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TJandDoc · 04-11-2023, 07:00 PM

We went to take delivery of our new 2023 28' Flying Cloud this morning but ran into an issue when we found damage to the skin on the initial walk-around. Needless to say, the unit is staying at the dealership until it's fixed and we have not made the final payment yet...but that's a story for another day.

We had also requested the lithium upgrade as we have the solar package, but somehow, no work had been made towards that either. In speaking with the electrician, she's going to put together a quote to have the work done, so hopefully we have that in the next day or so. We will be going with 2x 100amp Battleborn batteries that the dealership will let us supply as their cost is double what we'd pay from BB. Things she mentioned that will be on the quote:

- change the solar control panel so it reads lithium
- upgraded wiring from the batteries to the converter
- install a DC/DC

The thing is, I don't know what a DC/DC is or whether we need it.

I've searched through threads here, and it seems like it has something to do protecting the tow vehicle battery but I may be wrong. We are towing with a 2022 Ford F350, and a different thread said an F350 wouldn't need a DC/DC.

Does anyone have any input or suggestions? My head is spinning with all the electrical info. Do we need a DC/DC? Does the wiring need to be upgraded?

**richard5933** · 04-11-2023, 11:40 PM

Welcome to Air Forums!

A DC-to-DC charger largely comes into play due to the different charging parameters for the battery in your truck and the lithium batteries you'll have in your trailer, as well as in the basic setup for how charging is otherwise done using the 12v+ connection in the 7-wire harness connecting the truck to the trailer. There are also a few other issues such as preventing damage to your truck/trailer batteries when parked & still connected, but many of those are only issues on older tow vehicles.

On most newer trucks the output to the 12v+ charge wire in the 7-wire harness will be limited to 20 amps or so, and it will be fed with a relatively small-gauge wire. When sending voltage over a wire, especially covering the distance between the truck's battery and the trailer's batteries, there will be a drop in voltage due to the resistance inside the smaller gauge wire. By the time the 20 amps or so arrive at your trailer's lithium batteries, the voltage may be too low to properly charge them.

So here's where the DC-to-DC charger comes in. It will take whatever power is arriving to it via the 7-wire harness, regardless of the volt level, and convert it to the proper voltage to charge your lithium batteries. It will do this by dropping the amps and raising the volts. In the end your batteries will properly charge, but if you stick with the factory wiring the charge rate (the number of amps, or flow rate) will be quite low and result in long charge times.

Another commonly installed piece of this along with the DC-to-DC charger is a pair of dedicated heavier-gauge wires running from the truck's batteries to the rear of the truck, where they ultimately connect to a matching set on the trailer connecting to the DC-to-DC charger. This heavy-gauge pair of wires allows the DC-to-DC charger to pull higher amp rates and maintain the proper voltage, and this permits the batteries to charge more rapidly.

Hope this helps explain things a bit. I know that I didn't cover everything, but I just wanted to give you a bit of an introduction to things.

Do you need a DC-to-DC charger? Depends. If you have a few hundred watts of solar on the roof and travel when there is sun hitting the panels, maybe not. The solar could possibly be able to provide adequate charging to your lithium batteries while on the road, and then your charge wire from the 7-wire harness could be disabled. Or, you might have a low enough power need while driving that the stock charging system on the 7-wire harness is adequate. It will provide a minimal charge to the batteries, but for some people that is enough. More information is needed to know if you need the DC-to-DC charger.

field & stream · 04-12-2023, 07:29 AM

The above is a most excellent answer to your questions about DC-DC converters!

Not responsive to your question, but other things you should consider at this time include:

— the dealer probably knows this but the converter also needs to be in lithium mode

— under good conditions, 200W of solar will barely keep up with the electrical demands of the electric-only fridge so this would be a good time to bump that up to at least 400W

— under unfavorable solar conditions you will get very little recharge, so you might find it necessary to get a generator

— this is pricey, but depending on how much unplugged camping you want to do, many on these forums have upgraded to four (or more) lithium batteries

— a shunt based battery monitor (like a Victron 712) is necessary to really understand the state of charge of lithium batteries and what your power demands are

The sad fact is that — despite the images in their marketing — modern Airstreams do not come from the factory designed for off-grid camping. They can be made capable, but it is up to the buyer to do so.