RV Electrical Repair and Power Systems

Because they do different jobs and neither one can do the other's. Understanding the split is the difference between describing a symptom usefully and describing it uselessly.

The 12-volt DC system runs off the house battery bank. It powers lights, water pump, furnace blower and control board, slide and jack motors, refrigerator control boards, vent fans, the propane and carbon monoxide detectors and almost every control circuit in the vehicle. When the house bank is dead, the coach is dead even when it is plugged in, on many units, because the converter needs the battery present to regulate against.

The 120-volt AC system comes from shore power or the generator. It powers the air conditioners, the microwave, the residential refrigerator if fitted, the water heater's electric element and the outlets. It also feeds the converter, which charges the house bank, which is why an AC-side fault presents as a DC-side symptom.

Between them sit three components that cause a disproportionate share of problems. The transfer switch chooses between shore and generator and its contacts burn. The converter or charger turns AC into DC to charge the bank. The inverter turns DC into AC so outlets work off battery. Any of the three failing produces symptoms that look like something else entirely, which is why the diagnostic step is charged as time, at $285 for the first hour, applied as a credit against an authorized repair.

Under load, with a meter, section by section. Continuity testing with everything off finds broken wires and nothing else, and broken wires are the minority of faults on these vehicles.

The dominant failure is resistance: a connection that is still connected but has corroded, loosened or been crimped poorly. It passes a continuity test perfectly. Put ten amps through it and it drops a volt and heats up. The technique is voltage drop testing, measuring across a connection while the circuit carries its normal current, and it finds the bad joint in minutes where a continuity test would say everything is fine.

Grounds are the most common location. RV chassis grounds sit under the vehicle, exposed to road spray and, in coastal Southern California, salt-laden air. A corroded ground produces symptoms that make no sense: lights that dim when the water pump runs, a slide that stalls only when the furnace is on, a refrigerator control board that faults intermittently.

The second most common is the shore power inlet and cord. A loose neutral in a 50 amp connection produces voltage imbalance between the two legs, which can put 200 volts on one leg and damage everything on it. Inspecting the inlet and the cord ends is standard on any whole-coach electrical complaint.

Lighting and wiring diagnostics run $285 to $2,500 across 1 to 10 hours. Full electrical diagnostics and repair runs $285 to $5,000 across 1 to 20 hours. Rates are posted on the price sheet.

The charging profile, the wiring, the protection and the monitoring. Treating a LiFePO4 conversion as a battery swap is the most expensive mistake in this category.

Charging profile: AGM and flooded lead acid want bulk, absorption and float, and they tolerate sitting on float indefinitely. LiFePO4 wants bulk and absorption with no float, and holding it at a float voltage stresses the cells. A converter without a lithium profile either undercharges the bank or holds it at the wrong voltage. Verifying the converter, the inverter-charger and any solar controller can all produce a lithium profile is step one.

Wiring and protection: lithium will accept charge current far faster than lead acid, and it will deliver current far faster on discharge. Cable that was adequate for an AGM bank may be undersized. Fusing has to match the new capability. If the bank charges from the chassis alternator, a DC to DC charger is required, because an alternator asked to charge a large lithium bank directly will overheat and fail.

Temperature: LiFePO4 must not be charged below freezing without internal heating. In Southern California that is rarely the limiting factor, but a coach that travels to the Sierras in winter needs a bank with low temperature charge protection.

Monitoring: lithium holds nearly constant voltage across most of its discharge curve, so a voltmeter tells you almost nothing about state of charge. A shunt-based battery monitor that counts amp hours in and out is required for the owner to know what they have. Battery and charging system work runs $500 to $5,500 across 2 to 10 hours.

More roof work and more wiring than panel mounting. Panels are the easy part.

The roof side is layout and penetration. Panels have to clear the air conditioners, vents, antenna and any roof rack, and they have to be positioned so shading from one does not fall across another, because a partially shaded panel in a series string drags the whole string down. Mounting feet are bonded and mechanically fastened, and every fastener through the roof is a new penetration that must be sealed correctly for the membrane type.

The wiring side is the controller and the run. An MPPT controller converts the panel's higher voltage down to battery voltage while extracting more usable power than a simpler PWM controller, which matters most in cool bright conditions and with longer wire runs. The run from roof to controller has to be sized for the current and the distance, and it has to enter the coach through a proper gland rather than a hole with sealant over it.

Then the integration. The controller has to be configured for the battery chemistry. The system has to coexist with the converter and the inverter without them fighting over who charges. And the monitoring has to show the owner what is actually happening.

Solar installation runs $1,500 to $12,000 across 8 to 40 hours. Where roof reinforcement is needed to carry an array, that adds $750 to $6,500. Sub services here include solar panel installation and repair, inverter and converter repair, 12-volt systems, 120-volt systems and wiring and fuse box repair.

Sibling lines under mechanical and systems services are generator repair, plumbing repair and appliance repair, and electrical touches all three.

A generator that will not transfer to the coach is usually a transfer switch problem rather than a generator problem. A water pump that runs slowly is often a voltage problem rather than a pump problem. A refrigerator that fails to switch modes is frequently a control board seeing bad voltage rather than a cooling unit failure. Diagnosing systems complaints without a meter on the electrical side produces a lot of replaced parts and unhappy owners.

Electrical work also crosses into interior remodeling, because every lighting upgrade, added outlet and relocated appliance is a circuit change, and into custom fabrication on van build outs where the entire 12-volt system is designed from nothing. Mechanical and electrical labor is posted at $260 per hour.