Inverter Backup. Some Facts

My Inverter is not giving sufficient backup”. This is the most common complaint raised against the home inverter system. We expect maximum backup time from the inverter system with a tubular battery, but unfortunately we get half or less backup time than we expect. What is the reason for that? Before blaming the inverter, let us see what is happening.


The back bone of the Inverter system is the battery. We use a high current tubular battery to give a maintenance free performance. The charge in the battery is used to convert DC to AC by the inverter. Measure of charge is Coulomb and each electron carries 1.602 e- 19 coulomb charge. As a rule, when 1 amps current passes through a conductor in 1 second, it uses 1 coulomb charge

So charge Q = It

If 1 amps current flows through the conductor in 1 hour, 3600 coulomb charge will be utilized.
The amount of charge in the battery is represented in Amps hour (Ah). That is Amps times Hour. It is the amount of charge present in the battery. But Amps hours cannot be used to measure the charge level, since the voltage changes during discharge. So the measure of charge is Watts Hours. Watt hour can be calculated by multiplying the nominal voltage with the battery capacity in Amps hours.

E = C x Vg. where C is the capacity of the battery in Ah and Vg is the discharge rate.

Charge requirement of the load

The following equation tells you, how much battery charge is required for your load.
First find out the capacity of the battery. If ‘X amps’ current is drawn by the load in ‘t hours’, then the capacity of the battery.

C = Xt

Suppose the load is drawing 120 mA current in 24 hours, then the capacity of the battery should be

C = 0.12A x 24 = 2.88 Ah

It is not a good practice to discharge the battery completely till the load shut off. Stop running the load, if the battery charge reduces to 20%.

Battery capacity

If the load takes 120 mA current in 1 hour, maximum capacity of the battery should be 0.12A x 24 = 2.88 Ah. Best method to keep the charge/discharge cycles perfect is to stop discharging the battery till it maintains 20% charge. Hence to retain 20% charge, the capacity of the battery should be

C / 0.8

If the battery requires 2.88 Ah in one hour, then to keep 20% charge in it, the capacity of the battery should be

2.88Ah / 0.8 = 3.6Ah.

Discharge Rate

Lead acid batteries have few Amps hour if the discharge rate is fast. Generally, the lead acid battery is rated for 20 hours discharge rate provided the discharge rate is slow. At high discharge rate, the capacity of the battery drops steeply. Suppose the battery is 10 Ah and its discharge rate is 1C. One hour discharge of the battery at the rate of 1C (10 Amps in 1 hour), the capacity reduces to 5 Ah in one hour. So the following tips will guide you to keep a steady discharge rate of the battery.

Suppose you want to run a load at 20 Amps for 1hour. Then the capacity of the battery should be

C = It = 20A x 1 Hour = 20Ah.

Keep discharge rate to maximum 80%. Then the battery capacity should be

20Ah / 0.8 = 25 Ah

So a 25 Ah battery can give 20 Amps current for 1 hour to run the load.

But it is better to drain the battery to 50% only then,

25 Ah / 0.5 = 50 Ah.

Hence as a rule of thumb, it is better to use a 50Ah battery to run the load at 20 Amps per Hour to keep 50% charge in the battery.

Suppose the load is not drawing 20 Amps continuously in 1 hour. During the first second, it draws 20 Amps and then 100 mA during the remaining period. So the average current drawn by the load is

20A x 1/ 3600 + 0.1 / 3600 = 0.1044 A

3600 is the total seconds in 1 hour.

In short, if the load is not drawing the charge in a steady manner, the capacity of the battery will be increased.

How to calculate the charge?

It is difficult to measure the current drawing by the load at different times. The easy way is to consider the power rating (Watts) of the load. Suppose the power rating of the load is 250 watts and is drawing current from the inverter system for 5 hours.

Then, its Watts hour is Watts x Hour = 250 x 5 = 1250 Watts hour.

Consider the efficiency of the inverter as 85 %( no inverter is 100% efficient).

So 1250 / 0.85 = 1470 watts hour
So the load has 1470 watts hour instead of 1250 watts hour.

Then calculate the capacity of the battery

As you know, Watt is Amps x Volt
So if the Watt hour is divided by Voltage of the battery, you will get the Amps hour

Watt hour / Volt = Amps hour

1470 / 12 = 122.5 Ah

Thus to run 1470 watts load, minimum capacity of the battery should be 125Ah to run the load for 5 hours. As already stated, it is better to use a 150 Ah battery to keep discharge cycle 50%.

How to select an Inverter

Total load to be connected = 500 watts
Power factor = 0.8 (all inverters have a power factor between 0.6 to 0.8)
Inverter VA = 500 / 0.8 = 625 VA
So select 800 VA inverter to run 500 Watts load

How to select the battery

Backup time = Watt / Battery voltage x Hours

500 / 12 x 3Hr = 125 Ah
12 volt tubular battery has a terminal voltage of 14.8 volts in fully charged condition. Usually the inverter has cutoff facility to protect battery from deep discharge. Most of the inverters are set for 80 % (Retaining charge) cutoff voltage. That is after 20% discharge, inverter will shut off.
Inverter cutoff voltage = 14.8 x 0.8 = 11.84 volts
Watt hour = watt x hour = 500 watts x 3 hours = 1500 watt hours
Ah of battery = watt hour / volt = 1500 / 11 = 126 Ah.

In short, an 800 VA inverter with 126 Ah battery can power 500 watts load for 3 hours.



Source: - http://www.electroschematics.com/5730/inverter-backup-some-facts/
Continue reading...

Inverters-D.I.Y.The Facts you need to know

Do you need an Inverter? Then you need to read this through.

An Inverter is a key piece of equipment in your wind or solar power setup, even if you are just planning to run a Tv from your Camper or Caravan,to powering up your home . Get the right Inverter for the right job.Get the facts here.

.An Inverter, simply put, is an electronic box that makes house hold electricity for everyday items. It converts power from;eg; car Batteries, Wind Turbines, or Solar Panels, then turns it into normal household power.BUT BEWARE YOU CANT JUST USE ANY INVERTER.READ ON TO FIND OUT WHY.
New NEW DIY Grid Tie Inverters Just Plug and play..

Why are there different types of Inverters? What do they do and how they work? I will attempt to guide you through the different types of Inverter that are available today..it is a very important piece of equipment in your wind or solar installation, so it is important that you get the right Inverter for the job, or the setup you are running. Inverters can be expensive and there is a good reason for this as I will explain later.There is a lot more to the Inverter than you might think, thats why it is important that you buy the right one.Here you will find Inverters for sale for as little as $30 right up to $3500.00. There are Inverters that can be used for running anything, and there are Inverters that cannot be used for LED lighting,TVs,some PCs and other sensitive electronics.

Inverters Explained

The hows and the why's and the dont's.

The Inverter takes the power from the batteries and then turns it into your household AC current, normally 120volts AC or 240 AC and this is what your house needs to run all your everyday appliances.
The Inverter in most cases will need to take power from Batteries as these give a steady flow of power ,In most cases you cant run an inverter directly from your turbine or solar pannels as the power flowing from them is not stable or constant.Ie the sun goes in ,the wind drops.As I said not always the case as some grid tie inverters can ,and I will explain more in depth later. So for this type of setup you need to make sure your Inverter has the right voltage for your setup, either 12volts 24/36/48. This is your input voltage from your batteries. Then make sure you have the correct output voltage, either 120 volts or 240. The next important bit is the power output that you need.

To do a whole average house you will need between 4000watt and 5000watt continuous power not peak. If you just want to run the lights and you are using low energy bulbs, and maybe a TV and stereo and PC then you may be OK with something around a 1000 watt. These figures are just a guide though. Speak with your local electrician and tell him what you want and he will give you a better idea as to the size you will need.
There is one more thing you need to be very careful about and that is do you want clean or dirty electricity? What i mean here is that there are 2 types of electricity that Inverters can produce.
Pure Energy of the type that you get from the electric company or the grid.this is known as a Pure sine wave Inverter.

Its clean and you can run any appliance's safely even sensitive equipment.

Then we have Modified sine wave ,this is dirty power, you can use this to power a lot of things that don't have sensitive electronics.Kettles for example Fridges, Cookers,Pumps,Fryers,Hot Plates. You CANNOT run LED lighting on these Inverters as they over heat and die within a couple of hours. You have to be careful with some TVs and PCs as they don't like it either, but i have heard that a lot of people use them for this with no problems, but I like to be safe rather than sorry.

Type 1 Grid Tie Inverters.

For those who want to keep things simple.

Grid Tie Inverters are great for those that want to keep things simple. You don't need a set of Batteries for these Inverters. Although these are the most expensive they still work out well as you don't have to fork out for those expensive batteries. one thing though you need to remember is that if you have a grid tie system when the power goes off that's it , no power. On some of the newer models you just attach the power from your Solar panels /Wind turbine, and then plug it into a normal mains socket somewhere in your house, simple. However these Grid Tie Inverters are not allowed in some places so you will need to check with the relevant authorities in the area you live. This is because when you run them they match the supply exactly to the electricity that you are receiving,so when your system is producing power it makes your electric meter run backwards or slows it down. This is called Backward metering. Personally i think this system is the way to go as anyone can install it ,its that simple. As the inverter gets bigger though you may find that you will have to get a qualified electrician to install it. So if you are at work all day and you turn off all your appliances the meter would go backwards reducing your electric bill. Important Updates on this article below .
Typical grid Tie setup

D.I.Y. Grid Tie Inverters

Simple Plug and play directly to the Grid .Without the huge expense.

Lets say you want to connect to the Grid but only have a couple of pannels , and perhaps a small budget , you maybe want something that can be expanded when funds allow , you want something that is not to technical and easy to install.

what would be the cheapest way to achieve this? Well good news because there are new Inverters on the market that we call plug and play , prices have really dropped Just over £200 will get you all the above . They are great grid tie Inverters that will connect you directly to the grid. Very simple to install, very cost effective , very reliable. So whats involved ? Well not a lot really ,its just a matter of connecting the solar pannels to the inverter and then plugging the inverter into a normal household wall socket, how easy is that? There a GREAT peice of kit I know because I have used a few different types of inverter and one came out tops by a long way .You will need one that is MCS Approved so its no problem with the electric companys . It has Island protection so if the power goes off,it cuts out automatically ,so no nasty shocks for anyone working on grid .Its a great environmently friendly way to get yourself connected to the grid. It has two multicontact {MC4} DC terminals for super easy plug and play instalation. The all come with a communication port so that you can monitor them remotely .It has a very wide input range that makes it a very good flexible system. In all its a great Inverter for small scale solar power systems, and you can just add to as you can afford it .

Does it have any downsides?

Well not really, but I found one, you cant use it for the goverment feed in tarifs .

They also make the same Inverters specially designed for Wind Turbines.

In all if you want idependance, your on a budget ,or just starting out then these Inverters are a great start..You dont need expensive Batterys, less maintenance ,lower costs .

Just a tip for some of you. When my batterys are fully charged my solar voltage regulator stops charging the batterys and diverts the power directly to the grid tie Inverter automatically. I also got a couple of extra pannels and connected them directly to the inverter, so we do all washing and heating of hot water etc during the day to take full advantage of the extra power. I would recomend this system to anyone just starting out, its so easy to do anyone can do it ,but you still have the peace of mind that at the end of the day if all fails you still have that connection to mains power.

eBay Inverters for sale new and secondhand bargains. - The new D.I.Y plug and play Grid Tie Inverter

I have found some great bargains and often start my search here . I have bought Wind Turbines solar pannels and lots more.
Be carefull buying used and ask if it is in good working order.Dont be afraid buying good second hand equipment ,you can save yourself a fortune and often get good advice from the seller .
This Inverter listed below is great value and its just PLUG and PLAY.Great piece of Kit

Source: - http://steve1717lm.hubpages.com/hub/Inverters-power-inverter
Continue reading...
Subscribe to: Posts (Atom)