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RV Solar Series: Understanding Electricity

Electricity – 101

RV Solar Series: Understanding Electricity is not optional but is not a concern in every day modern life. What is electricity? Before you make a change to your RV electric system, you better understand at least the very basics of electricity.

When you turn on a flashlight, you create a circuit.  The components are the energy source, typically a battery, a load — the bulb and a conductor that connects the source to the load. If any of these three items are missing, you don’t have a flashlight you have a paperweight. 

Flashlight graphic
Flashlight graphic

Circuit

The word circuit, derived from the word circle, describes the path the electricity takes from the battery, through the load and then back to the battery, this is called a closed circuit. If the circuit is not connected, typically by turning off the switch, then the path is not intact and the light will not work. This is called an open circuit.

Work is accomplished by passing the electrical energy through the load. This flow of electrons is called amps. Think of amps like the current in a river, the wider and deeper the river, the more water it moves. More water moving, more work can be accomplished.  

Volts describe potential energy. Volts alone don’t do anything; they just sit there, like water behind a dam. When the valves are open (or the switch is turned on) flow starts and then you measure flow to determine how much energy. If the reservoir (battery) is empty it does not matter if you open the valve or turn on the switch. Everyone knows that by using the flashlight you deplete the battery, and if you leave it on too long the battery will be “empty” and will then need to be recharged or replaced.

How to measure electrical use

So to measure my electrical use, I needed to measure how many amps flowed through my RV components. This device is called an amp meter. My amp meter not only had to measure the flow but also add up the flow over time. I measured every amp I used from my battery for almost a year, and then also measured every amp I put back into the battery and arrived at some very interesting results, including exactly how much I drained from my battery each day and how hard it is to fully recharge my battery.

Stock Photo Victron Battery Monitor
Stock Photo Victron Battery Monitor

I installed a Victron 712 recording amp-meter (battery monitor). This device (by sending a signal to my cell phone)  measures every amp sent out from the battery, when using electricity, and returned to the battery while charging.

Voltmeters

Almost all RVs come with voltmeters and 99% of the voltmeters are only used to give RV owners a warm fuzzy feeling and are not a good reflection of battery charge or health. It would be a rare owner that disconnects the battery for a few hours before measuring the voltage. Instead, owners push the button and then feel good that the number is pleasantly high.

stock photo voltmeter
stock photo voltmeter

If you push the button on the voltmeter when you are charging you will read the volts charging the battery, not what is stored in the battery. What you get if you push the button immediately after recharging the battery is called a surface charge reading, not a reading of the true state of charge of the battery. The only way to measure the true potential energy in a battery is to disconnect it and let it rest for a prolonged period prior to using the voltmeter or on a flooded lead-acid battery to measure the fluid with a hydrometer.  

What about AC and DC?

AC (alternating current) is the electricity you have in your house (with rare exceptions) and was pioneered by Nicholi Tesla. (It is somewhat amusing that the name Tesla is now associated with Tesla cars, which use mostly direct current.)  DC (direct current) is the electricity stored on a battery, like your car battery.  The difference is that alternating current cycles pressure at a frequency (called hertz) and can pass through much smaller wires without loss of voltage.  Direct current does not cycle; instead, it flows from the negative terminal of your battery through a load to the positive terminal of your battery.

Visualizing direct current is the same as water flowing in a river.  Visualizing alternating current is like watching waves in an ocean. In the ocean,  the energy is expressed in peaks and valleys that move with the energy. The water rises and falls with the wave energy but does not flow like the water in the river. 

Inverter graphic
Inverter graphic

Your RV, with few exceptions, has both AC circuits and DC circuits.  The DC circuits are connected to your battery, and AC is supplied by either an external power cord or comes from your battery via an inverter.

Solar electric panels and battery chargers create direct current (DC) which is used to recharge your battery.

RV Solar Series: Understanding Electricity

This is only a small part of RV Solar Series: Understanding Electricity is only the first step. We will step by step through the process. This was step number one.

We created this site to help our friends with their RV questions. Feel free to ask questions or comment and we will address them to our best abilities.

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