A Mad Scientist’s Take on the Ultimate Electrical System (Part 1)

In previous electrical and solar power articles published by Truck Camper Adventure, we purposely simplified the systems and terminology to make it easier for novices to understand. In this article, written by Pat Davitt, we’ve taken the opposite approach by presenting an advanced article with an advanced solar power system design for those who are more technically savvy. But beware, Pat’s approach to electrical system design isn’t cheap, primarily because of the batteries. If you’re new to RVs and truck campers, and you’re interested in learning more about batteries and solar power, we recommend that you take a look at our Building a Great Solar Powered Truck Camper Rig article.

Months ago, during what must have been a “senior moment,” I decided to explore buying a truck camper. It couldn’t have been a mid-life crisis, since I went through that glorious time about 20 years ago. I’m familiar with camping either by walking or with horses and/or mules. As my research progressed, it became apparent that I wasn’t going to be happy with the electrical systems. So, I put on my Systems Architect hat and decided to design my own.  Talk about things rapidly getting out of hand.

I don’t claim to be a truck camper expert, just the opposite, I don’t own one yet. I have, however, been in or, looked inside of one, a few times. This lack of knowledge may be a good thing since I have no preconceived notion of the “way it should be.” Living in an off-grid solar home for the last six years and, at another time in my life, living on a motor vessel with extensive AC and DC circuits brings helpful insight to the design process.

The two important things to remember are:

The purpose of this prototype project is to push the limit of electrical power that can be installed in a camper. I’m not concerned about if one “needs” the power, but rather “how much will fit.”

The engineering intent is to have all the electrical equipment/components, except for the batteries and solar panels, in a single enclosure. And, that all external connections, including load circuits, solar panels, batteries, etc., will be made on the exterior of the enclosure. The goal is to have a pre-built electrical enclosure that can be installed, as a unit, in a camper. Even though I’m “going large,” this concept can be downsized to fit smaller equipment and campers.

Part one of this article is an introduction and the design process, part two will be the technical information and, part three will be my thoughts on where the future may lead.

I knew, from my research, that for a system to work in a truck camper, or any RV for that matter, it must be small and light weight. The design criteria are:

• Maximize Solar Panel Wattage
• A powerful, yet lightweight, 48 volt Battery System
• AC Power to run an induction cooktop, convection microwave, and air conditioner
• DC Power to run Danfoss Refrigerator, Pumps, LPG Furnace and Water Heater, Ventilation, and LED lighting
• 50 amp 120 volt 6,000 watt shore power/generator capabilities (Not 120/240 volts)
• 48 volt Solar Charge Controller and Inverter/Charger
• High quality components Installed in a single electrical cabinet
• Meet ABYC (American Boat and Yacht Council) Standards
• Cost not as Important as functionality

Design Sequence

1. How much Solar wattage can I put on the roof? An 8.5-foot cabover camper should have roof dimensions of about 7 feet wide by 13.5 feet long. With the proper rack, four 36 volt 350 watt panels will fit with a couple of feet left over for a vent fan. That gives me a total of 1,400 watts of solar. It will also require a non-rooftop mount air conditioner.

2. Batteries: The smallest, lightest, and most powerful batteries I found were Victron Lithium-Ion HE. They are 24 volt 200 amp hour, 7.6 inches wide by 14 inches long by 14.25 inches high, and weigh 63 pounds apiece. Two of them in series will give me 200 amp hours at 48 volts. That equates to 7,680 usable watt hours assuming a maximum 80 percent Depth of Discharge (DOD) (48 x 200 x .8). Their Cycle Life is 2,000 at 80 percent DOD. These batteries are Lithium Nickle Manganese Cobalt Oxide (LiNiMnCoO2) and weigh about half as much as the more popular Lithium Iron Phosphate (LiFePO4).  The Victron’s also have a data feed directly into the control/monitoring computer (more on this later).

Just for grins I figured out what it would take to equal 7,680 usable watt hours with Lifeline GPL-27T AGM 12 volt 100 amp hour batteries. Each battery has (12 x 100 x .5 = 600) or 600 usable watt hours assuming a 50 percent DOD. Divide 7,680 by 600 and you get 12.8; it would take 13 of the Lifelines to equal the usable watt hours of the lithium’s. Also, the Lifelines weight 62 pounds apiece, so 13 of them weigh in at 806 lbs. vs. the Victron’s 126 pounds; not to mention how much space they would need. The cycle life of the Lifeline batteries is about 1,000 at 50 percent DOD.

The downside of the Victron lithium’s, with the required Victron BMS, is the initial expense. The retail cost for two batteries and the BMS is $10,770, with the batteries making up $8,800 of that total. But then 13 Lifelines would cost you about $4,200 and they have half the cycle life of the Victron’s. So, the TCO (Total Cost of Ownership) over the expected lifetime of the two battery types, is about even. That surprised me.

3. Core Components: (Solar Charge Controller, Inverter/Charger, Control and Monitoring Device). The Victron components I chose were:

• Quattro 48/5000/70-100/100 120 volts – Inverter/Charger
• Blue Solar 150/45-tr – 48 volts Solar Charge Controller
• Lynx Ion BMS 1000 – Battery Management System
• Color Control GX – System Setup, Management, and Control PLC
• Two Victron HE 24 volts/200 amp hour Batteries

4. AC/DC Panels and Load Centers:

• MidNite Solar MNDC 175 – DC Load Center
• Blue Sea Custom DC Distribution Panel
• Blue Sea Custom AC Load Center/Distribution Panel

5. Solar Panels: Four 350 watt 36 volt LG Solar NeON R LG350Q1CA5 PV Panels

6. Miscellaneous Equipment:

• Mean Well HRP-600-12 – Industrial Grade 120 volts AC to 12 volts DC 50 amp Power Supply
• CUI PYB10-Q48-S12-DIN – Industrial Grade 10 watts 48 volts DC/12 volts DC Converter

Obvious Questions

1. Why a 48 volt DC Battery System? Part of it is familiarity with 48 volt systems, I have one in my house. The main reason is, that when you get into high power designs, the size of things really matters. The batteries I’m using have a maximum discharge current, that is fuse and breaker limited to 200 amps at 48 volts, that’s equivalent to 800 amps at 12 volts. The size of wires, circuit breakers, fuses, and other components becomes prohibitive at these power levels. The only down side to a 48 volt system is the requirement for a 48 volts DC to 12 volts DC converter to power the loads. Or, as I have chosen to use, a 120 volts AC/12 volts DC 50 amp power supply.

2. Why did I choose to supply power to the DC loads from an AC/DC Power Supply? I had a heated argument, with myself, about that, but finally decided to go the AC/DC route. It has to do with redundancy. If I power the DC from an AC source, and have a problem with the batteries or inverter/charger, I can still have full DC and AC power by connecting to either shore power or a generator. Also, the AC/DC Power Supply is more efficient than the DC/DC Converter.

3. Why did I choose a 50 amp/120 volt/6000 watt service instead of a 50 amp/120-240 volt/12000 watt service? I was trying to avoid the complexity of split phase, and I wanted more power than the standard 120 volt/30 amp/3600 watt service. I also wanted the Inverter to power all the AC Loads, and while they make 120/240 volt inverters, they are not practical to use in a camper.

4. Why Victron Equipment? To start with, Victron Energy is a long-established, international company with a reputation for manufacturing quality products. Especially in the mobile sector. But the main reason I went with their equipment is the integration of all their components with a central setup, control, and monitoring computer (CCGX or Venus GX). Theirs is the first system I have seen where the battery BMS directly controls the charging Voltage and Amperage being sent from both the inverter/charger and the solar charge controller. They call it DVCC (Distributed Voltage and Current Control). It’s quite a concept, the battery system controls its own charging rather than relying on setups in external charging devices.

Conclusion

Well, that about does it for this first article. I look forward to getting your feedback, both positive and especially negative. You can’t learn anything if all people say are good things about a design. My batteries don’t get here until early August, so I’m going to start on the technical article and hopefully get it finished in late July. (Ed. note: part 2 of this article can be found by clicking here).

I have included some “teaser” photographs of the project’s progress to date.