Inverter-sizing Calculator              Backup Time Calculator        Solar-panel-sizing calculator    

 

MORE ON INVERTERS

What  is an Inverter?
Inverter Installation
Inverter Capacity Selection
Battery Size Selection
Caring for Your Inverter
Inverter Prices
Inverter Advantages

 

What  is an Inverter?
Inverters essentially are electrical appliances that primarily convert DC voltage to AC voltage usable on our electric appliances.Their function is an opposite of what rectifiers  do,which convert AC voltage to DC voltage.Inverters come in various capacities and brands,from as low as 500VA to 100KVA and brands common around here include Mercury,Su-Kam,Genius,Bluegate,luminous,Genius and others.Most of these inverters are quite efficient,their durablility usually depends on how these quality brands are  installed and how well they are isolated from mains supply.Inverters do not produce electric energy on their own,thus every inverter uses a source of energy,mostly a battery bank or an array of solar panels.Most inverters that run from battery banks usually have inbuilt charging module which recharges the batteries at the availability of primary or generator power supply.Thus,an ideal inverter would ordinarily charge its batteries.An inverter-solar-panel system can also be connected such that the battery bank is charged by both the public power supply or generator and the solar panel array. A typical inverter connection is shown below.Top of Page

Inverter Installation
In installing your inverter system,we strongly recommend that the inverter output is strictly isolated from the mains supply in all ramifications and you don’t need to have cables run all over your house to achieve this.This will save you a lot of headache and have your inverter running for several years without any problems.It is a good idea for an expert/professional to do this for you,as you cannot afford to risk your investment.Most inveter problems we have corrected for our clients are as result of poor installation previously done.Before embarking on the installation of an inverter system as an alternative power solution, you need a good idea of

  1. What appliances to be powered and for what minimum length of time this would be required.This is  inverter capacity selection and the battery size selection.
  2.  Another specification to look for when buying your inverter is the wave output of the inverter. If you'll be powering any  equipment that is sensitive to square waves or modified sine waves like some hospital equipemnts, look for an inverter with a "perfect sine" wave output. However,these inverters are usually much more expensive and also waste some more power they should deliver to your appliances.Go for them only if they are absolutely necessary.

 Let us consider the inverter capacity selection and the battery size selection. Top of Page

Inverter Capacity Selection
The inverter capacity determines how  many appliances can be powered by the inverter. Most people use inverters to power small appliances that consume low power since the cost of inverter system goes geometrically high up as the load consumption increases.Usually,the bulk of the cost of an inverter system  is in the battery cost,which usually is more than 60% of the cost of the total system,but thankfully is the least susceptible to damage. In calculating the  total amount of power of all appliances that you want to run from the inverter,you must bear in mind that the starting power of devices that have electric motors, as well as some TVs, draw a higher power than their normal operating power when they first start up. This is called starting power and this information should also be listed on the appliance's label. Most inverters also have a peak rating, so make sure the inverter's peak rating is higher than the starting power of the device(s) you intend to power.

Summary of the steps

  1. Change all your high energy consuming appliances with low consuming ones
  2. Note the power rating in Watts of each of the appliances you must necessarily run on inverter ,usually on a label on the back.
  3. Sum all the power rating in Watts of all these appliances you must necessarily run on inverter.This is your Total Load.
  4. Enter this value of the Total Load in the Inverter Sizing Calculator
  5. Enter the Efficiency of the inverter you want to use and Battery Depth of Discharge(both values are usually between 70 to 90%).
  6. Click Submit to see the inverter capacity required in KVA.

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Example 1
 Assuming you have  2 ceiling fans, 1 TV,8 of 60W electric bulbs ,2 decoders and 2 DVD players.

First,you will certainly need to change all the 60W bulbs and replace them with 8W to 11W energy or LED bulbs which consume about 7times less power than the 60W bulbs.In short,try as much as possible to replace all appliances that consume so much poower with more efficient ones that work equally as good or better.

For the Ceiling fans: 100W * 2 = 200W     (each ceiling fan consumes about 100Watts)
For the TVs  : 100W*1   =100W                 (power consumption of TVs varies between 50Watts for small TVs to 400W for large plasma TVs,chcek the back of the TV or any appliance to see exact power rating .Note that LED TVs comsume less power than LCD TVs and far less than plasma TVs)

For the Energy bulbs: 10W * 8 =80W
For the decoders: 25W * 2         =50W
For the DVD players: 25W * 2         =50W

Total Power consumption= (200 + 100 + 80 + 50 + 50)W =480W
From the Inverter Sizing Calculator, the best option is 1.5KVA/24V with a backup time of 9.12 hours at full stipulated load and 22.45 hours at 50% load. However,since the difference in cost between a 1.5KVA/24VDC inverter is little compared to 2KVA/24VDC,therefore it may just be wise to go for a 2KVA/24VDC inverter system in case you may need to put more appliances on the inverter in the future.

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Example 2
Assuming you have  6 ceiling fans, 4 TVs, 20 of 10W energy bulbs ,4 decoders and 2 DVD players.

Total Power consumption = (100W * 6 ) +  (100W * 4) +  (10W * 20 )  + (25W *4) + (25W *2) = 1350W

From the inverter sizing calculator,the best option in terms of backup time and cost is 2.5KVA/36Volts with a back up time of 9.92 hours on 50% Load.Alternatively, a 3KVA/48V inverter system would also be good with a back up time of 14.41 hours on 50% Load, though this would be more expensive.
Note that you need to check the label on your appliances to know exactly their power rating in watts for calculating  the required inverter capacity.  Top of Page

 

Battery Size Selection
Bateries used in inverter systems are deep cycle batteries,which are designed for  long discharge cycles of up to 400 depending on the depth of discharge and most have life spans of 3 to 5 years depending on usage.Deep cycle batteries can actually last up to 10 years if they usually experience low depth of discharge before recharging.You can learn more about this on the battery page. The size of the battery bank determines how long your appliances can be powered by the inverter and this depends on the total loads/appliances running off the inverter.

Battery Banks

A 12V inverter with one 12V battery has a battery bank, n of one. With two batteries in parallel,it has a battery bank of two and so on. A 24v inverter with two 12V batteries in series has a battery bank of 1.With two batteries in series,connected in parallel to another two in series,the battery bank is 2. More battery bank means more power available. See diagram of battery banks below:

battery  bank

 

battery bank2

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An easy and  approximate formular most people use for calculating battery size is given as follows:
Battery Capacity(c) = Total Load(p) * Backup Time Required(t)  /[Inverter DC rated voltage(v) * depth of discharge(d) * efficiency of the inverter(e) ],e is usually between 0.70 to 0.95 and d is usually also between 0.70 to 0.95 because deep cycle batteries are never completely discharged when in use.

From above, c = p * t / [v * d * e]

However this formular does not take into account the very important Peukert’s effect resulting from battery  internal resistance and current.The higher the battery internal resistance, the higher the losses during charging and discharging, especially at higher currents. This means that the more power a battery delivers(discharges), the lower its capacity in ampere hours(AH). Conversely, if it is drained slower, the AH capacity is higher.In simple terms, a battery of 100AH would deliver 10Amps in 10 hours  and would be expected to deiver 20Amps in 5 hours ,but this is not so due to Peukert’s effect. It will actually deliver 20Amps for less than 5 hours due to more battery loss at this higher current. Top of Page

With consideration of Peukert’s effect,the accurate battery sizing formula for most deep cycle batteries have been used in our inverter sizing and backup time calculators.

 

 

You can register to learn more from our world class seminars and trainings.

 

Most inverters are ‘smart’ and will shut down once discharge depth of battery is within this 70% to 95% of battery capacity. Thus for a 200AH(Ampere Hour) deep cycle battery,actual available capacity is about 140AH to 190AH. Bear in mind that battery  life spans are measured in cycles, or how many times they can be discharged and recharged before they will no longer take a full charge.Depth of discharge (D.O.D.) of a battery has a major effect on its life span  - discharging only 80% of the total capacity of the battery will typically get you 25% more cycles than 100% discharges, and discharging to only 20% will make the battery last essentially ‘forever’. Most deep cylce batteries can survive up to 400 total discharges. Top of Page

 

 

Summary of the steps

  1. Note the efficiency and D.O.D of your inverter system.(efficiency and depth of discharge are usually between 70 to 90%)
  2. Note the inverter DC voltage rating(v) e.g  12V or 24V or 48V or 96V and so on.
  3. Sum the total loads(p) you will run on the inverter
  4. Choose the minimum hours/time(t) you want to run the loads on the inverter
  5. To determine the required battery size(c),apply the backup time calculator in reverse manner,which means you will keep increasing the no of batteries or size of battery or both, until you get close to the backup time you require.

Example 3

                                 

Assuming you want to have about 6 hours on your 1KVA/12V inverter while 1TV,2 fans and 6 light bulbs are turned on,then we have total load as 360W.

 

The 12V rating of the inverter means that you need 1 or 2 or 3 or 4 e.t.c of 12V battery. So you can keep increasing the number of batteries or the battery size or both.

 

Deep cycle batteries usually come in 50AmpH, 65AmpH, 100AmpH, 150AmpH,155AmpH, 200AmpH and 260AmpH.

 

From the Backup Time calculator, 1 of 260AmpH battery provides 7hours of backup time,

2 of 150AmpH battery provides 9.94hours of backup time

and 2 of 100AmpH battery provides 6.63hours of backup time

 

Thus you select any of the above with due cost considerations,perhaps 2 of 150AmpH battery

 

If  a load of 100W runs for 5hours on a battery,we would expect that a load of 50W would run for 10hours,but this is not so due to Peukert’s effect which is  related to the internal resistance  and current passing through a battery.In fact,the 50W load would run much longer than 10hours,say about 12 hours due to a lower internal battery power loss. Top of Page

 

Example 4

 

Assuming the TV in example 3 above is turned off as it is when we go to bed at night ,and if the 12V/260AH battery is at full charge, we would now have a total load of 260W and from the backup time calculator,we would have a back up time of 10.68hours compared to 7hours .Therefore shutting down the appliances you do not need could go a long way in increasing available backup time.

 

 

It is recommended,for best results to connect together only batteries of same model, ratings and capacity whether in series or in parallel.

 

We have realised that the arrangement of a 1 to 3KVA inverter  system is ideal for most small offices and homes where about 4 to 6 hours of public power supply is available daily for charging the batteries. In fact,somes homes/small offices where the people are so disciplined on the appliances turned on while running on inverter,a 1KVA inverter with 200AmpH battery have been quite adequate,thereby cutting down on the cost of  installing the system. Really,where public power supply outage does not last for up to 10 hours in a stretch,having an appropriately selected inverter would ensure there is 24hours power supply to your appliances.

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Example 5

 

For a 5KVA/96V inverter, with eight 12V/200AH Battery in series(in order to have the 96V rating of the inverter), and for a total load of 1000W, autonomy time or backup time is 21.29hours.

 

With one 1-horse power AC,one freezer,one Plasm TV and 6 ligth bulbs, Total Load = 746 + 250 + 480 + 6*15 =1566W. Therefore autonomy or backup time is 11.89hours.

 

Note
12V inverter needs only one 12V battery or more,but all in parallell.
24V inverter needs two 12V batteries in series or four or six or eight batteries and so on,all arranged in parallel of two in series.
48V inverter needs four batteries in series or eight or twelve or sixteen batteries and so on,all arranged in parallel of four in series.
And so  on….. But bear in mind that the more batteries you have in parallel,though you will have more backup time, but the system will also take a longer time to charge the batteries fully.
In all the selections above,we have ignored cable losses and other losses which are usually small compared to all the power components considered in the calculations. Top of Page

Caring for Your Inverter System
1. Ensure your inverter system like all electrical appliances, is not installed in a humid environment. In an aircoditioned environment,the aircondition must be set to dry mode.Keep your inverter system (with its batteries) in a dry,clean cool environment. Temperature of 20 to 30 degrees Celsius is recommended.Hot environments would cause your batteries to deliver more power but will have a shortened life span.
2. Ensure your inverter has enough room for free flow of air or ventilation.You need to allow a minimum of 10cm space from any object on all sides of the inverter.
3. Most failure of inverters are due to excessive spikes and surges from malfunctioning generators which are used to charge them.Ensure your generator is ouputing the right voltage of 200V to 230V and frequency of 50/60Hz.Never leave your inverter charging input on while turning on your generator.Turn your inverter charging switch on only after you have turned on all other appliances not connected on the inverter.
4. It is a protective practice for your inverter and all your electronic appliances to be turned off from the wall switch while turning on inductive appliances like fridge,freezers,pumps,industrial fans especially when you are on generator.Turn the inductive loads on first before you turn on the charging switch of your inverter and other appliances.
5. Never leave your batteries in a discharged or partially discharged state.The battery should be recharged as soon as possible after discharge.Failure to do this can drastically reduce your battery performance and life span irrecoverably.
6. Store your batteries in a fully charged state and well ventilated environment.If the batteries are stored for more than 6 months,they must be recharged,since batteries discharge themselves though at a very small rate,when not in use.

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Inverter Prices

Inverter prices  vary from manufacturer to manufacturer.Like we said earlier,perfect sine wave inverters are much more expensive than modified or square wave inverters. You need to go for pure sine wave inverters only when it is absolutely necessary.

Here below is the  price range of most common inverters in the market

SN

CAPACITY(KVA)

PRICE RANGE(N)
K=1000
M= 1000,000

1

1

30k to 50k

2

2

40k to 80k

3

3

70k to150k

4

5

210k to 300k

5

6

290k to 350k

6

7

400k to 460k

7

10

420k to 500k

8

15

1.2m to 1.3m

9

20

1.5m to 1.6m

10

30

1.7m to 2.0m

11

50

3.5m to 4.5m

 12

100

9m to10m

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Inverter Advantages
1. Maintenance free
2. A lot of convenience! Convenience!! Convenience!!
3. Depending on what you can afford and your energy needs,you could have electricity whenever you need it and this boosts productivity a great deal,whether at home or at the office.
4. You have a cleaner power to your expensive appliances devoid of electric spikes and surges from generators.
5. you learn the discipline of power conservation and a lot of savings.On 12 of 60W incandescent bulbs that run for about 12 hours every day,you save about N1,300 monthly ,N15,600 yearly by using energy saving bulbs and N468,000 in 30 years!
6. Generator fuel cost is drastically reduced if not entirely wiped off your budget.

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