turbopilot
RVF Supporter
- Joined
- Nov 2, 2019
- Messages
- 966
- Location
- Prescott, AZ
- RV Year
- 2026
- RV Make
- LightShip
- RV Model
- Turbo Edition
- RV Length
- 27
- Engine
- Electric
- TOW/TOAD
- 2025 Ford F-150 PowerBoost HEV, 7.2 kW Propower Generator
- Fulltimer
- No
For an complete technical analysis of this trip see this page.
For an HTML version of the content below see this page.
What we learned towing a LightShip 3,719 miles
One truck, one trailer, eight driving days, Arizona to Wisconsin and back. Every second of it recorded. Here is what worked, what it cost, and what we still can't tell you.
The setup: a Ford F-150 PowerBoost hybrid towing a LightShip AE.1, 15,320 lb combined on a certified scale. The two were connected by a charging cable so the truck could refill the trailer's battery from its engine while driving. Nothing was staged — real trip, real destination, real July heat, normal highway speeds. The difference is that the truck was wired to a data logger recording 42 measurements every two seconds, plus a separate GPS logging position once a second. About 1.3 million readings.
Three questions, answered with numbers instead of brochure claims.
1. Yes, the truck can charge the trailer while driving
This works, and it works consistently. The truck's onboard generator sent 5.8 kilowatts into the trailer's battery whenever it was running — day one, day eight, mountains, plains, 60°F and 100°F. The rate never sagged. Single most reliable finding of the trip.
Cost is about three-quarters of a gallon of gas per hour of charging. We measured that two completely different ways — once by comparing a matched round trip in June, and again by statistically separating the charging load out of 18,500 highway measurements from this trip. The two methods share no assumptions and landed within a few percent of each other. That is about as good as field measurement gets.
What one gallon of gas buys you, in trailer power:
| 7.7 kWh | Delivered into the trailer (~7.1 kWh actually stored, after normal charging losses) |
| ~23 hrs | Of refrigerator, at its continuous draw |
| ~5 hrs | Of air conditioning on a hot night — up to about 17 hours in cool weather or at altitude |
| ~$0.48 | Per kilowatt-hour stored, at $3.50 a gallon. Rises and falls directly with pump price. |
Put another way: five hours of driving with the charger on puts roughly a third of the trailer's battery back, and costs about three and a half gallons. Filling the pack from empty would take about fourteen hours of driving and ten and a half gallons.
What it does to fuel economy: towing without charging, the rig returned 15.3 mpg. That figure is unusually trustworthy — we got it twice, on two different days, over 1,080 miles, in weather 15°F apart, and the two results differed by one percent. Turn the charger on and hold it on, and you should expect about 13 mpg at highway speed. Across the whole trip, charging accounted for 3.8% of all the fuel burned — under ten gallons out of 259 — because the charger wasn't running most of the time.
2. The honest catch: on hot afternoons we back the charger off
Here is the finding a brochure would leave out, and it isn't the one I thought I'd be writing. The charging rate never dropped. What dropped was how much I was willing to run it as the day got hot — and that was my decision, not the equipment's.
One day in Nebraska shows it cleanly, because I drove three segments in a row as the afternoon heated up:
| Outside air | Share of driving time actually charging |
| 90°F | 66% |
| 93°F | 43% |
| 97°F | 10% |
Same day, same rig, three consecutive segments. Output rate held steady at 5.8–6.1 kW throughout.
The obvious reading of that table is that the equipment gives up in the heat. That is not what happened. I deliberately cut the charger back as the ambient climbed into the 90s, to keep engine coolant temperature in hand — the truck is already working hard pulling 15,000 lb, and running the generator on top of that adds heat exactly where there's least margin for it. Nothing in the recorded data separates a driver's decision from an equipment limit; the two produce identical-looking traces. I know which one this was because I wrote it down at the time, and that's now standard practice on every charger state change.
Is there an actual heat limit? Genuinely open. One temperature-related stop in 3,719 miles — a connector on a Colorado climb, which restarted on its own as the air cooled. One event doesn't establish a threshold, and the "quits somewhere in the low 100s" figure I started the trip with was an estimate I never got to verify. That same event took 30–45 minutes to restart, well after everything had cooled. I'm fairly confident the delay wasn't truck-side, since the truck's own cutoff sits about 100°F above where this happened. How long that delay usually runs, I've seen once. Once is not a number.
Plan around it. Charge in the morning — not because the system quits in the afternoon, but because that's when you have engine thermal headroom to spend, and because arriving at camp with a full battery matters more than it sounds. An occupied trailer overnight in summer draws one to two kilowatt-hours an hour just for A/C.
Something I first wrote down as waste, and had to take back. With the cable connected but the trailer battery not actually taking a charge, the system still moves about a kilowatt. My first pass through the data called that overhead — a kilowatt burned for nothing — and recommended switching it off between charging sessions. That was wrong, and it's worth saying so rather than quietly deleting it. A kilowatt is very close to what the trailer draws just existing: fridge, 12 V system, fans, controls. The truck isn't wasting it, it's covering those loads directly, so the trailer battery drains more slowly than it otherwise would. It doesn't push SOC up, which is why it looked like nothing was happening. About 16 kWh went across that way over the trip, roughly two gallons. Switching it off would just have moved that load back onto the trailer's own battery. Caveat: the kilowatt is measured, but what the trailer does with it is my reading, not my measurement — the truck's logger sees what leaves the truck and nothing of what happens at the other end of the cable.
3. The trailer's motor helping push: a more complicated answer
The trailer has a motor in its own axle. Switch it on and it takes over some of the work of moving itself, and the truck's fuel consumption drops immediately and obviously.
We ran a careful test outside Denver: the same 35-mile loop twice, back to back, once with the trailer motor off and once with it on. Same road, same traffic, elevation within two feet at the end.
The raw fuel rate fell 47%. That number is real, but it is not the honest one — the two systems can't run at the same time, so switching the trailer motor on also switches the charger off, and part of that 47% is simply the charger no longer running. Separating the two effects, the trailer motor's actual contribution is a 27.8% reduction, distance for distance. Still a substantial number, and still the largest single efficiency lever in the system.
The catch. The trailer spent more battery than the truck's charger could put back — by a wide margin, under every reasonable way of valuing the energy. Used as a fuel-saving device on a trip with no plug at the other end, it loses. Used on a trip where you plug in overnight, the arithmetic flips and it wins, because the energy it spends is cheap grid power rather than gasoline run through a generator.
So the fair statement is: the trailer motor is a range-and-comfort feature for people who plug in, not a fuel-economy feature for people who don't.
4. The surprise: heat is a mountain problem, not a desert problem
We expected the hard thermal miles to be the 100°F plains east of Denver. They weren't. The hottest the engine ever ran was on a long climb at 8,000 feet, on a day that was 79°F outside.
Sorting nearly 20,000 highway measurements by altitude, engine load, and outside temperature makes the pattern unmistakable:
| What changes | Effect on engine coolant temperature |
| Climb 1,000 feet | +1.2 °F |
| Work the engine 10% harder | +1.9 °F |
| Outside air 10 °F warmer | no measurable effect |
Thin air is the reason. At altitude there is less air to carry heat away and less air to cool the turbochargers, and both problems arrive exactly when you're asking the engine to work hardest. The engine peaked at 241°F, about 24°F above the point where its thermostat is already wide open and the cooling system has nothing left in reserve. It spent about ten hours of the trip above that point, though only 16 minutes above 230°F and a matter of seconds at the peak — brief excursions on grades, not a sustained condition.
Why this matters. The automated assist system we're proposing was originally designed to trigger on hot weather. This trip says that's the wrong signal — it would have missed the worst thermal event of the entire trip, and two of the three episodes where the engine was actively dumping extra fuel to protect itself. It needs to trigger on the climb instead. That is a design change we would not have found without driving it.
What we still can't tell you
Two things we set out to measure and didn't get, stated plainly because a summary that only reports successes isn't worth much.
- How much of the fuel goes to wind resistance. Splitting the rig's road drag into the part caused by pushing air and the part caused by tires and weight requires deliberately driving at 50, 55, 60, 65 and 70 mph and comparing. We used cruise control the whole trip, which meant 92% of the data sits in a single narrow speed band — not enough spread to separate the two effects, no matter how much data you collect. It's scheduled early on the next trip rather than left to chance.
- Exactly what the trailer's motor draws. The truck's data logger can see everything happening in the truck and nothing happening in the trailer. So when we say the trailer motor spends more energy than the charger returns, the direction of that conclusion is solid but the exact size rests on the trailer's published specification rather than on our own measurement. Reading the trailer's battery directly is the first item on the next trip's list.
The short version
- [MEASURED] Charging the trailer while driving works reliably, at 5.8 kW, for about three-quarters of a gallon an hour — roughly 7.7 kWh into the trailer per gallon of gas.
- [MEASURED] Towing economy is 15.3 mpg without charging and about 13 mpg with it running continuously.
- [MEASURED] On hot afternoons I deliberately run the charger less, to protect the engine — so charge in the morning. Whether the equipment has a heat limit of its own is still an open question.
- [MEASURED] The trailer's motor cuts fuel use by about 28% while it runs, but spends battery faster than the truck refills it. It pays off if you plug in at night, not if you don't.
- [MEASURED] Engine heat is driven by altitude and load, not by the weather. This changed a design decision.
- [OPEN] Aerodynamic drag and the trailer's own power draw remain unmeasured, and are the first two items on the next trip.
How to read the labels: MEASURED means we recorded it on the road and can show the data. ESTIMATED means it comes from a calculation with stated assumptions. OPEN means we tried and could not get it, and we say so rather than filling the gap with a guess.
Ford F-150 PowerBoost hybrid towing a LightShip AE.1, 15,320 lb combined on a certified scale. 3,719 miles, 258.59 gallons, 71.8 hours, July 11–24 2026. Route: Prescott AZ → Salida CO → Broomfield CO → Oshkosh WI → Grand Island NE → Moab UT → Prescott AZ. Instrumentation: OBDLink MX+ (42 channels at 2 s) plus TrackLogger Pro (1 Hz GPS). Happy to get into method in the thread if anyone wants the details.
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