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Off Grid Battery Bank Building a battery bank and having a method of keeping them charged is one of the first steps in building an alternate energy system for off grid applications. A battery bank can be used to run lighting, t.v., radio, microwave, etc. Sizes range from a few batteries, a charging system and an inverter, to hospitals and universities that need power for lighting and important equipment. All battery systems have to be properly recharged. This is done by the generator or other source of alternate energy. The larger the system, the larger the generator or other source of charge has to be. Batteries are rated in voltage and ampere hour capacity. The greater the amp hour capacity of the battery bank, the longer it can power equipment before needing to be recharged. Energy from the generator or alternative energy source can be stored for later use. With the cost of fuel, oil and maintenance it makes sense. Rather than running a generator all the time to get power, it only has to be operated when equalization charging takes place and when the system does not have sufficient capacity to power heavy loads. The initial investment in a battery bank is well worth it, providing power 100 percent of the time. Battery backup is increasingly used in grid tied systems as well. Battery banks are wired and sized to produce energy needed in voltages ranging from 12, 24, 48, 60,vdc and sometimes higher. The higher the loads (demand) placed on the system, the higher the voltage has to be to match the input voltage required by more powerful inverters that are needed for larger loads. Once you have figured out your daily watt hour consumption and have revised that figure by practicing energy management, you can calculate your battery capacity. Use the following formula. (watt hours) wh/day x days of storage x bat.eff. x dod(depth of discharge) =
ampere hours. battery efficiency ( 7590%) effbat battery voltage
( 12,24,48,60+,etc ) maximum depth of discharge from( 2080% ) 

Item 
Starting Wattage 
Running Wattage 
1/4' Drill  300  300 
12' Concrete Cutter  3600  1800 
7 1/4' Circular Saw  3000  1500 
Air Compressor (Average)  4000  2000 
Belt Sander  1000  1000 
Central Air Conditioner  
10,000 BTU 
2200  1500 
20,000 BTU 
3300  2500 
24,000 BTU 
4950  3800 
32,000 BTU 
6500  5000 
40,000 BTU 
6700  6000 
Chain Saw  1200  1200 
Circular Saw  2400  1200 
Disc Grinder  4000  2000 
Disc Sander  1200  1200 
Drill  1800  720 
Edger  2400  960 
Electric Chainsaw  2400  1200 
Electric Lawn Mower  4320  1440 
Electric Pressure Washer  3600  1200 
Electric String Trimmer  1500  600 
Electric Weed Trimmer  500  500 
Furnace Fan, gas/fuel oil furnace  
1/8 horsepower 
500  300 
1/6 horsepower 
750  500 
1/4 horsepower 
1000  800 
2/5 horsepower 
1400  700 
3/5 horsepower 
2350  875 
Jig Saw  1800  720 
Jigsaw  300  300 
Miter Saw  2100  840 
Orbital Sander  1800  600 
Paint Sprayer  1080  360 
Planer  2400  960 
Router  1500  600 
Water Pump  3000  1000 
Wet/Dry Vacuum  2500  888 
Winch  5400  1800 
Worm Drive Saw  3100  1560 
Basic Energy Formulas And Equivalents  Appliance Average Consumption Ratings
Energy is ability to do work. 1 newton of force over 1 meter is 1 newtonmeter or joule or watt second of work done.
Power is the rate of doing work. lifting 1 pound weight 1 foot in one second is 1 footpound per second. if you lift 550 pounds one foot in one second that's 1 horsepower of power required.
Most people would have problem lifting 550 pounds (249.48 kg), directly. but you can lift that weight with a winch over longer time and the same amount of work was done, just took longer so required less power. same principle with levers or pulleys. the force is reduced but distance the force is applied increases. so total of force * distance remains the same. (minus any friction loss) the same amount of work can be done by letting the weight fall, but then you have to do work to lift it back up.
1 btu = 252 calories
1 btu = 1055 joules (watt seconds) = .293 watt hours
1 btu raises 1 pound of water 1 degree fahrenheit
1 calorie raises a gram of water 1 degree celsius 1kilocalorie is used for diets = 1 kilogram water 1 deg celsius
1 calorie = 4.186 joules
1 therm = 100,000 btu = 29.3 kwh
1 ton of refrigeration = 12,000 btu/hr
1 lb residential garbage = 2,500 btu =0.73 kwh
1 lb coal = 13,000 btu = 3.81kwh 1ton=7.62 mwh $1.31 per million btu = 0.44 cents per kwh
1 lb wood = 3,500 btu = 1.03 kwh
1 gal propane= 92,000 btu = 30 kwh
1 gal fuel oil= 138,000 btu = 40.45 kwh ($1.00 gallon = 2.5c/kwh)
1 cu. ft. nat. gas = 1,000 btu = .29 kwh (44cent per 100 cuft=1.5c/kwh)
1 hp = 745.7 watts = 2545.3 btu hr
1 hp = 33,479 btuh (boiler)
1 hp = = 550 footlbs/sec = 33,000 footlbs/min
1 hp = 42.44 btu/min.
hp = torque in poundfeet x rpm/5252
(revolutions per minute /60) *2 *pi = radians/second s rpm * 0.1047 = radians/sec
note: torque is measured in "foot pounds" but should be described as "pound feet" or 1 pound force at 1 foot radius to avoid confusion with work done lifting 1 pound 1 foot, unit of energy.
1 joule = 1 watt second = 1 newton meter
energy is a scalar, with basic si units of kgm^2/sec^2 (also defined to be the joule).
einstein's equation: e = mc^2 would be for 1 gram of mass and c = velocity of light =3 * 10^8 meter/sec 1 * 10^3 kilograms * 9 * 10^16 = 9 * 10^13 joules or 9 * 10^13/3.6 * 10^6 = 2.5 * 10^7 kwh.
kinetic energy of a moving mass is 1/2 * m * v^2 joules, m is mass in kg and v is velocity in meters/sec.
momentum is a *vector*, with basic si units of kgm/sec.
rotational momentum is p = j x w, where j is the moment of inertia (same as used for calculating rotational kinetic energy).
ke of rotationally moving objects equation ke = 0.5 x j x w^2, where j = moment of inertia (rotational analog of mass, related to the object's mass and its distribution around the axis of rotation), an w = rotational speed, radians/second. acceleration is the change in velocity/time earth gravity acceleration is about 32 feet/sec^2 or 9.81 meters/sec^2. that means that velocity of something falling without wind resistance or other force, will increase 32 feet per second, every second or 9.81 meters/second, every second. stopping or deceleration is calculated the same.
v is velocity, d/t, meters/second or feet/second d is distance a is acceleration, change in velocity/time, m/s^2 t is time in seconds
v= at, t = v/a, a=v/t, d = 1/2at^2, t= 2d/v, t = (2d/a)^0.5 {sqrt}, d = 1/2v^2/a, a = 1/2v^2/d, v = (2ad)^0.5 {sqrt} d = vt for constant velocity
using same units such as a = 32 feet per second^2, in two seconds the distance traveled would be 1/2 * 32 feet/sec^2 * 2 sec^2 = 64 feet or 1/2 * 9.8 m/s^2 * 2 sec^2 = 19.6 meters
1 watt = 1 volt x 1 amp
1 amp = 1 coulomb of charge per second (6.02 * 10^23 electrons)
1 ohm = resistance that has 1 volt for 1 amp current
ohm's law e for voltage, i for amperage, r for resistance ohms, p for watts
e=ir, e=p/i, e=(rp)^0.5, i=e/r, i=p/e, i=(p/r)^0.5, r=e/i, r=p/i^2, r=e^2/p, p=ei, p=i^2r, p=e^2/r
1 watthour = 3.412 btu
1 kilowatthr = 3412 btu = 3.6 * 10^6 joule
1 kilowatt = 1,000 watts
1 kilowatt = 1.3405 horsepower
1 atmosphere = 14.7 lbs./sq. inch
1 atmosphere = 29.92 inches of mercury
1 pound per square inch = 6.899 kilopascals.
1 pascal is newton of force over 1 meter square, pressure.
1 centimeter = .3937 inches
1 cubic foot = 1728 cubic inches
1 cubic foot = 7.48 gallons us
1 cubic foot/minute = 7.482 gallons/minute
1 cubic foot water = 62.4 lbs @ 60 deg. f
1 foot of water = .4333 lbs/sq. inch
1 footpound = .001286 btu
1 footpound = 1.356 newton meters
1 newton meter = 0.7376 foot pounds = 1 joule
1 newton accelerates 1 kg at 1 meter per second^2 (about 9.81 newtons = 1kg force in earth gravity)
1 foot/second = 0.68182 miles per hour
1 mph = 1.46667 feet per second.
1 meter/second = 3.6 kilometers/hour
1 meter = 39.37 inches = 3.28084 feet = 1.0936 yards
1 foot = .3048 meters
1 inch = 2.54 centimeters = .0254 meters.
1 gallon us = 3.785 liters = 231 cubic inches.
1 gallon us water = 8.35 lbs
1 inch of water = .03613 lbs./sq. inch
1 foot of water = 0.4335 psi
1 liter = 1.057 quarts
1 fluid ounce = 1.805 cubic inches
1 fluid ounce = .02957 liters
1 cubic inch = 16.387064 cubic centimeters 1 pound = 0.4536 kg or 1 kg = 2.2046 pounds
1 oz = 28.35 grams
celsius deg * 9/5 +32 = fahrenheit, f32 * 5/9 = centigrade
212 deg fahrenheit = 100 degree celsius, water boils
32 deg fahrenheit = 0 degree celsius, water freezes
40 deg fahrenheit = 40 deg celsius
absolute 0 degrees or kelvin = 459.7 fahrenheit or 273 c
speed of light in a vacuum is approx 2.998 * 10^8 meters/second or 186,000 miles per second. rounded off 3 * 10^8 meters/second.
1 megahertz frequency wavelength is 300 meters.
the formula for determining load in watts is:
watts = amps x volts or p(watts)= i(current) x e(voltage)
note: 1 kw = 1000 watts
Equipment Averages
space heater 1200 watts
weed trimmer 850 watts
clothes dryer (gas) 720 watts
clothes dryer (electric) 2400 watts
light bulb (100w) 100 watts
small radio am/fm cd 50 watts
radio, cb 50 watts
fan 200 watts
television 50250 watts (cathode tube), plasma flat screen 125250 watts
LED flat screen tv 50120 watts
microwave oven 1200 watts
air conditioner (12,000 btu) 3250 watts
furnace fan (1/3 hp blower motor) 600 watts
vacuum cleaner 600 watts
sump pump (1/3 hp) 700 watts
refrigerator/freezer 800 watts
deep freezer 500 watts
circular saw 6" 800 watts
floodlight 150 watts(incandescent) LED 75 watts
drill 1/2" electric 1000 watts
toaster 1200 watts
coffee maker 1200 watts
skillet 1200 watts
chain saw 14" electric 1200 watts
water well pump (1/2 hp) 1000 watts
hot plate/range (per burner) 10001200 watts
table saw 10" 2000 watts
elect. water heater 3000 watts
dc battery/device charger 120 watts