Battery Bank / Power Inverter (READ PART ONE HERE –EMERGENCY POWER ALTERNATIVES MADE SIMPLE Part I Solar Panels and Charge Controller)
By Robert B – http://keepingupwiththepreppers.blogspot.com/
The battery bank is the most important component of your system. Once the sun goes down, the battery bank will provide electricity throughout the night if built correctly. The trick to the battery bank lasting throughout the night is to obtain the correct ratio of solar panels to the number of your batteries in your battery bank. It’s equally crucial to have the correct number of batteries in your battery bank. Your battery bank should provide enough power storage to run your refrigerator over night until the sun returns to fully charge your batteries during the day.
Building the battery bank is the most intimidating part to most people, but it’s really not that difficult. There is plenty of information on how to build a 12 volt, 24 volt, or 48 volt system, but I will be illustrating how to build a simple 12 volt system.
Types of Batteries
There are several different types of batteries on the market that will work with your system. These batteries range in price and efficiency, so it’s best to find the right balance between your budget and your power needs.
The batteries used in any solar or wind generator must be deep cycle type batteries. Regular car batteries are not made to charge and discharge like a deep cycle marine, RV, wheel chair, or golf cart batteries. Regular car batteries are not designed for this purpose.
Lead Acid Batteries (Pictured above) – Lead Acid batteries are probably the most inexpensive but are not the most efficient. I am using five Lead Acid batteries for the battery at my home. While they do work just fine, when they start losing their efficiency, I will replace them with AGM batteries such as the batteries at my bug out location.
Vmaxtanks Vmaxslr125 AGM Deep Cycle 12v 125ah SLA rechargeable batter for use with Pv Solar Panels
Absorbent Glass Mat (AGM) batteries (Pictured above), in my experience so far, has been the most efficient. However, they do cost significantly more. While the AGM is still considered a Lead Acid battery, the construction of the battery is superior to a regular Lead Acid battery and tends to be more efficient. The Lead Acid RV batteries cost approximately $100 each while the AGM batteries cost approximately $250 per battery.
You will have to do your research and determine your budget for your batteries.
Wiring Your Battery Bank
First, you will need battery cables that will run from your charge controller to your battery bank. I recommend using two gauge battery cables or lower for this purpose and zero gauge cables (The largest cables available) to run from your battery bank to your power inverter,
I wired my battery bank in parallel meaning that the positive cable from the charge controller goes to the closest positive terminal on the first battery in your bank. The next cable runs from that first positive terminal to the next positive terminal on the next battery and so on.
The negative cable coming from the charge controller will run to the negative terminal on the LAST battery in your battery bank. The cables running from your battery bank to your power inverter will be connected just the opposite.
The positive cable from your battery bank will be connected to the positive terminal on the last battery in your bank and the negative cable will be connected to the negative terminal on the first battery in your battery bank (Closest to the charge controller).
The ground wiring will attach to the same negative battery terminal where the negative power inverter cable is attached. It’s best to run that cable to a grounding rod obviously outside your home.
Pictured above is my battery bank prior to adding a fifth battery and purchasing a cabinet to put them in.
If you place your battery bank inside an enclosed cabinet or container, make sure that the batteries get proper ventilation.
Note: Do not let your batteries fall below 11.9 volts as to keep them from discharging too much which could possibly damaging them.
When choosing your power inverter, I would recommend purchasing at least a 3000 Watt (6000 watt peak) Pure Sine Wave inverter. The pure sine wave inverters along with the MPPT charge controller will provide a much more stable current for running sensitive electronics and appliances.
Unfortunately, like the MPPT charge controller, the pure sine wave power inverters are more expensive, but again, you’ll thank yourself later.
Do your research and read reviews on all of the components. I haven’t had any trouble from the one I use at my home (pictured above).
Volt / Amp Meters and Fuses
There are all kinds of other things you can attach to your system such as meters and fuses. I have a simple volt meter attached to my battery bank to make it easier to read the voltage of the battery bank. I simply disconnect the cables from the solar panels if there is a thunderstorm coming as to not take the chance on frying my entire system.
There are plenty of different types of systems out there from all inclusive, to pieced together the way I built my system. I like my system because I can purchase the components a few at a time, and I can expand the system as needed very easily.
Plugging in your refrigerator
Once you’ve completed your system, watch your voltage either on your meter or on your charge controller if you have a meter built into the controller. During the charging phase, you will see your voltage reach upwards of 14.5 volts. This is normal and the voltage will level out around 13.5 volts during the day.
On your first attempt at this, you will be a bit nervous, so do it when your bank has a good charge coming in from the panels. I highly recommend doing this at least around noon or so after a few hours of sun.
Turn your ice maker off (ice trays work just fine) and turn the settings of your refrigerator and freezer down. I turn mine to about “two” and it still works just fine. Once the sun goes down and you’re totally running off the battery bank, limit opening and closing the freezer or refrigerator. This is where common sense comes in. During the day, with continuous power coming in, you can use it normally.
Before unplugging your refrigerator, wait for the current cycle of your fridge to complete itself so you’re not interrupting the cycle.
Next, unplug your fridge and using a low gauge extension cord (much thicker than your normal extension cords), plug your fridge into one end of the cord. I used a 25 foot cord that is professional grade. Common cheap thin extension cords are NOT good for this purpose as they do not transmit the power from your inverter as well. Spend the money on a good extension cord. Also, the closer your battery bank is to your fridge, the better.
Turn your power inverter on and check the voltage. The display on my home inverter tells me the available voltage of the battery bank, but the inverter at my bug out location displays the voltage of the battery bank and the optimal voltage to run a device.
Once your inverter is on and your voltage is up to speed, plug the extension cord into the inverter. This is where the magic happens. Even if your fridge is not currently running, you will see your voltage drop a bit. This is normal and if you have enough battery power, you’ll see it level out. Mine levels out around 12.5 volts. This will last several minutes.
When your fridge compressor comes on, you’ll see the voltage come back up. Not sure why and perhaps someone out there can explain why, but I’ve only seen this huge draw that one time after plugging the fridge into the inverter. After that, the compressor coming on barely drops the voltage at all. After that initial draw, even over night, I only see the voltage drop approximately .2 volts mean if the voltage level of the battery bank is 13.5 volts, it only drops to 13.3 or so.
In the morning, my voltage usually reads around 12.6 volts dropping only to 12.4 volts during operation.
As long as your voltage doesn’t drop below 11.9 volts, you’re good to go.