Lesson: RV Electrical Systems
Description: RV’s contain a number of electrical systems that interact with each other
Goal: To provide participants with a deeper understanding of the two primary electrical systems in the RV. How the systems interact.
Required Skills: None
Details of Lecture:
- Amps is equivalent to the amount of work that can be done
- Volts is the amount of energy flow
- Watts is the work done (Watts = Amps * Volts)
There are two primary electrical systems in an RV
- 12VDC – Direct Current
- 120VAC – Alternating Current, Shore Power, Line Voltage
12VDC– Direct Current
Direct current is produced by
- The alternator from the engine
- The Solar Panels on the roof
- The converter or converter/inverter in 20+ RV’s from 120VAC power.
Direct current is stored in the batteries. The amount of energy that can be stored in batteries is measured in Amp Hours
- Flooded batteries can use 50% of their AHr Rating
- AGM/Gel Batteries can use 60-80% of their AHr Rating
- Lithium Batteries can use 80-90% of their AHr Rating.
There are two different sets of batteries.
- Coach Batteries
- Chassis Batteries
There two different chemistries batteries
Lead Acid (Chassis and Coach)
- Lithium Iron Phosphate
- Other classes of Lithium batteries not commonly used in batteries adaptable for storing energy for the coach
Direct Current is used by
- Inverter to produce 120VAC energy (coach batteries)
- Coach lights (coach batteries)
- Televisions in older RV’s (coach batteries)
- Entertainment Systems (coach batteries)
- Water pump (coach batteries)
- Fans (coach batteries)
- Refrigerators including propane (controls) and compressor (coach batteries)
- Propane Heater (coach batteries)
- Dump System Macerator (coach batteries)
- Starting System for Generator (coach batteries)
- Slide Extension and Retraction (coach batteries)
- Passenger Side Steps (chassis batteries)
120VAC – Alternating Current, Shore Power, Line Voltage
Alternating current is produced by the generator by combusting either diesel, propane or gasoline. (There are some View’s that have gasoline engines and gasoline generators.) It is additionally produced at some distant location and provided in a campground at a power post
Alternating current is not able to be stored as alternating current. It can be converted to Direct Current and stored in batteries.
Alternating current is used by:
- Air conditioning
- Converter, Converter/Inverter (20+) (converts 120VAC to 12V DC)
- Induction Stove
- 102VAC Appliances
- Coffee Pot
- Electric Kettle
- Hair Dryer
- Curling Iron
- Electric Shaver
- Hot Pot
- Electric Griddle
Pre 2020 coaches generally do not have an Automatic Transfer Switch (ATS) unless added. Post 2020’s have an ATS. The ATS eliminated the requirement to plug the power cord into the generator outlet in the electrical bay to obtain 120VAC power when the generator is running.
Interaction of 120VAC and 12VDC Systems
The alternator produces 12VDC
- Runs the electrical systems of the chassis (headlamps, ignition, etc).
- The alternator supplies energy to the coach
- Pre-2020 coaches combine the 12VDC Systems with a relay (Trombetta, Cole Hersee)
- Post-2020 coaches have 12VDC supplied only with a 40A Charge Mate Pro.
The Generator and Shore power supplies 120VAC energy to the coach.
- Runs the 120VAC devices
- Provides energy to the converter, converter/inverter to charge the 12VDC batteries
Amps, Volts and Watts
A power post at a campground supplies 120VAC power.
The amperage is the amount of work you can do.
- 30Amps of power will power the Air Conditioning and the Microwave at the same time.
- 15Amps of power will supply the Air Conditioning OR the microwave at the same time.
- 50 Amps of power will supply 30 Amps of power by using a ‘dogbone’. Our RV’s are capable of only using 30A.
Conversion from 12VDC to 120VAC
The energy needed to do work, watts, is constant. A 3 Quart Instapot is rated at 700 Watts. It uses about 6.5Amps to cook. At 120VAC it uses 6.5A, less than half the capacity of a 15A circuit.
To obtain the energy from the batteries, you would use the inverter to convert 12VDC to 120VAC. There is some conversion loss, but Pressure Cooker German Goulash takes 30 minutes to cook.
At 120VAC 6.5A for .5 Hours = 3.25AHr. VAC
At 120VAC energy derived from Inverter supplied power, 12VDC 6.5A for .5 Hours = 32.5AHr. VDC
The use of an Inverter to obtain VAC from stored VDC requires you to multiply your amperage use by a factor of 10 because the VDC voltage is 1/10th of the VAC voltage.
Math for 12A VAC Air conditioner
Assume the Air conditioner is consuming 13A VAC 33% of the time.
13A VAC * 120VAC = 500 watts consumed per hour
Energy derived from 12VDC requires about 45Ahr. Four hours would be 180Ahr, which would be beyond the initial shut off stage for Lithium batteries (200Ahr @ 80%)
Depending upon the year and floorplan of your coach, there may or may not be an inverter installed. There may or may not be a large number of devices powered by the inverter. Pre 2020 RVs generally do NOT, unless modified, have inverters powering the microwave.
There are a number of protection devices to protect the RV in case of a short circuit.
- Circuit breakers
- DC Breakers
- GFI Outlets
- Must be powered by 120VAC to be reset
Locations of Protection Devices
- 120VAC Breaker panel is under the refrigerator or bed
- 12VDC Fuse panel is adjacent to the 120VAC panel
- 12VDC Breaker panel is located to the outside of the passenger seat
- Propane Generator located on the forward portion of the generator, and is difficult to see.