I'm often asked about my solar setup.
I didn't know anything at all about electrical engineering before I started Van Life.....
I've learned a TON since then and I hope that this post will help you understand and visualize what's happening when you flip a switch and a light comes on in your vehicle or house or anywhere!
Watts = Volts * Amps
MY SOLAR SETUP
I bought my solar from a company called Renogy in Ontario, California.
I bought the Renogy 400 Watt 12 Volt Eclipse Solar Premium Kit.... which means I have 4 100-watt PV panels fixed to my Sportsmobile fiberglass pop-top roof with a combination of Z brackets and roofing screws and some VHB or very high bond 3M double-sided adhesive tape. Currently, they take up nearly my entire roof and I don't have them on adjustable tilting brackets yet.
Those are wired together in series which means that the positive of one panel is connected to the negative of the next panel, ultimately making one large solar panel. I have them raised an inch or two and spaced about 3 or 4 inches for better wind flow and to eliminate the wind from creating too much lift on my pop-top when I'm roaring down the highway.
According to my MT-50 meter, those panels generally generate around 70 volts @ 6-14 amps....fluctuates with the sunlight and battery level. I haven't measured the output of the panels directly before the charge controller.
So the panels convert sunlight (photons) into electricity (electrons being knocked free from the photo voltaic material in the panels) which flow through positive and negative wires through a Renogy 40 Amp Commander MPPT Solar Charge Controller w/ MT-50 and then to my (2x) Interstate GC2-HD-AGM 6V 210 Ah deep cycle heavy duty batteries.
The role of that fancy 40-Amp MPPT charge controller is to protect my batteries by keeping them constantly topped off with the electricity generated from the panels above without overcharging. When you overcharge batteries, depending on the type of battery you have, dangerous hydrogen gas comes out, lead acid boils, or cells dry out and you damage the longevity and usefulness of your batteries.
BATTERY BANKS WIRED IN SERIES vs PARALLEL
The 2 6V AGM batteries are also wired together in series - so positive terminal of one battery is wired to the negative terminal of the other which effectively makes one large 12V battery. You then connect appliances to the free positive terminal of one battery and the free negative terminal of the other. Or if you have many appliances, you connect a bus bar to those terminals and connect the devices to the bus bar.
When you wire things like batteries and solar panels in a series, you add their volts together but the amps or amp-hours stay the same. Alternately, when you wire in parallel, the volts stay the same but the amps or amp-hours double, but the Watts or Volts * Amps stay the same.
Example.
Most of my "house" electrical devices, or devices that aren't powered by the starter battery, van engine and van alternator, are 12V devices. They require 12V and a certain amount of amps to operate.
When I wire my 6V batteries together in a series, this doubles their voltage making a 12V battery bank (more than one battery). But the amp-hour rating of the individual batteries does not change. If I were to wire my 6V in parallel, I would end up with a 6V battery bank with double the amp-hours.
WHAT ARE AMP-HOURS?
An amp-hour is a rating that explains how long a battery or battery bank can power a device that requires a certain amount of electricity before it "dies".
Example.
Each of my 6V batteries are rated @ 210 Ah (amp-hours). Basically, and in a perfect scenario where there is no heat loss or any other strange chemical scenarios that diminishes battery performance or causes voltage drop, in one hour, that 6V battery can power a device that requires 210 amps for one hour.
From there you can do math to figure out what else it can power....
A 12V device that uses 210 amps per hour for 1 hour
A 12V device that uses 21 amps per hour for 10 hours
Two 12V devices that uses 10.5 amps per hour each for 10 hours
or....
A 12V fridge that uses 4 amps per hour, a 12V water pump that uses 5 amps per hour, a 12V power supply for a UV filter that uses 1 amp per hour, ten 12V LED light bulbs that each use .5 amps per hour, a 12V LED light strip that uses 2 amps per hour, a 12V backup and forward facing camera DVR mirror with LCD screen that uses 2 amps per hour, and an Anker 12V cigarette lighter socket USB hub to charge iPhones and external batteries that uses 3 amps per hour......
All of that can be powered by my two 6V 210 Ah batteries wired in series to make a 12V 210 Ah (amp-hour) battery bank for 10 hours before the battery bank voltage drops to 11.9 volts which means it is "dead" and can no longer power 12V devices.
Another interesting thing about batteries and electrical is that when we saw "twelve volts" we are really talking about a nominal voltage range.....it's like.....anything roughly between 12.0 and 14.2 volts is "twelve volts..."
So, when a battery is charged, the voltage actually increases and when it is discharging or being used, the voltage is decreasing. A "dead" 12V battery isn't at 0 volts, it's at 11.9V - and a charging 12V battery is generally at 14.2V or 13.6V or something similar. A charged 12V battery can be at 12.9V or 13.1V or something similar.
12V Electrical Circuits in Vehicles
My battery bank powers all of my 12V house devices by making a complete circuit from the positive terminal of one battery to the negative terminal of the other battery.
The negative terminal of my battery bank is connected to "ground."
In my van, the ground is the metal frame of the van itself.
The devices are also "grounded" which means they have a wire connecting to the metal frame of the van.
The positive terminal of my battery bank is connected to a 12V distribution box with fuses. These fuses are rated to break when a specific amount of amps flow through them. This serves to protect the sensitive electrical devices being powered by the battery. If a surge of too much electricity rushes from the battery to the device, the fuse will be destroyed instead of the device itself.
From the 12V fuse box, individual wires connect to each electrical device - and remember, these devices are "grounded" or connected to the frame of the van and the battery bank is also connected to the frame of the van, so we have our completed circuit!
Most devices have an on-off switch in the circuit which breaks the completed circuit and stops electrons (electricity) from flowing in the off position (open circuit) until you flip that switch to the on position which "closes" that circuit and allows electrons to flow from the negative terminal of the battery bank to the positive terminal of the battery bank.
It's easy to mistakenly visualize electricity with batteries as water pouring out of one side of the battery, going through a tube to power a device, then landing at the other side of the battery....but that's not how it is. ***SEE MY TANGENT BELOW FOR MORE ON THIS
MILLIONS of electrons are ALL OVER inside the entire tube. But when the circuit is open or not completed, those electrons just kind of shake in place and they don't travel.
But, when you close or complete that circuit, ALL of the electrons start to travel in a chain reaction in the direction of the positive terminal of the battery bank from the negative terminal.
It's confusing when you look at it, because it seems that the electrons or electricity flows from the positive terminal towards the negative because of the location of the protective fuses....remember, these are directly after the positive terminal of the battery.
The fuses can really be anywhere in the circuit. When that fuses breaks, it opens the circuit, making it incomplete, which prevents ALL of the electrons in the ENTIRE circuit from flowing or traveling instantaneously.
A Tangent About Electricity
So check these videos out....SUCH a good explanation of the difference between (conventional) current direction and electron flow direction 1, 2, 3
It's like....Current or "Conventional" current is a description of WHY the electrons flow from (NEG) to (POS) ...current is the chain reaction of electron donation and subsequent positive charge of all atoms in the conductive material of a circuit that contain the electrons...the direction of that chain reaction or the direction of the "desire for electrons" goes from (POS) to (NEG) and results in electrons being pulled in the opposite direction.
INVERTERS
What about if you need to charge your laptop? What if you want to use a powerful vacuum cleaner or a blender or power tools?
This is when you need to buy and use a device called an inverter.
You're probably familiar with inverters as the little box with 3 prong power outlets that you connect to your vehicle's 12V cigarette lighter socket.
Larger inverters - higher wattage inverters - connect directly to the positive and negative terminals of your house battery bank or starter battery.
So far all of the electrical stuff I've covered is what's called DC or direct current. Now we're getting into AC or alternating current which is what you are most likely more familiar with. We're getting into Tesla vs Edison territory here.
An inverter does just what it's name suggests. It takes 12V of DC electricity and inverts it or "steps it up" to 110V or 120V AC electricity to power things that you would normally plug into the outlets in your home or office but you can't normally power in your vehicle.
So, If you have a small amp-hour battery bank and you have very minimal energy requirements, you can very easily use a smaller wattage inverter - the type that you see in gas stations or at Walmart.
You can determine what wattage inverter you need by looking at the power supply of the device you wish to power. The label will generally have an output rating... conveniently, my Macbook Pro power supply has a label that says 85W or 85 watts....which means my inverter would need to comfortably be able to provide 85W of power.
Most of the time, power supplies don't list watts as the output, they list volt and amps. Remember watts = volts * amps... so, whip out the ol' calculator and do the math to figure out the required wattage for your device and buy the appropriate inverter for you.
I bought a Renogy 2000W 12V Off-Grid Pure-Sine Wave Battery Inverter. 2000 watts is enough to comfortably power electrical devices that use a lot of electricity like ninja blenders and power tools.
Going with a pure sine wave inverter vs a modified sine wave inverter will best protect sensitive electronics and give you better performance over time. Pure sine wave inverters do a better job at creating a nice curvy sine wave like that smooth alternating current that you get from the Grid from your power outlets at home, than the shortcut-taking, boxy-patterned modified sine wave inverters.
A 2000-watt inverter would be EXTREME overkill if all you wanted to do was power a laptop.
So remember to decide what you wish to power, and buy the appropriately sized (wattage) inverter for you!
This is a lot, and honestly, I'm still wrapping my head around all of it. But like I said, I've learned a lot!
So feel free to hit me up with questions.
All of your real electrical engineers out there, please correct me if my descriptions are wrong in the slightest! I really love to learn and understand how things actually work to help me better troubleshoot when they fail.
Cheers!
Feel free to share your solar / house battery / appliance / electrical setups in your camper!