Prepared by Edwin E. Irving (firstname.lastname@example.org)
September 2, 2010
I want to thank Elden DuRand for preparing the CAD drawing which is part of this description and for helping me to better understand operation of the major components. Thanks too to Byron for his patient responses to my questions requiring detailed explanations of the electrical component operations. I also derived editorial information from Capt. “Ed” and Ed Von Gehr; and from others who have added helpful input during the many discussions of this subject over the years. Introduction:
Many motorhomes contain two 12-volt electrical systems and batteries. One, called the chassis or cranking battery, is used to crank the engine and operate chassis/drivetrain-related components such as headlights and the dashboard. The second, called the house battery, operates the RV part of the motorhome and also provides starting power for the generator.
Since we don’t want to run down the chassis battery while using the RV lights, the two systems must be isolated from one another. Yet it is desirable to let the engine alternator charge both systems when the engine is running. Ergo, we need some means to connect the two to the alternator when the engine is running and separate them when it isn’t.
The description included herein is from a layman based on knowledge obtained from practical use of a 2006 Winnebago View, Model 23H. I have had the text reviewed by people more knowledgeable than me for the accuracy of its content.
The electrical charging system’s major components to be discussed are:
- Shore Power
- Generator and its Manual Power Cord Switch
- AC/DC Converter
- Battery Boost Switch & Battery Boost Contactor (Continuous Duty Solenoid)
- House Battery Switch and Latching Contactor (Momentary Duty Solenoid)
- Chassis and House Batteries
- Automatic House Battery “Floater” / Trickle Charger (optional)
The Starter Solenoid is shown only to differentiate it from the House Battery and Battery Boost solenoids but will not be discussed here. The CAD drawing is to be referred for illustration during the discussion.
Future addenda to this document may involve a chart depicting operating conditions of the major components showing all of the normal conditions of switches/solenoids and additional trouble-shooting analysis.
The source of commercial electrical power should be monitored at the wired pedestal for protections against incorrect wiring, low voltage, spikes, and AC voltage frequency, typically 60 hertz.
Check for incorrect wiring (reverse polarity, and dangerous current on ground wire) and voltage prior to plugging in the power cord. There are inexpensive devices (e.g., http://www.extech.com/instruments/product.asp?catid=31&prodid=125 ) that can check for this if you don’t have a Surge Protector; however, even if it is wired correctly, you should have a Surge Protector connected between the wired pedestal and the RV power cord or between the power cord and the fuse panel for subsequent protection from erroneous power and wiring. E.g., http://trci.net or http://progressiveindustries.net.
A Surge Protector can provide electrical protection for your RV! Automatically shuts off the power when detecting incorrectly wired pedestal, power surges, low (<102V) and high (>132V) voltage, reverse polarity, and dangerous current on ground wire. Automatically resets on power restoration. Features caution indicator light to indicate cause of power stoppage. 2 minute 16 second reset delay protects AC compressor. Weather resistant, 10/3 AWG cord. Offers 1050 joules of surge protection
The power cord is wired through a main 30-amp fuse on the main distribution panel from which all AC outlets and the 120 Volt AC to 12 Volt DC Converter is connected. Each AC circuit/outlet and each DC circuit is also fused and in some cases the AC outlet is wired through a Ground Fault Interrupter (GFI). Make sure that the power pole circuit breaker is switched OFF before inserting the shore power plug, and then switch it back ON.
Generator and the Manual Switch:
The generator performs the same function as shore power. The generator is used to supply 120 volts AC to the RV house through a main 30-amp fuse and various distribution fuses. It supplies the converter that is used to convert AC to DC for the house DC circuits and to charge the house batteries.
To switch from shore power to Generator power or vice versa requires a manual operation. This is because the power cord must be removed manually to switch between the shore pedestal and the Generator Power Outlet. When the power cord is plugged into the Generator Power Outlet, the RV obtains 120-volt AC input from the Generator with the Generator operating. There are after market devices, such as Transfer Switches, that will perform this function automatically making the manual operation unnecessary.
If the Generator is running but the power cord is not plugged into the Power Outlet, you will not have AC power to the RV. The power cord must always be in the Generator Power Outlet if the generator is to be the source of power. To switch from generator power to shore power, stop the generator if it is running, remove the Shore Power Cord from the Generator Power Outlet and plug it into the shore power pedestal. The manual operation of removing the power cord from the Generator Power Outlet and inserting it into a shore power pedestal and vice versa is considered a manual switch. The House Battery Switch must be in the ON position to start the Generator using the House Batteries.
The primary function of the AC/DC Converter is to convert 120 volts AC, either from the generator or shore power, to DC voltage. Thus, you need input of 120 Volts AC to the Converter for it to function. The input to the Converter is 120 volts AC and the output is approximately 13.6 to 13.8 volts DC. The DC voltage is applied through fuses to the DC circuits, such as the coach lights. DC is also applied, through the House Battery Latching Contactor, to the House Batteries and, through an Automatic House Battery “Floater” such as a Trek-L-Charger, to the Chassis Battery. The Trickle Charger will automatically charge the chassis batteries when generator or shore power or solar power is supplied
The House Battery Switch must be in the ON position for the Converter DC output to be applied to the House Batteries. The House Battery Switch closes the House Battery Latching Contactor so the Converter DC voltage can charge the House Batteries. The DC circuits will still work even if the House Battery Switch is in the OFF position – no voltage passes through the House Battery Latching Contactor – and you are connected to shore power because the DC output of the Converter and the House Batteries are in parallel to each other. However, with the House Battery Switch in the OFF position, the house batteries will not be charged from the Converter.
Also, the DC circuits will work from House Batteries only if the House Battery Switch is in the ON position when the Generator is not running and the RV is not connected to shore power. If you are connected to shore power or the generator is running and the House Battery Switch is ON, the Converter will be supplying the power to the house DC circuits. At this same time, the house batteries will be charging but the house batteries will not be supplying power to the house DC circuits. This is because the Converter is the charging source that supplies the power. To illustrate this, connect to shore power or use the generator as the AC power source. Turn on one of the overhead house lights. The House Battery Switch can be turned on and off and the overhead light will stay on. With the overhead light still on, remove the AC power source. Turn the House Battery Switch off and on and the light will go off and on correspondingly. If two sources are charging the house batteries in the case with the engine running and connected to shore power, the source with the greatest output power will be providing the charge.
Battery Boost Switch & Battery Boost Contactor (Continuous Duty Solenoid):
In its simplest form, the relay is a simple single pole single throw (SPST) relay with a 12-volt continuous duty coil. The Battery Boost Contactor solenoid allows 12 volts dc power to flow from the engine alternator to the house batteries when the engine is running, or flow from the house batteries to the chassis batteries with the manual Battery Boost Switch operated. The Battery Boost Contactor has two functions. It allows the engine alternator to charge the house batteries automatically while the engine is running and the Contactor can be energized manually by the Boost Switch to provide a “self-jump-start” in the instance when the cranking battery runs down. While the engine is running, 12 volts from the Engine Control Module (ECM) closes the Battery Boost Contactor to allow the alternator to charge the house batteries.
The Battery Boost Switch, at least on the original View/Navion models, only has a manual spring-return operation. The Switch returns to the OFF or resting position when depressed and released. Manually operating the Battery Boost Switch to the ON position connects the house battery in parallel, through the Battery Boost Contactor, with the chassis battery so the house battery can boost off a weak chassis battery.
The Battery Boost Switch also allows the chassis battery to “boost” the house batteries. For example, if the house batteries voltage is too low to crank the generator, hold the Boost Switch in the ON position to “boost” and crank the generator with the chassis battery. When the engine is running, it may not be necessary to operate the Boost Switch to crank the generator because the engine alternator is supplying power to the house batteries.
The Battery Boost Switch should never be kept in the Manual ON position for longer than its purpose because it eventually will run down both chassis and house batteries. Remember, with the Battery Boost Switch operated, the house and chassis batteries are electrically connected in parallel and any house circuits, such as lights, TV, CO2 protection, being used will drain both house and chassis batteries. The chrome one is the battery boost solenoid.
House Battery Switch (Aux Batt) and Latching Contactor (Momentary Duty Solenoid):
The purpose of the House Battery Switch and Latching Momentary Contactor is to isolate the house DC circuits from the house batteries and to provide an electrical path for the converter to charge the house batteries. When the House Battery Switch is put in the ON position, the coil in the Contactor is momentarily energized to close the contactor and mechanically latches closed when the coil is released. Energize the coil again and it releases. When the House Battery Switch is pushed ON, the Contactor Solenoid is CLOSED and an electrical path is provided. When the House Battery Switch is pushed OFF, the Contactor Solenoid is Open and the electrical path is Broken. The advantage of this type of contactor is that it draws no current except when being opened or closed. The Switch and Contactor is commonly used to disconnect the house battery from the RV for storage.
When the House Battery Switch is in the OFF position, it disconnects all DC house circuits and prevents the converter from charging the house batteries. To reiterate, when connected to shore power, this allows the converter, not the house batteries, to provide DC power to all house DC circuits, regardless of the position of the House Battery Switch. However, the house batteries will be charged only if the Switch is in the ON position while connected to shore power or the generator is running. Typically, the switch and an indicating LED are located in the stairwell of the RV. The one with the fuse is the battery disconnect relay.
Chassis and House Batteries:
House batteries provide DC voltage to all of the house DC circuits and cranking voltage to the generator. If the House Batteries’ voltage is too low to turn over the generator, push and hold the Boost Switch while cranking the generator. Once the generator has started, release the Boost Switch.
The House Batteries are kept charged in five possible ways:
- while the chassis engine is running (automatic process via the Boost Contactor Solenoid; manual
- switches not required)
- when connected to shore power via the converter (house battery switch must be ON)
- when the generator is running via the converter (house battery switch must be ON)
- with an external battery charger (optional)
- with solar panel(s) (optional)
When the engine is running, the alternator charges the House Batteries through the Battery Boost Contactor and it also charges the Chassis Battery. The engine alternator has an internal regulator (see dwg. Engine Control Module) to help prevent overcharging the batteries. While the engine is running, 12 volts from the Engine Control Module (ECM) closes the Battery Boost Contactor to allow the alternator to charge the house batteries automatically. It is not necessary to operate the Battery Boost Switch to have the engine charge the house batteries. There is diode protection in the control line from the ECM to the battery boost contactor. When the engine is running, both 12 volt electrical systems in the motorhome are connected together.
Automatic House Battery “Floater” / Trickle Charger (optional):
This is an optional device that can be added to keep the chassis battery charged whenever the house batteries are being charged. The purpose of an Automatic House Battery “Floater”, hereinafter called a Trickle Charger, is to help maintain proper chassis battery voltage to crank the chassis engine. When connected to shore power and with the house battery switch turned ON, the chassis battery is being charged at the same time as the house batteries.
The Trickle Charger connects the house batteries to the chassis battery when shore or generator power is supplied to the converter or when a solar panel is charging the house batteries. A Trik-L-Start will help maintain the chassis battery anytime the unit is plugged into 110V shore power and the battery disconnect is in the “on” position.
The Trik-L-Start device monitors battery voltage in the house batteries and compares it to the chassis battery. When the Trik-L-Start senses the chassis battery voltage is approximately 1/2 volt lower than the house battery, it allows up to 5 amps current flow to the chassis battery. The circuitry within the Trik-L- Start prevents back feeding of electricity from the chassis to coach battery so if 110V power is interrupted, the chassis battery will not be discharged. (Source: http://www.winnebagoind.com/resources/service/pdfs/2006-04%20Trik-L-Start.pdf). Additional information can be found at http://www.lslproducts.com/TLSPage.html.
Links for Further Study:
- 2006 Winnebago Wiring Diagram
- http://www.rv-dreams.com/rv-electrical.html – Includes drawings with, inverters, converters.
Care and Feeding of Lead-Acid Batteries.doc by Cybergeezer1, November 14, 2006
- https://www.cheaprvliving.com/electrical/electricity/ – Mentions the book, “Managing 12 Volts: How To
Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems” by Harold Barre
- http://www.windsun.com/Batteries/Battery_FAQ.htm – Everything you wanted to know including history, definitions and types