சுதர்சன் சாந்தியப்பன் » Electrical

Calculating Ampere-Hour AH requirement

sudarsun — Sun, 20 May 2012 17:07:21 +0000

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	831.3=108AH~100AH*

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

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.
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.
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.

sudarsun — Mon, 26 Mar 2012 17:24:21 +0000

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

sudarsun — Sun, 01 Jan 2012 17:25:08 +0000

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:

theboard:

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] = {
  B00010,
  B00101,
  B00010,
  B00000,
  B00000,
  B00000,
  B00000,
};

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

  // read the 5v analog value in the calibrate port
  delay(500);
  int val = analogRead(CALIBRATE);

  // read again the 5v analog value in the calibrate port
  delay(100);
  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()
{
  pinMode(PWMPORT, OUTPUT);

  lcd.createChar(0, smiley);
  lcd.begin(16,2);

  lcd.setCursor(0,0);
  lcd.print(“Calibrating..”);
  float scale = Calibrate();
  lcd.setCursor(0,1);
  lcd.print(“Scale=”);
  lcd.print(scale);
  delay(1000);
}

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 );
    delay(100);
  }

  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.clear();

  lcd.print( “C=” );
  lcd.print( cold_temp );
  lcd.write(0);
  lcd.print(“C”);
  lcd.print( ” H=” );
  lcd.print( hot_temp );
  lcd.write(0);
  lcd.print(“C”);

  lcd.setCursor(0,1);
  lcd.print( “Mixed=” );
  lcd.print( mixed_temp );
  lcd.write(0);
  lcd.print(“C”);

  delay(1000);
}

AWG Vs Current Flow Capacity

sudarsun — Tue, 13 Sep 2011 09:05:39 +0000

This write up is taken from http://www.engineeringtoolbox.com/wire-gauges-d_419.html

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 (mm)	Diameter (in)	Square (mm²)	Resistance (ohm/1000m)
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)
Length (feet)	Current (amps)
Length (feet)	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

sudarsun — Sun, 07 Aug 2011 15:35:53 +0000

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

sudarsun — Sun, 17 Jul 2011 14:15:40 +0000

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)

sudarsun — Sun, 10 Jul 2011 11:23:10 +0000

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.

Fitting LED Strip to Getz Radiator Grill

sudarsun — Sun, 15 Aug 2010 11:30:19 +0000

White (Blueish) LED strips with 3M water proof stickers are available for 300-350Rs/30cm. These LED strips are pretty bright when illuminated and draws lesser power when compared to incandescent lamps.

Step 1: Open the Bonnet of the Car

Step 2: Identify the Parking Lamp + Head Lamp Positioning Motor Power Line

Step 3: Remove the Parking Lamp, Lamp Positioning Motor Power Connector

Step 4: Remove the Connector Shield to find the Power lines

Step 5: Find and Tap the Parking Lamp Line.

Step 6: Put the connector shield back on the connector
Step 7: Put the connector back on the Lamp assembly
Step 8: Turn on Parking Lamp; Hurray LED Strip is AWESOME.

Thunderbird Battery Charger

sudarsun — Wed, 30 Jun 2010 17:19:43 +0000

BSNL Broadband Connectivity Issue on Noise phone lines

sudarsun — Sat, 10 Apr 2010 08:10:39 +0000

If you are an exclusive BSNL broadband user, you might not have attached the telephone to the phone line. I have connected my Netgear modem to the DSL/Phone line splitter and left the other connection floating. Lately, when I noticed that the Netgear modem was not able to make the connection with BSNL servers, originally I thought the telephone line is dead. To my surprise the telephone line was fine, but I perceived the lines to be little noisy. I made a complaint to the BSNL portal and as usual nothing much happened. Accidently, I had to connect my telephone to the splitter for making a local call. To surprise, the Netgear modem managed to connect to the server this time. So, the hypothesis is;

When the telephone line is noisy, attach the telephone to the splitter along with the modem connection to get connected to the BSNL Servers. Most likely it could be because of the Reactive load offered by the telephone on the phone line ends up conditioning the Phase modulated signals for the Netgear modem to connect to the Servers.