Cummins RV Generator Handbook

Starting and Stopping Procedures

Your Cummins generator can be started (except RV QD 3200) and stopped from the integral control panel on the generator, or from the optional remote control panel inside the vehicle if your RV is so equipped. It is a good practice, before starting the generator, to turn off air conditioners and large electrical loads. If the unit has not been started in the last several hours, prime by holding the stop button on the remote start panel or the control on the generator itself.

To start:

• Press and hold START at the interior control panel or outside at the set.
• Quiet Diesel: When you press START, the control verifies several parameters, including temperature. Glow plug burn and fuel pump prime happen prior to the starter engaging. On a cold morning, this ‘Prime’ could take up to 30 seconds before you hear the starter engage. This is normal.
• Don't over-crank with no start—crank no longer than 20 seconds; allow the starter to cool for at least two minutes between attempts.
• Allow generator to run for 30 seconds prior to applying large loads. In many cases the RV’s automatic transfer switch has this delay built in.

To stop:

• Press the STOP button at the control panel or at the set.

It is a good practice to turn off air conditioners and large electrical loads and allow the generator to run for three to five minutes prior to stopping. This allows the generator to cool down.

Automatic Generator Starting Devices

Many modern RVs are equipped with a panel or device which automatically starts the generator based on low battery voltage, interior RV temperature or loss of shore power. These devices’ operation vary depending on the manufacturer. In some cases, the autostart gen device may trigger a start or stop command without removing load. For these cases, this operation is normal and will not harm your generator. Autogen/start panels are discussed later in this manual. Several manufacturers besides Cummins offer auto gen start systems and coaches. Please check with your manufacturer (or OEM) for their exact operating terms.

Breaking in your New Generator

Your generator will perform better if you follow the break-in procedure recommended in the operator’s manual. The break-in process typically involves running the generator at about 50 percent load for two hours, then at about 75 percent load for two hours, then letting it cool down. Refer to the maintenance chart on page 30 for maintenance intervals. A break-in procedure will decrease oil consumption and improve power characteristics.

Exercising your Generator

It may seem surprising that “not” using a machine could cause performance problems, but with RV generators that’s exactly the case. Regular “exercise” is a very important part of keeping your generator healthy. Lack of exercise can cause moisture build-up and fuel system degradation that will make it run poorly. In fact, in as little as 30 days, the fuel in gasoline-powered generators can begin to gum and varnish the fuel system. Fuel varnishing results in hard starting and surging. (A surging generator never settles at a stable operating speed.)

To prevent such problems, it is recommended to run gasoline generators at a minimum of 50 percent capacity (2,000 watts, or one air conditioner for a 4,000-watt set) for two hours once every four weeks. This is necessary to help keep moving parts lubricated, expel moisture and control fuel varnishing in the carburetor. A long two-hour exercise period is preferable to several short periods. While traveling, this can be accomplished by running the air conditioning. If you own an LP or diesel generator, regular exercising can help reduce internal condensation and helps keep seals lubricated. Remember to exercise, not just start and run your generator.

Understanding Power: Amps, Volts and Watts

Electrical power is represented by volts, amps and watts. Understanding how much power you need or have available to use in your RV is important; what follows is how these terms interact with each other.

• Amps—is a representation of the amount of current flowing in a wire or conductor. While the shore power receptacle and breaker, along with the generator determine the maximum power potential, the size of the wires and internal breakers really determines the RV ‘amp’ capacity for any individual circuit and as a whole.
• Volts—is a representation of the amount of electrical potential present. Typically for an RV this is 120 VAC or 120/240 VAC when running from shore power, generator or onboard invertor. When operating from batteries, the voltage is 12 VDC. The propulsion engine alternator produces 12 VDC to charge the batteries. Likewise, battery chargers charge/maintain the batteries while plugged into shore power or a generator. Many interior lights, absorption refrigerators, LP furnaces, etc. operate on 12 VDC. Modern Inverters take 12 VDC and convert it to 120 or 240 AC to operate appliances when shore power or a generator is not present.
• Watts—is the true, “apples to apples” representation of power. It is simply calculated by multiplying voltage x amps = watts.

For Example: A hair dryer, plugged into a 120 V outlet that uses 10 amps of power would require 10 amps x 120 Volts = 1,200 watts, or 1.2 kilowatts (kW) of power.

30-Amp Vs. 50-Amp Shore Power

Most modern RVs are wired for 30- or 50-amp shore power. An important distinction with these two options is rated voltage.

• A 30-amp shore cord is rated at 120 V. Therefore, the max total power available is 3,600 watts.
• A 50-amp shore cord is rated at 240 V. The total max power available here is 12,000 watts.

This means that a typical 50-amp shore cord has close to three times greater the amount of potential power than a 30-amp shore cord. The actual power the RV will have available to use will depend on its individual breaker size, configuration, and wire size designed by the manufacturer.

• An RV generator capable of matching the potential power of a 50-amp shore cord plugged into a 240 V receptacle would have to be rated at 12,000 watts, or 12 kW.
• An RV generator capable of matching the potential power of a 30-amp shore cord plugged into a 120 V receptacle would need to be rated for 3,600 watts, or 3.6 kW, at a minimum.

Load Management Basics

In order to get the most out of your Cummins generator, you need to understand how it interacts with the electric system of your RV. At a very high level, your generator is connected via the circuit breaker panel to a wide variety of loads. Two of the most important loads that will impact the performance of your generator are the air conditioner(s) and the converter or battery charger.

To understand how battery chargers, automatic generator start systems and other baseloads affect your generator, you need to be aware of three things:

• Your generator’s power capability
• How to manage electrical loads
• Battery charging times

Determining your Generator's Power Capability

To determine what your generator can power, use the chart below to estimate the total combined watts of all the appliances, lamps, battery chargers, air conditioners and other electrical products you typically use at the same time. (All electrical appliances and lights are labeled with their power requirements expressed in watts or amps). You can use any number of appliances simultaneously, as long as their combined wattage doesn’t exceed the electrical output of your Cummins generator or your RV’s circuit breaker rating.

Operating Motor-Driven Appliances

When using an appliance with a motor, turn it on and let it reach normal running speed before starting other appliances. Air conditioners, like all electric motors, can draw up to three times more power during the first few seconds of startup than during normal operation. While this is common for all electric motors, it is especially true for air conditioners if the compressor tries to start against built-up high pressure in its refrigeration system.

Air Conditioner "Short-Cycling"

When an air conditioner runs, the compressor builds refrigerant pressure. When the compressor is then shut off, either manually or by satisfying thermostat demand, it must stay off for some period of time, usually 3–4 minutes, to allow pressure in the system to equalize before safely restarting. Trying to restart the air conditioner compressor before pressure equalizes is known as “short-cycling”.

A “short-cycled” air conditioner could 1) trip the air conditioner circuit breaker; 2) shut down the generator due to overload; or 3) trip the air conditioner due to thermal overload. The air conditioner thermal overload will reset itself after the compressor cools. Typically, you cannot manually reset.

Some, but not all, RV air conditioner thermostats have built-in time delays to prevent short-cycling. Short-cycling occurs in some RVs when the thermostat is mounted so that cold air blows directly on it. If this happens, the thermostat shuts the compressor off before the cabin has cooled, but quickly warms back up and signals the compressor to restart before refrigerant pressure equalizes. In this case, direct the flow of air from the air conditioner away from the thermostat or relocate the thermostat. You can prevent air conditioner short-cycling by always ensuring the air conditioner rests for 3–4 minutes after the compressor shuts off before trying to restart it.

Effects of High Altitude and Extreme Temperatures

If you travel at high altitudes or in extreme temperatures, your generator can lose power. In such lower-density air conditions, you can’t operate as many electrical devices as you could under normal operating conditions.

Power decreases 3.5% for each 1,000 feet above an altitude of 500 feet. For example, to operate at 4,500 feet (4,000 feet above rated generator altitude), multiply 3.5% x 4 (4,000 ft) = 14% power loss. Then multiply .14 x your generator’s power rating: 4,000 watts x .14 = a loss of 560 watts at that altitude.

Power decreases in extreme temperatures by 1% for each 10 °F (5.5 °C) above 77 °F (25 °C).

Managing Electrical Loads

If you try to operate too many things at once, you’ll “overload” the generator. Your lights will flicker or the circuit breakers on the generator or the main electrical panel will trip open, stopping the flow of power.

Battery chargers replenish power drained from starting the engine and generator or appliances operating on inverter power such as a microwave, refrigerator, mechanical slide out or pump.

Battery charging can aid in overloading your generator and you may not realize this is happening because the charging starts automatically without any action by you whenever you start your generator.

Typical “invisible” charging loads:

• During startup, air conditioners need “reserve” power and can draw 3–4 times the typical 1,400–2,400 watts needed to run. Too much baseload can prevent air conditioners from starting.
• Battery chargers are activated automatically and can draw a large load (up to 3,000 watts). Manage your electrical loads by adjusting battery charge rates to best suit your needs. Consult your inverter/charger manual or manufacturer.
• If you have an automatic generator stop/start system, learn how to control it. Consult your inverter/charger manual or manufacturer for adjustment procedures. Adjust battery charge rates to best suit your total electrical needs. This system is not part of a Cummins generator.

Example in Chart Below:

Dashed box below shows that a 2,000-watt inverter running at 100 A battery charge capacity creates the same load as a 13,500 BTU air conditioner plus a microwave oven.

Preventing Generator Speed Hunting 

The electrical supply (voltage and frequency) for any appliance must remain within very close limits for it to operate properly. Changes in the generator engine speed (called surging) can damage the appliances in your RV. Proper care of your generator will enable it to supply a stable power source and prevent surging.

RV generator engine speed is controlled with a governing system. Most generators have a mechanical governor, although the latest Cummins EFI and Quiet Diesel generators use an electronic governor. Without a governor, engine speed simply drops as appliances are turned on, until the generator finally stops running. With a governor, the carburetor throttle opens or the EFI system adjusts to compensate for the increased load and thus maintains a constant speed/frequency.

The governor works in careful balance with the generator engine, fuel system, regulator and generator. If the balance is upset, surging may result. A variety of things can cause surging, including an inadequate fuel supply, lack of exercise and poor maintenance. (See the Troubleshooting Guide).

Tips to Help Prevent Surging

• Ensure adequate generator fuel supply. Fuel is drawn from a remote fuel tank, which in many cases is usually the vehicle’s main fuel tank. Typically the generator’s fuel pickup only extends 3/4 of the way to the bottom of the tank—to prevent you from completely draining the tank and finding yourself stranded at your campsite! In other words: fuel in the tank does not guarantee fuel to your generator, especially if you have two fuel tanks in your vehicle. A cracked, leaking fuel line or a defective fuel pump can also cause inadequate fuel supply to the generator. Contact your local Cummins authorized RV service and parts dealer to diagnose fuel supply problems.
• Follow the generator exercise recommendations or the out-of-service protection recommendations outlined in your operator’s manual. Gum and varnish from stale fuel can plug small carburetor passages causing a lean fuel mixture and surging. Treat the fuel system with a good quality fuel system cleaner in the clean-up mode ratios. Contact your local Cummins RV service and parts dealer to have the carburetor cleaned and adjusted or replaced if the problem persists.
• Adjustment should be done on gasoline or LP model’s carburetor, choke, and governor by your local Cummins authorized RV service and parts dealer, who has specialized instruments made specifically for this job.
• If your generator continues to surge, take it in for service and do not operate. Damage could occur to your electrical devices in the RV and to the generator.