# DIY: Grid Tie Inverter



## Guest (Sep 5, 2011)

http://www.mwands.com/


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## Guest (Sep 5, 2011)

If you never connect to the grid and just connect to the inverter and only use things that can handle chop shop power vs pure sine wave then go for it. $25 bucks is cheap. I'd doubt that it would last long if you really pulled 3kw through it for any length of time. What batteries are you going to use and what charge controller do you plan on using. The posted link has some interesting things. I have been checking it out myself. 

Pete


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## bo'sdad (Jul 10, 2012)

I actually built one of these recently. I was getting very poor results until I changed the capacitor and it started climbing in watts. the problem was then the capacitor started getting hot and I couldnt tell is I was receiving 200 watts or inputting 200 watts. has anyone else tried to build on of these ?


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## bjfreeman (Dec 7, 2011)

Grid tie has to have a circuit to detect AC on the Grid side. it is not existent then do not connect. this has to be approved to tie to grid. it is because a line man my have killed the AC to work on the line and does not want to be electrocuted by someone Grid tie unit.
A second feature is a sync circuit so you use more than one to the grid at the same time. like 240 and 3phase.


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## PStechPaul (May 1, 2012)

I call BS on the cheapo grid-tie inverter. About the only thing it can possibly do is pass AC through the capacitor to the battery. This will just alternately charge and discharge the battery with AC current. Since there is no current limiting other than the impedance of the capacitor, it could (and probably will) damage it. 

If you have built one of these contraptions, measure the actual power drawn from the AC line. Then measure the true RMS current into and out of the battery. To see the actual power to and from the battery, you could use a wattmeter, or you could measure the DC current to or from the battery and multiply by the battery voltage. But unless the capacitor is shorted, or still charging, the DC current will be zero. 

The http://www.mwands.com/index.php?main_page=index&cPath=50_51 seems to show real grid tie inverters, at a more realistic price of about $1/watt. When I first saw the links, I thought it was for "*m*agic *wands*", which you would need to get the cheapo inverter working.


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## Caps18 (Jun 8, 2008)

It would be nice if there was a way for off-grid people to save lots on money on solar installs by DIY. I wouldn't trust it to work 7 days a week, 365 days a year in a grid environment however. 

Plus, the enphase inverters are something like 96% efficient, I wonder what this one would be. Not that you wouldn't take some inefficiency to save $1800.


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## bo'sdad (Jul 10, 2012)

this inverter was not made to hook to a battery. and it does have island protection. the triac's are the protection. as soon as they loose power the system shuts down. 
I have ordered a new set of capacitors and will post what I find when they come in.


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## PStechPaul (May 1, 2012)

bo'sdad said:


> this inverter was not made to hook to a battery. and it does have island protection. the triac's are the protection. as soon as they loose power the system shuts down.
> I have ordered a new set of capacitors and will post what I find when they come in.


OK, here it is:









Well, if it is an inverter then it gets DC from somewhere and adds this to the AC line which connects via transformers to the grid. So if there is no battery, where does the power come from? 

The only possible way I can see something like this even remotely working, is to wait until the grid voltage is something like a few volts less than my DC supply (battery? solar cell? DC generator?) and then inject it into the grid. It might boost the waveform a little bit but unless you can keep up with the sinusoidal voltage variation sof the grid voltage, it would not contribute very much. So - maybe - you could convert the grid power to a step waveform where it does not go to zero but instead rides at the DC voltage until the zero crossing, and then get a negative DC level by reversing the battery connection until the voltage again rises beyond the DC level. 

But the circuit shown does not and cannot do that. You cannot pass DC through a capacitor. So, unless I can see some meter readings and at least a basic explanation of what it's supposed to do, I remain skeptical at best. *Show me! *


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## bjfreeman (Dec 7, 2011)

the circuit as you laid out won't work.
Second if grid tie you don't have the sync circuit to match the grid with the AC generated, not with this circuit though.
first stage is a DC to DC that gives you the source to then use PWM to create a sine wave. The Sine wave is created by feeding the PWM into Inductors.
so you need hardware to create and adjust the PMW that will eventually be your output.
you can do this discrete or CPU.
The inverter I built, is supplied by 390 VDC battery pack. so no DC-DC is necessary.
it supplies 110/240 AC output but not grid tie.


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## Coulomb (Apr 22, 2009)

PStechPaul said:


> I call BS on the cheapo grid-tie inverter.


Yup. My BS meter is reading pretty high, too.

Alternistors, uhuh. DC power comes in through a capacitor, right. There doesn't seem to be anything to turn off the triacs, assuming that they are triacs. So I think that this will just short the mains and blow the fuses (assuming those box around a line things are supposed to be fuses).

Sorry, no almost-free lunch here, unless I'm missing a *lot*.


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## PStechPaul (May 1, 2012)

Well, duh, it's a "flux capacitor"! 

http://uncyclopedia.wikia.com/wiki/Flux_Capacitor


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