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| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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DC Generator
All,
A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. The generator is "going bad" (I don't know the details) and he is looking for a replacement (fairly quickly). He is looking for a 10,000 watt DC generator, 240 volt, electric start and it can be either gas or diesel...... Any suggestions or ideas? Thanks Ken |
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DC Generator
He is looking for a
10,000 watt DC generator, 240 volt, electric start and it can be either gas or diesel...... Any suggestions or ideas? 10 KW AC generators are pretty common. High current diodes are also easy to come by. AC to DC using a single or three phase input along with a reverse connected diode to catch the pulse when the coil is disconnected. Too easy? Earle Rich Mont Vernon, NH |
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#3
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Ken Sterling writes:
A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? |
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"Richard J Kinch" wrote in message . .. Ken Sterling writes: A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? 45 amps is easy and the parts can be had for very little money. It's done in many welding machines everyday. 600 Volts piv should be fine with a reverse diode for the inductive load. But I do agree with your comment on that amount of power. Doesn't seem right. |
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DC Generator
He is looking for a
10,000 watt DC generator, 240 volt, electric start and it can be either gas or diesel...... Any suggestions or ideas? 10 KW AC generators are pretty common. High current diodes are also easy to come by. AC to DC using a single or three phase input along with a reverse connected diode to catch the pulse when the coil is disconnected. Too easy? Earle Rich Mont Vernon, NH Too easy?...I guess not if you know what you are doing.... 240v DC single phase I assume....don't know the current needed, not sure how to connect a reverse diode and what it would be connected to.... Ken. |
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DC Generator
Ken Sterling writes:
A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? Don't know any details other than the original post. Have no idea what kind of current a junkyard magnet would draw. I personally am wondering if he could simply run a dc generator from the motor in the crane from an extra drive pulley or driveshaft someplace. Also don't know what is meant by "going bad" - whether it's the generator portion or the engine is finally wearing out.... I got all this "second hand" as the fella that asked evidently knows the junkyard guy, and thought I may have an idea as to where he could find this generator. Ken. |
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DC Generator
"Richard J Kinch" wrote in message ... Ken Sterling writes: A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? 45 amps is easy and the parts can be had for very little money. It's done in many welding machines everyday. 600 Volts piv should be fine with a reverse diode for the inductive load. But I do agree with your comment on that amount of power. Doesn't seem right. As I understand it, he (the junkyard guy) claims one of the welding machines won't work as the output is not stable enough.... Ken. |
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DC Generator
"Richard J Kinch" wrote in message . .. Ken Sterling writes: A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? Richard 40 amps at 240VDC may be about right for a big magnet. I've fixed my buddy's magnet several times. It runs from a BIG engine driven welder. It draws over 80 amps at 70 VDC and it isnt a very big magnet. I never thought about how warm that magnet gets. I'll sure feel it next time I see it working. I'm not skilled at making rectifiers but, I'm confidant that even I could build an adequate rectifier for this magnet since all the switching devices are already there for the controls. I was considering suggesting that the guy who is looking for the DC source for that magnet, might be able to save some $$ by finding a military surplus 400 Hz 3 phase 208 VAC power source, since they are much cheaper than 60 Hz. Jerry |
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"Ken Sterling" wrote in message s.com... "Richard J Kinch" wrote in message ... Ken Sterling writes: A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. Someone might have abstract ideas about doing this by rectifying an AC generator, or a similar scheme. But 10 KW is a lot of power and it isn't so simple to just hook up a few parts and have it work for long. Does this thing really use that much ooomph? Where does all the heat go? 45 amps is easy and the parts can be had for very little money. It's done in many welding machines everyday. 600 Volts piv should be fine with a reverse diode for the inductive load. But I do agree with your comment on that amount of power. Doesn't seem right. As I understand it, he (the junkyard guy) claims one of the welding machines won't work as the output is not stable enough.... Ken. I was not suggesting use of a welder, only that the diodes are in the range of what is required. The best approach would be a three phase generator, maybe something military at 400 Hz. It would be easy to go from 220/3ph/400 to Dc. tm |
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Ken Sterling wrote:
All, A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. The generator is "going bad" (I don't know the details) and he is looking for a replacement (fairly quickly). He is looking for a 10,000 watt DC generator, 240 volt, electric start and it can be either gas or diesel...... Any suggestions or ideas? Thanks Ken Gosh - with this one - you can have coffee also! $7535.00 http://www.weldingmart.com/Qstore/p001554.htm INGERSOLL-RAND GENERATORS G11 INGERSOLL-RAND GENERATOR ID: G11 Model Power Watts Max - 11000 Power VA Max (.8 pf) - 13750 Motor starting power(watts) - 3660 Rated power rating(watts) - 9900 Noise Level(dBa at 7 M) - 73 Enclosure - Enclosed Engine Engine Brand - Mitsubishi Engine Model - S3L2SD Displacement(cm^3)/Type - 1318/OHV Rated Horsepower/RPM - 17/1800 Standard Starting System - electric start Automatic Idle Control - No Spin On Oil Filter - Yes Spark Arrest Muffler - No Fuel/Capacity(US Gallons) Diesel/11.4 Running Time Full Load(hours) - 12.4 Running Time 75% Load(hours) - 15.6 Running Time Half Load(hours) - 18.9 Gauged Fuel Cap - yes Generator Output Voltages - 120/240 Circuit Breaker Protection - Yes Outlets - (1) 120v 15a duplex Outlets - (1) 125 V - 30 A Outlets - (1) 125/250 V - 30 A Overload Protection - Yes Number of Poles - 4 Package Length (in/cm) - 66/169 Width (in/cm) - 30/77 Height (in/cm) - 47/119 Dry Weight (lbs/kg) - 1177/534 Wet Weight (lbs/kg) - 1265/574 Protective Shutdowns - Oil PSI + water Temp. Lifting eye - Yes Electric Start with Battery & Cables -Yes Hourmeter - Included Something like this one - Rent Lease until the one there gets fixed. Mabye buy. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
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DC Generator
"ERich10983" wrote in message
... AC to DC using a single or three phase input along with a reverse connected diode to catch the pulse when the coil is disconnected. If you use a FWB, you have two diode drops to take care of the flyback pulse.  Tim -- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @ http://webpages.charter.net/dawill/tmoranwms |
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Gosh - with this one - you can have coffee also!
$7535.00 http://www.weldingmart.com/Qstore/p001554.htm INGERSOLL-RAND GENERATORS G11 INGERSOLL-RAND GENERATOR ID: G11 Model Power Watts Max - 11000 Power VA Max (.8 pf) - 13750 Motor starting power(watts) - 3660 Rated power rating(watts) - 9900 Noise Level(dBa at 7 M) - 73 Enclosure - Enclosed Engine Engine Brand - Mitsubishi Engine Model - S3L2SD Displacement(cm^3)/Type - 1318/OHV Rated Horsepower/RPM - 17/1800 Standard Starting System - electric start Automatic Idle Control - No Spin On Oil Filter - Yes Spark Arrest Muffler - No Fuel/Capacity(US Gallons) Diesel/11.4 Running Time Full Load(hours) - 12.4 Running Time 75% Load(hours) - 15.6 Running Time Half Load(hours) - 18.9 Gauged Fuel Cap - yes Generator Output Voltages - 120/240 Circuit Breaker Protection - Yes Outlets - (1) 120v 15a duplex Outlets - (1) 125 V - 30 A Outlets - (1) 125/250 V - 30 A Overload Protection - Yes Number of Poles - 4 Martin, Don't know if 30A would be enough.... also don't know if the outputs are "cumulative" to total current capabilities of the generator, ie, 15+30+30 for a total or would this just be 30A max? Ken. Package Length (in/cm) - 66/169 Width (in/cm) - 30/77 Height (in/cm) - 47/119 Dry Weight (lbs/kg) - 1177/534 Wet Weight (lbs/kg) - 1265/574 Protective Shutdowns - Oil PSI + water Temp. Lifting eye - Yes Electric Start with Battery & Cables -Yes Hourmeter - Included Something like this one - Rent Lease until the one there gets fixed. Mabye buy. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
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#15
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Back to the original poster.....
I don't know how much power you want to make. If you want to make from 500 to 1600 watts of Sine wave AC, forego all "build your own from scratch" ideas and look up "redi-Line" on Ebay. These are "motor generators", designed to take DC voltage from a car battery 12-36 volts), turn a motor, which in the end drives a generator that puts out Pure sine wave (Clean) power. These are the precurser to newer electronic "inverters". Though not as "efficient" as newer electronic units (of which you likely do not care - running Steam and all), this should work Great! These can be had on the used market for far less than the Electronic types (you couldn't use the electronic types for what you are doing anyhow !) Your mission would be to simply dissassemble the device (you pick the power level you want - I would advice the 1600 watt cause you will likely have the power to turn it) - and expose the motor shaft of the unit, and drive the generator via your Steam engine (3600 rpm is the recommended at full load). Cool Eh ? Run the microwave via steam power ! I want to see pictures when you are done ! Chris L |
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#17
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Don Foreman writes:
At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. |
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DC Generator
Richard J Kinch wrote:
Don Foreman writes: At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. It's always dangerous to accuse someone of ignorance. A little research on the web shows that a 10KW/240VDC magnet is actually a small one. Here's a company that sells used round lifting magnets: http://www.caseyusa.com/resultspho2....d=DC%20MAGNETS Here's the specifications on the biggest one I could find: http://www.caseyusa.com/resultselec4...t2=94&cat3=231 That's about 46KW. I guess there must be a way for the heat to dissipate. I have an old Audel book with a chapter on lifting magnets. It describes the controllers and how the high induced voltage is handled. There's no mention of current or voltage ratings, but the relative size of the controller components and connections would indicate something in the 50-100 amp range. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. The Audel book does not speak of any use of the prime mover to control the current, just a controller with contactors and resistors. |
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Jim Stewart writes:
It's always dangerous to accuse someone of ignorance. True. But he did say as much, which is why he asked for advice. I'll confess I have no experience with these things. Still, 46 kW in an 80-inch disk that has to stay cool enough to maintain 240 V insulation doesn't seem like it could have much of a duty cycle. That's about one toaster per square foot of surface area. |
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On Wed, 23 Jun 2004 02:04:24 -0500, Richard J Kinch
wrote: Jim Stewart writes: It's always dangerous to accuse someone of ignorance. True. But he did say as much, which is why he asked for advice. I'll confess I have no experience with these things. Still, 46 kW in an 80-inch disk that has to stay cool enough to maintain 240 V insulation doesn't seem like it could have much of a duty cycle. That's about one toaster per square foot of surface area. Not that I would want to break into this thread too late but, from the discussions so far it appears the loss of power through the wire harness is being forgotten. IR losses in DC circuits this size must be enormus. Any one brave enough to take a voltage reading at the load end of the wires. If attempted leave your wallet with your credit cards in the car. Don't ask how I know this. As for duty cycle, the magnet is off for the majority of the time. When engaged, I'm betting the wires are the hottest this in the whole rig. My 2 cents Jim Vrzal Holiday,Fla. |
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DC gensets should be relatively easy to restore to full operation. The
brushes and/or the commutator need to be replaced and serviced. A knowledgable alternator guy should be able to work this. Jim Vrzal Holiday,Fla. On Mon, 21 Jun 2004 11:00:21 GMT, (Ken Sterling) wrote: All, A fella runs a junk yard and has a crane with an electro-magnet for moving scrap metal - he uses a 10,000 watt DC generator to power the magnet. The generator is "going bad" (I don't know the details) and he is looking for a replacement (fairly quickly). He is looking for a 10,000 watt DC generator, 240 volt, electric start and it can be either gas or diesel...... Any suggestions or ideas? Thanks Ken |
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#24
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On Tue, 22 Jun 2004 22:46:36 -0500, Richard J Kinch
wrote: Don Foreman writes: At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. It's a bit dangerous to accuse another poster of too much ignorance when you are not too sure of your own facts. Jim Stewart has already dealt with your comment on power rating. Your comment on reverse diodes is equally misleading. In an earlier post I recommended that the reverse diode be rated for at least the nominal coil voltage and current. This is because, at the instant of disconnection, the current that was flowing in the inductor is diverted to and flows through the forward direction of the reverse diode. This current then decays at a rate determined by L/R of the magnet coil. The stored energy (1/2 L x I squared) is dissipated in the resistance of the magnet coil - not the diode. The reverse rating is determined by the voltage that appears across the magnet in normal operation. Jim |
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Seems to me to be some confusion between the term Kilowatts and heat.
KVA or Kilowatts in the case of motors and machinery is the energy used or available, and not just as heat. Properly designed and operated, a 25 Kilowatt MG set gets no "hotter" than a 50 KW machine, or a 1KVA transformer won't get any "hotter" than a 10KVA, nor should a properly designed and used magnet. They just use that much energy, and not necessarily as heat. If they were just heat dissipators like a grid, then yes, one would get significantly hotter than the other. And I don't know, but I doubt that anywhere in this system will there be a single simple across-the-line contactor to operate the magnet, DC or not. It would scare the **** out of the operator if he just had that. Pieces of metal would be flying everywhere instead of being properly and slowly attracted and dumped to/from the magnet. Take care. Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXXX On Wed, 23 Jun 2004 04:52:40 GMT, Jim Stewart wrote: Richard J Kinch wrote: Don Foreman writes: At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. It's always dangerous to accuse someone of ignorance. A little research on the web shows that a 10KW/240VDC magnet is actually a small one. Here's a company that sells used round lifting magnets: http://www.caseyusa.com/resultspho2....d=DC%20MAGNETS Here's the specifications on the biggest one I could find: http://www.caseyusa.com/resultselec4...t2=94&cat3=231 That's about 46KW. I guess there must be a way for the heat to dissipate. I have an old Audel book with a chapter on lifting magnets. It describes the controllers and how the high induced voltage is handled. There's no mention of current or voltage ratings, but the relative size of the controller components and connections would indicate something in the 50-100 amp range. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. The Audel book does not speak of any use of the prime mover to control the current, just a controller with contactors and resistors. |
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#27
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In article ,
Brian Lawson wrote: On Tue, 22 Jun 2004 22:37:48 -0500, Don Foreman wrote: [ ... ] Hey DoN, Wrong DoN. I'm "DoN. (Donald Nichols)", not Don Foreman, who wrote what you were responding to. Owwww....what about the AC hum when he's got ahold of a 1/2 ton of scrap pieces? Ouch!! Probably not too bad. Based on my mag chuck for my surface grinder, there is some residual magnetism which lasts for some while after the chuck is turned off, and this could control the hum rather well. As a matter of fact, it is wired up to feed raw AC to it to demagnetize it so you can get the workpiece off without having to fight for it. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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#28
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Brian Lawson writes:
Seems to me to be some confusion between the term Kilowatts and heat. Nope. Read the magnet specs someone else posted for the DC resistance of the coil and the DC current. I*I*R ends up as heat in the magnet coil. They just use that much energy, and not necessarily as heat. Seems to me to be some confusion between the term energy and power. |
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Right Ken - but there are other models - IR does make them this size and much larger.
I see them on construction sites and always wished I had one to fire up after an earthquake. Maybe someday. Martin Ken Sterling wrote: Gosh - with this one - you can have coffee also! $7535.00 http://www.weldingmart.com/Qstore/p001554.htm INGERSOLL-RAND GENERATORS G11 INGERSOLL-RAND GENERATOR ID: G11 Model Power Watts Max - 11000 Power VA Max (.8 pf) - 13750 Motor starting power(watts) - 3660 Rated power rating(watts) - 9900 Noise Level(dBa at 7 M) - 73 Enclosure - Enclosed Engine Engine Brand - Mitsubishi Engine Model - S3L2SD Displacement(cm^3)/Type - 1318/OHV Rated Horsepower/RPM - 17/1800 Standard Starting System - electric start Automatic Idle Control - No Spin On Oil Filter - Yes Spark Arrest Muffler - No Fuel/Capacity(US Gallons) Diesel/11.4 Running Time Full Load(hours) - 12.4 Running Time 75% Load(hours) - 15.6 Running Time Half Load(hours) - 18.9 Gauged Fuel Cap - yes Generator Output Voltages - 120/240 Circuit Breaker Protection - Yes Outlets - (1) 120v 15a duplex Outlets - (1) 125 V - 30 A Outlets - (1) 125/250 V - 30 A Overload Protection - Yes Number of Poles - 4 Martin, Don't know if 30A would be enough.... also don't know if the outputs are "cumulative" to total current capabilities of the generator, ie, 15+30+30 for a total or would this just be 30A max? Ken. Package Length (in/cm) - 66/169 Width (in/cm) - 30/77 Height (in/cm) - 47/119 Dry Weight (lbs/kg) - 1177/534 Wet Weight (lbs/kg) - 1265/574 Protective Shutdowns - Oil PSI + water Temp. Lifting eye - Yes Electric Start with Battery & Cables -Yes Hourmeter - Included Something like this one - Rent Lease until the one there gets fixed. Mabye buy. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
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Richard J Kinch wrote:
Don Foreman writes: At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. You don't know how they turn it on or off. On something like that there could be several coils a main one and a stepper. The stepper is the extra you need to grab and take . The windings are likely browned down and up - not on/off. You want to get it below pickup to drop and above the safety level to grab. Martin -- Martin Eastburn, Barbara Eastburn @ home at Lion's Lair with our computer NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder |
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On Tue, 22 Jun 2004 22:46:36 -0500, Richard J Kinch
wrote: Don Foreman writes: At 240 volts and 10KW, the avg (DC) current is about 41.6 amps, while the AC ripple current from rectified single-phase AC will probably be well under 1 amp. The difference between this and "pure" DC excitation would not be noticable. The original post question betrays too much ignorance of what is going on. 10 kW is just to much heat to dissipate on any kind of duty cycle. He may be trying to duplicate a poorly cobbled prior repair or design. Besides, that many amps into that big an inductor has gotta produce one wollop of a surge when you switch it off. Saying you can absorb that with a reversed diode is like saying you can brake a big diesel engine to a dead stop by putting your hand on the flywheel. I suspect part of the reason for the DC generator is that you can clutch out the prime mover, and the generator becomes a motor to slowly dissipate the stored energy in the inductor. Dump current can be no greater than excitation current, so diodes than can deliver excitation can handle it no problem. 35 amp 600 volt diode bridges cost less than $2. The energy from the collapsing field is mostly dissipated in the resistance of the load just as excitation power is. Diode dissipation is fwd drop * current whether exciting or dumping. 10 KW is about 13.4 HP. A 25% efficient 5 HP lawnmower engine dissipates more heat than that, with far less surface area. Gae thee to a scrapyard, behold the size of the electromagnet.... The original post asked for a replacement generator of specified power for a system that has worked in service. Declaring him ignorant is neither helpful nor defensible by technical premise you present. |
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Don Foreman writes:
Declaring him ignorant is neither helpful nor defensible by technical premise you present. Indeed it was the wrong term, I apologize. A 25% efficient 5 HP lawnmower engine dissipates more heat than that, with far less surface area. Perhaps, but it has the advantage of blowing most of that heat out the exhaust, instead of raising itself to a temperature that blackbody radiates it. |
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DC Generator
On Thu, 24 Jun 2004 03:51:08 -0500, Richard J Kinch
wrote: A 25% efficient 5 HP lawnmower engine dissipates more heat than that, with far less surface area. Perhaps, but it has the advantage of blowing most of that heat out the exhaust, instead of raising itself to a temperature that blackbody radiates it. Good point. The engine also has forced-air cooling on the fins. Still, those magnets are pretty big so there's lots of area for convection air cooling. To your first point, we don't know that the magnet draws 10KW, only that it was driven by a generator capable of 10KW. How much power the magnet really draws is indeed a relevant question. |
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DC Generator
On Thu, 24 Jun 2004 03:51:08 -0500, Richard J Kinch
wrote: A 25% efficient 5 HP lawnmower engine dissipates more heat than that, with far less surface area. Perhaps, but it has the advantage of blowing most of that heat out the exhaust, instead of raising itself to a temperature that blackbody radiates it. Good point. The engine also has forced-air cooling on the fins. Still, those magnets are pretty big so there's lots of area for convection air cooling. To your first point, we don't know that the magnet draws 10KW, only that it was driven by a generator capable of 10KW. How much power the magnet really draws is indeed a relevant question. Yes, and as such, I know now that I need to try to obtain more info concerning his particular situation. As I mentioned in another post, I'm getting all of this "second hand" and basically was told he was looking for a 10KW DC generator.... Hell, for all I know, he may be using an AC generator :-) Next time I see this "second hand guy", I will let him know that I could use a bit more into. Thanks for all the help and suggestions. Ken. |
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