The other pages on this site follow energy toward the trailer. ProPower System covers how the truck makes it; The Measured Case covers what it costs to move it. This page covers what happens to it once it arrives — which is the part that decides whether a given source is useful or merely present.
The short version: a trailer is not a passive battery. It runs a refrigerator, a 12 V system, and a thermal-management plant that operates whether or not you are charging. Those loads are served first. The cells get the remainder.
House load is not a proportional loss like a conversion inefficiency. It is a fixed draw removed from whatever the source delivers, and what accumulates in the pack is the difference.
That distinction is the entire subject. A fixed draw taken off a large source is a rounding error. The same draw taken off a small source can be most of it.
It also means the familiar way of comparing charging sources — Level 1 is slow, Level 2 is faster, roughly in proportion to their ratings — is wrong for a trailer. The proportionality breaks because the subtrahend does not scale.
This is the softest number on this site, and it is presented that way deliberately. What follows separates what was measured from what was observed from what cannot currently be measured at all.
Across Campaign 1 the truck-side converter held three distinct output states: 0.000 kW when disconnected, 0.938–0.951 kW connected but not bulk charging (six independent legs), and 5.69–6.06 kW delivering (seven legs). Those magnitudes are firm and repeatable across 3,719 instrumented miles.
They are measurements of truck output — what left the inverter, not what the trailer consumed.
With trailer loads shed as far as they can be shed, base draw has been observed as low as 200–300 W. On Campaign 1's hot-weather legs it ran up to roughly 900 W.
The middle converter state above sits near the top of that range because those legs were hot. It is not a floor and it is not a constant — earlier versions of this project's notes treated it as a fixed hardware baseline, which was wrong. It tracks demand.
Two limits keep this from being pinned down with the rest of the campaign data.
The instrument has a floor. The truck's ProPower telemetry does not reliably register loads at roughly 200 W and below — sometimes it reports them, mostly it does not. The bottom of the range is therefore partly inferred from behaviour rather than read off a channel.
There is no trailer-side channel. The OBD stream carries what the truck sent, not what the trailer consumed or stored. Attributing the difference to house load is operator judgment supported by circumstance, not an instrumented result.
Working figure until that is closed: house base load is somewhere between unmeasurable and about 1 kW, condition-dependent. Any number quoted more precisely than that is quoting one leg's weather.
The obvious response to a standing draw is to turn things off. The trailer's own circuit layout explains why that does not work, and it is worth walking through because it converts the base load from a mystery into an inventory.
The AE.1 carries two 12 V distribution boxes, 47 protected circuits between them. Sorting those circuits by whether an operator can switch them off produces a lopsided result.
| Category | Circuits | Operator control |
|---|---|---|
| Always-on — control modules, monitoring, safety | 21 | None |
| Thermal & battery management — automatic | 14 | None |
| Discretionary or event-driven | 12 | Partial |
Thirty-five of forty-seven circuits have no operator control at any point — not in the trailer's app, not on a panel, not anywhere. And the split is not incidental: the thermal block contains essentially every high-current circuit on the trailer.
The panel shows three separate coolant pumps, two radiator fans, and two interior blower fans, alongside coolant reversing valves, expansion valves, a coolant valve, four pressure transducers, a dedicated thermal-system controller, and two battery-monitoring units.
All 12 V. All thermostatically commanded. None switchable. This is the mechanism behind the observed variance — the devices drawing meaningful current on the 12 V rail are cooling equipment, and cooling equipment runs when it is hot. Base load rises with ambient because the things riding on it exist to move heat.
Reversing valves plus expansion valves plus four pressure transducers describe a reversible refrigerant circuit — a heat pump, not a one-way air conditioner. Three separate coolant pumps imply at least three thermal loops (battery pack, power electronics, cabin) with valve-commanded cross-connection between them.
The practical consequence: there is no state in which the thermal system is simply off, because pack conditioning and cabin conditioning share hardware. Reducing cabin cooling does not stop the pumps if the pack still wants conditioning. This mirrors the tow vehicle's own arrangement, where the compressor also serves battery chiller duty and cannot be fully commanded off.
Strip out the circuits that only draw momentarily — waste valves, canopy actuators — and the drive-motor circuits that only exist while towing, and the entire operator-controllable standing load is USB ports and LED lighting.
That is the finding. Turning things off in the trailer's interface addresses a rounding error, because everything with real current is either always-on or thermally commanded. Note also that the onboard charger and the DC/DC converter are themselves in the always-on block: the charging hardware is part of the base load.
Carry the observed range through to what actually accumulates in the pack, and the asymmetry is the point.
| Source | To the trailer | Net at 0.2 kW base | Net at 0.9 kW base | 10 kWh takes |
|---|---|---|---|---|
| Level 1, 120 V | ~1.2 kW | 1.0 kW | 0.3 kW | 10 to 33 hr |
| V2V, measured on this rig | 5.8 kW | 5.6 kW | 4.9 kW | 1.8 to 2.0 hr |
| 240 V export from an EV truck | 7.2 kW | 7.0 kW | 6.3 kW | 1.4 to 1.6 hr |
Source figures are measured or rated; base-load figures span the observed range; the subtraction and resulting times are arithmetic. Charging is treated as linear, which it is not near the top of the pack, so these are best-case durations at any given base load. No conversion losses beyond the delivered figure are applied.
Read the last column rather than the middle two. At 5.8 kW the entire uncertainty in house load moves the answer by about ten minutes across two hours — a detail. At 1.2 kW the same uncertainty is the difference between an overnight top-up and something that runs for a day and a half.
This is also why the connected-but-not-bulk-charging state is worth having rather than switching off. It is not filling the pack, but it is holding the house loads off it — which matters most in exactly the conditions where the house load is largest and the pack can least spare the energy.
Everything above is a question of convenience until the pack approaches empty. Then it becomes a question of whether the trailer can be recovered in the field at all.
The failure is a cascade rather than a single event. The high-voltage pack depletes; the battery management system declines to close its contactors; the DC/DC converter that feeds the entire 12 V system loses its source; the 12 V system goes flat. At that point nothing remains to wake the onboard charger, and the trailer cannot accept a charge even with a perfectly good source standing next to it. It is not discharged. It is unresponsive.
That is a service call, and by the argument on the Charging Infrastructure page it happens where service calls are hardest to obtain.
| Tow vehicle export | Recovery capability |
|---|---|
| 120 V only, ~1.5 kW cap | Marginal at best. Net to pack may approach zero in heat. |
| 240 V from an EV tow vehicle | Real, but drawn from the traction pack that is also your range. Recoveries are a limited resource. |
| 240 V from an onboard generator | Real, and refills in ten minutes at a pull-through lane. Bounded only by fuel. |
The distinction in that last row is not efficiency. It is whether the recovery capability is itself limited. An EV tow vehicle rescuing a flat trailer is choosing which half of the rig to strand; a generator-equipped vehicle is not choosing at all.
Whether the trailer's onboard charger engages at all from a 120 V source, and at what minimum current, has not been established by this project. That answer determines whether a 120 V-only tow vehicle is a weak lifeboat or no lifeboat. It is a bench test, not a campaign, and it is scheduled.
Also unresolved: recovery attempts happen disproportionately in heat, and the one confirmed temperature-driven charging stop in this project's data occurred on a V2V session, not at a public charger. A lifeboat that derates is still a lifeboat, but the recovery plan should assume it might.
The base-load range is wide because it has never been measured directly — only inferred from the truck side, through an instrument with a blind spot at the bottom of the range. That blind spot is a tow-vehicle artifact and has nothing to do with the trailer's own wiring, which means it can be stepped around entirely.
The target output is a single base-load-versus-ambient curve. That curve would let any owner of any electric trailer compute net charge rate for a given source in given conditions — which is the question this entire page is circling, and the one no manufacturer currently publishes.
Everything on this page is reconstructed from the outside — from truck-side telemetry, factory panel layouts, and inference. The builder of any electric trailer holds the parasitic-load inventory and the thermal control logic directly, and could publish a load-versus-ambient curve without instrumenting anything. It is unglamorous documentation, and it would materially change how buyers evaluate tow vehicles.
If you have questions or comments, please visit the LightShip RV Owners Club on RVForums.com and post them to this topic. I monitor that site regularly and would enjoy your feedback.