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Post by the light works on May 28, 2014 14:11:19 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. we use 277/480 for our big stuff. its how I know 277 leaves a mark. |
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Post by the light works on May 28, 2014 14:15:04 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. Really, I thought you had to strip off the old winding and wind a new one every half rotation.  [/sarcasm] |
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Post by GTCGreg on May 28, 2014 15:15:31 GMT
I've never said we should scrap solid-state control and go back to relay logic and DC motors. The point I was trying to make, which was obviously missed, is that it takes a LOT of technology to replace a very simple system that worked very well.
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Post by the light works on May 28, 2014 15:20:59 GMT
I've never said we should scrap solid-state control and go back to relay logic and DC motors. The point I was trying to make, which was obviously missed, is that it takes a LOT of technology to replace a very simple system that worked very well. actually, other than the fact that we've added a lot of bells and whistles, it is the same technology, only much smaller. a transistor is, after all, just a very tiny relay. |
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Post by GTCGreg on May 28, 2014 15:33:59 GMT
actually, other than the fact that we've added a lot of bells and whistles, it is the same technology, only much smaller. a transistor is, after all, just a very tiny relay. I realize that. I design digital HVAC control systems for emergency vehicles. But I often look at my own designs that use a number of micro-controllers, each of which contain thousands of transistors and have to shake my head. It took all this to replace one mechanical thermostat and a three position fan speed selector switch. But the customers want a digital color touchscreen display even if it doesn't do any better job than the two knobs did. And if I don't sell it to them, they will find someone else that will. |
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Post by the light works on May 28, 2014 15:52:06 GMT
actually, other than the fact that we've added a lot of bells and whistles, it is the same technology, only much smaller. a transistor is, after all, just a very tiny relay. I realize that. I design digital HVAC control systems for emergency vehicles. But I often look at my own designs that use a number of micro-controllers, each of which contain thousands of transistors and have to shake my head. It took all this to replace one mechanical thermostat and a three position fan speed selector switch. But the customers want a digital color touchscreen display even if it doesn't do any better job than the two knobs did. And if I don't sell it to them, they will find someone else that will. not a thermostat: a proportioning valve. which is one of my biggest ongoing beefs about small HVAC tech. few of them have real thermostats, just what is essentially a throttle. |
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Post by GTCGreg on May 28, 2014 16:29:32 GMT
The proportioning valve, which we refer to as a modulating valve, is really a better system. The problem is that you are trying to control the temperature in a relatively small space. There is a lot of over and undershoot even when using a fast electronic thermostat. Our system use a modulating valve but we use an electronic sensor to actually measure the ambient temperature in the vehicle and then regulate the valve's flow to maintain the set point temperature. This tends to keep a much steadier temperature in the vehicle. There is still a lot of "fine tuning" that has to be done depending on the size of the vehicle, insulation, and type of heater core we are using.
Cooling is another matter altogether. You may as well just put an on-off switch because no matter where you put your set point, you are never going to have enough. The problem here is that most ambulance manufactures use the vehicles OEM compressor to also cool the patient action area. We use a refrigerant solenoid valve to turn off the back cooling when it is not needed and add additional condensers but it's still hard get enough capacity, especially in the Southwest. We use to add a separate compressor to the engine but that's no longer possible on GM or Ford chassis because there just isn't any room. International does offer a second compressor option on their truck chassis and that's nice.
Because of the new no-idle laws going into effect in many cities, we have a system that runs on batteries that can keep the vehicle heated or cooled for up to 8 hours with the engine turned off. That system definitely needs to be computer controlled because of all the energy conservation measures required for battery operation. We use a variable speed brushless DC compressor that only gives us the exact capacity of cooling required. This greatly increases battery run time. It also gives us the ability to operate the compressor even when the engine is running which gives much better cooling capacity than just depending on the engine mounted belt-driven compressor. The negative side of this system is that it's big, heavy and expensive but many cities are being forced to use it because of environmental laws. Like I said, give the customers what they want. I have a new appreciation for green technology. It's just my idea of "green" is a little different than the environmentalists.
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Post by the light works on May 28, 2014 16:58:07 GMT
The proportioning valve, which we refer to as a modulating valve, is really a better system. The problem is that you are trying to control the temperature in a relatively small space. There is a lot of over and undershoot even when using a fast electronic thermostat. Our system use a modulating valve but we use an electronic sensor to actually measure the ambient temperature in the vehicle and then regulate the valve's flow to maintain the set point temperature. This tends to keep a much steadier temperature in the vehicle. There is still a lot of "fine tuning" that has to be done depending on the size of the vehicle, insulation, and type of heater core we are using. Cooling is another matter altogether. You may as well just put an on-off switch because no matter where you put your set point, you are never going to have enough. The problem here is that most ambulance manufactures use the vehicles OEM compressor to also cool the patient action area. We use a refrigerant solenoid valve to turn off the back cooling when it is not needed and add additional condensers but it's still hard get enough capacity, especially in the Southwest. We use to add a separate compressor to the engine but that's no longer possible on GM or Ford chassis because there just isn't any room. International does offer a second compressor option on their truck chassis and that's nice. Because of the new no-idle laws going into effect in many cities, we have a system that runs on batteries that can keep the vehicle heated or cooled for up to 8 hours with the engine turned off. That system definitely needs to be computer controlled because of all the energy conservation measures required for battery operation. We use a variable speed brushless DC compressor that only gives us the exact capacity of cooling required. This greatly increases battery run time. It also gives us the ability to operate the compressor even when the engine is running which gives much better cooling capacity than just depending on the engine mounted belt-driven compressor. The negative side of this system is that it's big, heavy and expensive but many cities are being forced to use it because of environmental laws. Like I said, give the customers what they want. I have a new appreciation for green technology. It's just my idea of "green" is a little different than the environmentalists. yes, but having JUST the proportioning valve and having to babysit it can be a pain in the neck when you are dealing with people who have no concept of moderation. (although for that matter, thermostats are a pain when you are dealing with people who have no ocncept of thermostat) I think most of our ambulances around here have a Cadet heater connected to an inverter for the patient compartment. having a dedicated heat pump would probably make more sense, but the cadet is much simpler to fit in there. part of my annoyance comes from when I was in L.A. I left for work at 50 degrees in the morning and got back at 100 degrees in the afternoon - having a thermostat would have let me set the AC to come on at 90, or even 80 if I was feeling like being wasteful. (the settings I had available for the AC was off, low, and high) |
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Post by GTCGreg on May 28, 2014 20:54:13 GMT
...for that matter, thermostats are a pain when you are dealing with people who have no ocncept of thermostat That's why we put an AUTO button on ours. Doesn't eliminate all user problems, but it does help. |
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Post by the light works on May 29, 2014 0:12:03 GMT
...for that matter, thermostats are a pain when you are dealing with people who have no ocncept of thermostat That's why we put an AUTO button on ours. Doesn't eliminate all user problems, but it does help. you can try to build it idiot proof, but they will just build a better idiot. |
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Post by c64 on May 29, 2014 5:11:30 GMT
That's why we put an AUTO button on ours. Doesn't eliminate all user problems, but it does help. Reminds me of the ancient VPS system. This makes your VCR easy to program, but it often happens that it just will record a random program at a random time. |
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Post by silverdragon on May 29, 2014 7:56:18 GMT
HVAC....
Just to remember the old caretaker I had to deal with in a school that went to a new boiler system.
He was used to running up the boilers to full every morning when he started work... at 6 am.
Hot water for the cleaners on the new system would be available from 7am when they started, and the school would be heated to occupation temps as required, the new heating would take as little as half-hour to get to that temp, even in the coldest winters....
(The Morning cleaners preferred cold as they didnt get too warm whilst working?...)
So the heating was not actually needed until 8:30, school starts at 9am.
Yet every day when he went in, he would hit the Day Extension Timer to bring the boilers on....
Argument was that he couldn't stand around waiting....
We eventually had to disable the boiler controls on the switch panel to stop him interfering.
No one EVER complained that the school wasnt warm enough when the school day started....
Surprisingly, without him hitting the start button every day, after one month, the school saved a quarter of its usual fuel bill...
Part of that was the better boilers, part of that was him not wasting fuel.
I think after two years we had effectively halved that schools fuel bill.
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Post by c64 on May 29, 2014 11:26:45 GMT
I think after two years we had effectively halved that schools fuel bill. And it helps the environment. My problem is, installing something new costs me a lot of money, especially in this size. And the savings are mainly for the tenants, not me.  |
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Post by the light works on May 29, 2014 13:50:53 GMT
HVAC.... Just to remember the old caretaker I had to deal with in a school that went to a new boiler system. He was used to running up the boilers to full every morning when he started work... at 6 am. Hot water for the cleaners on the new system would be available from 7am when they started, and the school would be heated to occupation temps as required, the new heating would take as little as half-hour to get to that temp, even in the coldest winters.... (The Morning cleaners preferred cold as they didnt get too warm whilst working?...) So the heating was not actually needed until 8:30, school starts at 9am. Yet every day when he went in, he would hit the Day Extension Timer to bring the boilers on.... Argument was that he couldn't stand around waiting.... We eventually had to disable the boiler controls on the switch panel to stop him interfering. No one EVER complained that the school wasnt warm enough when the school day started.... Surprisingly, without him hitting the start button every day, after one month, the school saved a quarter of its usual fuel bill... Part of that was the better boilers, part of that was him not wasting fuel. I think after two years we had effectively halved that schools fuel bill. We went the other way 'round in my church. the previous "church electrician" had put the church's furnaces on a clockwork shutdown timer, and all of the heaters for the outlying rooms on twist timers. when we replaced the furnaces a few years ago, we bypassed the shutdown timers, and I started changing the twist timers over so the thermostat maintains minimum temperature and you twist the timer if you want the room extra warm. between the newer furnaces and having them run other times than Sunday Morning Before Church, our fuel and power bills haven't gone up significantly, and the church is warm enough. (and the mildew problems have gone away) I also have two "overcontrolling idiot" stories - one is the aforementioned railroad bridge. they had to install a "fred" override (name changed because I can't remember the actual name) in the software, because Fred insisted on hitting the stop button and bringing the bridge in to rest manually. the controller would run the bridge at about 1 MPH until it cleared the stops, then ramp it up to full speed; then ramp it down to 1MPH just when it got to the other end of the swing; and then walk it into place at 1 MPH. when the bridge guy hit the override, it would do a panic stop, then manual would run it at about 1/2 MPH - meaning it took about twice as long to cycle the bridge manually as to let the controller do it. so they added a line of code that disabled everything but the full emergency stop button if it was within 15 degrees of the stops. (the emergency stop button being the one that flashed all the lights and sounded all the klaxons, and called the port authority and told them the bridge was broken and to call the electricians and ironworkers and tell them to come NOW.) the other was an in-ground sewage lift station. the same company that did the bridges had installed a new modular lift station, and got a callback a month later that it had flooded. so they went, after the station had been pumped out and hosed down, and pulled out all the controls and replaced them, checked everything to make sure it was functioning properly, closed the tank access door and wen on their way. (losing all the money involved) about a month later, the station overflowed again. this time, the sewage department demanded that the controllers be moved to a cabinet installed outside the pump station, so they did that. about a month later, the station flooded again, and this time they got there just when it happened, because the alarms didn't short out from being flooded - and they could look down the access hatch to what had been the control room and see the pumps were both running despite being nearly submerged in sewage, but weren't moving anything. when the truck crews pumped the sewage down, they saw that the tank hatch was open before the crews could have opened it and started digging. they found the maintenance man - an old-timer - didn't like the level the automatics pumped the tank down to; so whenever he came by he would open the tank hatch and pump it down manually to where HE thought it should be... this meant about once a month he would pump it down too far, and the pumps would lose their prime. they reinstalled the electronics inside the station, added a redundant set of level floats that only lit up indicator lights, added a redundant stop float that refused under any circumstances to allow the pumps to run if the level was even close to critical, and sealed the hatch down with security bolts. - and sent the wastewater company a bill for the entire process - pointing out it was their employee who was responsible for ALL the service calls. |
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[/sarcasm]
