DIY Size & Build a Battery Power Backup Generator W/ 12V Deep Cycle Batteries

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Introduction: DIY Size & Build a Battery Power Backup Generator W/ 12V Deep Cycle Batteries

***NOTE: Be careful when working with batteries and electricity. Do not short batteries. Use insulated tools. Follow all safety rules when working with electricity.***

Be prepared before the next time the power goes out with a standby battery powered generator. Build your own battery backup system for your home or business. A battery backup system allows you to power your essentials when the grid is down. Using sealed AGM deep cycle batteries, this system is safe for indoor use; you can install this system in your closet, in the corner of your office, or make it portable by using a 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 battery and inverter, and how to put the system together.

You will need:

-1 or more sealed deep cycle batteries

-1 DC to AC power inverter

-1 Smart Charger/Maintainer

-Inverter cables and battery link cables (if using more then one battery)

For this system I used the following:
-2 VMAX SLR155 12-Volt 155Ah AGM batteries connected in parallel (vmaxtanks.com)

-1 12V DC to AC 2000 Watt Inverter (online or from a hardware store)

-1 Vmaxtanks BC1220a 12V 20A 7-Stage smart charger

-1 Set of 2 gauge 6' 100% copper inverter cables (4Ga would have also worked, be sure to check the ratings of the inverter cables you buy)

-1 Pair of 4 Gauge 12" 100% copper link cables

Step 1: Choose a Power Inverter

When choosing an inverter, pick one with a wattage rating higher then what your devices use; add up the wattage of the devices you would like to power. Your appliances will usually have a label which indicate the input wattage or amps. Wattage is simply volts times amps. For example if your laptop charger uses 80 Watts, and your phone charger uses 20W, you need an inverter rated for at least 150W. Blenders typically use 300W, so to power your blender, laptop and charge your phone you would need a 500W inverter. It is always better to oversize your inverter. I chose to use a 2000W inverter.

Step 2: Choose a Battery

A deep cycle battery is recommended since deep cycle batteries can be cycled many times. If you use a flooded car battery it will be damaged by being deeply discharged. I chose to use AGM deep cycle batteries by VMAXTANKS, since they can be cycled many times and are sealed. AGM batteries are also maintenance free and safe for indoor use. By adding up the wattage of the devices you want to power, you can figure out what size battery bank you will need. Take the watts, ex. 400W, and multiply by how many hours you want to power the 400W load.

To power a 400W load for 5 hours:

400W x 5 hours = 2,000 Watt Hours

For 2,000WH, choose a battery bank which provides at least 4000WH(4kWH) to keep your batteries from going below 50% capacity (this will help your batteries achieve more cycles over time).

In my battery bank I used two VMAX SLR155 batteries, rated at 2.1kWH each, for a total of 4.2kWh, or 4,200 Watt Hours. Deep Cycle batteries can be cycled past 50%, but keeping your batteries above 50% will give you many more charge cycles. High quality batteries will give you more cycles, Vmaxtanks batteries have very high cycle counts and are military grade. Always fully recharge deep cycle batteries after every use. Below are several different vmaxtanks battery options:

SLR60: 0.8 kWH (800 Watt Hours)

SLR100: 1.35kWH (1,350WH)

SLR125: 1.7kWH (1,700WH)

SLR200: 2.66kWH (2,660WH)

XTR8D-350: 4.7kWH (4,700WH)

Step 3: Choose a Battery Charger

You will need a smart charger compatible with your batteries. For deep cycle batteries you will need a multistage "smart" charger/maintainer. The battery charger should be matched to fully charge batteries in ~15 hours or less.

I used a Vmaxtanks 12V 20A 7-Stage charger(BC1220a), which is capable of charging and maintaining my battery bank. Vmaxtanks chargers can be left on the batteries all the time, so your batteries will always stay charged and ready to go.

Step 4: Connecting It All Together; See Images for Steps

For my system I used the following:

-2 VMAX SLR155 12-Volt 155Ah AGM batteries connected in parallel (vmaxtanks.com)

-1 12V DC to AC 2000 Watt Inverter (online or from a hardware store)

-1 Set of 2 gauge 6' 100% copper inverter cables (4Ga would have also worked, be sure to check the ratings of the inverter cables you buy)

-1 Pair of 4 Gauge 12" 100% copper link cables

-1 Vmaxtanks BC1220a 12V 20A 7-Stage smart charger

Step 5: (OPTIONAL) Use a Charger/inverter With a Built in Auto Transfer Switch.

If you have a server, printer, computer station, or any other device you do not want to shut off when the power goes out, use an inverter which features a built in charger and an automatic transfer witch. The Charger/Inverter will plug into an AC outlet and keep the batteries charged. You can plug in your appliances into the inverter to draw AC power, when the power is out the inverter will automatically switch to battery power. This is very useful if you are running a server/printer/computers/medical equipment etc. and can not afford to have it unexpectedly shut down in the middle of a task.

A Charger/Inverter will also provide a cleaner looking setup since the charger and inverter will be combined into one unit.

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    29 Comments

    1
    FreonS
    FreonS

    Question 1 year ago

    I don't see anything on the most important part: How do I connect it to my home wiring? It really isn't very useful without that information.

    0
    WayneFriesen
    WayneFriesen

    Answer 1 year ago

    This unit is meant to power devices that you plug into the inverter. You do not wire it into your home in any way. It is a stand-alone power supply during an outage.

    0
    chefjake07
    chefjake07

    Reply 3 months ago

    But, to keep batteries charged and maintained 24/7 It would be connected to home grid power wouldn't it be?
    The charger?

    0
    johnallen1952
    johnallen1952

    Question 5 months ago on Step 1

    Hi, I like your idea of a Battery source for power with an inverter.
    I'd like to use a Honda whisper quiet generator 2000watt to keep the batteries charged but would like the generator to start when batteries need to be charged and shut off when full?
    do you have any ideas? how to make that work?

    0
    jakecoffee1503
    jakecoffee1503

    Answer 3 months ago

    Look at Power Converter/Chargers. Used mostly with solar. It does exactly what u want. Detects when to open or shut the flow of power depending on the charge level. How to incorporate that to the generator, I'm unsure. But it's a good place to start.

    0
    Ranger420
    Ranger420

    Question 9 months ago on Introduction

    Would you possibly be able to help me with something. I am moving to the middle of nowhere and will only have generator power. I want to have enough power to run TV, lights and fan at night when generator is off. What would be the best set up for this?

    So far I have
    1 X 120 deep cycle
    1x 100 lead acid
    Thinking of buying Victron 15amp Battery Charger
    And 1000watt inverter
    6gauge inverter cables

    Would this be fine and what else would you recommend?

    Also would it be advisable to put the battery and inverter in a small room away from the house in case of a fire? It averages 28-45 degrees Celsius where I will be.

    Kind regards,
    Matt

    0
    mickeyrosenberg
    mickeyrosenberg

    Question 10 months ago on Introduction

    How would I figure Battery and inverter needs for "survival "circuits in urban area when grid goes down (usually short, but one winter it took 40 hours) : Refrig and Natural Gas furnace with blower and electric ignition. Each of those has a surge need of 600 watts, but only 200 watts continuous. Also each of those will only run approx 25-35% of the time.
    If they both kick on at the same time is that an issue re the surge ?
    The GoalZero Yeti 3000X Lithium can be recharged via cigarette lighter from an automobile running outside. Can this system do same, while delivering power to those circuits ? Would that decrease the # of batteries needed ? Can this system be hardwired into a sub panel/breaker box with those two circuits and an ATS ? Thanks Mikcey

    0
    kcknoeber
    kcknoeber

    Question 3 years ago on Step 1

    I apologize if this is a stupid question. I do a lot of off road drivng. Reinflating my tires is always an ordeal and I don't want to shell out money for a small gas generator if I could build one of these that can power a compressor, and perhaps a few other items. A) is this a ridiculous idea? B) would the general guidelines here be the bulk of what I need to follow regarding capacity and sizing?

    0
    sp4rkn
    sp4rkn

    Answer 11 months ago

    A good on-vehicle solution would be to add another battery with an isolator. That way your vehicle can charge the battery, but your starting battery won't drain while using the extra battery. If you use the battery up, you'll still be able to to start the vehicle. Also, it would be a good idea to carry a super capacitor jump starter. It has the unique ability to charge from a DEAD battery (unusable to your car but usable to the jump starter) and jump start the vehicle that has the dead battery (it can self jump a dead vehicle). The pack is very small and fits in less space than your tire inflator. It's piece of mind and can make you the hero when 4x4ing with buddies.

    0
    rittersdad
    rittersdad

    Answer 1 year ago

    I don't know if kcknoeber solved this problem on his own, but it might be worth mentioning that are a lot of 12v automotive tire inflators on the market. If he already has an AC compressor, just use a 12v to 120v power converter connected to his vehicle and inflate away! Just be sure to match load to the ability of the converters' ability to deliver power.

    1
    1topgun357
    1topgun357

    Question 11 months ago

    Thank you for all of this great Information. I want to build a battery power system for my motorhome for a few electronics (TV, Computer, Camera System). I want to leave the power system plugged into one of the 110 outlets in the RV to charge it. The outlets in my RV don’t have power unless I am using my generator, or I am connected to a power source. Therefore, my plan is when I plug the motorhome up at home, or a RV Park, or run my generator, it would automatically charge my power system. Do you have any recommendations on a inverter charger, with a transfer switch? I don’t want to hardwire it, but I keep reading that pure sine power is better. Also, how do you feel about one large battery instead of using two small ones? Thank you.

    0
    Meke71
    Meke71

    Question 1 year ago

    Can this setup be used outside to run lights on?

    0
    kd4gcf
    kd4gcf

    Answer 1 year ago

    Yes but be sure to keep water from being introduced into the system.

    0
    Meke71
    Meke71

    Question 1 year ago on Step 3

    How would you introduce solar panels into this charging?

    0
    kd4gcf
    kd4gcf

    Answer 1 year ago

    Instead of the AC battery charger you will need a Charge Controller. The output of the controller will be connected the same way as the AC charger shown. When you look up Solar Charge Controller you should see at least 2 connection points. One set where the solar panels are attached and one set that attaches to the Battery bank. You would then attach inverter as shown. As you study you will learn you need to size your solar panel current output large enough to maintain your batteries, with this in mind your controller has to be able to handle the current supplied from your panels. I know that last sentence sound complicated but it is not and you will discover that as you design your system.

    0
    kd4gcf
    kd4gcf

    Answer 1 year ago

    Instead of the AC battery charger you will need a Charge Controller. The output of the controller will be connected the same way as the AC charger shown. When you look up Solar Charge Controller you should see at least 2 connection points. One set where the solar panels are attached and one set that attaches to the Battery bank. You would then attach inverter as shown. As you study you will learn you need to size your solar panel current output large enough to maintain your batteries, with this in mind your controller has to be able to handle the current supplied from your panels. I know that last sentence sound complicated but it is not and you will discover that as you design your system.

    0
    EmaD9
    EmaD9

    Question 1 year ago on Step 5

    Hi, maybe this will sound stupid but since I am new to this ... I am wondering how do you plug a power strip into a portable power bank? I am thinking of using this off grid, for appliances being connected to this kind of electricity trough power strip. Where do I plug it? And, thank you so much for writing this article.

    0
    rittersdad
    rittersdad

    Answer 1 year ago

    Almost all power convertors have standard 120v/10 or 20 amp receptacles built into them. Refer to the photo at the end of the article for example. Just plug your power strip in and go. Be sure not to overload the convertor though.

    0
    mcgyverdad
    mcgyverdad

    Question 1 year ago on Step 3

    If we wanted to use solar panels to keep up with daily kilowatt usage what would it take in terms of panels?