250 watt grid tie inverter build - Page 3 - Electronic Circuits Projects Diagrams Free

Thunderchild · 30th March 2009, 06:30 PM

Quote:

Originally Posted by tcmtech

Hahaha

My last time around at college for my electrical engineering degree showed me otherwise!

The math classes I had to take tried to tell me 1+1 = 9

Calculus was the dumbest thing I have ever seen that was even remotely related to mathematics.

My Calculus instructor spent a week on how claculus based formulas can change any number to be equal to any other number.

One day in the middle of class I asked him; Can you use this in real life situations?
He said; Definitly!
I then asked; Are you doing anything after class?
He said; No, Why?
I said; Then will you come with me and prove that what your are saying is true and can be used in real life?
He said confidently; Sure! Where would you like me to prove it?

I said with a big grin; Lets go to my bank and you can prove that your equations are real and do work in real life situations by making the $40 in my checking acount equal to $40 million. AND I will give you $38 million of it in cash if you do it!

The whole class cracked up!

He then said; Thats not how it works. These formulas are only good for when you have mathematical problem and the answer you keep getting does not match what you need to make the equation work.
I said; But how I want to live does not add up with what my checking account says. The number I need in my finacial formula does not match what I have in my checking account.

The class though my argument was good. It did meet all the requirements of what he was saying, and it did fit in the formula on the board perfectly!

But after much debate I still only had $40 in the checking acount the next day.

funny counter story but you erm... missed the point. I'll make it simpler.

I'm going to control a 2 A current with a mosfet (or other transistor) now i don't go and actually use a 2 A transistor do I ? same rules apply in any design and situation evaluation, perticularly where human nature is even a minor factor !

tcmtech · 30th March 2009, 06:37 PM

Still not following. I am seeing an apples and oranges comparison. I need a better pont of reference. Did I completely miss something?

tcmtech · 30th March 2009, 07:09 PM

Quote:

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 ?

Sorry I am not much of a solar panel guy. Someone else will have to answer that question. The few panels I have just use a spring loaded connector to grab onto them. (ancient and cheap)

I am more of a wind generated power person.
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Quote:

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

Ebay sells some in that 250 watt range for around $300 or so. But I think they are designed more for the American and Canadian power systems and run at 120 volts AC 60 cycles. At least for the smaller units anyway.
That way they are just plug in and go.

I am not sure what they have relating to the other parts of the worlds electrical systems. There has to be stuff outhtere some place but I am not aware of what they have available or what is leagal for differernt countries.

Thunderchild · 30th March 2009, 09:31 PM

Quote:

Originally Posted by tcmtech

Still not following. I am seeing an apples and oranges comparison. I need a better pont of reference. Did I completely miss something?

when designing anything or planning a specification (in this case that which determines the application of GTI's) you always leave room for allowances because the unforseen will always happen especailly when its not a one off instalation.

tcmtech · 30th March 2009, 10:18 PM

Ah... Much better! I understand completely! Margen of error.
I did cover that in the first post here relating to and recomending the minimum 4:1 switch device current rating Vs the average sytem running Current, and the minimum 2:1 switch device voltage rating Vs the peak system voltage.

Quote:

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.)

You get a B+ for participation but a D- for not reading and or understanding the text book!

But thanks for giving me a good reason to look closely at what I wrote. I do most of these longer posts as a cut and paiste from Office Word and once in while I do miss a paragraph when I am moving the text over.

When I get to the part about the actual circuit layout I will also cover some thermal protection tips.

But ultimately no matter what I print up, if the person building it cuts corners, uses undersized or inadiquate parts, or runs it way past what the design is built for there is nothing I can do about it!

blueroomelectronics · 30th March 2009, 10:27 PM

I wonder how much you actually get per kWh when you sell power back to the power company. After all when you buy it you also have to pay taxes & delivery charges.

killivolt · 30th March 2009, 10:44 PM

Quote:

Originally Posted by blueroomelectronics

I wonder how much you actually get per kWh when you sell power back to the power company. After all when you buy it you also have to pay taxes & delivery charges.

Ha, I'll bet if they had it there way we would have to pay taxes and delivery fee's just to sell it back to them.

Utility Company's are like big tobacco or Big Oil. They charge we pay.

Even if someone were to stand out a little and they were to take notice they won't lobby against it. Over all it reduces wear and tear on their equipment. Resulting in a Maintenance Reduction.

If everyone were to attempt to do it. Suddenly there would be so much regulation ( After the Lobbyist got through with it.) No one would be able to afford it.

kv

tcmtech · 30th March 2009, 11:05 PM

What I have been told as of lately is that my local power comany pays equal cost per KWh returned. BUT I have also been told that may not be true all over the united states.

Right now I pay around 9 cents per KWh. Plus a fixed $29 month conection service fee. IF I were to sell back to them I would get 9 cents per KWh or I could just bank my retuned KWh's and reuse them later at no aditional cost. My local utility is pushing very hard to encourage its customers to invest in alternative enegry and energy saving devices.

But not all power utilities are like that as I undrstand it.
I have heard that now that its legal nationwide to sell back they do have to buy it from you. BUT they only have to pay you the going rate of what they pay for it at super bulk rate. Which as I have understood can be anywhere from 1.5 cents per KWh to around 5 cents per KWh depending on the location and demand in the country.

Plus If they want to they can require you to have a second meter on your service connection to read what is going back and then charge you for that second meter.

SO if your getting 1.5 cents and spending $30 amonth for a second meter on top of the $30 a month you pay for the first meter you would have to make around 4000 KWh returned just to break even.
And you still have to make what you normaly use too!

But if you are lucky and have ulility company like what I have then you only need to make enough at 9 cents per KWh to pay for the one meter that runs both ways. Or about 334 KWh returned to break even.

In the first example I would have to make about 5500 KWh a month to break even including my own monthy use.

However in the second example I only need to make 1834 KWh a month to break even.

And my numbers may be off a bit on actual meter costs and utility bulk rates. I just used the numbers I have been seeing in articals I have read.
And the rules are changing all the time so this may not be exactly acurate in every detail.

I dont know what Canada is like for any of this though.
But its worth checking out!

Val Gretchev · 30th March 2009, 11:52 PM

Here are a couple of documents released recently in Ontario:

Price Schedule.

Fit Rules.

Sceadwian · 31st March 2009, 12:18 AM

Just be careful from a legal standpoint if you ever actually start selling back any decent amount of power, you still have to claim that as income on your taxes I would think. Forget about it for too long and if you ever get audited you might be in for a nasty surprise.

Thunderchild · 31st March 2009, 12:50 PM

Quote:

Originally Posted by blueroomelectronics

I wonder how much you actually get per kWh when you sell power back to the power company. After all when you buy it you also have to pay taxes & delivery charges.

after you have paid for all the equipment particularly their meter to measure what you put back you get the grand sum of 30-50% of what you buy it at if your lucky so unless your house is made of PV panels with giant turbines on each corner, the patio paved with PV tiles and all fence/gate posts replace by turbines you won't make much money from it, I would think that with what it costs to set up you could buy a nice bank of batteries capable of storing 5-10 KW making you indipendant anyhow

Thunderchild · 31st March 2009, 12:56 PM