U.S. CitiesCity-Data Forum Index
Go Back   City-Data Forum > General Forums > Science and Technology > Consumer Electronics
 [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
View detailed profile (Advanced) or search
site with Google Custom Search

Search Forums  (Advanced)
Reply Start New Thread
 
Old 08-01-2017, 06:55 AM
 
10,169 posts, read 10,499,754 times
Reputation: 5450

Advertisements

I keep reading that in 1882 Thomas Edison's established the first low voltage DC electric distribution. What does that mean? What kind of voltages were used at the dawn of electricity distribution?

DC "low" voltage levels:
0.7V Nominal voltage drop on normal silicon diode or similar semiconductor junction
0.8V Voltages from 0V to 0.8V are considered to be logic 0 on TTL logic IC inputs
1.25V NiCd, NiMH battery cell nominal voltage
1.5V Carbon and alkaeline battery cell nominal voltage
1.6V The voltage you normally get from a fresh alkaeline battery cell
1.8V Quite commonly used very low voltage digital circuit operating voltage (many CPU cores)
2V Lead acid battery nominal cell voltage
2V Voltages from 2V to 5V are considered to be logic 1 in TTL logic IC inputs.
3V Lithium battery nominal voltage
3.3V Low Voltage Logic Threshold Levels (LVTTL) logic circuits operating voltage
3.6V Typical voltage used to power cell phones (either from NiMH or Li-Ion battery pack)
4.5V operating voltage for many small electronics gargets powered from three batteries
5V TTL logic circuits operating voltage
6V operating voltage for many small electronics gargets powered from four batteries
9V Commonly used battery voltage
10V Normal control voltage limit in 0-10V and 1-10V analogue control systems (light dimming and industrial use)
12V Car battery nominal voltage
13.8V the voltage you expect to get from car 12V power when car motor is running (charging battery)
24V Truck battery.
24V Automation systems most common nominal voltage used for logic signals and and current loop powering
24V common standard input voltages in Avionics and Defense applications
28V Maximum battery charging voltage for 24V battery system (for example batteries that power automation systems).
28V common standard input voltages in Avionics and Defense applications
36V Battery voltage used on some electric golf carts, electric scooters, electric bikes, high power cordless tools etc..
42.4V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be Safety Extra Low Voltage (SELV).
42.4V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)
48V Battery backed up -48V voltage is used on telecom systems for powering telephone exhanges and other telco equipment. The normal service voltage range for the -48 Vdc nominal supply at interface “A” shall be -40,5 Vdc to -57,0 Vdc according to ETSI EN 300 132-2
48V Some data centers use 48V DC to power servers (battery backup easy)
48V Phantom power feed for microphones in audio mixers most often uses +48V phantom power voltage
48V some automation systems use +48V power for equipment and I/O (electrical power distribution)
50V Work on energized circuits or apparatus below that voltage requires no “Hazard/Risk Evaluation.” NFPA 7OE
60V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be SELV.
60V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)
Reply With Quote Quick reply to this message

 
Old 08-01-2017, 09:27 AM
 
2,906 posts, read 1,707,067 times
Reputation: 2988
According to my sources, Edison's original generators put out 120V DC. Why AC won is an interesting story about which much has been written, and beyond the scope here.
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 09:55 AM
 
10,169 posts, read 10,499,754 times
Reputation: 5450
Quote:
Originally Posted by bigbear99 View Post
According to my sources, Edison's original generators put out 120V DC.
I suppose that is "low" voltage


The Folsom Power House was one of the earliest alternating current power plants in the United States. In 1895 it opened and operated as the longest transmission lines of any power plant in North America. It produced power and sent it 22 miles to Sacramento. That was the longest power transmission in the U.S. until that time.
Notable features: First commercial 60 cycle 3-phase power system (now our modern system), was the farthest commercial power transmission until the next year (1896), when Niagara Falls power was transmitted using a GE system to Buffalo from the 1895 Westinghouse powerhouse.
Frequency: 60 cycle
Three-Phase, Alternating Current
Power Transmission Length: 22 miles at 11,000 volts using #1 wire
Power system built by: General Electric
Notable Engineers: Elihu Thomson (generators), William Stanley (original transformers), Dr. Louis Bell (became chief transmission engineer)
Maximum Power Output: 3000 kW
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 11:06 AM
 
Location: Somewhere in northern Alabama
18,567 posts, read 55,502,062 times
Reputation: 32361
Low voltage in that case would have been 120 volts +-
It was ridiculously low for distribution, severely limiting the range from the generator, even with massive cables.
When electricity travels through a wire, there is "line loss." That loss is best understood as a lessening of the available watts at the end of the wire, and the analogy of a long pipe or hose is useful.

In the 1880s, electrical insulation was not good. The first trolleys used 600 volt DC power, with gutta percha as insulation. The traction motors couldn't handle greater voltage because of the likelihood of insulation failure at operating temps. Hence the interest in keeping voltages low. Even if distribution wires were high voltage, direct current cannot use transformers, and has to rely on costly and inefficient rotary converters (essentially a generator that is powered by an electric motor) to change voltages. Those converters also require regular maintenance, with oiling and changing out brushes, etc.

I did some fairly extensive research on one trolley line, and found that at 600 volts, the effective range of a trolley was roughly ten miles from the generator using two four aught "fuel" wires. A 120 volt distribution system would be practical for a few blocks in Manhattan, but not at all in the country.
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 12:50 PM
 
2,906 posts, read 1,707,067 times
Reputation: 2988
The reason Edison used DC was because at the time AC was unusable. It took a combination of inventions, such as the AC motor, and especially low loss transformers, to make AC generation and distribution feasible. Tesla (the person, not the car) and Steinmetz were the major contributors.

Rotary converters were primarily used as rectifiers - changing AC to DC. Many rail transit lines, subway and trolley especially, ran on DC because speed control was much easier than with AC. A good description, for those that want to know more, is here: www.nycsubway.org: Rotary Converter Power Technology
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 03:01 PM
 
Location: Somewhere in northern Alabama
18,567 posts, read 55,502,062 times
Reputation: 32361
"Many rail transit lines, subway and trolley especially, ran on DC because speed control was much easier than with AC."

Not really. The real problem is easily demonstrated. Take your average AC motor that isn't geared down, such as a fan motor. You can hold your hand on a fan blade and then power on the motor and it will stall, providing almost no torque. This is due in part to the design of the motor and in part due to AC providing equal amounts of magnetic flux in both directions at a rate of sixty cycles per second. The motor works by constantly shifting the armature forward and fails when stalled.

A DC traction motor doesn't stall. Instead it will lug down and allow the voltage to drop and current to rise, giving an increasing amount of torque. The motor will hence get hot and eventually burn itself out if the armature is locked up, but even if massively overloaded and yet still rotating, the motors are designed to have a safe few minutes of time before they are damaged.

In rail transport, the torque required to get the large mass of a train or trolley started is immense at first, but then once it is moving all that must be overcome are the various frictions, A DC traction motor has exactly the characteristics required for the job.

Modern multiphase motors used in transit overcome the problems of AC with sophisticated design.

I agree that most rotary converters were used to change AC to DC. I've used a few in theatres, where they supplied clean DC power to carbon arc lamphouses. The silicon rectifier stacks that were the alternative were nasty things, often overheating or having other issues.
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 03:47 PM
 
2,906 posts, read 1,707,067 times
Reputation: 2988
Harry, you really need to bone up on your electrical engineering. Ease of speed control is exactly why DC motors were used until the rise of variable frequency AC motor drives in recent years. Cable elevators (as opposed to hydraulic) also used DC motors until recently. (many older elevators probably still do.

Rail transport? You must have never seen a hill? Wind resistance/drag? You never saw a train back up before starting forward? Reason is precisely to avoid "immense" torque, since only one car at a time starts rolling.

Finally, "Modern multiphase motors used in transit overcome the problems of AC" with VFD. If that is what you meant by "design", wish you had said so. If not, keep reading. Technology is advancing.

Modern Variable Frequency Drives, together with matched poly-phase AC motors are truly an amazing innovation. When used in household air conditioning, they allow much better heat load matching, and improved efficiency, to use an example. Mitsubishi seems to be a leader in this field.
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 06:28 PM
 
Location: 5,400 feet
2,759 posts, read 2,700,927 times
Reputation: 3949
There's a very interesting book, Empires of Light by Jill Jonnes, that is about the Edison vs. Tesla, Westinghouse and DC vs. AC usage.
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 07:38 PM
 
Location: Somewhere in northern Alabama
18,567 posts, read 55,502,062 times
Reputation: 32361
Quote:
Originally Posted by bigbear99 View Post
Harry, you really need to bone up on your electrical engineering. Ease of speed control is exactly why DC motors were used until the rise of variable frequency AC motor drives in recent years. Cable elevators (as opposed to hydraulic) also used DC motors until recently. (many older elevators probably still do.

Rail transport? You must have never seen a hill? Wind resistance/drag? You never saw a train back up before starting forward? Reason is precisely to avoid "immense" torque, since only one car at a time starts rolling.

Finally, "Modern multiphase motors used in transit overcome the problems of AC" with VFD. If that is what you meant by "design", wish you had said so. If not, keep reading. Technology is advancing.

Modern Variable Frequency Drives, together with matched poly-phase AC motors are truly an amazing innovation. When used in household air conditioning, they allow much better heat load matching, and improved efficiency, to use an example. Mitsubishi seems to be a leader in this field.
You either have misinterpreted or we are going to have to agree to disagree. My commentary about the technology of the time (late 19th century) is accurate according to both what reference material has survived and people who actually operate the old trolleys that survive. Speed "control" on trolleys was crude even with DC and there were basically a couple of balancing speeds that were reached through short-term use of resistor banks. Those resistor banks would burn out with continuous use.

Please understand that I was talking about the technology of the time, not what is possible today. For general use, trolleys pre-dated the dedicated engines used as electric locomotives, although they were used in fixed locations. For use in fixed locations, recognize that many were installed to replace existing power sources, such as waterpower or steam. That means that the most cost effective speed control would have initially been achieved by continuing to use the pre-existing leather belts and lineshafts.

I REALLY don't want to engage in a pissing match. If you want to buy my book on exactly how the trolley I researched worked, you can argue with it.


If Edison was competing when he was alive against "Modern Variable Frequency Drives, together with matched poly-phase AC motors .... When used in household air conditioning, they allow much better heat load matching, and improved efficiency, to use an example." then I stand corrected.

A couple of fun links:

Slow Electricity: The Return of DC Power? - LOW-TECH MAGAZINE

Electric Road Trains - LOW-TECH MAGAZINE
Reply With Quote Quick reply to this message
 
Old 08-01-2017, 08:53 PM
 
Location: Sarasota FL
6,865 posts, read 9,550,455 times
Reputation: 6592
Volts in residential A/C
24V- thermostat, relays, contactor, defrost PCB, heat pump- reverse valve coil
240v- heat coils, evaporator fan, condenser fan, compressor
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply
Please update this thread with any new information or opinions. This open thread is still read by thousands of people, so we encourage all additional points of view.

Quick Reply
Message:

Over $104,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > General Forums > Science and Technology > Consumer Electronics
Similar Threads
Follow City-Data.com founder on our Forum or

All times are GMT -6. The time now is 03:37 AM.

© 2005-2019, Advameg, Inc. · Please obey Forum Rules · Terms of Use and Privacy Policy · Bug Bounty

City-Data.com - Archive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 - Top