Winter Project Season: 12V Tech Upgrades Worth Fitting in Your Van

Winter Projects Guide

A practical guide from Bedam Leisure — caravan & motorhome specialists

There's a particular kind of October job that only makes sense now. The van's off the road, the evenings are dark, and the jobs that are miserable on a campsite in August — lifting a seat base, running a cable behind a locker, fitting a socket you've wanted for two seasons — are suddenly quite pleasant with the heater on and a cup of tea to hand. This is tech-upgrade season, and the upgrades that pay you back most aren't the flashy ones.

Here's what we'd actually fit over a British winter, in the order we'd do it, and the wiring rules that apply to every one of them.

1 Monitoring

Start by finding out what your battery is really doing

Almost every 12V complaint we hear — "the battery doesn't hold charge any more", "we only got two nights off hook-up" — comes from the same place: nobody actually knows what the battery is doing. A voltmeter on the control panel tells you something, but resting voltage is a poor guide to state of charge, and it's badly skewed the moment anything is drawing current or charging.

A shunt-based monitor fixes that. It measures every amp going in and out, so it reports consumed amp-hours and a true state of charge rather than a voltage you have to interpret. Fit one and you stop guessing: you learn that the fridge on 12V is the real culprit, or that the battery genuinely is tired. It's the most useful thing you can add to a 12V system, and it's a two-hour job.

The one thing people get wrong is where it goes. The shunt is not a tap off the positive side — it belongs in the negative lead, and everything on the negative side of the system must go through it, or the readings will be nonsense. Victron label the two big M10 posts clearly: B for battery minus, A for the system (load) minus. A thin red sense wire runs to the battery positive so the unit can read voltage.

Check the manual for your fuse rating. The sense wire carries almost no current, so it needs only a small fuse — but fit the rating Victron specify for your model, as close to the battery positive as you can get it.

Two companions worth fitting at the same time. A low-voltage disconnect saves a battery from being flattened to death by something left on, and a panel voltmeter with switched outputs is a tidy way to control lights and the pump in an older van or a self-build.

One important limit on the BatteryProtect. It only passes current one way, from IN to OUT, and Victron are explicit that reverse current from OUT to IN will damage it. Inverters and inverter/chargers must never be wired through their DC inputs — switch those with their remote port instead.

2 Charging

Charging properly while you drive

If your habitation battery is still charged through a simple split-charge relay, it is almost certainly not getting full. Modern vehicles run smart, ECU-controlled alternators that vary their output voltage and back off entirely when the ECU decides the starter battery is full — and a relay simply passes that reduced voltage through. The result is a leisure battery sitting at 70-80% after a four-hour drive. Lithium makes it worse: it will happily accept a big current the alternator was never asked to provide.

A DC-DC charger solves it by taking whatever the alternator gives and producing a proper regulated multi-stage charge — bulk, absorption, float — at the voltage your battery chemistry actually wants. Victron's Orion-Tr Smart range has engine-running detection built in, so it won't sit there draining the starter battery when you're parked up, and the whole charge profile is set from your phone in VictronConnect, with presets for lead-acid, AGM, gel and lithium.

3 Living with it

The small jobs you'll notice every single trip

Here's the unglamorous truth: the upgrade you'll appreciate most isn't the £200 charger, it's a charging point where you actually sit. Most vans were built with one 12V socket in an awkward corner and no USB at all, so everyone ends up with an adaptor hanging out of it and cables draped across the seat. A recessed USB point in the lounge and another by the bed takes an hour each and removes an irritation you've stopped noticing.

Check the part number, not the look. CBE, Fawo and the generic ranges all use different backing boxes and frame sizes. Measure your existing aperture and match the part number before ordering — it's the commonest cause of a returned socket.

The other winter favourite is signal. If you've been propping a portable aerial in the window, a roof-mounted omni-directional aerial is a weekend job that ends the ritual of walking round the van looking for a picture. The Gazelle Pro receives TV, FM and DAB through 360 degrees, so there's nothing to aim, and its booster has adjustable gain from 0 to 19dB — which matters more than people expect, because in a strong-signal area turning the gain down often gives a better picture than cranking it up.

4 Doing it properly

The wiring rules that apply to every job on this list

Whatever you're fitting — a monitor, a USB point, an aerial booster, a reversing camera — the same handful of rules decide whether it's a safe installation or a problem waiting for a hot day.

The fuse protects the cable, not the gadget. This is the one that catches people. A fuse rated above what the cable can carry means the cable becomes the fuse. As a rough guide, 1.5mm² takes a 13A fuse at most, 2.5mm² a 20A, and 4.0mm² a 30A — and if the cable runs bundled in trunking rather than open air, derate it further.

Fuse at the source, not at the appliance. Every positive feed wants its fuse within about 300mm of where it taps off the battery or busbar. The unfused stub between the source and the fuse is the only part of the circuit with no protection, so you keep it as short as you physically can.

Size for voltage drop, not just current. Aim for no more than about 3% drop, which on 12V is a mere 0.36V, and remember to count both the positive and the negative conductor in your run length. This is why a long run to the back of a motorhome needs heavier cable than the current alone suggests. For small accessory loads — LED lights, USB sockets — 1.5mm² on a 7.5A fuse is the usual answer; a general 12V socket drawing up to 10A wants 2.5mm² on a 15A fuse.

Mind which live you take. Anything that must not drain the battery in storage belongs on a switched feed, not a permanent one. If you're fitting a camera, take its supply from a fused switched circuit rather than splicing into the reversing light, and you'll get a view you can leave on for towing and manoeuvring rather than only in reverse gear.

Seal every hole you make. Any cable passing through the roof, floor or bodywork needs a grommet and a proper sealant, and connections outside the van want weatherproofing. Water finding its way in along a cable is how a tidy upgrade becomes a damp problem two years later — and our guide to damp checks and habitation servicing explains what that costs to put right.

Know where to stop. 12V work is well within reach of a competent DIYer. Anything on the 230V side, and anything touching the gas circuit, is not — that needs a qualified engineer, and doing it yourself can invalidate your insurance as well as being unsafe.