Archive for the ‘Electrical’ Category

1.5KWp Solar Power Plant

April 22nd, 2013 3 comments

Another Solar Power Plant project @Mogappair, Chennai

This time, I have helped a friend of mine to setup up the power plant for his home.  He had given a requirement to run everything in his home except the heavy duty equipment like A/C, Microwave Oven, Water heater & Washing machine. While measuring the load requirements, he had a peak load of about 1.5KW and an average load of ~600W and at nights the load was <200W average.

This time, I wanted to get a simplified inverter solution that does not require and interaction per se for the end user. So, we have procured a 2KW ESU inverter from Emerson, which was priced as Rs 55000/-.This inverter model comes with an inbuilt 48V/35A MPPT controller and a unity PF 2KW power inverter.  So, for these models of Emerson 2KVA is 2KW as the PF is 1.

Although Emerson has a good track record of quality products, their service customer care is outsourced, who do not function very well. Also the delivery time for the inverter is 5-6 weeks, but on paper they say 4 weeks. For the Mogappair area, the service is handled by Sri Nandees Technologies, who technicians on call are pretty good and responsive.

As usual, we procured the batteries (4x180Ah) from Sharana batteries for Rs 54000. Since my last installation, the price of batteries went up by ~5% for all the battery brands.  And the panels (24v/250Wp x 6) were procured from Akshaya Solar @42/watt for Rs 63000 and the structures for planting the panels were also got from Akshaya Solar for additional ~Rs 10000. And for the electrical works and civil works, we spent another Rs 18000.  Overall, we have finished the entire project for Rs 200,000 all inclusive.

Thanks to our electrician Mr. Raja  & vendors (Mr. Raju @Akshaya Solar, Mr. Aruldass @Sharana batteries, Mr. Karthik @Sreenandees, Mr. Jayaraj @Emerson) who helped us see this project through.  Incidently, this is the only domestic installation in the 1.5KWp range in the entire Ambattur, Avadi, Mogappair, Padi, Anna Nagar range AFAIK. 🙂

1KWp Solar Power Plant

January 30th, 2013 22 comments

Phew! What a relief!

I have just finished installing a 1KWp solar power plant in my apartment.  It was an wonderful and tiring experience getting everything to work together, ofcourse with the help of several kind people who helped moving on with the work.  I think, my installation is the first domestic installation for a capacity >1KWp in my entire area, that is Thirumullaivoyil; may be the first in Ambattur + Avadi townships.  Whatever be it, I am very happy that I could get it up and running as per the plan.  The power plant can produce upto 4-5KWh everyday in winter+sunny and may be 5-6KWh in summer.  I have been able to attach everything in my home except for Fridge, Ovens, Water heater, A/C and washing machine.  Yeah! Mixie, Coffee Maker, Wet Grinder, Computers, Water purifier run in solar at my home!  I tried attaching Fridge to the unit, but the backup time in the nights drastically reduced.  By the way, the solar power supply is 24hours through out.  The secret is that the excess power produced in the day are backed up in huge batteries, so that the saved energy is dispensed through out the night for powering my bed room and other low power night utilities.

Things to procure for this DYI project:

  1. Solar Panels: There are several variety of panels available, but always choose polycrystalline (aka multi-crystalline) panels, as there are very efficiently within 30 degree deviation of sunlight inclination angle.  If you go for monocrystalline, they are efficient only when the sun is right on top of them, so you are forced to install a solar tracking device for an additional cost.  I had procured MNRE approved panels for Rs 46/watt including transportation and taxes from Akshayasolar.  My setup has 12V 150Wp x 6 and 100Wp x 2, put together 1100Wp of bright power.
  2. Inverter: There are several varieties of inverters available in the market. Solar Inverters are the ideal choice here, but for my specification I could not get a solar inverter within my budget.  Typically solar inverters are priced around Rs 30000 for a 1KW capacity.  So, I had decided to go to regular sine-wave inverters and convert that to a solar inverter myself.  To convert an inverter to a solar inverter, I had to get a solar charge controller and fabricate a control circuitry.  I have bought a 24V, 1.4KVA Amaron Inverter for Rs 7000, with 2 years warranty.  A typical inverter has a power-factor of 0.7 to 0.8, so I could load upto 1000W comfortably without frying the inverter.
  3. Batteries: This is the most critical part of any ESU (Energy Storage Unit), where the power is stored during surplus and released when solar incoming reduces.  On the contrary, there are EEU (Energy Export Unit), which directly converts the energy derived by the solar panels into useful power for consumption or resale back to the grid.  TANGEDCO does not buy from installations less than 1MWp, so ESU is my only option.  So storing the power, the popular choice is Exide Solar Tubular batteries.  But, I chose Sharana Batteries because their manufacturing unit is in Ambattur Industrial Estate, and their service guarantee was better than what Exide offered.  While buying batteries, one should be very careful about the capacity rating of the batteries.  By capacity, the common misnomer is the AH rating.  AH rating tells the current limits of a battery, but the capacity rating is mentioned as Cxx (eg: C10, C20, etc).  Typically, a 180AH/C20 battery is same as the 150AH/C10 battery or 100AH/C5.  In C20 rating, if the drain current should be 9A, the battery would supply energy for 20 hours.  The same battery would serve for 8.33 hours only if the drain current is 18A, but you would expect it to serve for 10 hours.  Likewise, the same battery would serve only for 2.77 hours, if the drain current was 36A where you would expect a backup time of 5 hours (see here the capacity has halfed!!).  I have purchased 2x180AH @C20 tall tubular batteries from Sharana with 2 years warranty for Rs 26000.
  4. Charge Controller: There are two types of charge controllers available namely PWM, MPPT. Solar panels, although rated as 12V, they generate voltages upto 21.6V (open-circuit).  They are optimal at around 16.4-17.4V, which is called the maximum power point.  In order to leverage the maximum power from the controller, I used MPPT charge controllers.  For 1.1KW at 24V, the Imax is 50A, but assuming 80% efficiency for panels, 40A MPPT is sufficient.  I got 40A 24V controller from Adaptek India, Adyar for Rs 13600 with 3 years warranty.
  5. Structure Fabrication: This is the messy part of the entire exercise as readymade units were not available.  Since I will be using 8 panels in total and I had to use just 100 sq.ft of space on the roof, I planned to build a two row beam structure to take the load.  The weight of a panel is roughly 10kg, to 40kgs per structure is the setting.  The design shall have a rectangular frame of size 10’x3′ made out of 1.5″ L section of steel.  The rectangular section shall be supported by two 2″x1″ C channel steel of height 1.5′, which I call the legs.  The legs shall rest on a 8″x8″ 6mm plate, which in turn shall be secured to the roof with four 10mm anchor-flush bolts.  I could get raw material and fabrication done in Mannurpet, Ambattur for Rs 8000.  The total weight of steel I had installed is about 50Kg to keep the 70Kg of panel structure load secured.

Solar Power Plant Sizing chart is here.

More to continue..

Understanding a Fan Motor

August 28th, 2012 4 comments
Have you opened up a fan motor before?  It is a simple brush less A/C induction motor, where the armature remains as the stator.  Look at the exploded image of a typical fan motor. The important parts are C: Ball Bearing, D: Stator, E: Armature/Stator, G: Capacitor, H: Connector. 

Also, look at the other image that shows the cross section of a motor.  You would notice that there are 4 wires coming out the motor.  Two pairs of wire, with one pair as the starting coil and the another pair for the running coil.  In general, all single phases induction motors have two coils (starting coil, running coil).  Using a capacitor, an artificial phase difference is created between the fields created by the starting and running coils.  The phase difference triggers movement of the armature.  When the armature reaches a particular speed, using a centrifugal switch, the connection to the starting coil is disconnected and the entire fans runs with just one coil.

Although there are four terminals, you would notice 3 terminals are emitted out, with the starting and running coils connected back-to-back.  Let’s say S1,S2 are the terminals of starting coil and R1,R2 are the terminals of the running coil.  To get 3 terminals out of the fan motor, S2 and R2 are shorted. 

Now, you just see 3 terminals; how do you find which terminal is starting, which one is ending and which one is shorted?  Easy.  Using a simple multimeter, you can find it out.

Let’s say you see terminals A, B, C. Our aim is to find which one of these are S1, R1, S2R2.  Now, let’s measure the resistance between A-B, call it X.  Likewise measure the resistance B-C as Y and A-C as Z.  If you would notice X < Y < Z, you would also notice that Z = Y+X.  Which mean, A-C is action A-B+B-C, that’s why the resistance was additive, also the terminal B is S2R2.  The challenge now is to find what is A and what is C.   As we’d notice A-B=X < B-C=Y, we can confirm that terminal A is starting coil S1 and terminal C is running coil R1.  The reasoning is that; starting coil resistance will be less than running coil resistance.

Hope, this article helped.

Calculating Ampere-Hour AH requirement

May 20th, 2012 No comments
We are in a sorry state of erratic and long power cuts, due to shortage of power production by the nation against the increasing load conditions.  To add fuel to this fire, a wholesome of abled people putting their hard earned money on to power backup solutions, where they store the power during power availability and consume the stored power during outage.  On the whole, this looks simple and elegant, but this is not doing any good to the state, which shed’s power at different locations to balance against shortage in power production.  So theoretically, in a place where a family consumed 1kW per hour, would consume 2.5kW per hour during power availability and generate 1kW during power outage.  Yes, you are right. The equation is not balanced, because atleast 30-50% of power is wasted during the backup-retrieve cycle.

Ok, coming to the point.  What is the solution? Go for harvesting solar power, availability in abundance and omni present.  And most interestingly, rationed to perfection based on the amount of un-shadowed free space a family has.  I will just limit this article to calculating the battery provisioning when you go for a solar-inverter solution.  Let’s say I want to have a power backup for 2 hours and my load is 1kW. What would be the ideal inverter solution for this load condition?

Normal Power 1000 Watts
Power Factor 80 %
Inverter Rating 1000W/80% = 1250 VA
Number of Backup Hours 2 Hours
Energy To be Stored 1000×2=2000Wh
Inverter Battery Voltage 24VDC
Battery Amp-Hours 2000/24=83AH
Add @30% AH Margin 83*1.3=108AH~100AH

So, for this configuration you need a 1250VA Inverter with 2x12v 100Ah battery bank.  Let me explain the calculation,

  1. Power Factor: In AC (alternating current), Power = Voltage x Current x Power factor unlike in DC, Wattage = Voltage x Current.  Power factor is measure as the cosine of the phase angle between voltage waveform and current waveform.  For home use, the power factor will be 0>PF<1.  When PF is lower, the efficiency of the system suffers a lot.
  2. Battery Voltage: For 1250VA inverter system, the choice of battery bank is 24V instead of 12V.  The rationale for this choice is to limit the current from the battery to the inverter unit.  If you use a 12V battery bank, at full load there will be a current of 1250/12=104A flowing from the battery to the inverter.  You may have noticed the thickness of the battery wire be very high.  Despite that the power loss on those wires when the current is 100A, would be much higher than it is with 50A on a 24V system.  For a 24V system, the peak current shall be 1250/24=52A.  Also, at 100A, with 1m cable between battery and inverter, the impedance should be 0.00001 ohms.
  3. AH Margin: Although battery AH rating considers absolutely draining of the battery, we will not be able to do that for normal SMF battery.  Meaning, we should not discharge below 10V and likewise should not charge beyond 13.6V per 12V battery.  In order for the AH rating to work, we have to apply atleast 20-30% margin.

Solar Panel contd.

March 26th, 2012 14 comments







Installation of additional 130Wp is in place now to make the power plant worth 300Wp.  The new panel added has a spec of 17Vmp against the 16.4Vpm of the 170Wp panel group.  So eventually I may be losing some power.  I am using 10sqmm copper cable to reduce the transmission losses.  I had measured the impedance of the cable to 1mΩ. So at 20A, I will be losing about 0.4W only.  But the cost of this wire is around 70Rs/m.  I am able to produce about 221W during the mid day, and about 170W around 10AM.  Upon little bit of investigation, it is found that the solar panels shell out less power at increased temperature.  It is also said that at 60-70°C, the efficiency is around 70%, which is matching with my measurements.  So, thinking about a water cooling solution; basically augmenting a solar water heating solution with the solar panel to establish double benefits.  Every day with the solar panels is a day of new learning and I am enjoying it. 🙂

Temperature Monitoring Device

January 1st, 2012 No comments

LM35 Temperature Sensor

The System.

The monitor.

The mixed water line:

The hot water line:

The cold water line:

monitor opened up:

the atmega8 microcontroller

the lcd unit:


inside the monitor:

The AVR code.

const int COLD = 0, HOT = 1, MIXED = 2, CALIBRATE = 3;
const int PWMPORT = 5;

float SCALE = 5000.0/1024.0; // 10 bit resolution for ADC
const float LM35SCALE = 10; // 10mV per Centigrade

#include <LiquidCrystal.h>

LiquidCrystal lcd(13, 12, 11, 10, 9, 8 );

byte smiley[8] = {

float Calibrate( void )
  // write 5v to PWM port
  analogWrite(PWMPORT, 255);

  // read the 5v analog value in the calibrate port
  int val = analogRead(CALIBRATE);

  // read again the 5v analog value in the calibrate port
  val = analogRead(CALIBRATE);

  // whatever digital value we read is the range of output that we would get for 5v input.
  // so, set the scale appropriately.
  SCALE = 5000.0/(float)val;
  return SCALE;

void setup()
  lcd.createChar(0, smiley);
  float scale = Calibrate();

int Temp( int inADC )
  float lm35volts = (float)inADC * SCALE;
  float temp = lm35volts/LM35SCALE;
  return (int)temp;

int ReadData( int port )
  int data = -1;
  for ( int i = 0; i < 3; ++i )
    data = analogRead( port );
  return data;

void loop()
  int cold = ReadData( COLD );
  int hot = ReadData( HOT );
  int mixed= ReadData( MIXED );
  int cold_temp = Temp(cold);
  int hot_temp = Temp(hot);
  int mixed_temp = Temp(mixed);

  lcd.print( “C=” );
  lcd.print( cold_temp );
  lcd.print( ” H=” );
  lcd.print( hot_temp );
  lcd.print( “Mixed=” );
  lcd.print( mixed_temp );

AWG Vs Current Flow Capacity

September 13th, 2011 No comments

This write up is taken from

The AWG – American Wire Gauge – is used as a standard method of denoting wire diameter, measuring the diameter of the conductor (the bare wire) with the insulation removed. AWG is sometimes also known as Brown and Sharpe (B&S) Wire Gauge.

The AWG table below is for a single, solid, round conductor. Because of the small gaps between the strands in a stranded wire, a stranded wire with the same current-carrying capacity and electrical resistance as a solid wire, always have a slightly larger overall diameter. The higher the number – the thinner the wire. Typical household wiring is AWG number 12 or 14. For telephone wires there are common with AWG 22, 24, or 26.

AWG Diameter
40 0.08 . 0.0050 3420
39 0.09 . 0.0064 2700
38 0.10 0.0040 0.0078 2190
37 0.11 0.0045 0.0095 1810
36 0.13 0.005 0.013 1300
35 0.14 0.0056 0.015 1120
34 0.16 0.0063 0.020 844
33 0.18 0.0071 0.026 676
32 0.20 0.008 0.031 547
30 0.25 0.01 0.049 351
28 0.33 0.013 0.08 232.0
27 0.36 0.018 0.096 178
26 0.41 0.016 0.13 137
25 0.45 0.018 0.16 108
24 0.51 0.02 0.20 87.5
22 0.64 0.025 0.33 51.7
20 0.81 0.032 0.50 34.1
18 1.02 0.04 0.82 21.9
16 1.29 0.051 1.3 13.0
14 1.63 0.064 2.0 8.54
13 1.80 0.072 2.6 6.76
12 2.05 0.081 3.3 5.4
10 2.59 0.10 5.26 3.4
8 3.25 0.13 8.30 2.2
6 4.115 0.17 13.30 1.5
4 5.189 0.20 21.15 0.8
2 6.543 0.26 33.62 0.5
1 7.348 0.29 42.41 0.4
0 8.252 0.33 53.49 0.31
00 (2/0) 9.266 0.37 67.43 0.25
000 (3/0) 10.40 0.41 85.01 0.2
0000 (4/0) 11.684 0.46 107.22 0.16

The higher the gauge number, the smaller the diameter, and the thinner the wire.  Because of less electrical resistance a thick wire will carry more current with less voltage drop than a thin wire. For a long distance it may be necessary to increase the wire diameter – reducing the gauge – to limit the voltage drop.

American Wire Gauge (AWG)
Current (amps)
5 10 15 20 25 30 40 50 60 70
15 16 12 10 10 8 8 6 6 4 4
20 14 12 10 8 8 6 6 4 4 4
25 14 10 8 8 6 6 4 4 2 2
30 12 10 8 6 6 4 4 2 2 2
40 12 8 6 6 4 4 2 2 1 1/0
50 10 8 6 4 4 2 2 1 1/0 1/0
60 10 6 6 4 2 2 1 1/0 2/0 2/0
70 10 6 4 2 2 2 1/0 2/0 2/0 3/0
80 8 6 4 2 2 1 1/0 2/0 3/0 3/0
90 8 4 4 2 1 1/0 2/0 3/0 3/0 4/0
Standard Wire Gauge (SWG)

SWG inches mm
7/0 0.500 12.700
6/0 0.464 11.786
5/0 0.432 10.973
4/0 0.400 10.160
3/0 0.372 9.449
2/0 0.348 8.839
1/0 0.324 8.236
1 0.300 7.620
2 0.276 7.010
3 0.252 6.401
4 0.232 5.893
5 0.212 5.385
6 0.192 4.877
7 0.176 4.470
8 0.160 4.064
9 0.144 3.658
10 0.128 3.251
11 0.116 2.946
12 0.104 2.642
13 0.092 2.337
14 0.080 2.032
15 0.072 1.829
16 0.064 1.626
17 0.056 1.422
18 0.048 1.219
19 0.040 1.016
20 0.036 0.914
21 0.032 0.813
22 0.028 0.711
23 0.024 0.610
24 0.022 0.559
25 0.020 0.508
26 0.018 0.457
27 0.0164 0.417
28 0.0148 0.376
29 0.0136 0.345
30 0.0124 0.315
31 0.0116 0.295
32 0.0108 0.274
33 0.0100 0.254
34 0.0092 0.234
35 0.0084 0.213
36 0.0076 0.193
37 0.0068 0.173
38 0.006 0.152
39 0.0052 0.132
40 0.0048 0.122
41 0.0044 0.112
42 0.004 0.102
43 0.0036 0.091
44 0.0032 0.081
45 0.0028 0.071
46 0.0024 0.061
47 0.002 0.051
48 0.0016 0.041
49 0.0012 0.030
50 0.001 0.025

Solar Battery Charger Cutoff Circuit

August 7th, 2011 4 comments

Using very few components, I have built a solar battery charger cutoff circuitry that would enable automatic cutoff of battery charging when the potential across the battery terminals reached a voltage level chosen by the preset setting in the circuit.  Medium power transistor is operated in Cutoff mode most of the time, so the quotient current of the circuit is fairly low in the order of few mA.  It should be noted that the Vopen-circuit of the solar panel is few volts higher than the voltage when the panel is connected across a load.  So, don’t adjust the preset without connecting the battery. When the circuit is turned on, the battery is directly connected with the solar panel, and hence the voltage perceived by the voltage divider is the load voltage.  When the voltage across the load goes beyond the set point, zener conducts to turn the transistor on, which would pull the relay down and break the charging circuit.  After the battery is disconnected, the voltage perceived by the potential divider circuit is the open-circuit voltage of the panel, which eventually creates a latch effect for the battery charger off condition.  The relay will be ON, till there is sun light and when in the dusk, the input voltage should drop below the threshold voltage to turn off the transistor.

There is a flaw in this circuit. 🙂

When the sun light drops, the relay turns off as the transistor is turned off.  But now, the battery potential will be again available across the potential divider circuit.   There is a potential, oscillation condition here!!

Solar Panel Structure Design

July 17th, 2011 No comments

This was the original design of the solar panel mounting structure.  Later, I had simplified the design and fabricated them at the local metal fabricators.  Please click on the images to open the big sized drawing.

Pole that would hold the weight of a heavy solar panel over a base structure (not shown).

Hinge design that would transfer the weight from the base structure to the pole, with one degree of freedom.

சூரிய ஒளி மின்சாரம் (Solar Electricity)

July 10th, 2011 5 comments

The completed Solar Panel mount structure.

Bottom side view of the panel.  The Panel is fully resting on the Iron frame constructed in the nearby fabrication shop based on my design.

This is my assistant Aakash, the boy next door.  He has been my aide for all the mechanical and automobile works.

The base frame of 30″ x 21″ with the center piece at 15″.

The base frame from perspective projection.  The center piece is a 5″ x 2″ 10mm plate welded at the center.  The holes are 10mm diameter drilled at 1″ and 3″ from the top and centered.

The main load bearing vertical pole measuring approx 2m and 2″ diameter.  The base plate is 6″ in horizontal length and 6″ on vertical depths.  The holes are 1/2″ and drilled at 3″ and 5″.

This is the solar panel bought from Akshaya Solar Pvt Ltd, AP.  The panel is rated 12v 70w and of dimension 1200mm x 21″ and weighting approximately 5kg.

The swing arm connecting the base frame and vertical pole.  The holes are 10 mm diameter and punched at 1″ and 3″ from the top.  The bottom pipe is 2.25″ diameter and about 5″ long.  The cross bolt is 0.5″ diameter.  This swing arm mounts on the pole on one side and attached to the base frame on the other side.  The base frame is pivoted on the top hole with swing setting using one of the 3 bottom holes.  The positions are provided to compensate of uttrayanam (north bound sun movement) and dakshanayanam (south bound sun’s movement).

The bottom link of the vertical pole.  This U link attaches to the parapet wall, which is 6″ is width and the cross bolts pass through the wall to lock the vertical plates.  The horizontal and the vertical plates are 6″x2″ and 10mm in thickness.

These are the bolts used.  The 1″ (4 nos) bolts are used to secure the solar panel on the base frame.  The 1.5″ bolts are used to secure the base frame to the swing arm.  The 4″ bolt is used to secure the swing arm to the vertical pole and the 8″ bolts are the bolts to secure the entire unit on the parapet wall by passing through the wall.