Victron MPPT 75-10 Controller (existing controller is 10amp but not lithium compatible)
I want to install a dc-dc charger to protect the TV from high recharge surge from the lithium. I also want to check if there is anything protecting the TV battery from giving power to the TT when the TV is not running.
Questions
Where should the dc-dc charger be located?
A. Does in go in the Tow Vehicle?
B. Does it go in the Battery box to intercept the wires at the battery?
C. Does it go at the converter?
I am seeing “Isolated” and “Non-Isolated”. What is the difference?
Thanks in advance. I need to either get this done in the next couple of weeks before the first trip or simply buy another lead-acid as the battery I had sprung a leak over the winter and I now have nothing. There is nothing about this (so far) that would make me defer installation to somebody else, but my pride will not stop me from hiring somebody is this gets too techy. I have better-then-average skills for home repair (electrical, plumbing, etc.) and I have already installed some add-ons to the Travel Trailer but try to stay conscious of my limitations.
The Orion DC to DC chargers can be activated either by a connection to the ignition switch or by measuring the vehicle battery voltage. If the vehicle battery voltage is above the voltage of a full battery it is being charged. If it drops below this the Orion shuts down. When connected to the ignition switch it only runs with the ignition on.
The best place is in trailer next to the batteries so there is no voltage drop on the output. If there is voltage drop on the input then the Orion can boost this. You will need to oversize the input wires to keep voltage drop low and fit good quality connectors. Many DC voltage drop calculators on line.
See link below vs isolated and non isolated. The choice depends on if you common ground the vehicle and trailer. You can use isolated in a non isolated situation but not the other way.
Thank you gor this. My question about wiring remains. The trailer battery gets power from the 7-pin, from the solar controller and from the trailer’s power center(converter). However, there are only 2 sets of wires at the battery. One set is pretty hefty and the othe set is lighter, maybe 12ga, and has an in-line 20amp fuse. I am guessing that is power to the brakes. How do those 3 sources come together to one set of wires without fighting each other?
Chargers do not fight each other, they all try and regulate the current to maintain the rquired voltage. If one is set to a slighlty lower voltage it will stip charging first before the batteries are full. I have had solar, alternator and mains chargers all co existing. You can even set the solar 0.1V higher so it has priority and stays on the longest.
Given the distance from the car battery (presumably up front in engine bay) and the trailer batteries you need to be using at least 16 sq.mm cable for both power and earth connections and use a separate 50A rated Andersen type connector to limit volt drop. Supplying power to a dc dc charger in the trailer via the 7pin connector is not really viable because it is unlikely to accomodate the size of cables you should use or the current that your investment should allow you to transfer. External connectors also get dirty and build up resistance over time.
The Victron dc dc chargers can boost the voltage to compensate for volt drop from the start battery but they won’t let the dc dc input voltage drop below the voltage set for for engine run detection setting. So this dials back the current you can transfer leading to slower charging while driving. E.g. if your alternator puts out 13.8V and your dc dc engine detect limit is set at 13.2V then your system will limit the current to that which results in volt drop up to 0.6V.
In my system I have observed that the slightest contamination of the external connectors affects charging current.
The fuse in the tow vehicle for the trailer is 30 amp. I was going to use to the dc-dc charger to limit the draw from the tow vehicle to 10 amps. With that, I didn’t think that I needed to mess with anything in the tow vehicle. Am I missing something?
The smallest Orion charger is the 12/12-15 isolated, 15Amp model and you can not manually limit the current lower. The 15A is output current, input current will be higher due to efficiency losses and the need to boost the voltage. The Orion XS 50A model can manually limit the current, but that is probably a bit too large.
The trailer plug / wiring may be rated at 30A, but it is the voltage drop that is critical. Tjere ate plenty of voltage drop calculators on line if you know the wire gauge / conductor area.
Today for example my Lithium 100Ah battery was at 91% but I was getting only 4.5A charging current while driving. The contacts on my external Anderson connector are old and the tin coating has worn off. A month ago after cleaning them I was getting around 17A in similar conditions. My alternator putting out 14.2V at start and 13.8V once warmed up. My engine detect voltage is set at 13.1V so I only have 0.7V drop to play with. If I used the ignition circuit to trigger the Orion instead of the built-in engine detection it would probably tolerate more volt drop but then I’d need to run another small wire and dedicated connector. Will be crimping some new contacts on soon to see if that helps.
If you plan to limit charging rate to 10A then perhaps you could get by running it through the 7 pin but you’ll still need the largest cables that will fit and the shortest cable runs possible. Try your existing cable setup in a volt drop calculator and don’t forget to include both the earth and positive cable runs.
I very much appreciate you sticking with me on this. This is pushing the limits of my comfort level. However, even if I have this installed for me I still would like to better understand.
I found what I think is a 10amp dc-dc. I can’t figure out how to attach a photo to this message but it is as follows:
If the power wire from the tow vehicle is fused to 30amp and if this charger will only allow a 10amp draw, I am not clear as to why I could have a wiring problem. The only other draw would be the brakes (fused to 20 amps). My refrigerator does not run on 12v.
Right now, the battery is on the tongue and I hadn’t planned on moving it. I have a queen bed across the front of the trailer with a full-width storage area beneath it with outside access. That is where my solar controller is so that is where I planned to put the dc-dc charger. The wire from the 7-pin must go directly under this storage area so the distance from the dc-dc to the existing wire will probably be no more than 2 feet
The cable length from starter battery to dc dc location in the trailer will be around 7m (23’). Double that for the return path. If using 12awg (4 sq.mm) then online calculators predict around 0.9V drop at 10A, excluding resistance across joints and connections. The volt drop is around 7.5% of input voltage. Victron manuals recommend less than 3% volt drop for such applications. This would require wiring of more than double the cross sectional area (8 awg at least) for 10A.
A depleted lead acid or lirhium battery will accept much higher charging currents so your system will be limited by the combination of charger output and voltage loss. Choosing a charger with output in the 10A to 20A range will probably work ok with 8awg but when the battery is depleted its going to need hours of driving to charge them.
Most would go for a higher capacity dc dc charger and heavy gauge cables with a dedicated robust connector at the trailer hitch.
e.g. 4 to 6awg cable with 50A Anderson connectors and a Victron XS 50A charger which can be limited to lower output in the settings if needed. This will allow charging of a depleted 100Ah battery in 3 to 4 hours of driving
I am 17.5 feet bumper to bumper on the tow vehicle, so 23 feet is probably a touch conservative.
Yes, it is a 12v system. Ii read the labeling on the unit to imply that it could do 12 or 24 volt at 10amps. I saw units that looked generally the same and were 12v/9amps but they we identified as converters, not chargers.
I need to see if I can confirm the wire size coming from the tow vehicle to the 7-pin and from the 7-pin to the battery. All searches on-line are telling me that a 12v/30amp wire should be 10ga. I really don’t want to be running new wires to the tow vehicle battery. That is the whole purpose of the dc-dc charger
I do not expect to do much boondocking (no utilities) so I am trying to control cost. If the power fails a the campground I probably won’t be sticking around to deplete the battery. The switch to lithium is more weight and longevity. Swapping out the Group 27 Lead-Acid off the tongue will allow a mattress upgrade without increasing tongue weight