inverter and battery selection

HI friends !!
  Summer is on the way and now we hurry in installing inverter in our houses but before installing it please read this so that it may be helpful to you.

HOW TO CALCULATE THE RATING OF INVERTER AND BATTERY

Step1:

Calculate the total power to be run on the inverter. Note that the running power is indicated on the appliances but the starting power is more than the indicated power up to 20-30% for small appliances and 70-80% for heavy loads like refrigerator, CRT television sets which lasts for few milliseconds so while calculating the total power add the extra power i.e., starting power.

Basic Wattage of house hold appliances:

Fan	50-75W
CFL	18-25W
Computer	100-150W
Laptop	50-75W
Refrigerator	160-250W
Tube light	40-55W

Step 2:

Make the difference between VA and Watts. Some inverters are indicated in watts and some are indicated with VA rating which is a trick played by the companies. The companies which are indicating the power in watts mostly doesn’t mention about the efficiency of the inverter.

                Now let us know the outline difference between VA and Watts. Watts indicate the real power and VA indicate the apparent power. In general power generating and stabilizing equipment use VA rating and power consuming products use Watts for power rating. Watts is the real power supplied or drawn by the equipment. 

 Power in Watts   =   Power in VA   -   Losses

                                                (OR)

Power in Watts   =  Power in VA   x   Efficiency of the equipment

The ratio of power in watts to the power in VA is termed as power factor

I suggest that if the rating (Watts or VA ) is not specified on the equipment please don’t buy it

Step 3:

                Inverter or home UPS which one to buy??????

Let us see the outline difference Home Ups and inverter. The main vital difference is the switching delay. When the main power is off the backup power switching delay for the inverter is 100-500milliseconds and for the UPS the switching delay is 3-5 milliseconds. The switching delay of the inverter is not recommended for electronic equipment like modems, routers, printers etc but the switching delay of the home UPS can uninterruptedly run this electronic equipment also.

Step 4:

    In today’s market we can get three types of inverters for household use:

(a)    Square wave

(b)   Stepped square wave inverters

(c)    Pure sine wave

Digital inverters came into existence with higher efficiency which uses micro-controllers for monitoring and controlling

                In the above three inverters going for pure sine wave inerter is best choice but the cost would be slightly higher than the other two inverters. In case if you want to go for less cost then choose stepped square wave inverters. Actually the appliances we use daily are designed for the sine wave input but when the input is stepped square wave or square wave the appliances get heated which in turn decreases the life time of the appliance. The square wave will show more effect on the appliances than the stepped square wave.

Step 5:

Batteries:

                Choosing the correct rating of the batteries is one of the most vital thing for getting a good back-up time

NOTE:  “DO NOT USE AUTOMOTIVE BATTERIES”. They are high cycle batteries so they can be dangerous. “High Cycle Batteries “are designed for the discharge of high current for very short duration and they cannot be discharged more than 25% of their capacity

 Deep Cycle Batteries are commonly used for common applications which can discharge from 50-80% of their capacity. These deep cycle batteries are of two types for house hold

(a)Maintenance free

(b) Tubular batteries

(a) Maintenance free batteries are the flat plate batteries which cost more than the normal lead-acid batteries. The maximum life of this type of battery is 2-3 years. This battery should be used only where a person is unable to do maintenance.

(b) Tubular batteries are more complex in design and more efficient and cost more than the flat plate batteries. Choosing a good company battery is a good choice.

 The batteries are available in ratings varying from 100-180 AH (100,150,180)

·         Many companies recommend 12V batteries but as renewable sources like solar panels will come into existence in houses in a short period of time go for 24V batteries because solar panels are designed for 24V – 48V when solar panels are installed no need of changing anything we can directly connect to the existing system.

NOTE: Do not go for the local made batteries or the batteries given by the inverter company make a right decision by seeing the rating, company of the battery only go for branded batteries which are popular in market like EXIDE, AMARON etc

Warranty/Guarantee of the equipment i.e., Battery and inverter:

 Note the difference between warranty and guarantee. Service and repair but not replacement at any cost comes under warranty. Replacement of the product if there is any fault comes under guarantee. Some companies offer only warranty and some offer both warranty and guarantee in combination so for it.

CALCULATIONS:

Battery backup time (Hrs) = [Battery voltage (V) x Battery capacity (AH) x Efficiency of inverter]/ [load (watts)]

 Example:

Battery voltage (V)          = 24V

Battery capacity (AH)     = 150AH

Load (watts or VA if efficiency is given on the equipment)= 2 lamps of 40W each and one fan 75 watts

                                                                                           =(2*40)+75=155

                                                                    Starting power      =155W*starting power=(155*0.25)=38.75

                                                                         Total power       =155+38.75=198.75

Inverter efficiency (generally 85%) =0.85

·         If the efficiency is not indicated on the inverter take efficiency as 60% because most local made inverters are of 60% eff. Only

Backup time(Hrs)=[(24*150*0.85)/(198.75)]=15.3Hrs

·         But in practical the backup time maybe 10-30% less because of the surrounding temperature of the batteries and the load duration

·         If the battery is drained for a long time on full load the efficiency of the battery will deplete

Safety for user:

·         Earth leakage protection is must for home ups and inverter as there will be earth leakage if there is no earth leakage protection in the circuit we should arrange an ELCB generally rating of 30mA to safeguard the users from electrical shock

·         Voltage stabilizer which has high/low cut off should be used. If this stabilization is not inbuilt in the inverter then for high rating equipment like refrigerator stabilizer should be used to protect the appliance from voltage fluctuations.

Battery capacity:

 A 100Ah battery can supply 100A for one hour, 50A for 2hours, and 25A for 4 Hours by this we can understand that duration of the backup ascends or descends based upon the current drawn. If we increase the capacity of the battery the backup is increased.

I will provide a MS Excel spread sheet for calculation of the inverter and battery rating and backup time of the battery in a short period of time where we can add the appliances we run on the inverter

Hope this would help you

if you want select the types of solar panels and calculate the breakeven point for installing the solar panels at home please check my post @    renewelectricalenergy.blogspot.in

Thanks and regards,

D Surendra

Surendra216@hotmail.com

Surendra0216@gmail.com

your comments and suggestions are most welcome