Converting to Lithium

[Mike Lewis]

Using a 2A battery charger and a test light I have located what I believe to be the "battery +" wire from the 7-pin plug. It connects to what appears to be a fusible link between the WFCO unit and the rear of the trailer. If anyone knows differently, please let me know.

I have disconnected the wire from the link and intend to connect it to the input to the B2B charger in the battery compartment, along with the large wire from my other circuit from the truck, as AllanEdie did. That way all charging current goes through the B2B charger.


I tested this out with a jumper wire. I cranked the truck and let it idle with both umbilicals attached, then went inside to trailer to view the battery monitor. At first it read 13.1 amps charging, but after thirty seconds or so the charge gradually decreased to around 5-6 amps as before. At this point I believe that this is simply the way the truck's alternator and the B2B charger interact with each other, and is normal.

[millybob]

Does anyone know how many volts and amps the Victron smart DC-DC 12/12-18 charge controller says is coming in from TV(using stock tow harness wiring) and going out to the lithium batteries under normal highway speeds?

[John in Santa Cruz]

Originally Posted by millybob

Does anyone know how many volts and amps the Victron smart DC-DC 12/12-18 charge controller says is coming in from TV(using stock tow harness wiring) and going out to the lithium batteries under normal highway speeds?

the voltage would depend entirely on your tow vehicle AND the charge state of the trailer batteries.

i've not hooked my DC-DC up yet nor towed it anywhere with it.

[alanmalk]

Originally Posted by millybob

Does anyone know how many volts and amps the Victron smart DC-DC 12/12-18 charge controller says is coming in from TV(using stock tow harness wiring) and going out to the lithium batteries under normal highway speeds?

Per the Victron website - the DC-DC 12/12-18 unit is designed to deliver 220 watts to the batteries. So a back-of-the-napkin calculation is 16 amps at 13.8 volts on the tow side. In real life you will have to consider if your stock harness wire will actually supply 16 amps without dropping the voltage a bit between the alternator and the Victron. Likely the voltage will drop - perhaps significantly like my Toyota. In that case the amps will attempt to go up, perhaps to the point that the fuse will protect the wires. It gets messy and highly dependent on your particular installation.

[John in Santa Cruz]

case in point. long bed truck pulling a E21, there's maybe 40 feet of AWG 8 from the engine compartment to the connector to the 12/12-18 in the back of the trailer near the battery. 40 feet of AWG 8 is about 0.025 ohms, and if the DC-DC thing is trying to pull 18 amps, there would be a 18*0.025 volt drop, thats 0.45 volts, so if the truck alternator is outputting 13.85, there's only 13.40 V at the DC-DC

now in reality, the resistance is somewhat higher, because there's probably other voltage drops, like the RV connector, various harness connectors between the alternator and the RV connector, and maybe some splices in your trailer too.

newer vehicles often have 'smart alternators' that do all sorts of funky things trying to optimize gas mileage, like once the battery on my 2016 mercedes is fully charged, the alternator drops all the way down to 12.6V, sufficient to run the vehicle electrical load without drawing anything from the battery. I've been told late model Ford trucks do much the same, BUT if you put them in tow mode, they boost the voltage back up.

[alanmalk]

pull 18 ohms, ...




==> pull 18 amps, ...

[John in Santa Cruz]

Originally Posted by alanmalk

pull 18 ohms, ...




==> pull 18 amps, ...

oops, yeah. ENEEDMORECOFFEE

[millybob]

Good to know about tow/haul mode affecting a newer F150’s alternator output. Just happened to use one to tow my 5.0 trailer. I know that ETI uses a Victron dc-dc 12/12-18 charger when installing a lithium system. And they never mention a need to add a dedicated bigger gauge wire for whatever TV you might be using. I guess that’s ok/safe with the Victron 12/12-18 amp charger? I was reading similar threads on a F150 forum. Lots of information to consider. I included a screenshot of 2 posts that were interesting.

[John in Santa Cruz]

yeah, the whole idea of the DC-DC is it can step up too low of an input voltage OR step down too high. for the same watts output, if the input voltage is higher, then the input current is lower, and if the input voltage is low, the input current goes up, because watts is volts * amps.

the 12/12-18 is 220 watts, and has an 87% efficiency per https://www.victronenergy.com/upload...50-400W-EN.pdf so, for example, with 14.4V Lithium charging, 220 watts is 15 amps. at 87% efficiency it will require 250 watts input power, so if it only gets 12.5V in due to line losses, it will be drawing as much as 20 amps from the tow vehicle.

[Rossue]

Just hooked up My Goal Zero Yeti Link or Vehicle Integration Kit in the Transit Van and the numbers are unbelievable: Solar only (two 195W panels at 1 PM is 204W. Add the GZ Yeti Link and it topped out at 999W with the engine running. The van does have a 250 amp alternator.

In the photo you see the output number of 1292- that is the 2.5 gal Bosch AC water heater running off the 2K watt inverter. After 15 minutes to heat the time to recharge is 1.2 hours on solar only.

Our van has a hybrid system whereby the Maxxfan, LED lights and USB/12V ports are running on the van starter batteries(2 AGM under driver's seat) the rest- Isotherm 130/ Propex Heater/ Dual Induction cooktop/AC Water Heater all run from the Goal Zero 3000X. I would think that anyone wanting to just run a compressor fridge could also use this setup vs. building a component system as our 4.6 Isotherm draws 4 amps when running, which is less that 1/2 the time.