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Post by the light works on May 27, 2014 17:47:03 GMT
to get back to the relative merits of AC vs DC, recent technological improvements have made it a less clear cut division than it was during the current wars. in fact, while DC motors used to be preferred for slower speed operation, now most of our industrial facilities are retooling to AC motors using variable frequency drives. that way you achieve 100% torque at any motor speed you want. I.E. if you want your 3600RPM motor to run at 1800 RPM, you simply set the drive to 30 HZ. our most recent portable generator tech uses a DC generator with an inverter, so the generator has the scaling advantages of the DC generator, while still producing AC power.
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Post by c64 on May 27, 2014 18:51:05 GMT
recent technological improvements have made it a less clear cut division than it was during the current wars. in fact, while DC motors used to be preferred for slower speed operation, now most of our industrial facilities are retooling to AC motors using variable frequency drives. Actually, this is exactly what a DC motor does. It creates its own frequency in the rotor which perfectly matches the speed and phase of the rotor. It just does this mechanically using "brushes". these "AC motors using variable frequency drives" are actually called "brushless DC". This is just replacing the mechanical commutator with power electronics. The advantage is less losses in sparks over the commutator contacts, more power without expensive mechanics and lastbut not least less or no wear of the electric components. There are different kinds of AC motor. Some work like the classic DC motor and which can run on DC and AC. Others can't run on DC since they need the frequency in order to turn. Those are called asynchronous or synchronous motors. They can also be used with a frequency converter to change their efficient speed, but those are still weak handling high loads from zero RPM. |
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Post by GTCGreg on May 27, 2014 19:21:59 GMT
Another fine example of using the equivalent of 10,000 semiconductors and hundreds of lines of code to replace two carbon brushes. Guess that's progress.
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Post by c64 on May 27, 2014 19:23:57 GMT
Another fine example of using the equivalent of 10,000 semiconductors and hundreds of lines of code to replace two carbon brushes. Guess that's progress. Saving about €150 per year in electricity for a furnace water pump sure is! |
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Post by GTCGreg on May 27, 2014 19:54:52 GMT
Another fine example of using the equivalent of 10,000 semiconductors and hundreds of lines of code to replace two carbon brushes. Guess that's progress. Saving about €150 per year in electricity for a furnace water pump sure is! Maybe. Depends on how often you have to replace the €500 controller. |
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Post by the light works on May 28, 2014 0:28:01 GMT
recent technological improvements have made it a less clear cut division than it was during the current wars. in fact, while DC motors used to be preferred for slower speed operation, now most of our industrial facilities are retooling to AC motors using variable frequency drives. Actually, this is exactly what a DC motor does. It creates its own frequency in the rotor which perfectly matches the speed and phase of the rotor. It just does this mechanically using "brushes". these "AC motors using variable frequency drives" are actually called "brushless DC". This is just replacing the mechanical commutator with power electronics. The advantage is less losses in sparks over the commutator contacts, more power without expensive mechanics and lastbut not least less or no wear of the electric components. There are different kinds of AC motor. Some work like the classic DC motor and which can run on DC and AC. Others can't run on DC since they need the frequency in order to turn. Those are called asynchronous or synchronous motors. They can also be used with a frequency converter to change their efficient speed, but those are still weak handling high loads from zero RPM. well, darn, I never knew synchronous motors could be hooked up to frequency controllers to control their speed...  no, it is NOT what a DC motor does. a DC motor uses brushes and a commutator to generate its own rotating electric field by only exciting the parts of the winding that pull it in the direction you want to go. synchronous AC motors use slip rings with the brushes instead of commutators and turn at a multiple of the frequency of the supplied AC current depending on the number of windings the motor is engineered with. its also why most industrial facilities use rotary power (three phase to Americans). single phase has to have rotation induced by start capacitors, or shaded pole windings to make the motor turn in the right direction. |
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Post by the light works on May 28, 2014 0:37:19 GMT
Another fine example of using the equivalent of 10,000 semiconductors and hundreds of lines of code to replace two carbon brushes. Guess that's progress. not quite. its using 10,000 semiconductors and hundreds of lines of code to replace half a ton of relays, contactors, and lats and lots of resistors, and having a motor that isn't three times bigger than it needs to be so it can still pull the load at creep speed. the example they gave us in class was a railroad bridge. it had a main motor and a smaller emergency motor, and the bridge tenders cooked their lunch on the resistor bank they used for creep speed, and there were three or four controls they had to press at the right time to make the bridge open and close. they replaced it with three black boxes, no bigger than a breadbox. removed the main motor, added a new emergency motor a third the size of the existing emergency motor. they took out a pickupload of relays and contactors. and they had to put in a microwave so the bridge tenders could heat their lunches. one of my mill jobs was upgrading the main controllers to freq drives - it was about the equivalent of putting a desktop computer CPU into an empty clothes closet for each drive we upgraded. addendum: the relationship might be related to the difference between a diesel tractor where you control the engine with electronic fuel injection, and a diesel tractor where you control the engine by loading more pig iron onto the tractor. |
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Post by GTCGreg on May 28, 2014 1:01:27 GMT
That's true. but a ton or relays, contactors and resistors is sure a lot more interesting to watch (and hear) than a breadbox sized black box with a blinking green led on it.
They could at least build an MP-3 player in it with the sound of relays chattering. And lets not forget you had to buy that microwave.
All kidding aside, you have to admit that the simple DC motor served us well for over 100 years. And there is something heartwarming about the light blue arc of the brushes and the smell of ozone.
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Post by the light works on May 28, 2014 1:45:58 GMT
That's true. but a ton or relays, contactors and resistors is sure a lot more interesting to watch (and hear) than a breadbox sized black box with a blinking green led on it. They could at least build an MP-3 player in it with the sound of relays chattering. And lets not forget you had to buy that microwave. All kidding aside, you have to admit that the simple DC motor served us well for over 100 years. And there is something heartwarming about the light blue arc of the brushes and the smell of ozone. the pen and inkwell served us well for over a hundred years, too. and I misplace all that nostalgia when I troubleshoot the car wash by tapping commands on the control panel. |
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Post by GTCGreg on May 28, 2014 2:31:18 GMT
You didn't need a control panel to troubleshoot an old DC control system. Just follow your nose.
And when you did find what was irritating your sinuses, you could often just jumper it out until you could get a replacement.
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Post by the light works on May 28, 2014 4:22:26 GMT
You didn't need a control panel to troubleshoot an old DC control system. Just follow your nose. And when you did find what was irritating your sinuses, you could often just jumper it out until you could get a replacement. This compares to one logic control system I had a lesson on where if you crushed a controller, you could just plug in another one and the network would tell it who it was and what it should be looking for. |
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Post by silverdragon on May 28, 2014 6:18:07 GMT
When you boys with 120v get to Plant, and the big stuff, we play with 480vAC....
And that hurts.
When you wake up, first thank whatever god you believe in.....
Then you tingle for a bit.
You start to notice blue and black bits....
And that they really ARE bits of you....
Then they start to hurt.
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Post by silverdragon on May 28, 2014 6:21:20 GMT
"Brushless" motors... I have two/three in my pond.
No expensive controllers either.
They last a very long time, run permanently, as they are filter pumps, I cant fault them...?...
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Post by c64 on May 28, 2014 12:15:40 GMT
Saving about €150 per year in electricity for a furnace water pump sure is! Maybe. Depends on how often you have to replace the €500 controller. The entire 2" pump unit (yes, its a very big house) I had bought for €380 and it was running fine for 3 years until the cellar was flooded drowning the furnace. Now I have a caloric value unit hanging high on the wall and this one has its own built in pump. I still have the brush less DC neodymium pump unit with its built in computer. It monitors the demand of the house and adapts. This was the first time all radiators in the house could get hot at the same time. Before I had bought it, some radiators turned cold when too much radiators dew a lot of water. The old pump was not that old and back then rated as "green". It also had a green casing and it was self regulating, too. But this one drew at least 80W at minimum flow. The new one even has a display for its power consumption and can't use more than 49W. Usually when I looked at it, it was running between 9W and 18W and it did a far better job than the old "Green" one. Before I had bought the "green" one, the "classic" non regulated pump consumed about 300W, 24/7! And the "classic" one required a bypass valve or if all radiators don't want much water, the pressure increased until one radiator valve was forced open superheating this room. I just love my new caloric value unit. The old furnace took 4 hours until the house started to really heat up after the furnace was down for a while. The caloric value system takes only 2 hours for the whole house to fully recover as if nothing had happened. Also it has burned a bit less than 50% of the gas the old one had used up during the same time last year so that's €1500 less money so far! There is just one problem. After the chimney sweeper hosed himself with a gallon of hot condensate, he didn't like it and threatened to terminate the operating license. It turned out that while the plastic pipes in the chimney have exactly the maximum length for their gauge, they had forgotten to count in the bends so the pipe is actually 2.5 meter too long for its gauge causing an overpressure of 5 hectopascal. This is almost OK and the chimney sweeper was supposed to stop the furnace, plug in the probe and then switch the system to full blast. He switched it to full blast, filled out forms until the heat exchanger overheated and the chimney pipe filled with condensate and then pulled the "inspection cork" right in front of his face. Now I get wider pipes on warranty and the furnace company demands a smarter chimney sweeper for inspecting their system. |
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Post by c64 on May 28, 2014 12:19:28 GMT
"Brushless" motors... I have two/three in my pond. No expensive controllers either. They last a very long time, run permanently, as they are filter pumps, I cant fault them...?... PC fans are also all "brushless DC", designed to turn the fan millions and millions of times round before they fail. And all it takes to do the trick is one HAL sensor in a transistor casing monitoring the field of the magnet and switching between two coils. |
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Post by c64 on May 28, 2014 12:22:16 GMT
When you boys with 120v get to Plant, and the big stuff, we play with 480vAC.... And that hurts. When you wake up, first thank whatever god you believe in..... Then you tingle for a bit. You start to notice blue and black bits.... And that they really ARE bits of you.... Then they start to hurt. And don't forget the odd taste you have in your mouth  |
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Post by c64 on May 28, 2014 12:25:50 GMT
You didn't need a control panel to troubleshoot an old DC control system. Just follow your nose. And when you did find what was irritating your sinuses, you could often just jumper it out until you could get a replacement. And that's better than pressing a button, saying "It's dead, Jim" and then flip the switch for the stand by replacement unit to restart production? And if there is no stand-by backup, just swap the old controller with a new one and plug the configuration card from the old unit into the new one. This takes a minute or two at max. |
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Post by c64 on May 28, 2014 12:29:44 GMT
That's true. but a ton or relays, contactors and resistors is sure a lot more interesting to watch (and hear) than a breadbox sized black box with a blinking green led on it. They could at least build an MP-3 player in it with the sound of relays chattering. And lets not forget you had to buy that microwave. All kidding aside, you have to admit that the simple DC motor served us well for over 100 years. And there is something heartwarming about the light blue arc of the brushes and the smell of ozone. the pen and inkwell served us well for over a hundred years, too. and I misplace all that nostalgia when I troubleshoot the car wash by tapping commands on the control panel. Well, from the point of view of a technician (an not the owner!), it's more fun to figure out whats wrong by looking at how the system had beaten up the customer's car than looking at a dead system refusing to do anything and just listing vague error codes which could or could not have something to do with the actual problem. |
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Post by c64 on May 28, 2014 12:41:12 GMT
no, it is NOT what a DC motor does. a DC motor uses brushes and a commutator to generate its own rotating electric field by only exciting the parts of the winding that pull it in the direction you want to go. Those coils are used in both directions, when the motor had turned 180°, it uses the same coils with different polarity. And technically, switching coils is part of the process to create a rotary magnetic field. Of course using less coils controlled electronically is far better, that's the point why we use brushless DC motors nowadays. And it depends on the machine if you use rotary current systems (Asynchronous motors) or if you use the classic series/parallel circuit motors. Even the series circuit motors are often used using frequency converters since changing the frequency can be done with much less losses than changing the voltage. And the impedance of the motor will convert frequency changes into changes of power just like changing the voltage would - just with less losses. Unlike asynchronous motors, they don't need RPM to have torque so those are still the method of choice for powerful electric drives which must accelerate a load from zero. For smaller applications in the lower kilowatt range, asynchronous machines can be used nowadays and they are cheaper. But for real big stuff, asynchronous machines are not good enough. And tiny machines (up to a few kW) now use permanent magnets again to save energy. |
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Post by c64 on May 28, 2014 12:51:05 GMT
That's true. but a ton or relays, contactors and resistors is sure a lot more interesting to watch (and hear) than a breadbox sized black box with a blinking green led on it. They could at least build an MP-3 player in it with the sound of relays chattering. And lets not forget you had to buy that microwave. All kidding aside, you have to admit that the simple DC motor served us well for over 100 years. And there is something heartwarming about the light blue arc of the brushes and the smell of ozone. Showing sparks and chattering relays won't earn any money! I like the classic stuff, that's why I often work for technical museums. But the applications where classic technology is superior are very, very rare. Even the military had kissed their beloved "nuclear hardened teletypes" goodby for decades. They just won't work with the modern fiber optic wires. There is only one case where the classic technology is much better than the modern solution. Escalators! The classic ones use a huge asynchronous motor with 40 or more pole pairs running very, very slow. They drive the escalator directly without gears. When the system fails, the momentum slowly decelerates the escalator. The modern ones stop rather brutal when they fail and people tend to fall down the escalators when this happens. True, the modern ones save power because they can turn very slowly to protect the bearings until someone steps on and then it gently accelerates and will then gently slow down again when nobody uses it any more. This can make sense - but not in supermarkets and train stations where there is a constant flow of people and the escalator running full speed all the time just as the old ones which were on a timer. No trains, no escalator. Simple. Worked well. Less people falling down escalators because they stopped brutally for no apparent reason. |
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