220V 30A switching under 500hz - confused

Discussion in 'Off-Topic' started by ChrisHelvey, Jul 28, 2009.

  1. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    Hello everyone,

    I am designing a project that will require a switching device (probably IGBT or MOSFET) that will conduct up to 30A of a 220V rectified sine wave to the load (the positive sine pulses.) Switching frequency will be 120 to 500hz and never over that.

    Does anyone have any suggestions? I am looking over IGBT datasheets and am a little confused about the ratings for my situation. A typical IGBT with ratings as listed below show power dissipation limits that look like I will need to run quite a few in parallel... Bummer because they are quite expensive. If my project requires 30A x 240VAC = 7200W and the limit on the IGBT = 600W, then am I correct in saying I will need 12 of them in parallel to get the job done? I was under the impression using IGBTs in parallel was not a great idea. The "pulsed" collector current limit is 400A - I wonder if this will change things for me. I wouldn't think so since 600W is 600W no matter how you figure it.

    I welcome any suggestions. I am not an EE, just a self-taught inventor with limited funds. I figure you guys might have some creative ideas.

    Here are the specs:

    STGE200NB60S Electrical ratings - from the datasheet
    ______________________________________________

    VCES Collector-emitter voltage (VGS = 0) 600 V
    VGE Gate-emitter voltage ±20 V
    IC Collector current (continuous) at TC = 25°C 200 A
    IC Collector current (continuous) at TC = 100°C 150 A

    1. Pulse width limited by safe operating area
    Collector current (pulsed) 400 A
    PTOT Total dissipation at TC = 25°C 600 W
     
  2. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    To be more clear on the question:

    If the part description is 150A and 600V, does that mean "150A @ 600V" or that it is capable of "150A and 600V in any combination that doesn't exceed 600W within those parameters?"

    I'm hoping the former, but I'm not holding out too much hope......
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    150A or 600V are different limits. They do not occurs at the same time. So the datasheet is simply telling you the device can safely conduct 150A or withstand 600V without breakdown. Now you see these two limits are unrelated. There will be just a few volts(4 volts or less) across the device @150A current to stay within the 600W max. power limit.

    If your operation calls for the device to switch ON/OFF like a switch, then you will be fine with just one device, provided that the voltage rating and current rating suits your requirement.

    That's one mode of operation, i.e. using the device as a switch, just like a mechanical switch.

    If you wants the device to act as a linear regulator, which means there would be voltages more than 4V while it is operating/conducting (likes a resistor or regulator), then V*I= 600W is your limit.

    I have not used IGBT but 600V sounds to be not sufficient for a rectified 240V AC circuit with peaks of 340V. Maybe 800V is a more safe choice. This would be left for others who have experience with them to comment.
     
  4. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    at those power levels i would suggest using mosfet with very low Rds(on) spec. i am assuming you wish to turn it on/off quickly. better advice may be given if you tell us the application, etc.

    as for the DC, 240ac is rms AC and should rectify out in full bridge to be about 240v DC (when properly filtered on the output), but the fet or igbt needs to withstand the peak voltage. but you did say "the positive sine pulses" which sounds like half wave rectification. please clarify what you are doing.
     
  5. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    The voltage and current specs are always meant to be used within the maximum power spec,so it means up to 600 V and 150 A until you reach the power limit. Regardless of the device technology, it all boils down to how fast you can remove the dissipated energy from the device -- otherwise it heats up and bad things happen like insulators stop insulating and conductors suffer electromigration.

    The IRF840 and similar devices might be suitable MOSFETs to look at. I looked at the data sheet last week for constructing a load. The IRF840 is rated at 125 W, meaning a good design would probably take them to 80-100 W each. These devices were less than a buck apiece. There are likely other IR devices more suited to your application.

    The key to using these is getting rid of the heat, which takes good heat sinks with proper mounting. The heat sinks can cost more (sometimes much more) than the MOSFETs.
     
  6. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    Hmm. So this thing is going to be BIG and/or expensive. Powerex makes an IGBT that can handle 3785 watts (@1200V/600A) $165.00 US each!
    I would need two in parallel on each leg of what I am doing and it has four legs.....yikes, over 1200.00.

    OK. Without explaining something about this project, it probably won't make any sense, so I will reveal it here. Anyone who can pitch in is welcome. You will be helping to experiment with efficiency of making Hydrogen.

    Hydrogen/Oxygen Electrolyzers are pretty inefficient overall. But electrolyzing water has some big advantages in the Hydrogen economy, mostly the fact that water as a carrier is almost everywhere and so is electricity (solar, wind, etc.) I don't wish to get in a big debate as to how to fix the world's energy needs. I am working on creating a better electrolyzer.

    I have been able to create vastly more efficient electrolyzers by using a large capacitive power supply instead of a transformer. Cell voltages remain under 2 volts. A series cell electrolyzer is a bunch of these cells in series running at 220V. As peak AC voltages rise to 270V plus, current flows heavily through the electrolyzer. About, say, 20% of the 1/120 of each second. As it is doing so, it can hit 30A (although I can limit that in the design.) It is plain old positive to negative, or the other way around depending on which "current" school you come from.

    I am working on a way to reverse the current direction without reversing the voltage polarity every half-wave cycle. I am using a PIC to detect zero crossing of the sine wave and operate a set of switches for that half-wave which will let the current through. Then, at the next zero crossing, that switch set is opened and a different switch set is closed. In theory, this will have a magnetic "shearing" effect on the Hydrogen, much like sliding two magnets apart insted of just pulling on them. This could vastly increase efficiency of the amount of Hydrogen/Oxygen created compared to the amount of electricity put into the system. There are two "positive" and two "negative" posts on the electrolyzer.

    However, it sounds like I will probably lose all of the gained efficiency to the IGBT heat. It may end up being a wash, or even significantly less efficient this way.

    So, I really need a very efficient way to rectify the sine wave and have one pulse go one direction and the next go a different direction, and completely cut off the "off" lines each time. A diode-only scheme does not work.

    Any creative thoughts are welcome.

    Chris
     
  7. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    Is there a way to calculate, at maximum power, how much heat needs to be dissipated? This could tell me how much efficiency I will lose in the design.

    If I only need to shed the equivalent of 5 watts of heat to a heat sink of 3785W total going through it, then it probably is not a problem as a percentage. (.1% loss is great if we gain 25% efficiency overall.) If it is more like 500W, then cost becomes an issue.

    See what I mean? I hope that question makes sense.
     
  8. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    Let me be the first to say just burn your money. HHO is a scam / moneypit. Doesn't work.
     
  9. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Hi, Chris:

    I fail to follow why you need the PIC and the switching to reverse the current. Why wouldn't you just rectify the incoming AC with a full-wave bridge, then apply the unfiltered DC to the stack of electrolytic cells? Then the only thermal losses in the overall circuit would be in the diodes and the conductors. Or are there some things I missed?

    Based on some questions from a colleague a few years ago, I took a brief look at the "well to wheel" sensibility of hydrogen. Hydrogen has some attractive features. But the most stultifying aspect was the capture, storage, transportation, and distribution of the stuff. We simply don't have the infrastructure for it and developing one will cost a lot of money -- a lot of money.

    Before you invest lots of time in this, I'd recommend taking a look at the energy costs of generating the hydrogen and compressing/liquefying it for storage. You should be able to find everything you need in something like Chilton & Perry's "Chemical Engineer's Handbook".

    blueroomelectronics: this is clearly not the usual moronic "run your car on water" crud that was popularly being used to scam people a few years ago.
     
  10. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
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    Not necessarily talking about HHO. Electrolysis is a tried and true technology and there are ways of increasing efficiency. This works on separate H2/O2 collection as well.

    It is way too easy to just say "it doesn't work."
    Have you ever built one? (I have built many.)
    Have you ever tested the efficiency rates of power in and potential power out? (Yes, it is negative - no free lunch.)
    Have you ever installed HHO on your own car, along with an O2 feedback modifier to your fuel injection ECU and seen your fuel mileage go up yourself? (I have.)
    Are you aware that Hydrogen radicals have been witnessed to decrease radiation of radioactive waste?
    Are you aware that HHO acts on the efficiency of gasoline combustion, not as a fuel itself? (If you are wondering where the "extra" energy comes from, it comes from more expansion of gasses at the beginning of the power stroke.)

    Since I am not selling anything, I don't think you can consider this a scam. I have support and limited funding from the University of New Mexico to undergo testing in academic environment. Academic peer review is typically what lends credibility to these things. LOTS of mis-information out there about Hydrogen, its capabilities, and limitations.

    Thank you, but please refrain. You can watch from the sidelines.
     
  11. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
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    Thanks "someonesdad," (Hey I'm someone's dad too!)

    Yeah, the first idea was simple rectification. But in real-life, it doesn't work. The first two cells on each end take on the same potential, essentially changing the polarity of the cells. Then we just have alternating polarities as well as direction. I think switches need to hook and unhook the second cell from the first.

    Maybe you are thinking of something I am not seeing.

    By the way, the reason you stated about Hydrogen transportation is the very reason why electrolysis becomes important. I person can't have his own own crude oil refiner in the back yard, but could have an electrolysis unit and make his own Hydrogen. Automobile internal combustion engines are FAR more efficient (less wasted heat) running on Hydrogen than they are on gasoline. (One plus.) Hydrogen conversions are essentially a way to turn your current vehicle into an "electric" vehicle (because that is ultimately where the power came from.) If you buy "solar electricity" from your grid provider, such as we can do here in Taos, NM, you now have a completely emissions free car.

    10,000psi tanks are inexpensive now.

    This is not a panacea. It's a start. Every time we increase efficiency of electrolysis (or combustion, or light,) we are a little closer.

    Thanks,

    Chris
     
  12. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    Thanks "someonesdad," (Hey I'm someone's dad too!)

    Yeah, the first idea was simple rectification. But in real-life, it doesn't work. The first two cells on each end take on the same potential, essentially changing the polarity of the cells. Then we just have alternating polarities as well as direction. I think switches need to hook and unhook the second cell from the first.

    Maybe you are thinking of something I am not seeing.

    By the way, the reason you stated about Hydrogen transportation is the very reason why electrolysis becomes important. I person can't have his own own crude oil refiner in the back yard, but could have an electrolysis unit and make his own Hydrogen. Automobile internal combustion engines are FAR more efficient (less wasted heat) running on Hydrogen than they are on gasoline. (One plus.) Hydrogen conversions are essentially a way to turn your current vehicle into an "electric" vehicle (because that is ultimately where the power came from.) If you buy "solar electricity" from your grid provider, such as we can do here in Taos, NM, you now have a completely emissions free car.

    10,000psi tanks are inexpensive now.

    This is not a panacea. It's a start. Every time we increase efficiency of electrolysis (or combustion, or light,) we are a little closer.

    Thanks,

    Chris
    [​IMG] [​IMG]
     
  13. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
    1
    Sorry about the double post...
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Don't worry about the double post...

    This got relocated, as this topic keeps coming up, but appears to be a scam every time.

    "Of course it works", they say, but grow strangely quite when pressed for facts and figures. When we start seeing things like testing methodologies and actual before and after figures, perhaps we'll have something to listen to.

    Electrolysis was completely and accurately described back in 1820. Nobody, especially Meyer and/or Boyce, has been able to improve on that rate of production with electricity. It has never been demonstrated that electrolysis can be made more "efficient", especially by strange combinations of voltage and frequency.

    Got any way to back up the claim? -
    We have had many claims tossed off, but not one actual fact to back them up.
     
  15. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    years of hydrogen can be had from nuclear power, efficiency doesnt matter. it will get more efficient when we see fusion reactors online. either way, the efficiency part of the equation becomes insignificant because the power source is plentiful. so in reality we can have all the hydrogen we want and sell it for profit, the problem is who is spending the $$$ to use it safely, thats where the problem is. is gasoline pumps could overnight turn into hydrogen stations, and gas tanks could overnight become H tanks, problem would be solved, but they wont, so back to the drawing boards.
     
  16. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    I'll give Chris the benefit of the doubt, as he originally asked a question about how to switch/control AC power at > 1 kW levels. He doesn't appear to be one of those folks who try to sell people information on how to run your car on water.

    Chris, you've said that you recognize the problems with transporting hydrogen; you stated that one way around this would be to have individuals generate their own hydrogen using electrical power from the grid. It's an intriguing concept, but a technical and economic case would have to be made for it.

    So, let's look at it from an objective, basic physics standpoint. This forum has a number of experienced engineers and physicists. If you're interested in continuing the discussion, it would be useful if you put down some facts and numbers that show that the basic idea of an individual generating their own hydrogen at home would make sense. Since everyone understands the dollar at a pretty visceral level, let's keep it involved too, since the economics are important. I've attached a graph showing the cost of electrical energy in the US (data for April 2009).

    Also, I'd like to see some factual backup of your statement that auto engines are far more efficient on hydrogen than on, say, gasoline. The auto engine is a heat engine and is pretty inefficient at that -- something on the order of 15-20% thermodynamically efficient, if I recall correctly. If one assumes combustion temperatures will have to be the same whether using gasoline or hydrogen (because otherwise engine life will be affected), then I'd like to know from a thermodynamic standpoint how hydrogen can be far more efficient than gasoline. The gas molecules doing the pV work don't care where their kinetic energies come from.
     
  17. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    more or less efficient in a piston type carnot heat pump, not much.

    hydrogen fuel cell to electric motors is indeed much more efficient than a carnot heat pump (aka gasoline engine). however, as of today total efficiency of the resource(s) can be comparable.
     
  18. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
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    I see... fusion reactors?

    Sandbagged. I should have known to not get sucked in and just keep to the electronics questions.

    Well, as far as Hydrogen ICEs are concerned, here is a typical article about the efficiency of Hydrogen combustion engines. http://www.worldcarfans.com/104092010255/bmw-sets-9-records-with-hydrogen-combustion-engine . BMW has published papers about the efficiency of Hydrogen engines. You can look them up for yourself. It is fairly well documented that these gains are due to higher temperatures where engine efficiency is measured as E=(Th - Tl)/Th ,where Th is the highest temperaure achieved and Tl is the lowest temperature at the end of the stroke. Also that force on the piston is the square of the flame speed, which is six times faster than gasoline. But then again, BMW probably doesn't know what it is talking about. Yes, there are still a lot of problems.

    And as for the efficiency of electrolyzers, well I guess there is no point in even trying. Academic peer review of US patent #7,041,203 by John Timothy Sullivan of creating a magnetic shearing effect in electrolyzers would just be a big waste of time. Kind of like Tesla's "Alternating Current" or the Wright brothers "flying machine." Good thing no one followed up on those hair brained ideas....

    And just for the record, this project is ALL about putting some of this theory and design into academia at UNM where there will be testing methodology along with before and after figures.

    But then again, instead of putting it in a lab and testing it, lets just restate everything someone else has told us and go "back to the drawing boards."

    I did get my question partially answered though. Thank you. We can consider this thread closed. I'm out.
     
  19. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
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    why out? i find this interesting. so the idea is to reduce the cost of H whereby $10 of H in a H combustion engine nets more miles than $10 of gasoline. ok, sounds plausible. so my question is, where are we today?

    i do not think this is a case of how to produce H more efficiently. i believe it is a infrastructure issue. correct me if i am wrong, but as of today transporting H is much more expensive and more dangerous than transporting gasoline. i guess at-home production is feasible. there's also a catch-22 here. if we suddenly switch to 100% nuclear power for electric this will eventually drive gasoline prices down, so the cost-per-mile may favor gasoline.

    i believe it doesnt matter what fuel you embrace or develop as "most efficient", it will boil down to a "green" argument.
     
    Last edited: Jul 28, 2009
  20. ChrisHelvey

    Thread Starter Active Member

    May 22, 2004
    45
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    Oh, I just couldn't help it. Someonesdad was pretty cool about continuing the discussion in a reasonable manner (I posted before I saw his post.)

    OK, economics of solar/wind sourced electricity as opposed to fossil fuels (Remembering that Hydrogen is just a storage medium of the electrical energy we put into it:)

    If we install solar/wind based power generation of any size, we will know exactly how much the power will cost us to create 20 years from now. The lifespan on these renewable sources is longer than 25 years and we know how much we paid for them. Divide it all out and you have your cost per kW well into the future. Can any one of us predict the cost of fossil fuels 20 years from now? Even one year from now? Didn't think so. So "cost control" is probably a bigger issue than cost. (This is probably the number one reason that power grid generators are seriously looking at renewable sources - cost tomorrow.)

    Fuel cells are great. Love them! Seen them in action (methane ones.) Very cool.
    Electric cars are awesome. Seen those too. Can't wait to have one of those myself.

    But, there are 500 million registered cars in the world today. Are we all expected to buy new cars? What if we could convert an existing ICE to electric?
    Electric motor conversions would be too costly and complex, and would place a strain on the supply to the copper market (all those big motors have lots of copper.) Kind of a lame argument, but one to consider.

    Well, we CAN (if people keep working on Hydrogen conversion issues and ways to make cheaper and more efficient electrolyzers.) Then, it could be an economical way to use grid power (or even better, your grid tied system) to put juice in your car. And when the fuel cells come along, you will be set there too. There is NO DOUBT that gas is cheap. But it will certainly not remain that way and all the economics needed are in that statement.
    This company has created electrolysis efficiencies of over 75%. http://www.qsinano.com/white_papers/2006_09_15.pdf

    Can we do better? Yeah, I think so. By combining some good ideas together, I think so. The wheel and the suitcase have both been around for a long long time, but it wasn't until recently that someone put them together to make the fabulous rolling suitcase.

    DC_Kid is right, it does come down to "green" issues. I support them. If someone doesn't, then all this talk is moot for them. I am not going to get involved in that argument, I'm simply trying to build a better power supply and a more efficient electrolyzer.

    As for Hydrogen ICE efficiencies. BMW claims efficiency levels on the order of 45% - approaching fuel cell efficiencies. The "far" more efficient part comes with WHEN the higher temperatures happen and for how long. (At the beginning of the power stroke and not many degrees before it, along with a higher INITIAL temperature.) In fact, Hydrogen engines run much cooler (they have converted more of their heat energy to kinetic energy.) My own Honda 9HP single piston engine converted to Hydrogen is a testament to that. You can almost hold your hand on it after idling 5 minutes. Additionally, Hydrogen engines run lean - no throttling. That vacuum is upward of 15% loss.

    As for nuclear....that's the most expensive electricity we can make. And unless someone really does find cold fusion (we can all hope - and I'm not against trying) that price isn't coming down any time soon.
     
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