Quote:
Originally Posted by SLOweather
To carry the analogy on a bit farther...
The engine alternator and some inverter/chargers are like fire hoses.
Converters are closer to big garden hoses.
Trickle chargers are squirt guns.
Solar can be anything from a squirt gun (solar "battery maintainers), to garden hoses or maybe small firehoses.
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This is a very good way to conceptualize these concepts.
I apologize if this sounds overly lecture-y... In a previous career I was a college professor and technical director. I have a strong background in this, I will try to explain things further.
You don't have a modern inverter/charger in your coach, so I will cover that first and fastest.
A modern RV inverter/charger (Magnasine is a good example) is three things: It is a 120v (High Voltage AC) transfer switch for the 120v loads connected behind it, and those loads can be powered EITHER by incoming 120v power or from the batteries by inverting. It is a charger for the batteries, and it is an inverter drawing power from the batteries to maintain the HV loads no matter which power source is available.
The incoming HV power to the inverter/charger is either generator or shore power - switched with another transfer switch elsewhere that you DO have.
The second function in the inverter/charger is the charger. This works to detect the current voltage of the batteries and when there is incoming HV, it "splits" that power - using the internal transfer switch to pass the HV power directly through to the HV loads, and at the same time the charger attaches and becomes one of those HV loads to refill the batteries.
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Now, about your coach specifically. Every RV has two primary power systems: high voltage and low voltage. The HV system is what you are most familiar with, wall outlets and 120VAC that powers your toaster and TV and everything else that you have in your house.
The LV system is 12VDC and is the same as what powers your car, cigar lighter cellphone charger, radar detector and any other car-accessory type things. An RV uses MOST THINGS on this LV system. Interior lights, water pump, fridge circuits, small fans. All are on the LV system pulling from the batteries.
Your coach is a motorhome, so it has a SEPARATE 12VDC system for the "chassis" systems of starting the drive engine, headlights, dash radios, etc. There will (likely) be a momentary-contact relay switch somewhere to connect the two LV battery systems together as a booster if one or the other has a dead battery. Usually this is to boost the engine batteries with the house system so you can start the drive engine.
The chassis alternator is primarily charging and powering the engine batteries, but MAY have a diode (one-way valve for electricity) set up to send power to the house batteries when the drive engine is running but prevent draining the engine batteries if you run down the house batteries.
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Everything on the low voltage side (LV) is determined by the voltage in the batteries and cables. Much of the rest of this will be concerning the low voltage house systems.
Electricity in the LV system is like a container of water - The battery is the container. Charging pours water (power) into the container until it is full of voltage, then the charge controller turns off the supply.
Turning on a light or using something else creates a drain from the container - and power flows from the battery or supply to the drain (load) and work is done - the light is lit.
After a certain amount of time, the battery has supplied everything it has and the container is empty. Don't let it get that low! I will address battery management later.
Solar is a small-refill capacity for the batteries. The 120V charge controller that your coach has is a large refill capacity, but this only supplied when there is a HV source such as your generator or shore power available.
Your solar system at only 50 watts / 1 amp is basically useless for anything other than keeping the battery fresh when your coach is stored. Sorry, but that just is too small for anything other than a couple LED lights. Batteries (even when disconnected) will naturally lose about 10% of their charge per month while stored, so having this panel on the roof of your RV and connected to the batteries while you are stored will actually do some good. In normal use while you are using your coach... It just can't keep up with the demand. There's a reason I put 1020 watts of solar on the roof of my coach! 50 watts... That's a demo system, but a good way to learn about solar and wiring.
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So how does the power "know" where to go?
Electricity flows based on "potential," which from an outside perspective looks like "balance" in the system. Potential is "does the power have someplace to go from a higher power source to a lower power destination. Everything flows downhill, the path of least resistance. The charger has a higher voltage and the battery slowly increases in voltage as it stores energy until they are almost equal, and the charger can detect this happening and it stops charging to avoid overfilling the battery.
When the charger or solar controller has power to supply, it has a higher "potential" than the battery, and the power flows there. If you simultaneously turn on a light, then that light ALSO has a "potential" but it is much much lower than the battery - so some of the power from the highest source (the charger) will be diverted to power the light, and the rest will still add power to the battery. If the load is too large for only the charging supply, then the total potential will drop below that of the battery, and power will flow out of the battery to make up the difference.
The easiest way to see all of this in action is with a Battery Monitor that uses a shunt. Magnum Energy sells one that works with their inverters, but there are many others available on Amazon as well for a variety of prices.
A shunt is a special type of rated terminal that sits at the negative terminal of the battery, and ALL power to the batteries must flow through it. It has two small sense terminals that connect to the monitor device, and the flow of electrons through the shunt can be very precisely measured. When the batteries are accepting power from a source, the shunt and monitor will indicate a certain amount of positive amperage. When the batteries are draining / supplying power to the loads, the shunt and monitor will show that as negative amperage. This will usually be able to also tell you the current SoC (State of Charge) of your battery bank.
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Battery care is important!
GC2 golf cart batteries are 6V and need to be connected in series pairs and if you have 4 or more, parallel groups of those series pairs. If this is confusing, STOP NOW and don't connect them until you know how! The worst thing to do is short circuit a giant battery like that.
Use of a flooded battery (standard lead acid / car battery / deep cycle marine, GC2, etc) is that you want to keep it above 50% SoC to avoid damage. Even so called "deep cycle" batteries will suffer if you drop them below about 40-30% SoC, and the overall lifespan will decrease substantially. A full 12V battery with no load on it should read about 12.7V, and at 50% SoC is 12.1V.
Note that this is NO LOAD and you should let the batteries "rest" for about 5-10 minutes after disconnecting power to test the voltage. A battery monitor SHOULD take the overall load into account when telling you the voltage and SoC, but this may be problematic as loads pull down the voltage in the wire, affecting the accuracy of the reading. It is better if you can minimize the loads while checking voltage, or just try to avoid operating your batteries below 11.9 volts indicated while loads are connected.
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