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 four 100-watt PV panels fixed to my Sportsmobile fiberglass pop-top roof with a combination of Z brackets, 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 to best track the sun...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 high voltage solar panel for better efficiency and less loss in my wires. I have them raised an inch or two and spaced about 3 or 4 inches 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, fluctuating with the sunlight and battery state of charge. I haven't measured the output of the panels directly before the charge controller.
The role of that fancy 40-Amp MPPT charge controller is to protect my batteries by intelligently detecting the voltage of my battery bank and delivering just the right amount of voltage and current. This keeps the batteries safely charging with the electricity generated from the panels. If you overcharge batteries or let them drain and stay dead too long, varying slightly with the type of battery you have, hydrogen gas can be released, lead acid can boil, cells can dry out and in general, you damage the longevity, capacity 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 through a fuse panel to a bus bar and connect that bus bar to the unused positive terminal of one 6V battery and the unused negative terminal of the other.
When you wire things like batteries and solar panels in a series, you add their volts together (6V + 6V = 12V) but the amps or amp-hours (Ah) stay the same. Alternately, when you wire batteries in parallel, the volts stay the same (6V + 6V = 6V) but the amps or amp-hours (Ah) double. The overall watt hours or Volts * Amps for one hour stays the same.
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 effectively delivery power to an electrical device or appliance.
My 12V battery bank is rated @ 210 Ah (amp-hours). Basically, in a perfect scenario where there is no heat loss or any other strange chemical losses that diminish battery performance, in one hour, that 12V bank can power a 12V device that requires 210 amps for one hour.
From there you can do math to figure out what else it can power:
12V device that requires 210 amps for 1 hour
12V device that requires 21 amps for 10 hours
Two 12V devices that use 10.5 amps each for 10 hours
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 battery bank for 10 hours before the battery bank voltage drops to around or below 11.9 volts, which means it is effectively "dead" and can no longer power 12V devices.
Another interesting thing about batteries and electrical is that when we saw "12 volts" we are really talking about a nominal voltage range. Anything roughly between 12.0 and 14.2 volts is a safe "12V"
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 necessarily at 0 volts, it's probably around or just below 11.9V - and a charging 12V battery is generally at 13.6V or 14.2V or something similar. A "charged" 12V battery will be stable at around 12.8V.
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 a common "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 current flows 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 inexpensive fuse will be destroyed instead of the device itself.
Most devices have an on-off switch in the circuit which breaks the completed circuit and stops electrons (electricity) from flowing when switched to the 'off' position (open circuit). When you flip that switch to the 'on' position, you "close" the circuit and allow electrons to flow from the negative terminal of the battery bank to the positive terminal of the battery bank once again.
It's easy to mistakenly visualize electricity with batteries as water pouring out of one side of the battery, going through a tube to arrive at and power a device, then continue on and eventually land at the other side of the battery, but that's not exactly what's happening. **Tangent below for more on this subject**
MILLIONS of electrons are ALL OVER inside the entire wire. But when the circuit is open, those electrons just shake in place and they don't travel.
When you close and complete that circuit, ALL of the electrons simultaneously travel in a chain reaction in the direction of the positive terminal of the battery bank from the negative terminal.
Another confusing aspect: it seems that electrons flow from the positive terminal towards the negative because of the location of the protective fuses, directly after the positive terminal of the battery.
The fuses can really be anywhere in the circuit and still effectively protect devices and appliances. 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.
Great explanations on the differences between "conventional" current direction and "electron flow" direction.
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: AC vs DC
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 that you connect to your vehicle's 12V cigarette lighter socket that has standard household 3-prong power outlets.
Larger, higher wattage inverters connect directly to the positive and negative terminals of your house/auxiliary battery bank or starter battery.
All of the electrical stuff I've covered so far 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 - 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, lower 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 be able to provide 85W (or more) of power for a decent duration.
Most of the time, power supplies don't list watts as the output, they list volt and amps. Remember watts = volts x amps. 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.
2000 watts is enough to comfortably power high draw 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, like your power outlets at home, than the boxy-patterned, modified sine wave inverters.
A 2000-watt inverter would be overkill if all you wanted to do was power your laptop.
So remember to first determine what you wish to power, do some W=VxA calcs, then 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 in the AMA section of the forum with questions.
All of the real electrical engineers out there, please correct me if my descriptions are wrong! I really love to learn and understand how things actually work to help me better troubleshoot when things inevitably fail.
Feel free to share your solar / battery / appliance / electrical setups in your camper!