Van Build #3 – The Electrical System
by Koda
There are two separate wiring systems used in van conversions, the 12-volt DC (Direct Current) system and the 120 volt AC (Alternating Current) system. The 12-volt DC system powers things like lights and fans and sometimes even refrigerators and air conditioning. The AC power is provided by a device called a power inverter and allows one to operate standard, 120-volt household appliances.
It is crucial to know where every item that will use electricity will be located so you can run the appropriate wiring behind what will become the finished walls. I chose to leave all the factory wiring in place since I didn’t know which wires were necessary, such as the rear lights and door locks. The factory interior lights would need to be removed since they would be covered later, so I simply removed the light fixtures and left the wire connectors undone.
There are normally three wires associated with the A/C system – positive, neutral and a ground wire. In a house the ground wire literally connects to the earth via a grounding rod pounded into the ground, but since the vehicle is isolated from the ground by the wheels the ground wire isn’t necessary. (Please leave a comment if you are aware of a way to properly ground AC wiring in a vehicle build.)
You will actually end up with two separate 12-volt wiring systems – the circuits which are part of the vehicle and connect to the main vehicle battery, and your solar system with its own battery storage. In the factory 12-volt vehicle system a positive wire from the battery goes to the device being powered and the negative wire “grounds” to the body of the vehicle. The negative wire of the solar powered circuits will connect instead to the negative terminal of your storage batteries.
Main Components of an RV Electrical System
Solar panels (collets electrical energy from sunlight)
Charge controller (regulates the amount of solar energy delivered to the batteries)
Storage batteries (lithium, lead-acid or AGM)
AC power inverter (converts DC power from the batteries into AC to run standard household appliances)
AC circuit breakers (protects from short circuits on AC power lines)
DC/DC charger (charges the batteries using the vehicle alternator when the engine is operating)
Shore power/charger (converts household AC power from an extension cord to DC to charge the batteries and power everything)
DC circuit breakers/fuses (large breakers/fuses used to shut off power from the solar panels and batteries)
DC fuse block (protects from short circuits on DC power lines)
Power shunt (device to monitor battery power)
Displays and switches
Outlets
(optional – generator)
All appliances are designed to run on either AC or DC power. In a van/RV conversion the DC appliances use less power because there are power losses involved in converting the 12-volt power from the batteries into 120-volt AC power, but DC appliances are often much more expensive. The price difference can sometimes be 3 to 10 times as much. Being on a tight budget I opted to have as much solar power and battery storage as I could afford in order to reduce the up front costs of the larger DC appliances. That is something I now consider a big mistake. I will explain why in a moment.
My Appliances and Accessories
AC
3.2cf refrigerator/freezer (90 liters)
700 watt microwave oven (draws 1,050 watts)
Single burner induction cooktop (up to 1,700 watts)
Coffee maker (1,000 watts)
Audio/video receiver
55-inch 3D TV
Blu-ray player
Two self powered (AC) audio studio monitors
Various audio signal processing devices
6-gallon electric water heater (1,800 watts)
UV water purifier
Twinkle lights
Other novelty lighting effects
Laptop and phone chargers
DC
Two reversible fans
LED light strips (I removed the AC transformer)
LED puck lights
Water pump
Air pump
Diesel heater
Cellphone booster
As you can see, I use a lot of AC appliances, so I opted for 400 watts of solar panels, 400 amp hours of battery storage and a 3,000 watt power inverter. On sunny summer days when I don’t use the TV sound system, the batteries remain close to fully charged, but two days of rain can drain them. On such days I have to start the van up to charge the storage batteries from the alternator using the 40 amp DC to DC charger. The 20 amp shore power connection allows me to top off the batteries while also drawing power directly from the grid using a standard extension cord — if I am some place where I can plug it in.
A few months after installing the solar panels I noticed my batteries were no longer becoming fully charged. Turns out two of the flexible panels had shorted out and melted large holes in the surface. The seller on Amazon sent free replacements, but it is a reminder that things can go wrong when you are out on your own and depending on everything to work as expected.
Watts, Volts and Amps
Power is measured in Watts.
Volts X Amps = Watts
12 volts X 10 Amps = 120 Watts
120 Volts X 10 Amps – 1,200 Watts
If you think of electricity as being similar to water flowing in a hose, voltage is how far you can squirt the water, and amperage is how fat the hose is, Wattage is how fast you can fill a bucket.
I made a huge mistake when designing my electrical system because I thought amps were amps, regardless of voltage, but that is not the case. I thought if my microwave draws 10 amps and I have 400 amp hours of battery storage, I should be able to run the microwave continuously for 40 hours on a full charge. Turns out I have 10 times less power to run AC appliances than I thought, because power is measured in watts, not amps.
Say you have a 12 volt, 100 amp hour battery. That means you can draw 100 amps at 12 volts for 1 hour, or 10 amps at 12 volts for 10 hours (10 amps X 12 volts = 120 watts/hour). But if you use the inverter to change the voltage from 12 volts to 120 volts and draw 10 amps (10 amps X 120 volts = 1,200 watts/hour) you use 10 times as much power.
Through an inverter, a fully charged 12-volt, 100 amp hour battery can continuously operate a 120 volt microwave oven drawing 10 amps for roughly one hour. The same battery can run a 12-volt refrigerator drawing 10 amps for 10 hours (much longer actually because fridges turn themselves on and off and are off most of the time);
When designing your solar system you need to calculate your power requirements in watts, not amps.
A 100ah lithium ion battery should produce about 1,200 watt hours of power, and 400ah of battery storage is roughly 4,800 watt hours. That may seem like a lot, but the audio system in my van draws 1,000 watts and watching a 2-hour movie would suck up nearly half the power, plus I use another 1,000 watts per day just making coffee, running the fridge, lights, fans, diesel heater, etc. If I cook anything using electricity I risk losing all the power entirely. And that is the best case scenario where I start with fully charged batteries, which is a rare condition in the winter.
The voltage of the battery changes depending on how charged up it is. Displays on the charge controller and power inverter both indicate the battery voltage but may not match exactly. I learned from other van lifers that one needs to install a shunt on the negative pole of the battery which measures the current passing through it and tells you a more accurate indication of the energy contained in the battery. I bought one, but it has to be installed when the batteries are fully charged and that hasn’t happened at an opportune time yet — long story there…
Lithium vs Lead Acid Batteries
Lithium batteries cost a lot, but they are so superior to lead-acid batteries that for most people it makes no sense at all not to use them. and the prices continue to fall. I copied most of the following info from the Amazon page for the Chins batteries I am currently using
- LiFePO4 (lithium-iron-phosphate) batteries provide 2000+ cycles compared to 300~500 cycles in a lead acid battery.
- The service life of LiFePO4 batteries is 8 to 10 times longer than the standard lead-acid batteries.
- The weight of the lithium iron phosphate battery is 30% lighter than the lead-acid battery of the same capacity
- lithium-ion batteries have higher energy density, more stable performance and greater power. LiFePO4 batteries will not burn when overcharged, over-discharged, experience overcurrent or short circuit, and can withstand high temperatures without decomposition.
- They can support fast charging and solar panel charging. CHINS LiFePO4 batteries do not contain any heavy metals or rare metals and are more environmentally friendly.
- CHINS LiFePO4 batteries have a built-in BMS (Battery Management System) to protect it from overcharge, over-discharge, over-current, and short circuit with excellent (low) self-discharge rate. Built-in high temp cut off prevents charging over 122 °F (50 °C).
Lead-acid batteries have no BMS to prevent over charging, etc. They can off gas dangerous fumes, are full of acid so spills can be a nightmare. You can only draw about half of their rated power before the power output drops dramatically. AGM batteries are sealed and that makes them better than lead-acid, but Lithium batteries are far superior.
The potential downside to lithium batteries is that they can’t be charged at temperatures below freezing. (More expensive batteries are available that have built-in heaters — which only work if the battery has a charge.) If you live in your rig full time and have the batteries inside this should not be an issue. Temperature is only a problem for people who will be storing their rig in winter months where the temperatures get really cold. It would be necessary to remove the batteries from your rig when you winterize it to keep the pipes from freeing. Here are the operating temperatures for Chins batteries.
Charge: 0°C~50°C(32°F~122°F)
Discharge: -20°C~60°C(-4°F~140°F)
Storage: -10°C~35°C(14°F~95°F
It appears to me that Chins has the best product at the best price on Amazon, and their customer service is the best I have ever encountered. I have used it a lot because it took me 3 months to realize I needed batteries with a higher continuous power output.
You Can’t Have Too Much Solar
I knew I would need at least 400 watts of solar panels to run an all electric system. Theoretically that should be plenty. 400 watts times 12 hours of sunshine each day would produce 4,800 watts and completely charge my 400ah of battery storage — even if the batteries were dead to start with. But that is not what happens in the real world.
The amount of power generated by the solar panels depends on how clear or cloudy the sky is and the angle of the sun. I was shocked to realize that even on sunny days during the winter the low angle of the sun meant getting less than half as much solar energy as I was getting in the summer. Add some clouds and the solar output can drop to nearly zero. Even on clear, sunny days in the summer the sun doesn’t climb high enough to produce the full rated output of the panels till after 10 AM and the output begins to drop before 3 PM.
One way to estimate how much solar power you will actually get is to divide the rated output of your solar panels by half and times that by the number of hours the sun will be up. 400 watts of solar panels becomes 200 watts, times say 12 hours, or 2,400 watts total. In the winter that number will be cut by more than half — and that is with sunny skies. Add a few hours of cloud cover or shade from buildings or trees and the total wattage can drop significantly.
Alternate Power Options
You can pretty much count on not getting enough solar power at some point. That is why it is essential to have other ways of producing electricity.
A DC/DC charger connects to the vehicle battery and turns on when you drive or idle the engine. It draws energy from the alternator to charge your storage batteries while insuring that the vehicle battery is not drained. This can also be accomplished with a much cheaper battery isolation switch, which prevents the vehicle battery from being drained when the ignition is not turned on, but there is a downside to using the isolation switch.
Alternators are cooled by air flow, and the faster they spin the better this cooling system works. The alternator will put out as much power as it can relative to the load it sees, so if your storage batteries are low, even when the engine is idling the alternator will generate as much power as it can and become hot due to lack of air flow. This can burn up your alternator.
A DC to DC charger regulates how much power it draws from the alternator and thus prevents the alternator from over heating.
Some people install a second alternator to charge their storage batteries. To justify the expense it is also necessary to buy a DC/DC charger with a much higher output. Nice to have, no doubt, but quite expensive.
Shore power chargers are similar to normal car battery chargers but have higher output amperage. You use an extension cord to plug the charger into an outlet at home or at campsites with power. I was under the impression that since most AC power circuits in someone’s home are rarely more than 20 amps (usually 15) that the biggest shore power charger I could use would be a 20 amp charger. This is where one needs to remember that power output changes with voltage. 15 amps of 120 volt AC power is 1,800 watts. 1,800 watts divided by 12 volts is 150 amps. That means you could theoretically connect a 12-volt 150 amp DC charger to a 15 amp AC extension cord. To determine the best size for your shore power charger you first need to make sure you will never put in more power than the BMS (Battery Management System) built into your lithium batteries can handle. Determine the maximum solar power that might ever be generated, add that to the DC/DC charger output, then subtract that from the max current the BMS can handle.
In my case the max output of my 400 watts of solar panels at 12 volts is roughly 20 amps, and I have a 40 amp DC/DC charger, and the BMS on my lithium batteries is rated for 100 amps. The biggest shore power charger I should use is 40 amps, but 30 would be safer. If you make sure you never turn the engine on while connected to shore power you can use a much larger shore power charger, but screw up one time on a sunny day and you might fry your expensive batteries. (Replacing my 100 amp BMS batteries with 200 amp BMS batteries would let me use a much larger shore power charger.)
The best way to insure you will always have the power you need when you need it is to use a gasoline generator. You are not going to make any friends running a generator in a campground so it is important to buy the quietest generator you can possibly afford. Few vans have enough space to carry a generator and the fuel for it, but they are far more efficient than idling your engine to use the DC/DC charger — because alternators put out less power when idling than at driving speeds. My 40 amp DC/DC charger might only put out 25 amps when the engine is idling.
What I Would Do Differently
I would not create an all electric system.
I would not use flexible solar panels because they don’t last nearly as long as rigid panels.
I would spend the money to buy DC appliances.
I would mount the solar panels on a roof rack so they can be tilted toward the sun. (This is the cheapest, most effective way to get more power.)
I would buy larger, rigid solar panels like those used on home installations and squeeze as much solar on the roof as I could fit, even if it meant losing the skylight or second fan.
I would use a near-wall projection TV (which can also be taken outside to project on the side of a white van.)
I would use 12-volt car audio components for the TV sound system (and make them portable so they can be used outside.)
I would mount the main electrical components in a box on the floor of the van garage rather than mount them against the wall. (Having the components against the wall makes it difficult to use the space in front of them.)
It is actually difficult to know how much of that I would actually do. Budget is always an issue, and having DC appliances reduces the amount of power required so the solar system would’t need to be huge. I have heard it said that no one ever regrets over-building their solar system, and I can believe that.
Remember to run wires for all your monitoring displays, cellphone booster, switches, gauges for your water and waste tanks if you have them, etc. Draw the wire runs on your building plans. Remember you will need space in your walls or cabinets deep enough to mount outlets and switches.
Low voltage (ie, 12 volts) high current (amps) wire needs to be very thick in order to avoid heating up and catching fire. This includes the cables attached to your batteries, circuit breakers, DC/DC charger, etc. You also need to attach lugs to the ends of these larger wires in order to make secure connections. This is not a how to guide but simply an overview of things to keep in mind when designing your van or other rig. There are charts available online that can tell you wire size you need to use depending on voltage, amperage and the length of the wire – longer wires need to be thicker.
I describe my months of nightmare power problems below, but if you just want to move on with van build information, next up is about designing your plumbing system. (I discovered some unpleasant surprises I after hitting the road.)
*****
Updated February 22, 2023
I started my van build in early April, 2022 and didn’t quite finish before the cold and snow in Salt Lake City forced me to head for Arizona right after Thanksgiving. The electrical system was installed by late July and I used it mostly just to run 2 ceiling vans all day long in the 100-plus degree F (40C) heat. By September I was living in the van full time and using the microwave and coffee maker regularly, and watching movies now and then with the home theater. Everything seemed to be working just fine, though as the cold weather moved in and cloudy days happened more regularly so I was connecting to shore power more and more often.
Then I hit the road and immediately found myself with no electrical power in the living area at all. I stopped in Kingman, Arizona, at an RV repair place and they plugged me into shore power for just a moment and the power came back on. (I assume the lithium batteries had gone so dead they didn’t have enough power to turn back on in order to receive solar power.)
I drove to a free BLM campground north of Lake Havasu City, AZ, thinking driving would charge my system, but again I had no power at all when I arrived. I talked to the site host at the campground (Frank) and he told me a guy who does RV builds and repairs for a living was camped nearby. That guy (Brian) pointed out that I had forgotten to connect the wire from the ignition to the DC/DC charger which turns it on, so I did that, and he again put some juice into the batteries to get them to kick back on.
I thought everything was fine but all the power in the van, including the DC lights, would shut off when I used the microwave for more than 3 minutes at a time. 5-30 seconds later the power would come back on. Since the DC power also shut off it meant the problem had to be with the batteries themselves. I figured they simply weren’t getting charged up enough because it was winter and the low angle of the sun meant I was getting half as much solar power as in the summer. I used up a lot of fuel running the engine to keep the batteries charged but I could never seem to get enough charge in the batteries to prevent them shutting down when using the microwave.
I noticed that the charge controller (the grey item in the top center of the photo at the beginning of this page) was never putting out the 14.4 volts required to fully charge the battery. I mentioned it to someone who happened to have a new charge controller he had bought for a project he didn’t finish, so I purchased that from him. Eventually the battery reached the 14.4 volts indicating a full charge, but the batteries continued to shut down after just a few minutes of high current draw. By that time I had been fighting with the power problem for over two months, so I finally contacted the battery company, Chins, via Amazon.
I had decided to purchase Chins batteries after seeing a review on YouTube where a young guy cut open the battery to see how well it was manufactured, and he was very impressed. Turns out Chins has the best customer service I have ever experienced,. They told me if the batteries were the problem they would refund my money or replace them, and also cover the cost of packing and shipping. They asked me to do some tests to check the battery voltage so they could determine which battery was bad. I had to buy a multimeter to measure the voltages, but it was a piece of crap from Walmart which didn’t read in decimals and the voltage displayed was nowhere near what the other displays were telling me.
I emailed the information to Chins From the time of day I receive emails from them I assume they are located in China, but the support person(s) write in fluent English. They told me to ship the oldest battery back (I bought them a year apart because I was collecting everything before I bought the van, but hadn’t used the first battery till I bought the second. (FYI: A lithium battery in storage should be charged every 3 months to keep it in good shape, and no battery should be stored directly on a concrete floor — because the electric field can interact with the ground and drain the battery.) I returned the battery 2 days ago and they promptly refunded my money, and the packing costs. I ordered a new one, expecting to wait 11-18 days but it arrived in a week.
The new battery still shuts itself off after around 3 minutes of running the microwave, but now I know why. All that info above about power being measured in watts, not amps, is something I only recently learned. My 200ah batteries are rated at 100 amps of continuous power output, and I pull roughly 120 amps DC from the batteries when operating the microwave and a some low current draw things. I have to replace them with 200ah PLUS batteries which are rated at 200 amps of continuous power output, and that will finally solve the problem. The PLUS batteries cost $70 more and I have to pay return shipping on my current batteries, but Chins is letting me swap them. Awesome customer support. Great batteries in lots of different sizes.
Overbuild your solar system. You will be glad you did.