The same errors recur in van and RV electrical build guidance and troubleshooting discussions. Here are ten checks to make before installation.
Avoid these mistakes from the start
Our free calculator sizes your wire, fuses, and battery correctly based on your actual build — no guesswork.
1. Sizing wire for current only, not voltage drop
A wire can be rated for the current and still cause significant voltage drop over a longer run, dimming lights and reducing charging efficiency. Always check both ampacity and voltage drop — see the AWG wire size chart.
2. Skipping or misplacing the main battery fuse
Place the main protective device as close to the battery as the applicable guidance and battery maker require. Any unprotected length between the battery and device remains exposed to a fault. See the fuse sizing guide.
3. Using a standard fuse on a LiFePO4 main circuit
LiFePO4 batteries can deliver high short-circuit current. Select a DC-rated main fuse with an interrupt rating above the available fault current. A Class T fuse is one common option, but the correct device depends on the battery and system specification.
4. Not accounting for smart alternators
Many newer vehicles have variable-voltage alternator control, so a direct connection may not provide the required charge profile or current control. Check the vehicle and battery requirements; a correctly configured DC-DC charger is a common solution — see DC-DC charger sizing.
5. Charging LiFePO4 below freezing
Cold-charge limits vary by battery. Charging outside the maker's permitted cell-temperature range can damage the battery. Some BMS units block charging and some batteries add heating, but neither feature should be assumed; verify the manual and test the configured cutoff. See LiFePO4 vs AGM.
6. Multiple ground points
Use a documented bonding and return-path plan for the actual inverter, shore-power and vehicle arrangement. Unintended parallel paths can bypass a shunt or carry current where it was not expected.
7. Oversizing the inverter "just in case"
A bigger inverter than you need adds cost, standby drain, and demands heavier cable and a bigger fuse for no benefit. Size it to your actual loads plus ~25% headroom — see sizing an inverter.
8. DIY work on the 120V side
The 120V AC side — shore power inlet, breaker panel, GFCI and fixed inverter output — must match the equipment instructions and rules that apply to the installation. Have this work designed, installed or inspected by a qualified person where required.
120V mistakes are the dangerous kind
A mis-wired 120V circuit can be lethal and isn't always obvious from the outside. If you're not confident on the AC side, get it inspected — it's a small cost relative to the risk.
9. Mismatched charge profiles across multiple chargers
If solar, DC-DC, and shore power all charge the same LiFePO4 battery, all three need a LiFePO4-compatible profile. A single charger left on an AGM profile can undercharge the battery or cause the BMS to behave unexpectedly.
10. No way to monitor the system
Without a battery monitor (shunt-based, like a Victron SmartShunt), you're guessing at state of charge — which leads to either running the battery too low (shortening its life) or topping off more than necessary. A monitor is one of the highest-value additions for ~$120.
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Jack Kennedy is a self-builder who has built two vans. He created Roam Wired to simplify conversion planning and share free tools, supported by affiliate links.
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