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Electrical System Explained

Leisure batteries, solar, inverters, and why your lights keep flickering.

Intermediate⏱ 20 min read

Contents

1

The Basics: What You Need to Power

Before buying anything, list what you'll actually use:

Typical daily power draw:

•LED lights (5-10W): 2-3 hours = 30Wh
•Phone charging: ~15Wh per phone
•Laptop: 50-60Wh per charge
•12V fridge (compressor): 300-500Wh per day
•Water pump: 20Wh per day
•Fan (MaxxFan): 50-100Wh per day
•**Total: ~500-800Wh per day** (modest use)

If you add these, double your budget:

•Diesel heater: 30-50Wh (fan only — fuel is separate)
•Induction hob: 1000-2000Wh (you need a massive battery bank)
•Hair dryer: 1500-2000Wh (just don't)
•Air conditioning: forget it unless you're plugged into mains

**Rule of thumb:** Size your battery to last 2 days without charging. So for 700Wh/day, you need 1400Wh of usable battery capacity.

2

Battery Types (The Big Decision)

Lead-acid (AGM/Gel) — £100-200 per 100Ah:

•Cheapest upfront
•Heavy (25-30kg per 100Ah)
•Only 50% usable (100Ah battery = 50Ah usable)
•Lasts 3-5 years
•Fine for weekend warriors

Lithium (LiFePO4) — £300-600 per 100Ah:

•Expensive upfront, cheaper long-term
•Light (10-12kg per 100Ah)
•80-90% usable (100Ah battery = 80-90Ah usable)
•Lasts 8-15 years (3000+ cycles)
•Works in cold (built-in BMS)
•**The right choice for full-timers**

What we'd recommend:

•Weekend use: 100Ah AGM = £150
•Full-time living: 200Ah LiFePO4 = £500-800 (look for EVE cells + Daly BMS on eBay/AliExpress for best value)

**Don't buy:** Cheap "100Ah" lithium batteries under £250. They're usually 50Ah cells in a 100Ah case. Buy from reputable UK sellers: Fogstar, BMS Battery, or build your own from EVE cells.

3

Solar Panels (Worth It?)

Short answer: Yes, but they won't fully charge your batteries in UK winter.

Panel sizing:

•100W panel = ~300-400Wh per day (UK summer) / 50-100Wh (UK winter)
•200W panel = ~600-800Wh (summer) / 100-200Wh (winter)
•300W+ = overkill for most, but great if you have roof space

Types:

•**Rigid panels** — cheapest per watt (£80-120 per 100W), most efficient, need roof mounting brackets
•**Flexible panels** — thinner, can bond directly to roof, less efficient, more expensive (£150-200 per 100W)
•**Portable panels** — unfold on the ground, point at sun, great for wild camping

Solar charge controller:

•MPPT (not PWM!) — extracts 20-30% more power
•Victron SmartSolar is the gold standard (£80-150)
•EPEver is the budget option that actually works (£30-50)

**Reality check:** In December/January, even 300W of solar won't keep up with a fridge. You'll need to drive (alternator charging) or plug in (hookup charger) to top up. Solar is brilliant March-October though.

4

Wiring It Up (Without Burning Down)

The golden rules:

1. **Fuse everything.** Every positive wire from the battery needs a fuse within 300mm of the battery terminal. No exceptions.
2. **Wire thickness matters.** Undersized wires = voltage drop = fires. Use this guide:

- Up to 5A (lights, USB): 1.5mm² cable

- Up to 15A (fridge, pump): 2.5mm² cable

- Up to 30A (inverter): 6mm² cable

- Up to 100A (main battery cable): 25-35mm² cable

3. **Use a fuse box, not a bird's nest.** Blue Sea or Bussmann blade fuse box. Label every circuit.
4. **Negative bus bar.** All negatives go to one point. Don't daisy-chain negatives.
5. **Battery isolator switch.** One big red switch to kill everything. Essential for safety and when working on the system.

**Common mistake:** Connecting the leisure battery to the van's starter battery with just a split charge relay. Modern vans (2015+) have smart alternators that don't play well with simple relays. Use a DC-DC charger (Victron Orion or Sterling) — it's more expensive but it properly charges lithium batteries and protects the van's electronics.

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