Some of the fondest moments during our travels were actually at the local farmers’ markets. While traveling, we always have our eyes out for them. We firmly believe in supporting the local economies wherever our traveling is taking us. As soon as we spot a farmer’s market, we will make sure to stop and purchase the local farm produce, but that always bring us to our biggest gripe about keeping foods fresh while traveling. You see, most of our diet consists of a lot of fresh fruits and vegetables. Okay, so I neglected to mention a few beers, wines, and sodas but who’s counting here? The miniature refrigerators in most RVs are not very conducive to keeping large amount of fresh fruits and vegetables. Luckily for us, as technology marches on, having a residential refrigerator on an RV is no longer rocket science it once was. So, I’ve decided to dedicate this post to the top level design considerations for the RV’s Electrical Service System. Let’s hope that the result is as rewarding as the picture below:
Let’s start with the 30,000 feet level requirements:
- Lots of foods and drinks
- More foods and drinks..
- Lots of comfortable naps
- Lots of on the road entertainments
- Lights and appliances are On when their switches are turned On. Lights and appliances are Off when switches are Off.
- Keep #1 through #5 going as long as possible
Okay, so let’s see what those requirements mean. As I have mentioned earlier, we’d like to have a regular size residential refrigerator unit. For longer camping travels, it is essential that we are able to maintain our regular diet to stay healthy. In addition, did I mention that I hate the blinking lights from the microwave oven when the RV is disconnected from shore power? There is something very annoying about it that I just can’t handle it. So I am thinking. Why not just keep AC power to these units all the time? What does it take to keep them On for a few days even without shore power? If that’s the case, it should take care of #1 and #2 requirements. So, we will look at how the Electrical Service System is designed to serve this purpose later.
Now onto the subject of comfortable naps i.e. heating and cooling. We definitely wants AC unit in addition to running the propane furnace when needed. Although we are making provisions for those efficient vent free propane heaters as well, but they don’t require electricity to run. In order to run AC, we will need either shore power or generator. We fully anticipate to have an on-board generator for the RV.
As for requirements #4 and #5, the reliability of lighting and appliances are paramount. While you are on the road, the last thing you need is having appliance failures. With the minimal space for packing, there is simply no spare unit nor tools for repair. Fortunately, most home appliances are fairly reliable. It is just a matter of providing a clean uninterruptable power source and they should work as intended. So, requirements #5 and #6 actually speak about the robustness of the system design. Electrical services from camp grounds are notoriously irregular. In addition, Modified Sine Wave Inverters can also cause problems to some sensitive electronic appliances as well. Fortunately, there are a number of devices that can be used to mitigate those problems. So, without further ado, here’s what the Electrical Service System Block Diagram looks like:
Electrical Power System Block Diagram
So basically, the RV Electrical System is a 120 VAC, 30 AMP system. Input power is either from a 120 VAC, 30 AMP shore power or from on-board power generator. There are two 120 VAC busses:
- The AC Bus 1 is direct AC bus from the generator or shore power. This bus will be used to run heavy load AC appliances such as Air Conditioning Unit, Electric water heater, etc. The AC Bus 1 is protected from irregular shore power by the Surge Guard unit.
- The AC Bus 2 is the AC power supplied from the Inverter. This AC power came from two sources: either Shore/Generator power or Converted AC Power from 12VDC Batteries. This bus will be used to run on-board AC appliances such as Residential Refrigerator, Microwave, AC Convenient wall receptacles for small household appliances such as blenders, shavers, etc.
- When either Shore Power or Generator is On, AC bus 2 gets its power from these sources. So the entire coach will be using shore power/generator power when available.
- When neither Shore Power nor Generator is On, the Inverter will convert 12 VDC Battery power into 120 VAC to provide AC power to AC Bus 2. This AC Power bus will keep the residential refrigerator and Microwave unit running while we are on the road or when we are at primitive camp grounds without electrical hookup. However, when running the microwave, I probably will have the generator On since it will drain the battery too fast. At least, this way I don’t have to put up with the blinking microwave light! Notice that when neither Shore Power nor Generator is On, AC Bus 1 has no power; therefore, you will not be able to run the Air Conditioning Unit or any of the heavy load AC appliances (e.g. Electric Water Heater, etc.)
Electrical Service System Major Components
Following are some of the major components that I have somewhat settled on:
Power Surge Protection
Surge Guard Model 41260 seems to provide adequate protection in addition to the capability for automatic power switching between generator and shore power. Here’s a quick blurb from the manufacture:
50A Hardwire – Model 41260 Automatic Transfer switch
120/240 VAC, 50A, 60 Hz
The Surge Guard line of automatic transfer switches ensures continuous power to your coach by monitoring shore power and automatically switching to generator power when it detects electrical issues that could impact performance of equipment in your motorhome. The 41260 provides basic surge protection of 2600 joules at 76,400 Amps. Additional features include:
- Protects RV bumper to bumper from faulty park power
- Provides the following protection:
- Open neutral
- Reverse polarity
- Time Delay at Power Up (Shore 3-4 Sec., Generator 30 Sec.)
- Multi-mode Surge Suppression
- Mechanical interlocking contactors
- UL Approved ATS – full transfer switch rating, UL1008
What I was looking for is a unit that provides between 2,800 – 3,000 Watts of Pure sine wave with built-in battery charger. Pure sine wave is the same as the clean AC power source in your home. In addition, the inverter can be programmed to start the generator when:
- Pre-set room temperature is reached (i.e. Air Conditioning unit will be turned On)
- When demand load exceeds pre-set Ampere (i.e. to prevent rapid battery discharge) and when someone unintentionally runs multiple heavy load household appliances such as microwave, blender, hair dryer, etc. I like to have maximum protection for the batteries. They are expensive
- When Battery voltage is at threshold for re-charge
The Magnum Inverter seems to fit the bill nicely, but wow, they are pricy. I am considering the MSH3012 and its associated controllers. It gonna hurt the pocket bad. I am still looking for alternatives, but for now, at least there is one that I can buy right now.
I am anticipating a need for around 400 AH capacity so that I can power the residential refrigerator unit for a couple days on battery alone if needed. When the microwave is used, I plan to turn on the generator or to use the shore power. The nice thing about having the microwave on AC Power Bus 2 is that I don’t have to put up with the darn blinking light!
At the moment, there are two options. First is to go with the route of LiFePO4 Lithium batteries. They are nice, compact and pricy. Did I say pricy again? I thought that the Inverter Charger unit already puts me in the poor house. The second alternative is using the AGM batteries. They are not cheap but they cost less than LiFePO4 batteries. I could put in series two Fullriver’s DC400-6 AGM batteries. That will give me 12 VDC at 800 AH. However, you can only discharge them at 50% the maximum rated capacity. So, the nominal capacity is about 400 AH. Good enough to go. You can get the specifications here:
I am considering the following candidates:
- The Honda EU3000iS providing 3,000 watts at 49 to 58 dB
- The Yamaha EF3000iSEB providing 3,000 watts at 53 to 60 dB
- The Yamaha EF4500iSE providing 4,500 watts at 58 to 60 dB
- The Honda EU7000iSAT providing 7,000 watts at 52 to 60 dB
I have not chosen a candidate yet. I would need to create a comparison charts then decide. At the moment, I am sizing the space for the largest generator since there will be a dedicate spot for the generator that fully sound insulated, so that you won’t be able to hear it running.
Let’s summarize the RV’s Electrical Service Capabilities:
- The system is designed to work with a 30AMP 120 VAC shore power
- The system has an on-board, sound insulated generator capable of providing at least 3,000 continuous watts
- Input AC power is fully protected from faulty shore power. The system is capable of auto-switching between shore power and generator power
- The system has two AGM batteries providing 400 AH nominal and a Pure Sine Waver Inverter capable of producing 2,800 to 3,000 Watts of AC Power from batteries. In the absence of shore power and generator power, a Pure Sine Wave Inverter is used to convert 12 VDC battery power into Pure Sine Wave AC power source for running household appliances
- The Pure Sine Wave Inverter is programmable to automatically charge the batteries at a preset level to maintain optimum charge state
- The Pure Sine Wave Inverter is programmable to automatically turn on the generator when the load has exceeded certain preset Amperes
- The Pure Sine Wave Inverter is optionally programmable to automatically turn on the generator at a preset room temperature (i.e. turn on the house Air Conditioning Unit) to maintain preset room temperature
- The Pure Sine Wave Inverter is programmable for quiet period when generator usage is not allowed
- The system has a display panel to monitor battery charge/discharge state and electricity consumption rate
That’s the recap for the RV’s Electrical Service System design. Feel free to provide comments. I’d love to hear from you for any suggestions for improvements. If you have any good or bad experiences with the above equipment, I’d love to hear them, too. I haven’t purchased any of the above equipment yet, so now is the time. Next post, the rubber hits the road as I will start with the frame building and the required federal mandated trailer wiring.