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Inverter question

Discussion in 'Amps and Cabs [BG]' started by Jennifer, Jan 18, 2001.


  1. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    Ok, I have been working on getting off the grid and have another question. Does anyone here have experience with inverters? How imperative is having a sinewave inverter compared to a modified sinewave?
     
  2. MikeyD

    MikeyD

    Sep 9, 2000
    I have not used an inverter, but I know something about electronics. I don't know what you mean "modified sinewave". Can you point me to a product or web site that discusses it? Ideally, the inverter would create a perfect 60 Hz. sine wave (in the USA) at the proper voltage level. Some equipment, such as incandescent lights, won't mind a distorted sine wave. Some - such as radio or audio equipment - might pick up too much noise from the inverter. If you could provide more background, that might help.

    - Mike
     
  3. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    MikeyD, I haven't found a really good information site for inverters yet. Mostly just bits and facts from companies that sell them. From what I think I've learned so far, there are 3 types of waves that inverters create: sinewave, square wave and modified sinewave (which is actually a modified square wave when you look at a graph of it). I think that there would be problems trying to run various appliances with a MS. Flourescent lights and and digital radios can be a problem, like you mentioned, and also I think if you try to run something with a variable speed motor, you might get one speed only. I don't know how the MS would affect things like a TV or computer or well pump. Naturally, the sinewave inverter is much more expensive than the other two types. I am slowly working on getting my house self-sufficient power-wise. I'll be running off batteries powered by solar panels to begin with and then add a wind generator. After that, my goal is to install a geothermal heat pump. I am going to do most of it myself (if not all) cause this stuff is expensive!! There's alot of info out there, but it gets confusing if I go too fast. :)
     
  4. On standard old-school electronics, it is pretty important to have a real sine wave. The power supply sections work off the peaks of the sine wave. If the inverter is faking it, and only supplying a square wave with an RMS value of 120V, electronic equipment will not work properly, although a light bulb will work fine on it.

    I'm not sure what you mean by modified sine. That could mean PWM, which is pulse width modulation, or something else. Depending on how "modified", it may or may not work.

    Electronic gear is very non-linear in its current requirements, so the inverter will probably have to be over-rated quite a bit to work properly.

    All that I know.

    Chris
     
  5. MikeyD

    MikeyD

    Sep 9, 2000
    Hey, Jennifer,

    It's totally cool that you're trying alternative energy. I haven't done that much with it myself, although I have done quite a bit of reading on it, and I'm an engineer. A few years ago I checked out a house in Maine that was totally off the grid. It was a big place, too. Pretty interesting set-up. You are right that it takes a lot of up-front capital, though.

    I'm thinking that "modified sine" is something like you get when running it through SCR (thyristor) choppers - part of the sine has the right shape, but then one side is lopped off. Such things do generate a lot of RFI (radio frequency interference).

    For the sake of this forum, we can probably talk more about what such devices should be used relative to bass amps and electronics. For more general information about "going off the grid", I suspect there are lots of other forums from which you might get much better information. I have no idea what or how many appliances you are going to run off of that inverter. There are people around who specialize in "going off the grid" who can help you with this. I think I can find a few links for you, if you're interested.

    Rather than get into a general discusssion about alternative energy, I'll try to address this in the context of a bass amplifier. I think there are a lot of parameters for you to consider. One idea might be to run the non-critical stuff off a cheaper inverter, and power your computer and electronics off of a better one (with cleaner output). Another option might be to have one big inverter for the house (but with decent voltage regulation), then have separate power conditioners where you plug in electronics. The latter would probably have their own isolation transformers and filters, so that the output is very close to a clean sine wave.

    To throbbinnut: I agree with your comment about square waves - a square wave's peak and RMS voltage are identical! So the waveform will not have the sine wave's 170-volt peak, as you suggest.

    - Mike
     
  6. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    There's alot of learning involved, that's for sure! But it's really quite interesting, something I've been wanting to do for a long time. That would be great if you could hook me up with a few forums, I'd appreciate that.
     
  7. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    Mike, since you have a background in electronics, I'm sure that we can disaggree on a couple of points without it becoming an argument about the finer points.:)

    I don,t believe that an SCR chopper circuit just lobs off one side of the current waveform to achieve A.C. voltage regulation. By segmenting the waveform the R.M.S value of the waveform is reduced while maintaining a sine shape. A circuit such as you describe would be better accomplished with a peak limiter, or zener "circuit" of some sort. I totally agree with the RFI problems with the square wave. I also agree that a chopper utilizing SCR's generates square waves. However the square waves after they are chopped are really at a higher frquency than 60 hrtz. The higher the frequency the lower the value (and expense) of the components needed to filter the RFI. If you put 10 segments in a 60 htz sine wave, you will be dealing with a frequency of 600 htz. Much easier to deal with than 60 htz square waves.

    Juggle the component values in an integrator circuit and you will see what I am attempting (very poorly) to say.:)

    As far as this subject being in the amp forum, I, in essence, agree with you. However, as an engineer, you will have to agree that the very same rules of electricity apply to bass amps that apply to alternative energy schemes and vice versa.

    Some of the tech types have requested a forum on "theory". I'm sure that the requests have been considered by Paul and that when this sort of subject becomes a nuisance on this forum that a more suitable forum will be provided.

    I am very interested in Jennifers project and according to the response by other members I am not alone.

    I hope you understand that my post is not meant to cut your opinion down. Just another opinion. Your credentials make your opinions valuable to me. As always, I stand to be corrected.

    ==========================

    Jennifer: I think I might consider not disconnecting from the grid at all. I'm sure that you are aware that the same company that you buy electricity from is required by law to buy the electricity that you generate at the same price that you pay for it. In other words, you can use the power grid as your battery bank normally. Instead of temporary storage, you sell the power to them. In the event of grid loss, you then use your storage batteries. As long as the wind blows or the sun shines, you could sell everything that you don't use.

    As far as the technology to make yourself self sufficent goes, it's already there. As Throb said, there are lots of websites that are dedicated to just that subject. However with guys like Mike to provide a little guidance, you at least know what questions to ask.

    Now, hoping I haven'y p***** Mike off, I'll shut the heck up.

    Pkr2



    [Edited by pkr2 on 01-19-2001 at 02:19 PM]
     
  8. Jennifer

    Jennifer

    Jul 31, 2000
    Erie, Illinois
    pkr2, I wasn't planning on totally disconnecting for the very reason of selling back excess. However, I hadn't thought about using the utility for storage. That sounds interesting, selling the energy without storing it myself. It would require a much less expensive battery bank for back-up purposes only. That certainly gives me something to think about.
     
  9. The utility will install a seperate meter (at your cost of course) to allow you to sell electricity back to them. Why a seperate meter, you ask? Because they will buy it from you at a cheaper rate than you buy from them, hence the need for 2 meters. They are required by law to buy the energy from you, but not at the same rate you pay to them.

    Tron-heads,
    You guys are talking about SCR's, but remember that they have no way to turn themselves off, just on. They are used in motor controllers to delay the conduction time of the sine wave, for instance. In this case the SCR has a time to turn off every time the AC wave passes through 0-point. In the application we are talking about, we are talking about chopping up DC, so FET's, BJT's, and by now IGBJT's are the norm, I think.

    My personal fave--Motor Generator set. Yeah, DC Motor direct coupled to an AC generator with control circuitry for regulated voltage and frequency. Nice. What you lose in efficiency, you make up in waveform cleanliness and coolness of moving parts. :D And you could theoretically hook in a gas or diesel engine to drive the generator if needed. Oh yeah, engineering rocks.

    More diarrhea of the mouth.

    Chris
     
  10. Forgot to muddy this up....

    I think you speak of PWM, pulse width modulation, which uses higher frequency chopping of DC to achieve a lower average value voltage. (A positive portion and a negative portion can be used to make an AC waveform. Class H amplifiers use this theory for sound amplification output!) This depends on the fact that what you are feeding is a low-pass filter and the higher frequency content is not even seen by the equipment, just the lower frequency equivalent.

    The true SCR control on AC waveform does just hack off the front of the humps of the sine wave for RMS voltage control, and then it does not look like a sine wave, the hard cut-on point has frequency content way above 60Hz, so it's a nasty waveform. It too by definition is a PWM action, since it is changing the width of the Sine wave pulse, it's just doing it at 60 Hz. The SCR stays off til you turn it on by "firing" the gate, and then the gate loses all control and the current continues to flow until it falls below the holding current threshold due to the voltage swinging through 0-point. If you were to turn on a SCR (thyristor) being fed by DC, it would never turn off.

    Even more diarrhea of the mouth.

    Chris
     
  11. How about we make this more practical for a bass player.
    Have your dc motor or gas engine run a dc generator with external excitation. Hook a preamp up to the exciter wires and a speaker(s) up to the load: 5,000 watt amp

    Rockbottom
     
  12. MikeyD

    MikeyD

    Sep 9, 2000
    I love it! :) I was thinking of taking a farm tractor I had and using the extra hydraulic circuit, modulated by a electromagnetic valve, to drive a hydraulic loudspeaker. Now we're talking 22,000 watts or more! It would be the ultimate subwoofer!

    - Mike
     
  13. You guys are all nuts! I like it. Posts like this help me to refocus on why I'm studying engineering. It helps me to put up with being tortured at school. Thanks! Engineering DOES rock!
     
  14. MikeyD

    MikeyD

    Sep 9, 2000
    Hi, Jennifer,
    Good for you! I wish more people were thinking and doing as you are. Anyway, below are some links I have on alternative energy you might check out. I haven't spent much time with them, so they may or may not be useful to you. I'm sure there are a zillion (that's a big number, I think) more. BTW, I've started using Google ( http://www.google.com/advanced_search ) for my searches lately. A pretty good engine. Here are a few:
    _ http://www.advancedenergy.com/
    _ http://nesea.org/
    _ http://www.homeenergy.org/
    _ http://www.mrsolar.com/
    _ http://solstice.crest.org/index.shtml
    _ http://solstice.crest.org/discuss.shtml (discussion groups)
    _ http://www.talmagesolar.com/ (I personally toured Talmage's house, which I mentioned in my previous post.)

    Some Usenet groups (via a newsreader such as in Netscape Communicator - later versions, or http://www.deja.com) to check out:
    _ alt.solar.photovoltaic
    _ alt.energy.homepower
    _ alt.energy.renewable
    I *just* found them, and by the topic headings, they look like they are in the subject area of interest. I have not spent *any* time with these newsgroups, so I can't yet comment on the quality of discussion or information.

    And, finally, a cool magazine for back-to-the-land people: http://www.countrysidemag.com/ (I used to subscribe to the print version).

    Keep reading and asking questions!

    Regards,
    - Mike
     
  15. MikeyD

    MikeyD

    Sep 9, 2000
    Okay, I think there's some miscommunication (to which I also unwittingly contributed). I believe your point is correct in terms of a circuit which chops up a DC voltage and synthesizes a sine waveform from the resulting stream of "square" waveforms. I was incorrect in my reference to SCRs because I was thinking of a variable AC-to-AC converter, which I have worked on in the past for motor drives. The SCR does indeed lop off one side of the sine wave (and as throbbinnut has noted, makes a really ugly, noisy waveform) - I have seen it on an oscilloscope myself. I stand corrected (thank you, throbbinnut!): an SCR is not the basis of a DC-to-AC converter - it would be more like the circuit you suggest which simply chops the DC (some use pulse-width modulation, or PWM, as throbbinnut correctly noted).

    No, and I appreciate your comments. I was simply trying to avoid getting into a huge general discussion about alternative energy because (a) I could definitely get carried away with it myself, and it could quickly go off on a non-"bass" tangent, and (b) I'm sure there are lots of other forums on the web for this. However, I'm not the moderator, so I'll be glad to go with the flow.

    This is an excellent point.

    Nope, and nope: keep writing! Your comments are valuable, and my error in mentioning SCRs didn't help. Sorry about that.

    - Mike
     
  16. MikeyD

    MikeyD

    Sep 9, 2000
    Right you are, Chris! Thanks for waking me up! See my reply to pkr2. You be the EE dude in this forum! :) I'll have to knock on your door next time something like this comes up!

    I wouldn't call it that. Or the other thing is a misnomer! Ahem. Anyway... I wonder how the latest inverters compare to M-G sets relative to cost, efficiency, mainenance, quality of output, etc. The thing I like about "machines" is doing neat stuff like changing 1-phase power to 3-phase, etc. electromechanically. Probably for really big applications (100,000+ volt-amp), machines would be more cost-effective. I haven't been into it enough to say one way or the other. I believe Jennifer is looking at a normal house power set-up, so solid-state electronics might be the better way to go. No brush maintenance, either. However, it might be worthwhile considering the mechanical route, as you suggest, given that one could couple up an engine or tractor PTO to drive the thing on cloudy days. If ambitious, one could build a wood-fired steam engine to drive it, too!

    Thanks again for your comments!

    Regards,
    - Mike
     
  17. MikeyD

    MikeyD

    Sep 9, 2000
    Space: Correction, I'm a cashew. Your torture will be good for this forum. In your agony, just think of your fellow bassists, depending on your sacrifice and suffering for their well-being. You are a martyr for a good cause.
    - Mike
     
  18. The company that I worked for about 10 years ago used Redline motor generators in our test van. these were used to do F.C.C. tests on television cable lines. two diesel batteries and two redline generators powered a whole van full of test equipment all day and longer. The advantage of these generators are that they are load sensitive and only run if you flip a switch on the equipment that is being operated. They come in a varity of sizes and I used them to do testing so they are just like what you get from the power lines. But if you are going to do this as said in another post there is equipment that will let you interface with the power company.
     
  19. pkr2

    pkr2

    Apr 28, 2000
    coastal N.C.
    I was sincere when I asked to be corrected if wrong.

    Thanks, Chris, not being an engineer myself, I certainly wont challenge anything you pointed out. Thanks for sharing your knowledge. As was pointed out by mike "you be da EE". :)

    I also like the motor-gen set-up that was mentioned. Power the drive motor with methane and you almost have free fuel.

    On the other hand, I like the idea of the 22,000 watt, hydraulic tractor powered speaker. The code name for that wouldn't be Fred would "it" Mike? :)

    Pkr2