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250 watt grid tie inverter build

Discussion in 'Alternative Energy' started by Robby, Mar 27, 2009.

  1. Robby

    Robby New Member

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    Hi Tcmtech, I now have a 20 amp transformer as you suggest.Do you have a list of parts, and diagram to complete the GTI please.Thankyou,
    Robby.
     
  2. kevinr

    kevinr New Member

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    TCMTech, I am interested in your GTI. Currently I am using a Control Techniques DC Regen drive with the motoring thyristors diconnected to regen onto the grid. Very noisy but these drives are cheap to pick up. (Free from my work as old stock). Very interested in your 250W design.
     
  3. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Component Selection. Input Side.

    This GTI build up Thread is intended for residants of the united states only! Should you decide to build and use such a device as this you may be breaking laws and can face possible fines, and or jail and prison time for it. Should you chose to build such a device as this and intend to use it for saving energy in your home or dwelling you are still breaking the law. Beware you are considerd a pirate Grid tie operation, which is considered illegal in many countries! ;)

    ----------------------------------------------------------------------------------------------------------------------------------------------------
    I will start this build out with the basic two transformer design and we will build on it from there.

    THE MAIN POWER TRANSFORMER.

    I have a 20 amp battery charger transformer too so I am going to build this one right along with you. The one I have is out of a generic 20 amp charge 75 amp boost unit with 6 and 12 volt capabilities. Its physical size puts it in the 250- 300 VA range so it should be able to run at 250 watts all day with out being over worked. I intend to make this one into a 3 stage system also since the transformer is capable of it. You will see how later.

    However I do expect there will be some slight variations in the actual numbers in everyone’s design due to the vast differences of transformers and components out there.

    THE MAIN H-BRIDGE DEVICES.

    You will need to find some Mosfets or IGBT's capable of at least four times your amperage that you want to run at. SO if we are working with a 20 amp design I would recommend something with at least an 80 amp capacity. Also they should have a voltage rating of at least two times the maximum voltage peak voltage your main power transformer puts out. If it’s a 12 volt battery charger most of them use a center tapped transformer and can actually put out 24 volts with a full wave bridge rectifier set up.

    (The one I have will put out 28 AC volts open circuit. That gives me a peak of nearly 40 volts. 28 * 1.414 = 39.6 volts)

    Knowing that, I would recommend a minimum voltage rating of 80 volts on your Mosfets. Still higher is better. If you’re using IGBT's most of them have a 200 - 1200 volt rating. So there are no real voltage concerns with them on this low of voltage circuit.

    You can go with multiple units or one big unit for each leg. It’s entirely up to you how you want to approach this part.
    I would recommend going on EBay and getting some large IGBT or Mosfet devices if you don’t have any yet.
    The devices you use for the H-bridge do all of the work so over building never hurts here!
    (I have some commercial take outs that are 600 volt 100 amp half bridges so I will use them.)

    THE CAPACITOR.

    The capacitor is a standard electrolytic 250 volt 100 uf. The reason for it is to absorb the small switching spikes that occur every time the H-bridge devices reverse the cycle. I have found that around 5 uf per running amp works well. To big and they are wasting energy. To small and the switching spikes can get high enough to blow through the switching devices.

    The high voltage rating is just because that part of the circuit goes from 0 to maximum volts every half cycle when there is no load. That tends to heat up lower voltage capacitors. swinging from 0 to 40 volts every half cycle is too much ripple for a 50 volt capacitor. But its only a fraction of a 250 volts units working range.

    THE CONTROL TRANSFORMERS.

    To control this GTI I am going with the basic transformer drive system. What you will need a total of 4 isolated 12 volt AC sources to run the H-bridge. If you can find one transformer with that many independent outputs, Great! If not you may have to run 4 individual ones. Or two 12 volt single outputs and one 24 volt center tapped output.
    (What I have are two matching 7 VA units with 120:240 primaries and two isolated 12 volt AC secondary windings on each.)

    THE STAGE CONTROL DEVICES.

    Being my Power transformer has a center tap I am going to use it for one of the three stages. To switch it from one stage to the other I am going with a pair of SCR's that I have. I would recommend going with the same minimum ratings as the H-bridge devices. No less than 80 amps and 80 volts.
    (What I have are take offs that are rated at 150 amps and 800 volts. Overkill again but the price was right!)

    The basic input and H-bridge layout is below. :)
     

    Attached Files:

    Last edited: Mar 30, 2009
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  4. dave

    Dave New Member

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  5. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Component Selection. Output Side

    This GTI build up Thread is intended for residants of the united states only! Should you decide to build and use such a device as this you may be breaking laws and can face possible fines, and or jail and prison time for it. Should you chose to build such a device as this and intend to use it for saving energy in your home or dwelling you are still breaking the law. Beware you are considerd a pirate Grid tie operation, which is considered illegal in many countries! ;)

    ----------------------------------------------------------------------------------------------------------------------------------------------------

    The output side is running at line voltage levels so use some caution and a lot of common sense! If you are not sure you have enough common sense, lick your fingers then firmly grab hold of a grounded line with one hand and the power lead with the other. Either you will have common sense now or the world will have just gotten a little bit better for the rest of us!

    POWER FACTOR CORRECTION CAPACITOR.

    Being I am using a fair quality battery charger transformer that is in the 250 to 300 VA capacity range the output power factor correction capacitor and line filter setup is very simple. For a transformer of this size in this type of application and AC motor run type capacitor works very well. I have a 10 uf 370 volt capacitor from an old 1/3 hp fan motor.

    The PFC capacitor is part of the simple LC tank circuit that helps clean up the switching noise from the near square wave that is being dumped into the low voltage windings.

    Without it you will be getting some bad line noise and harmonics hash going into to your homes electrical system. The actual capacitor value is not exactly critical. I am using a 10 uf on a 120 volt system but you 230 volt guys will be able to get by with a smaller size.

    Depending on the quality of your transformer and other components you may only need 1 uf or as much as 6 uf to get the best results for a 230 volt system. The 120 volt units may need anything from 2 uf to 12 uf for this size of system. Again it’s a critical component but its location does allow for a good range of workable values.
    (C1 on the schematic)


    OUTPUT LINE FILTER.

    The output line filters are a simple dual choke and bypass capacitor design. I just use an old filter system from a computer power supply of a similar wattage rating. They already have the right values and components so it’s just a matter of installing them. Any line filter from a TV or computer monitor of similar voltage and wattage will do just fine. All you are doing is using it to block any residual line noise going out or coming into the GTI. (what I am using came out of a 300 watt computer power supply)
    (C2, C3, C4, L1, L2 on the schematic)

    LINE CONNECTION DEVICE.

    What I have found to work very well is simple solid state relays with a zero cross turn on design. For a single line setup you would need only one but if you want to use two and have one on each line that’s fine also. I recommend using ones rated for inductive loads and that have an amp rating of at least 3 times your average running amps. (I am using a 280 VAC 10 amp just because I have a bunch of them!)
    (TR1, TR2 on the schematic)

    If you want to use a standard mechanical relay or contactor, that will work just fine also. However this device does get turned on and off allot in normal operation so make sure the relay or contactor you use has a fair amp rating and a snubber capacitor or two. One across the contacts and one from the transformer side to the other transformer lead will help.
    The less arcing of the contact surfaces the better!

    The basic output, line filter and switch layout is below.
     

    Attached Files:

    Last edited: Mar 30, 2009
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  6. kevinr

    kevinr New Member

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    Thanks so far. I am going to try this out soon. You have been inspirational for me to do this. Ill try this before hooking up my DC drives in regen mode.
     
  7. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Your welcome. I will try to post a new section every day.

    I will do the basic control circuits next.
    Then how and why it works behind these three circuit systems. It will be a basic rewrite of whats in the other GTI thread just a little more specific to this one.
    Then how to modify a standard watt meter for higher resolution reading. You are going to need one for the actual set up and tweeking.
    Then I will do set up and tweeking.
    Last will be the actual grid tie in using the actual National Electical Code book rules to make it more legal and safe plus give you some solid gray areas to play in.
    After that open discusion of whatever needs to be looked at closer.

    Glad you are liking it so far!
    ----------------------------------------------------------------------------
    And any of you magazine publishers planning to pirate this. Just contact me so I get some credit for it. And a little finacial kick back would be nice too.

    This thread write up is for private use only!

    Haha! Now my lawyer can go after you if I ever find out this is in someones magazine without my knowledge or aprovall!
     
  8. bbhs

    bbhs New Member

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    tcmtech I have been following the GTI and this thread with great interest as I think there is a great market for both the high wattage and the low wattage market.
    The 250 watt will be ideal for small PV arrays with no sell back requirement to the grid supplier.
    Have you thought about marketeing the unit in kit form that way you could make some well earned money for all your efforts and time.
    Keep up the good work !!
     
    Last edited: Mar 29, 2009
  9. Robby

    Robby New Member

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    Dear Tcmtech, Thankyou for your parts list to date. Do you use a circuit board to build the system ? and do you have some close up photos of the inverter please ? I don't have a huge understanding of how electronic parts work, but I can follow diagrams and plans ok. I also enjoy the challenge to get it working, thankyou. Robby.
     
  10. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    I dont do kit anything.

    There are too many dumbass's with soldering guns out there as it is. Kits would just encourage more to try and do it. Plus then I would have to stock replacement parts and give tech suport to people that cant read a simple schematic or have no common sense. :mad:

    Plus unfortunatly this fits into the alternative energy devices catigory.
    And unfortunatly alternative energy anything seems to have very large following of hippies, misguided enviro nutters, overunity nutters, cheap ass's, people to lazy to get a job and suport themselves, and people with no real fabrication skill or abillities! :mad:

    I am working on a CD I plan to sell that will cover several sizes and types from 100 watts to around 10 to 15 kw. And the build for each of them is going to be based on how to do it with simple ,cheaper and often salvage or surplus components. :)

    I will have lists of everything both in new costs and what I have been able to find used.
    I am strongly leaning towards simple, reliable and cost effective DIY designs. The total cost outlay for each build will only depend on your scrounging and recycling skills. ;)

    I know that sounds rude but I have been in the service and custom design business and have played around with renewable energy long enough to know that the customer is typicaly 90% of the trouble shooting problem! :eek:

    You are my test run on an actual write up and construction phase. By doing this I will be able to refine my discriptions and aproch to the designs and have them easier to understand. ;)

    You are my lab rats! So I am happy to do this one! :p

    The control circuits will be on a boards but the rest is up to you and what you find or use.
    If your running a lot of smaller sized switching components you may want to board mount them but its entirely up to you how you lay it out and what you mount it in. ;)

    I will post pictures as soon as I get may camera back. I did a some service work last weekend and accidently left it behind. It should be ariving in the mail sometime soon. :eek:

    I did post a few pictures and a basic discription of my one units in the grid tie inverter schematic thread.
     
  11. be80be

    be80be Well-Known Member

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    Last night I took apart a 250 watt psu thinking it would have some good parts for some thing like this. Why i was looking at the board in it it was using a switching regulator to keep the 12 volt battery output at 12 volts that would be a good add in to a grid tie inverter and a easy way to change the output voltage to mach the grid.
     
  12. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    True, I do believe it could would work in some applications to help with overall eficiency but I am not totaly sure.

    Do solar panels have an optimum volts Vs amps sweet spot that they are most efficient at? The 4 panels I have are ancient. They put out about 3 watts per square foot. 6 volts at 500 ma or 4 volts at 600 ma. With a total of 12 watts for 4 sq feet its nothing more than a toy for me.

    I do feel that a solar panel may very well have a different power curve than a wind generator sinse solar panels dont have to worry about stalling from overloading at low source power inputs.

    I know that with wind you need a more exponential load. Very little draw at low voltage but a large draw at higher voltage. Using the variable current variable voltage system like on these simpler designs works super with a wind generator. They match the winds relative energy very well. The GTI design I have been using and am designing here has a somewhat more exponential power draw curve.

    Using a 12 volt ac transformer it would be fairly linear up to the peak voltage point of say 17 volts but then it goes more exponential. At 17 volts it may only draw 10 amps but at 19 volts it could be more like 20 amps. And possibly 60 amps by 21 volts.
    This power curve keeps a wind generator well loaded in high winds so runaway is very difficult.

    But as I said in the other thread I am just trying to give everyone a solid base to work from. Once you have the basic control and power handling sytem designed and working and then if you do understand why it does what it does there is no reason you cant get more complex and fine tune your units design and power curve to match what you are using for a power source.

    I am leaving that part entirely up to the end user. Work with what you understand. Start basic and build up from there.
     
  13. killivolt

    killivolt Well-Known Member

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    "University's" are good location for spare parts that are often overlooked and under appreciated by electronic hobbyist.

    I believe most surplus sales if the person who actually is aware of this would not throw them away and could sell you a UPS that can no longer charge and might be cost effective and would be a reliable source as well as have several of the same manufacturer.

    kv
     
    Last edited: Mar 29, 2009
  14. bbhs

    bbhs New Member

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    Hi tcmtech I agree re the dumass's with soldering irons just thought it could have proved a good revenue stream for you.
    I worked for Ericsson in the UK service department for 20 years so have worked on a range of telecommunication equipment so it should be a nice project for me time permitting as I now work for myself.
    I look forward to your developments as I am interested in a small 250 watt for PV and a larger unit for wind generation - possibly a bought unit as I would need the G83 certification (ouch) or maybe not :)
     
    Last edited: Mar 29, 2009
  15. Robby

    Robby New Member

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    Hi Tcmtech, I would like to know if it is necessary to solder the solar cell tab wire the full width of the cell, or just solder it on the top edge ? Thankyou.
    Robby.
     
  16. Thunderchild

    Thunderchild New Member

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    I hate to spoil the DIY spirit but where can one buy a reasonablt priced GTI ?

    also don't you have to have a GTI passed by the electric board. if every tom dick and harry with a soldering gun starts making them from kits or from instructions surely this will be a huge problem for the power company when 80 % of these people fry something they shouldn't ? ie: every kit / home build will need inspecting individually
     
  17. bbhs

    bbhs New Member

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    Yes in the UK it must be approved i.e. G83 certified.
    I have checked with my supplier Atlantic Electric (Scottish div) and they will supply and fit an export meter free of charge as long as the GTI is G83approved.
     
  18. Thunderchild

    Thunderchild New Member

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    well unless for large setups that practically invalidates this discussion, it will probalby be more expsensive to get a 250 W GTI validated than buying one.

    building from a validated design/kit will not neccesarily make the home made one validated as the operator will not be deemed to be reliable, in a company making them there is more control over build quality as stuff is checked regularly by QC which maintain the standards set by the original validation on the design
     
    Last edited: Mar 30, 2009
  19. Jules_Theone

    Jules_Theone Member

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    I think the phrase: "what they don't know won't hurt them" comes to mind. Besides I don't think that *everyone* will try making one, there are fuses in the house, power line etc. and these systems will produce small amounts of energy in comparison with power stations. So individuals cannot affect the grid very much.
     
  20. bbhs

    bbhs New Member

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    I still think this discussion will be relevant - I am looking to use a 250W GTI for my PV array and because the output is so low I will not export it back only use it locally.
    I would say that as long as you are not exporting back then the G83 spec would not come in to it - thats my interpretation - thoughts anybody.
     
  21. Jules_Theone

    Jules_Theone Member

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    Exactly - how would the power company know that you were generating electricity if your meter never ran backwards (newer meters cannot run backwards). All the power company would see is a decreased consumption of electricity, although if you generated 100% of your usage, they may send an engineer to check your not cheating.
     

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