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Old 08-23-2010, 09:37 AM   #1 (permalink)
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DIY Grid-Tie INVERTER??

Found this today, Grid tie Inverter



"Warning: This system could drain a car battery in a few minutes."

"Advantages: * Wide range of DC voltage from 3->50V."


At first glance, it looks way too simple to work (as a GTI)..
I can see no way a low DC voltage source (like 3v) can add power to the grid.

I wonder if this thing is actually a battery discharger?



Any engineers out there care to comment?

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Old 08-23-2010, 07:35 PM   #2 (permalink)
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I don't understand how it can work either. I plan to design and build a grid tie inverter from scratch, but I first need an oscilloscope to debug the design.
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Old 08-23-2010, 08:25 PM   #3 (permalink)
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maybe it only pushes on the grid when the phase is below the rail? pretty cheezy if so
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Old 08-23-2010, 08:53 PM   #4 (permalink)
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I looked at the AC current flow in both directions. The diodes on the gates make the triacs work like plain old diodes.
If I'm right, the 4 triacs and 4 diodes make up a simple full wave bridge Rectifier..

Having 120 hz positive pluses appear on the left side of the cap, doesn't seem like it's going to do much magic.

So, a full wave driving a series cap & battery.

Depending on the size of the cap, it Kinda looks like a battery charger, but the battery is connected backwards..?.

So, does that mean it's a battery dis-charger?

If it is a dis-charger, does the battery's power end up on the grid??

~~~
For sure, I would connect the AC via an isolation transformer..
No sense getting killed..

And maybe a Variac adjustable autotransformer to feed the isolation transformer!!
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Old 08-23-2010, 09:03 PM   #5 (permalink)
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If I understand it, it is not a true inverter, it pushes on only part of the sinewave (i.e. when it is less than battery voltage) and thus distorts it, perhaps to the dismay of the rest of the grid.
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Old 08-23-2010, 09:39 PM   #6 (permalink)
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If the capacitive reactance is low, the + pluses will be felt on the - battery terminal.
The + battery terminal will be connected back to the "minus" side of the AC.

It seems like those two voltages would add. Positive peak + battery.
Like to batteries in series.. -+ -+

So maybe, it's not the just a part-time push. If the battery is going to add it's voltage to the whole up-down cycle of each pulse.. No distortion.?.

So, a 12v battery would try to push your 120AC up to 132AC..?.
But, it's limited by the amount of current that can be carried by the cap...
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Old 08-23-2010, 10:28 PM   #7 (permalink)
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mebbe, dunno. the triacs are like $6 apiece so not the most expensive experiment in the world.

BTA25-600BW STMicroelectronics Thyristors - Diacs, Sidacs, SCRs & Triacs
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Old 08-24-2010, 07:17 AM   #8 (permalink)
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And of course, since it isn't UL listed to the appropriate standards, it can't be legally connected to the grid, whether it works or not.
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Old 08-24-2010, 08:23 AM   #9 (permalink)
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Quote:
Originally Posted by WisJim View Post
And of course, since it isn't UL listed to the appropriate standards, it can't be legally connected to the grid, whether it works or not.
Maybe if you used only UL listed parts.?.

I wonder if those 1930s insulators I see on some power lines are UL listed??
Some of those street lights look like they were installed in the 1940s..

Must have Grandfathered in.?.
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Old 08-24-2010, 08:47 AM   #10 (permalink)
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The more interesting question is if it distorts the grid or not. Show that it works, then worry about the law, maybe we can play dominoes on sunday in alabama again?

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