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.
-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.
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)
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
The Function of a Battery in a Generator?
As you may be aware, batteries work by double conversion of energy through electrochemical processes. This involves the conversion of electrical energy to chemical energy during charging and from chemical energy to electrical during the discharge process. This is achieved by the use of two electrodes of different metals and a liquid electrolyte that acts as an ionic medium connecting both the electrodes and allowing the transfer of electrons between them.
In a portable generator, the battery carries out the following main functions:
- To provide power to the starter motors of the generators equipped with an electric start feature.
- To power the generator control panel, engine controls like automatic choke, oil level, and pressure, idle control, solid-state ignition, etc.
Most large generators have an additional 12V stator winding in the main alternator with a full wave bridge rectifier and a battery with an engine block and frame acting as the ground return. The circuit for this arrangement is shown below.
In smaller engines, the power to the engine controls and the battery is sometimes provided by the flywheel alternator. Permanent magnets are placed or cast into the flywheel rim. These magnets get linked with the stator windings of the flywheel alternator to generate an intermittent output as the alternator usually has only a single pair of windings. Usually, a capacitor acts as the voltage regulator for the system. The diagram for this arrangement is given below.
A full or half wave rectifier converts this output to DC. At 3600 rpm engine speed, you can expect 13.5 V DC at the battery terminals. Otherwise, you must carry out the rectifier’s multimeter resistance tests.
Powering Starter Motors
The power arrangement for battery charging has been discussed in the previous section. When the key to start the engine is turned slightly to the “ON” position, the engine controls receive power supply from the battery. When you turn the ignition key to the “start position,” a solenoid closes the contact that actuates a plunger which pushes out the pinion against a return spring pressure, making it engage with the flywheel gear.
This movement of the plunger closes a contact that connects the battery power to the starter motor. As discussed later, the starter motor requires a burst of power from the battery to crank start the engine. This is because the motor is designed to generate high torque at low speed or low torque at high speed, depending on whether the system uses a direct drive or gear reduction system.
The gear reduction arrangement differs from the direct one in that it has one or more gears between the starter motor shaft and the engine, with different gear reduction ratios to generate sufficiently high torque to crank the engine. A direct-driven starter motor will be much larger in size.
Once the engine picks up speed, there is a chance that the flywheel will start driving the starter motor. At a flywheel speed of about 300 rpm, with a gear ratio of 15:1, the starter motor speed will be 4500 rpm. The drive mechanism should never be allowed to drive the starter motor. To avoid this, a one-way clutch, called the overrunning clutch, is deployed between the pinion and the starter motor shaft and allows engagement in one direction only, slipping in the other to disengage the starter motor.
The below video explains the entire process with animation.
Powering Engine Controls
As shown in one of the above diagrams, the battery provides power to various engine controls like automatic choke, oil level, and pressure, idle control, solid-state ignition, etc.
What type of battery is in a generator?
Most generators use a standard lead acid battery for their functioning. The lead acid battery has been around for over 100 years, and its applications continue to grow. They are finding use in electrical and hybrid vehicles to provide the required energy for vehicle starting, lighting, and engine ignition. They are available in sizes ranging from a few AH (ampere-hours) to 10,000 AH ratings.
Their high electrical turnaround efficiency of about 75 to 80% makes them an ideal choice for these applications. They are available in all sizes and designs around the world at a very low cost. These batteries have reasonably good low and high-temperature performance. A lead acid cell has an open circuit voltage of 2V, which is higher than any other type of battery. The individual cell components can be recycled.
Common disadvantages of Lead Acid Batteries
On the flip side, they have a low cycle life, which we will discuss later. In addition, they have a low energy density, are difficult to manufacture in very small sizes, emit hydrogen gas which is a very explosive gas, are prone to thermal runaway if the batteries all the chargers are not properly designed, and they can’t be stored in discharge condition for long due to sulfation or irreversible polarization of electrodes.
Different Types of Lead Acid Batteries.
Lead acid batteries are commonly available in two forms – the conventional and the maintenance-free design. The latest maintenance-free versions’ latest designs are also called Valve-regulated lead acid batteries (VRLA). You don’t need to add/replace any electrolyte to these types of batteries.
The conventional design, sometimes referred to as the flooded type or ventilated lead-acid (VLA) design, contains large quantities of electrolytes. They have a small ventilated access by means of renewable plugs that allows you to measure the specific gravity and the state of charge of the cells. They emit large amounts of gasses, hence must be placed in a vented area with adequate care for circulation. In addition, the internal reactions reduce water levels in the battery. Hence distilled water has to be periodically added.
But, VRLA changed that by carrying only a limited amount of electrolyte in the form of a gel or absorbed in a separator (absorbent glass mat). The internal reactions maintain an equilibrium, such that the electrolyte is consumed and regenerated without actually consuming it unless you disturb the equilibrium by charging the batteries at higher voltages.
In case of excess pressure build-up in the cells of the set value, the valve opens and releases the internal gasses.
Ignition Batteries
Ignition batteries are a category within the types discussed above, with the difference that they are specifically designed for automotive or similar applications.
These types of batteries deliver a large value of current in a short amount of time (as required during the starting of an engine), as against those suited for long-duration low current applications.
Temperature and Lead Acid Batteries
The temperature has a huge impact on the performance of the lead acid batteries. High temperatures enhance the chemical reaction rate, increasing the battery’s instantaneous capacity but reducing its life. The lead acid batteries are designed to provide their full capacity at 25°C. Every 10°C increase in the operating temperature reduces the life span by half.
Reduction in outside temperature during winter reduces its capacity. A lead acid battery can provide only 65% of its nominal capacity at.20°C. The batteries should be charged at higher voltage and the charging current at lower temperatures. Similarly, you need to reduce the charging current (C-10) to 75% at higher temperatures.
How long does a generator battery last?
Many manufacturers specify the life of their batteries in a number of years. These are very misleading statements as what is usually specified is the design life, which is under the lab conditions where all the required parameters are maintained at optimal values, and the battery is just subjected to float charge without any load.
In actual practice, the life of the battery mainly depends on the depth of discharge (DOD) and the number of cycles the batteries are subjected to with this DOD value.
Consider a battery charged at 100%. It is then connected to a load and discharges to 20% of its nominal charge. The depth of discharge is then said to be 80%. The more DOD a battery encounters in service, the lesser the number of such cycles it can withstand and the lower its life span will be. One cycle constitutes a battery discharging to a particular DOD value and then getting charged back to its 100% capacity.
A typical battery can withstand 5000 cycles at 10% DOD, 2500 cycles at 20% DOD, 1200 cycles at 50% DOD, and 700 cycles at 80% DOD. If the battery is subjected to two 80% DOD cycles a day, its lifespan will be only one year. The presence of excessive temperatures can reduce it further.
When should I replace my generator battery?
The lifespan of your generator’s battery is determined by the condition of the unit. Cranking the engine repeatedly discharges the battery many times. Temperatures can range from freezing in the winter to more than 40 degrees in the summer. Proper charging is crucial to maximize battery life. Most newer generators come with built-in chargers, but older units may need a portable charger. Check the battery voltage with a multimeter to ensure that it’s between 12 volts and 12.6 volts. If the voltage level is below 12 volts, it’s time to replace the battery. The battery’s ability to supply the DC electrical part of the generator’s engine will suffer if it’s not recharged properly.
Generally, a standard generator battery should be replaced every two to three years. Nevertheless, many customers wait until the generator stops starting. This causes a host of problems, including interruptions of work and a decrease in the health of patients. An expired battery can easily be linked to such a problem. If you have a problem with your generator, we recommend that you get it checked by a professional.
How do you charge a generator battery?
In order for your generator to start, you must charge the battery. If the battery is dead, it will not be able to function as intended. The charger must be installed correctly to ensure that the battery will be charged at the proper rate and voltage. If it is not installed correctly, you will end up running out of juice faster. The charger should also be checked for proper fluid levels. If any of these are not present, you will have to use a different charger or purchase a new one.
A good Smart charger plugs directly into the AC outlet on your generator and connects the positive and negative battery terminals. A good Smart charger will also come with charging cables. Victron Blue IP65 Smart Charger is an excellent charger for generator batteries, and includes a charging cable. Other top-quality battery chargers are available from leading manufacturers. You should also be able to find the type of charger you need by searching for the product.
How many volts is a generator battery?
If you’re concerned about the health of your generator’s battery, it’s easy to find out how much power the unit has left with a simple voltmeter test. Batteries in generators are crucial components of their function. Without them, the generator will fail to operate, or may even become corroded. With a voltmeter, you can check if the battery has lost its charge, or whether it’s only partially charged.
Start by placing the voltmeter across the battery. Make sure the meter’s reading matches the rating of the generator. If it matches, the generator is functioning properly. Not, the voltage should be less. If the voltmeter reads more than 12.6 volts, there’s something wrong.
How To Keep Generator Battery Charged
Power generators with remote and electric start feature built-in lead-acid or lithium starting batteries, which are required for cranking the internal combustion engine and for powering remote start electronics while the unit is in standby mode.
For a generator to be as reliable as possible, it is very important that its battery is fully charged and ready to be used at the moment’s notice. However, some people wonder how to charge the generator’s battery.
Published: December 22, 2022.
Generator Battery Charger
First of all, power generators come with detailed Owner’s Guide/Manuals and explanations on how to maintain the power generator and how to store it over a longer period of time. if You have a power generator, but You never read the Owner’s Guide, do yourself a favor and read it.
Onboard Battery and Onboard Battery Charger
Every power generator featuring electric and remote start also features an onboard cranking battery. these batteries are mostly lead-acid batteries, but some newer power generators feature lithium starting batteries.
As soon as the engine has started, the onboard battery charger (part of the generator‘s electric/electronic system) starts to recharge the battery and keep it fully charged.
So, if You use your power generator regularly, on a daily or at least weekly basis, your battery will practically always be fully recharged.
Power Generator Battery Types
Most power generators feature 12V batteries with a nominal capacity in the 5-20Ah range.
As said before, most power generators feature lead-acid onboard batteries, which are relatively heavy, but they tolerate vibrations very well, can be easily charged, and are rather cheap.
Lead-acid batteries can be flooded/wet, AGM (Absorbent Glass Mat), and Gel-Cell batteries.
When used regularly, lead-acid batteries can last for a long time. But, when the unit is not used for a longer period of time, the battery must be recharged at least every 1-3 months, depending on the temperature and the exact battery model.
When being recharged using external battery chargers, lead-acid batteries should be charged using 0.1C-0.15C charging currents.
Lithium batteries are mostly Lithium Iron Phosphate (LiFePO4) starting batteries, which are not cheap when compared with similar lead-acid batteries, but they tolerate vibrations and mechanical impacts rather well, they are rather lightweight and must be charged using dedicated lithium battery chargers.
Lithium starting batteries feature a relatively low self-discharge rate and should be recharged every 2-6 months, depending on the model, using dedicated lithium battery chargers or charging modes.
When being recharged using external battery chargers, lithium batteries can be recharged using 0.1C-1.0C charging current, with 0.333-0.5C charging currents being often recommended.
Battery Chargers and Maintainers
When the power generators are stored for a longer period of time, their batteries are disconnected in order to prevent any parasite load from discharging the batteries.
However, all batteries feature a certain self-discharge rate; lead-acid batteries usually have a faster self-discharge rate than lithium batteries.
Thus, when being stored, generator batteries should be recharged fully and then should be connected to the automatic battery maintainers, which will keep the batteries fully charged during the storage.
The good thing is that modern, microprocessor-controlled automatic battery chargers are often designed as battery maintainers, allowing the users to store the power generator, disconnect the battery from the power generator, and connect it to the automatic battery charger/maintainer, which will first recharge the battery completely and then keep the battery fully recharged during storage.
Note: some power generators even have an additional automatic battery charger/maintainer. If not, 0.75. 2.0 Amps battery chargers/maintainers are fairly cheap and can be easily found in local hardware stores or can be ordered from online shops.
Long Story Short: In order to keep the generator battery fully charged, crank the power generator regularly and let it recharge the battery. If the power generator is stored, using a dedicated battery charger/maintainer will keep the battery fully charged and ready for the next use.
Again, power generators come with Owner’s Guides/Manuals describing maintenance procedures, including how to keep the batteries fully charged even when the generators are not going to be used for a longer time.