Is your van's DIY electrical going to catch fire?

Where the fires start

On the Solar-Electric forum there is a thread about a van that burned out while the owner was away. The suspect was a DIY lithium pack built from 18650 cells with no visible battery management system. An Australian caravan industry piece on shoddy wiring describes the same pattern on the trailer side: undersized cable, loose lugs, no fusing where it counts.

The 12 V side is where DIY builds go wrong, because it does not feel dangerous. Low voltage at very high current heats a loose crimp or a thin cable fast, and that heat sits behind a wall panel next to insulation.

Battery chemistry and the BMS

LiFePO4 (lithium iron phosphate) is the chemistry most van builders use for a reason. Battle Born, which makes them, says the chemistry resists thermal runaway far better than the cobalt-based lithium in laptop and tool cells. That is a manufacturer talking about its own product, but the broad point is widely accepted.

Chemistry is not the whole story. In July 2026 Hackaday covered a test where a short in a battery's BMS led to a fire, and the built-in thermal fuse did little to stop the current. One informal test, but it is a reminder: the protection electronics can fail, so you still need external fusing.

If your van has a homemade pack of loose cells, or you do not know what chemistry is in there, that is the first thing to replace.

Fusing at the battery

ABYC E-11 is a marine standard, but many van electricians build to it because nothing else covers 12 V systems in this much detail. As Blue Sea Systems summarizes it, every ungrounded conductor connected to a battery needs overcurrent protection within 7 in of the connection. If the cable runs directly from the battery terminal and is in a sheath or conduit on top of its insulation, that can stretch to 72 in. Check the current edition of E-11 for the exact wording before you rely on the longer distance.

Go look at your van. Follow the positive cable off the battery. If you reach the inverter, the bus bar or the far side of the van before you hit a fuse or breaker, that cable is unprotected.

Cable size for the inverter

Do the math. 3,000 W divided by 12 V is 250 A, and inverters lose some energy as heat, so actual draw at full load is higher. That cable has to carry it without getting hot, over its full length out and back. Use the cable size and fuse rating in the inverter maker's manual for your cable length, not the cable that came in a kit.

Check every crimp. A lug that turns by hand is a lug that will heat up. Use proper crimpers, heat shrink, and secure cables so they cannot chafe on the body as the van flexes.

Which code applies, and who should sign it off

For a van sold as an RV, the 120 V side falls under NEC Article 551 and the RV standard NFPA 1192. The 12 V side borrows from ABYC in practice. A DIY van does not have to meet any of them, which is exactly why insurers get nervous.

Pay a licensed electrician or a certified RV technician to inspect the system and write a short letter on what they checked. It costs far less than the van, and it is one of the first things an insurer asks about. Our guide on RVIA certified van conversions covers the rest of that paperwork.

If you are buying from a builder, ask who does their electrical and whether you get that sign-off in writing. Trailer3D can get you quotes from up to 4 van builders in your area, free.

Questions

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