DIY Home Battery Backup Generator in a Wooden Cabinet

A DIY battery generator will allow you and your family the ease and comfort of having backup electricity during a power outage. A backup generator can restore power to lights, refrigerators, cell phone chargers, medical devices, tablets and other gadgets while the power is out. This cabinet style generator system looks great at home, is easy to setup and allows for backup power during an outage. This system is also safe for indoor use; it can be installed in a closet, in a cabinet, or made portable by using a wheeled cart. By building your own battery backup system you can size it to your desired needs. We will go over how to choose the right size batteries and inverter, and how to put the system together.

In this example, we are using the following high quality components:

•(2) Vmax SLR125 AGM Solar batteries

•(1)1500 Watt Inverter/Charger

•(2) 9" 4 Gauge 100% Copper battery interconnect cables

•(1) 150 Amp Fuse

•(1) Cabinet

Step 1: Choosing an Inverter

You will need a DC to AC power inverter to convert the DC power from the 12 Volt batteries to AC power. For this DIY project we chose to use an inverter with a built in charger, this "Inverter Charger" will plug into an AC outlet and keep the batteries charged. Appliances can be plugged into the inverter to draw AC power when grid power is available, and when the power is out the inverter/charger will automatically switch from AC power to battery power. This is very useful if powering a server/printer/computers/medical equipment/fridge etc. and you can not afford to have a loss of power.

A Charger/Inverter will also provide a cleaner looking setup since the charger and inverter will be combined into one unit.(Uninterrupted Power Supply). For a more cost effective solution, use a smart charger along with a standard inverter instead of an Inverter/Charger.

When choosing an inverter, pick one with a wattage rating higher than what your devices use. Your appliances will have a label which indicates the power consumption. (If the Amperage draw is listed, wattage is calculated by multiplying volts and amps, 1 Amp at 120VAC=120 Watts). For example if your laptop charger uses 80 Watts, and your phone charger uses 20W, we need an inverter rated for at least 150W. Blenders typically use 300W, so to power a blender, laptop and charge a phone you would need an inverter rated for 500W or more. It is recommended to oversize the inverter, if your essential appliances consume 500W, a 750W inverter is recommended. For this DIY example we used a 1500 Watt Inverter Charger.

Step 2: Choosing a Battery

A sealed deep cycle AGM battery is recommended, AGM batteries can be cycled many times and are designed for this type of application. For this project we used high performance AGM batteries by VMAXTANKS, since they can be deep cycled many times, have an expected life span of 8 to 10 years in float service applications(~1,600 Cycles at 25% Depth of Discharge, ~1000 Cycles at 50% depth of discharge) and are safe for indoor use.

We can determine how many Watt Hours of energy you will need by adding the wattage of the devices we want to power and multiplying by how many hours we want to power the load.

A 400W load will consume about 2,000 Watt Hours in 5 hours: 400W x 5 hours = 2,000 Watt Hours. For 2,000 Watt Hours, choose a battery bank which provides at least 4000WH(4kWH) to keep the batteries from going below 50% capacity (this will help the batteries achieve more cycles over time).Vmax batteries feature military grade plates and are built tough to handle very demanding use, they can be cycled past 50% although keeping the batteries above 50% will result in longer lasting batteries.

Below are several different Vmax battery options:

SLR60: 0.8 kWH (800 Watt Hours)

SLR100: 1.35kWH (1,350WH)

SLR125: 1.7kWH (1,700WH)

SLR200: 2.66kWH (2,660WH)

For this project we will use two SLR125 batteries, for a total energy capacity of 3,400 Watt Hours (3.4kWh).

Step 3: Connecting Everything Together

Once you have the cabinet, batteries, fuse, inverter/charger and cables it is time to connect all your components. The two batteries need to be connected in parallel, essentially creating one large battery. To connect the two 12 Volt batteries in parallel, use the interconnect cables to connect the Positive terminal on battery #1 to the Positive terminal on battery #2, and the negative terminal on battery #1 to the negative terminal on battery #2. The inverter cables are connected to both batteries, the Positive inverter cable connects to the Positive terminal of one battery, and the Negative Inverter cable connects to the negative terminal of the second battery. Please read the instruction manual included with the inverter for a more detailed set of instructions on how to connect and set up the inverter. A fuse is also recommended, for a 1500W inverter a 150A fuse is suitable. After the inverter and batteries are wired, plug in the Inverter/Chargers power cord into an AC outlet. Allow the Inverter/Charger to fully charge the batteries before testing or using your battery backup generator. Your DIY home backup system is now complete!