actually disconnected. At the bottom of the hill, I pulled over and disconnected the charger cable. We went the rest of the way home in peace and with operational trailer brakes.



3.At this point, I concluded that the remaining voltage drop had to be in the ground circuit to the TV battery which was going through the TV chassis. I returned to the shop where the battery cable has been installed and asked them to install a ground wire from the connector on the rear of the TV to the TV battery. Incidentally, I had this done at a shop whose main business was installing high end car stereo systems. They did a good job on both visits. After this additional wiring, the voltage at the charger input with truck idling was 12.7-12.9 volts which was close to the calculated drop.



4.One other issue was probably peculiar to the 2018 Tundra. In researching this, I discovered a Toyota Technical Service Bulletin (TSB) that was issued for early 2018 Tundras to address the “trailer disconnected” message. (One of the anecdotes in the Tundra forum was from an Airstream owner!) The TSB lowered the voltage at which the “trailer disconnected” message appeared. Whether merely adding the additional ground cable alone would have fixed the problem, I do not know, I added the ground cable and applied the TSB at the same time.



5.Result, after expenditure of worry and time, is that everything is now working OK. I still had to lower the “engine off” and “input cutoff” settings for the charger slightly, but that is the only adjustment I made to the default settings.



6.Lessons:



a.7 way cable is simply not big enough and also not grounded back to the

TV battery.

b.A separate 4 AWG wire is adequate if grounded properly.

c.There is at least 1.5 volts of voltage drop in the circuit through the steel chassis of the TV.

d. I think the isolated Charger is helpful in this situation where separate ground wiring is applied. I could be wrong about this as both the Airstream and the TV are chassis grounded, but I was glad I had this clear isolation when I ran into problems.



Hope this experience is helpful. Let me know of any comments or questions.

Thanks for the post. I purchased the same dc to dc charger through AM Solar, primarily for their tech support. On their web site they have install instructions for a resource. They recommend 2 gauge and both the positive and negative wire from battery to the connector. The only negative they used a smaller connector that would only accept a 6 gauge wire so you had to step wire down. I used a 2 gauge Anderson connector to keep max flow. AM Solar is a great resource.

[vanderwielen]

nice post, but the isolated version used in this context offers no value since the negative of the truck and the airstream are always at the same potential. those buying the isolated version tie the negatives together intentionally or accidentally (unknowingly). A good take away from your post is that the best DC to DC converter without the mods you've done is the 18a. I have this. The drop is significant but always above 8 volts on an F150. So, my charger delivers over 100 watts while driving.

[jnm30327]

Originally Posted by vanderwielen

nice post, but the isolated version used in this context offers no value since the negative of the truck and the airstream are always at the same potential. those buying the isolated version tie the negatives together intentionally or accidentally (unknowingly). A good take away from your post is that the best DC to DC converter without the mods you've done is the 18a. I have this. The drop is significant but always above 8 volts on an F150. So, my charger delivers over 100 watts while driving.

I understand what you are saying. My issue was the decision to add the second wire to the TV for the ground rather than running the ground through the chassis. It was good to know I was looking at an isolated system. But you are right that in the end, the TV and trailer grounds are at the same potential.

As to the voltage drop, the situation I wanted to avoid was setting the cut out for the engine in the charger so low that the DC-DC charger was not able not recognize that the TV engine was no longer running. The risk is that the system keeps charging and drains the TV battery. I wanted the voltage drop to be so low that the Victron DC-DC charger would know the engine/alternator were no longer running.

[vanderwielen]

Actually, the Victron is smarter than you might think. The voltage drop only occurs when current flows. Current only flows when the charger is on after determining the engine is running. The charger ‘sees’ the entire engine voltage before turning on. It periodically turns off, rechecks the engine voltage and repeats.

[foobar]

Originally Posted by vanderwielen

nice post, but the isolated version used in this context offers no value since the negative of the truck and the airstream are always at the same potential. those buying the isolated version tie the negatives together intentionally or accidentally (unknowingly). A good take away from your post is that the best DC to DC converter without the mods you've done is the 18a. I have this. The drop is significant but always above 8 volts on an F150. So, my charger delivers over 100 watts while driving.

What settings are you using on your 18amp victron dc-dc?

[richard5933]

When I ran the wiring to the tow vehicle battery for my DC-to-DC charger, I ran a pair of 6 ga wires. It is fused near the TV battery and terminates at the rear bumper at an Anderson connector.

If you already have the Anderson connector and the positive running all the way, makes sense to just use a negative wire which runs along side it all the way.

Voltage drop can easily happen on the negative side of a circuit as well as on the positive.