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Power and voltage on in-wall slides

An in-wall room is only as good as the voltage at its controller while it's moving. Low voltage means more current and less force, and that can stop a side short of the end, which costs the controller its count.

The short version

Why voltage matters more here

The board accepts 8 to 18 V, but Lippert says that at lower voltage the current draw goes up and the force available to the room goes down. Both motors are small and work hard, so a tired battery shows up fast.

The controller stops each motor when it sees a stall, and it references its pulse count to the ends of travel. A side that slows and stalls early stops short, the controller treats that as the end, and its zero point is now wrong. That's how a voltage problem turns into a crooked room and a sync complaint.

The board also polices voltage directly: under 8 V at the start of a move is code 3, and a sag under 6 V while running is code 2. Above 18 V is code 4.

Read those two low codes differently. Code 3 means the supply was already low before the motors pulled, so look at the battery and charging first. Code 2 means it started fine and collapsed under load, which points at battery capacity or a connection that can't carry the current. Newer Lippert manuals also list a short in the switch wiring as a cause of code 2, so check that if the voltage holds up.

Testing at the controller under load

The number that matters is at the controller's power and ground spades while both motors pull. A reading at rest proves almost nothing, because a loose spade or a corroded ground only shows itself under current.

  1. Put your meter on the controller's power and ground spades (right side of the board).
  2. Have a helper run the room while you watch the meter. Note the lowest reading.
  3. Stays above 11 V through the whole move: voltage isn't your problem. Move on.
  4. Under 11 V: measure at the battery posts during the same move.
  5. Battery holds but the controller sags: the loss is in the feed or ground. Measure across each one while the room runs and fix the side that drops.
  6. Battery sags too: charge it fully and retest before going any further.

Feed, fuse and wire size

Lippert calls for a 30 A resettable or blade fuse supplied by the RV maker, or a 30 A minimum breaker, and 10 AWG minimum wire to the controller. Undersized wire on a long run is a built-in voltage drop that no battery will fix.

If a new fuse or breaker blows the moment the room is asked to move, Lippert says the wiring to the controller has a fault. Trace it before you install a third one.

Lippert's wiring drawing shows the feed from the battery through an OEM-supplied circuit interruption to the controller's power junction, so the fuse or breaker is the RV maker's part and lives wherever they put it. The RV maker's documentation shows where the 12 V box and the controller's breaker are.

On C2 and 8 Amp boards the wall switch has its own 12 V feed from the RV maker. If that feed is dead, nothing lights at the board even with perfect power at the spades.

Grounds and connections

Lippert's only spec here is clean, tight and free of corrosion, at the controller and at the battery. Check the spade terminals on the board for a loose fit, the ground lug where it lands, and any junction the RV maker added between the battery and the board.

Motorized coaches have one more catch: Lippert wants the ignition off to run the room. Charge with shore power or the generator, not by idling the engine with the key on.

Charge first, and jump at the battery

If the controller sees under 11 V, Lippert says to charge the battery fully, plug into shore power or run the generator. Temporarily jumping the RV battery may get the room moving; follow the RV maker's manual for how.

After any low-voltage episode, resync the room. Even once the battery is fixed, the controller may still be counting from a wrong zero point.

Careful: Never connect jumper cables, a jump pack or a charger to the controller's power terminals. Lippert warns this can cause serious injury; connect at the battery.

On the job

  1. Plug the coach in or start the generator if the battery is suspect.
  2. Meter on the controller spades, run the room, record the lowest reading.
  3. Under 11 V: charge fully and retest before diagnosing anything else.
  4. Battery holds but the controller sags: measure the drop across the feed and the ground while running and fix the bad side.
  5. Check the fuse or breaker is 30 A, and that a new one doesn't pop instantly.
  6. C2 or 8 Amp board with no LEDs: check the switch's own 12 V feed.
  7. Resync the room after any voltage fix.

Numbers

Shop tip

Don't trust a battery voltage taken with the room parked. A connection that reads 12.6 V at rest can fall apart the second both motors pull, so watch the meter at the controller while the room moves.

Where this comes from

Try it on a service call

Put the lesson to work on a hands-on troubleshooting case.