My intention with this site is to take the reader step by step, behind the scenes of this project - turning what was once a porch into a tiny home. This is a project that I've been planning for 20 years and now that I'm retired, I'm tackling.
We don't really intend to live at the Shack full time at this point. The Shack is off the grid and we bring our own water - digging a well with the permits and everything is pretty expensive and for a week at a time there's no reason for a well.
This page isn't designed to be a primer on battery bank design or in depth battery issues. There are plenty of sites on the web that provide that information. This is about how we set up our battery bank.
If you plan on building an off grid power system, there is a book you need to read called “Lessons in Electric Circuits, Volume 1 – DC” which will teach you about off grid power systems. You need this for low voltage wiring and learning how to do it safely.
Deep Cycle Batteries
Learn more about the system used at the Shack here.
We use good old flooded cell deep cycle 6 volt batteries connected in series/parallel for our power when the genny isn't running. No AGM, sealed or Lithium. Lithium is great but the initial cost is far, far too high as of this writing. I have a strong dislike for sealed batteries. There is no way to access the electrolyte or fill the cells.
A flooded cell battery (and all other batteries) don't contain any electricity. They contain a fluid and a metal that have the chemical potential for creating electricity. No battery holds electricity. They hold the potential to produce electricity through a chemical reaction.
If you're wondering what exactly a deep cycle battery is, the name says it all. They're designed to go through a charge/discharge cycle deeply. A deep cycle is designed to deliver amperage at a slower rate over a long period of time.
Flooded batteries have individual cells that produce 2 volts each. A 12 volt battery has 6 cells. A 6 volt battery has 3. Typically, a 6 volt deep cycle battery cells are more robust than a 12 volt battery.
The battery in your internal combustion engine uses a starter battery which is designed to produce a high output for short periods. A deep cycle battery is designed to put out a lower output for longer periods. So, a starter battery isn't designed to be discharged by 80% where a deep cycle battery can handle that sort of discharge.
Points to ponder:
- When a battery is discharged, it will develop what is called "sulfation."
- Sulfation is a buildup on the lead plates inside the battery.
- The less you discharge a battery before recharging it, the less sulfation you'll have.
- Obviously, the less you discharge a battery before recharging it, the less stress on the battery and the longer it will last.
- There are chemicals that can prevent sulfation.
- A flooded deep cycle battery needs to be "equalized" from time to time to balance the capacity of the cells.
All flooded (that have fluid. There's also maintainence free and gel. This article is about flooded deep cycle batteries) batteries have lead plates in them. In a starter battery like in your vehicle, the plates are thinner than in a deep cycle battery.
Starter batteries won't make good deep cycle battery banks because they are physically not designed to be discharged totally over and over again wherein a deep cycle battery is.
Some rules of thumb: - Never totally discharge any battery, deep cycle or not.
- The more you discharge a battery, the more sulfates build up on the lead plates
- The more sulfate build up on the plates, the less powerful (how much of a charge) the battery will produce.
- Flooded batteries require maintainence (replace water, clean terminals, etc.).
About Battery Sizes and Capacity
There are batteries that are called "dual purpose" or trolling motor batteries. These are not deep cycle batteries. My original battery bank was made up of these batteries which lasted less than 2 years - even though I never had less than a 85% charge on them! They sulfate quickly and because the plates in them are porous, it's difficult to get rid of the calcification.
Amp hours (Ah) are the rating capacity available produced using chemical energy that's converted into electrical energy. Amp hours is rated by a set amount of power produced by a battery for a set amount of time. This is very important to keep in mind when you're powering devices with a deep cycle battery!
Lithium Batteries
If you've been thinking about off grid or even grid-tied power systems, you've probably heard about the Tesla Powerwall. The is basically a laptop battery on steroids.
A lot of people to like to tinker and engineer stuff make their own powerwalls using discarded laptop batteries. Enough people are doing it that laptop companies have stopped selling old or used up laptop batteries.
The biggest concern most homeowners have is how much an energy storage system will cost them. The total cost to install a lithium battery storage system could be anywhere from $7,000 to over $30,000.
Here's a YouTube video about building a powerwall.
As an example, if your battery is rated at 200 amp hours, the rated was developed by testing the battery over a set number of hours at a set rate of discharge, usually 20 hours. If you go over that rate of discharge (like the difference between an old style light bulb and an LED bulb), that 200 amp hours is reduced.
Where the battery discharges at a constant rate of current over a number of hours, this is referred to as the “C” rating. For example, many small batteries rate at the C20 rate, this means that they will deliver their amp hour capacity if discharging over 20 hours. The types of batteries in large stand alone power systems rate at C100 which means that they are designed to discharge over 100 hours or 4 days. This will give you a life span typically of about 15 years.
I have one deep cycle battery that I've been using since 2006. With proper care, a battery will last a long time!
3/21/21
The last time I created a diary post was in 2010. I had just finished production on the last episode of "This Old Shack", the show I starred in about alternative energy. I had, you see, succeeded in developing and using our off grid system.
