The Express, Savana and E-series are the vans people convert on a budget, and the second-battery question comes up on every board that covers them. Most of the answers still describe a battery isolator, because that is what people fitted in 2010. The better answer today is a DC-DC charger, and it is not much more money.
Isolator versus DC-DC charger
An isolator, whether a diode block or a relay, connects the house battery to the alternator when the engine runs and separates it when the engine stops. It does nothing else. The house battery sees raw alternator voltage over whatever cable you ran, with no charge profile, no current limit, and on a van with a long run to the back, a lot of voltage drop.
A DC-DC charger is a regulated charger fed from the starter battery. It draws a fixed current, delivers a proper multi-stage profile to the house battery at the voltages that battery wants, and boosts to overcome the drop in the cable. It also isolates: with the engine off it is open-circuit, so the house loads can never flatten the starter battery. That last point is the one that matters on a work or camper van.
Sizing it to the alternator
The charger draws its rated current from the alternator continuously, on top of everything else the van is running. The rule of thumb that circulates on the boards, and that we agree with, is that the charger should take no more than about a third of the alternator's rating. Read the rating off the alternator label or the build sheet; it varies by year and engine on both vans, and we would rather you read it than trust a figure from a forum.
- Alternator around 105 to 130 A: a 30 A charger, the Orion-Tr Smart 12/12-30 non-isolated.
- Alternator 150 A or more: the 50 A Orion XS 12/12-50, whose input current limit can be set lower in the app if you want to be conservative.
Both vans have the starter battery and the body on a common chassis ground, so the non-isolated versions are correct. The isolated Orion-Tr is for boats and for installs where the two systems must not share a ground.
Engine detection on these vans
Older Express and E-series alternators are simple fixed-voltage units, and the charger's default voltage-sensing engine detection works. Newer vans with variable-voltage charging need either the charger's smart-alternator mode, which the Orion XS has, or an ignition-switched wire to the charger's remote terminal. Run the wire if you can; it is the one setting that removes all doubt.
Cable and fusing
The charger's input is a continuous load, and the cable is sized by the total length of the run, positive plus negative, from the starter battery to the charger. For a 50 A charger:
| Total run (both legs) | Cable |
|---|---|
| Up to 5 m (16 ft) | 6 AWG (16 mm²) |
| 5 to 10 m (33 ft) | 4 AWG (25 mm²) |
A long-wheelbase van with the charger at the rear is usually in the second row. Use a MEGA fuse in a holder at the starter battery, rated for the cable, and a second fuse at the house battery. Our cable and fuse sizing chart covers the rest of the system. Mount the charger near the house battery, not the starter battery, so the boosted output has the short run.
Lead-acid or lithium house battery
A deep-cycle AGM is the simple choice and the charger has a profile for it. A lithium battery holds far more usable energy for the same space, charges at the full rated current, and needs two things the AGM does not: a lithium profile on the charger, which both Orions have, and a fuse at the battery with an interrupt rating to match a lithium short. A 280 Ah lithium behind a 50 A charger is a full working day of fridge, lights and laptop, and our 280 Ah install guide covers the wiring in detail.
Either way, fit a SmartShunt on the house battery negative. On lithium in particular, voltage does not tell you state of charge; the shunt does, and it shares the app with the Orion.
What the boards get wrong
Two things. First, feeding the charger from the 7-pin or a trailer socket: those circuits are 10 or 12 gauge behind a 30 A fuse and cannot supply a 50 A charger. Second, mounting the charger next to the starter battery: the boosted output then has to cross the whole van, and the voltage you paid for is lost in the cable. Charger at the house end, heavy cable from the front.
Our guide to the Orion XS versus the Orion-Tr Smart covers the two units in detail. Send us the van, the alternator rating and where the house battery will live and we will confirm the charger and the cable. Everything ships from Upland, California.