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Forum Index : Electronics : Circuit for newer type Inverter
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| Arthur Newbie  Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Good day, I am looking for a circuit of the newer type of inverter. I'm interested in how they work rather than a circuit for my needs which are 24volt to 230volts a.c. 3Kw please no replies that I can buy one cheaper and safer because it just aint true. thank you Arthur |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
What would you consider a newer type inverter? What price would you consider appropriate for a 3kW unit? Gordon. become more energy aware |
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CraziestOzzy Senior Member Joined: 11/07/2008 Location: AustraliaPosts: 135 |
I agree with GWatPE in that you need to define "new" so I or others can answer your question, 1) Logic CMOS IC technologies that allow for fewer components? 2) "New" relative to overall design concept or one particular individual company or individual upgrade? 3) DSP's controlling the "new" high frequency PWM's? 4) Is your desired inverter to be off grid? 5) Source of DC to be inverted is from a single source (I assume that to be the case here)? 6) IGBT technology? (I am currently delving into this one myself as I like cranked switches) 
cheers http://cr4.globalspec.com/member?u=25757 http://www.instructables.com/member/OzzyRoo/ |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
|Hi Gordon, thank you for your reply, by newer I ment the newer generation that does not use a back breaking transformer as in the older type. I have transformers that would do the job (I'm a radio hsm) but intend having the inverter on line all the time and dont want it to draw 5 to 6 amps doing nothing, so thats the position also looking for a modified square wave inverter, many thanks Arthur |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Many thanks for your reply, I have worked in electronics for 25 years but retiered and ill health has kept me from keeping up with technology which moves on at the speed of light Hi!! I replied to Gordon but I can see that some things have been left out, Yes it will be off grid 230Volts 50Htz. The inverter is to replace the present Mains supply for half the house; I would need 2 to cover the other half and I dont think I can generat enough power from the wind generator I am building (700 Watts) to cover both at all times. I'm most greatful for your reply and hope I can be directed in the right direction. Thank you Arthur from a freezing Wales |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
The only way without the 50Hz transformer is to DC-DC convert and then switch the high voltage output to give 50Hz. I am not a fan of this approach. I have seen many broken by the loading. Gordon. become more energy aware |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Thank you Gordon, I'm wondering how these Chines inverters work they appear lightweight but produce well I have seen 1Kw once I'm sure there are larger once around. Arthur |
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Bryan1 Guru  Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
Hi Arthur, For bang for ya buck you can't go past the Kipoint sinewave inverters. The 3kw one i bought has similar spec's to my house inverter, a selectronic 2400 watt sinewave. I use the 3kw for 99% of my Re machineshop work and it happilyruns a 3 phase bridgeport mill via a vfd. The idle current draw is around 4 watts and you'll be very hard pressed to make anything close to that. The cost of the special toriod alone and the switchmode circuit will be 3/4'ers of the price of one of their inverters. Cheers Bryan |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Hi Brian, Thank you for your message; thats my problem I'm about 20 years behind the time in electronics; I dont know how these lightweight beasts work but would like to see the circuit of one. Arthur |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Hi Bryan, I'm in the market for a pure sine wave inverter though it would be a smaller one than your 3KW monster. Was your dealing with Kipoint trouble free? I gather the deal was done on e-bay? What I like on these inverters is the low idle current and large surge capability. I suppose you had yours long enough now to find out if it has reliability problems? Thanks Klaus |
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| CraziestOzzy Senior Member Joined: 11/07/2008 Location: AustraliaPosts: 135 |
G'day Arthur, Keeping in mind that you don't want to use heavy back-breaking transformers... I think this PDF document will help explain some of what is new with regards inverters and IGBT topology anyway. Circuits can be simple or complex. I hope you have an understanding of PWM (pulse width modulators) and DC control. Max038 IC PDF document has some interesting high current potentials ...but going off track with this one 
DSP High-Frequency DC-DC Switching Power Converter provides in-depth reading, just ignore the maths if you go crazy. I may have not answered all your questions or even any, as I have only given snippets of information that I hope will provide some understanding (however misguided from myself) into the new stuff people are employing into inverters and/or regulators without the use of transformers. I believe that a direct DC to AC conversion may be done by simply a phase timed pulse oscillation...damned forgot where I read that the other day. Cheers http://cr4.globalspec.com/member?u=25757 http://www.instructables.com/member/OzzyRoo/ |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
I'm sorry i dont know your name, but thank you so much you have told me what goes on inside the light inverters. I have searched for hours but now have saved the info you were so kind in giving me. Now to search for the devices used:) Arthur |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1211 |
Hi Klaus, I delt direct with Kipoint to get my inverter, it worked out cheaper and the direct feedback I got was great. When I got stuck with customs they even tried to tell the govt this was a sample but they wouldn't buy it. Maybe now it may be different now we got rid of that nazi of a primeminister (howard that is). This inverter of mine runs 24/7 and has done for near 3 years now and when ever I need power it delivers. Cheers Bryan |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
Hi Klaus, thank you for your comments. I;m an avid d.i.y. and have been for 50 odd years hence my looking for a circuit; have received some very useful information on this forum so far. Arthur |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
To crazyOzzie regarding the inverter, i see your on line but dont know how to connect to u if that is possible? my thoughts are thre power mosfets in a bridge, have some infol on feeding them pwm etrc but am lost as to hnow I'm going to get 230v ac at say 1,.5kw out of the thing, I beleive it involkves hf dc to dc inv erter which the bridge will conv ert to ac but how am i going to get that power into the bridgwe? if you have any circuits or suggestions would be welcomed, thanks Arthur |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Not sure where you are with this, as I have just noticed this post (busy lately). The mod sine inverters are fairly simple devices which consist of three stages basically Stage 1 We need to get the 12v (or whatever) up to 340 or so volts. This is done simply with a push pull pwm chip. It is important which chip you chose for this part, as you want one that will provide symmetrical wave pulses, or a DC bias may accumulate in the core of the tiny transformer and saturate it with predictable consequences. Switching will usually be in the 30-50hkz range... making for a very small transformer... no more backbreaking. The usual arrangement is positive to the outer of the primary, switching the commons to ground with n channel fets (more power, more fets). Current limiting is essential, and the pwm chip does this and provides the necessary pulse width to keep the output at 340v or so.... regardless of the load. Stage 2 Now we have 340vDC to play with, we simply use a H bridge of fets to switch the pulse +/- . We can use counter chips, or pics or whatever to provide the timed pulses. The pulses need to be made to allow for a peak of 340v, but with an average of 240v. It won't be a sine wave, but will carry the same peaks and rms as it's sine counter part. Driving the fets can be done with simple torroids making for easy coupling. Small inverters use cunning circuits to allow for the high side switching pairs to be driven more cheaply. Stage 3 We stand back and watch the pyrotechnics display. This is easy in theory, and easy in practice if you know how to design power electronics. I don't. I can fixem up no problem, but power electronics layouts seem to be steeped in black magic. It is relatively easy to get it to work , but as you ramp up the power, you hear the Fets start to scream.....(usually because of current loops forming, and switching noise getting into the drive lines... and things generally becoming unstable..... it gets exciting after that. A simpler way out, is to buy a tiny 240v converter (150 watts or so), and use it for the H bridge driver..... ie drive it with 12v, get the 240vac.... drive 4 tiny power transformers.. 240v:12v... this gives you direct drive for driving the H bridge mosfets or IGBT's. These will have plenty of low impedance driving capabilities. The frequency is taken care of, the wave form is taken care of... you only have to worry about the push pull dc:dc converter, which is fairly simple. Most of the bigger power devices use parallel units no bigger than 300w. So for 1000w, they use 3-4 small 250-350 watters in parallel to get the 340vDC, and then switch that out. See... simple if you say it quickly? ........oztules Village idiot...or... just another hack out of his depth |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5030 |
Hi Arthur I can see where your coming from. The new inverters are much lighter than the older designs, so the thinking is there is less to them internally. Older design inverters, and UPS's, used a large low frequency ( 50 or 60 Hz ) transformer to step up the voltage. The transformer was heavy and expensive, so manufacturers came up with a lighter and more efficient design. Modern inverters and some UPS's now use a high frequency ( 20kHz or higher ) transformer, much smaller and lighter than the old low frequency transformers. The thing is, driving these new high frequency transformers is much more difficult. The circuit design is critical, the transformer, drive circuit and load are all precisely matched, and there are built in safety and overload circuits to protect the components. So while modern inverters may be lighter and usually cheaper than old designs, there is actually a lot more circuitry and know how in the new designs. This type of power circuit is what we commonly call a "switch mode power supply", and is now very common in PC's, plug packs, UPS's, TV's, etc, etc, just about anything that once used a large power transformer. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Arthur Newbie Joined: 05/03/2009 Location: United KingdomPosts: 28 |
most greatful for your reply (I must print it out tho  )
I beleive that you have answered my question very eloquently and in a very readable manner. I can only thank you for your time and your knowledge of the subject. Arthur |
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| woodchips Newbie Joined: 05/01/2009 Location: United KingdomPosts: 27 |
Hello Just a suggestion, look in manufacturer's data books from Linear Technology and similar, lots of ideas. But this really isn't easy stuff to design. Since you are in the UK then have a look at www.cpc.co.uk, sell a whole range of DC/AC inverters. I have used code PW01702 for running the fridge and lighting for years, brilliant. Also try Switched Mode Ltd on 0118 930 2113, I have a 1500W inverter, again excellent, but they were also very helpful when I contacted them. Bob |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Arthur, I don't know how the rubbish system works over there, but the rubbish tip is an excellent place to find broken inverters and UPS devices. I am on a small island, and low and behold, I found a busted up 2kva pure sine wave 96dc-240vac ups. I shall be returning to the dump today, and try to find the rack/box/metalwork for it... as I think it should be working by tonight. (it only had the circuit board... someone had butchered it and left it to die. Your island is lots bigger than mine... there should be plenty of good pickings, or Ebay for damaged or non-working ones. Much easier to fix than build from scratch. Just getting the inductors/transformers is worthwhile and will save a lot of time and fiddly work.. Bob, your typing looks good. Hope your hand has made a full recovery. .............oztules Village idiot...or... just another hack out of his depth |
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