Our System Overview: The Batteries

Probably the thing we spend the most time thinking about and maintaining is our battery bank.  They are absolutely critical to the system.  Without we wouldn’t be able to have power at night, which in this modern world is pretty important right? 

Our beloved battery bank, Oh Storer Of The Juice.

Our Bank Specs
We have 16 Rolls Surette batteries, which are 6V 460 Amp-hour deep cycle batteries.  Now if none of that makes any sense to you, just note that they are 6V and deep cycle.  Deep cycle is what separates these batteries from the battery in your car.  The battery in your car is designed to generate a lot of amps (power) in a very short period of time and then immediately begin to be recharged.    They use short powerful bursts of energy to start your car.

Deep cycle batteries, as the name implies, are intended to be cycled down much lower and more slowly.  These batteries are used to power more even loads that slowly take the charge down, and then slow charges that fill them back up.  For instance it might take 3 days for us to run our batteries all the way day and then three days for the sun to fill them all the way back up.

Wiring
The wiring of batteries is critical.  The first thing you’ll notice in the picture above is the size of the wire.  The DC, or direct current power, that flows in and out of these batteries is sort of like water.  The larger the pipe the more flow you’ll get.  So we use big fat wire to help the flow.

How the batteries are wired together is also important.  You may have noticed they are arranged in a neat grid.  Each vertical column is wired in series, or positive to negative, so that voltage adds up.  This means that our 6V batteries in a series of 4 makes a 24V system, which is how our inverter and charge controller are programmed.  The columns are then wired to each other in parallel, or positive to positive and negative to negative, so that the amperage adds up to boost the system.  Voltage adds in series, amperage in parallel.

Related Terms
When dealing with deep cycle batteries you’ll hear the following terms, which are often referred to in terms of a three stage charging system:

• Bulk Charge: this occurs when the batteries are low and are accepting charge at a specified rate to fill them up.  It’s the most common type of charge, just imagine we’re filling up 16 buckets at the same time.  Our bulk charge is 28.8 Volts.
• Absorption Charge: this occurs after bulk charge is achieved, its sort of a topping off.  Imagine now that we’re making sure that all the buckets have the same amount in them so where adding water slowly and carefully.  We run the absorption for about 15 minutes.
• Float Charge: float is probably the hardest concept to relate to.  Basically after absorption and bulk are reached, the charge drops down a little to a stable (but still full) charge.  I like to think of this as taking a little back out of  the buckets, so that you don’t spill them.  Dropping the charge down a little prevents excess gassing from the batteries, which can be dangerous.  Our float charge is about 26.8 volts.

Next week we’ll talk about battery maintenance.

Have questions about our system, our settings, or anything else.  Leave us a comment or send us an email!