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Old 10-02-10, 01:40 PM   #1
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Default Moving solar from Grid to off grid (Sunny Boy GTI)

Hi All...

I have a 2KW system on my roof... and plan to move it to a cabin currently being built that is 100% off grid. My system uses a Sunny Boy US3000 GTI...

Of course, the GTI has sensing circuits that serve to interlock the inverter which will prevent it from functioning off grid.

Certainly, the Sunnyboy GTI is approx. the same as the off-grid inverters of the same family... just with the additional interlock circuits.

I would like to modify my GTI to act like an off-grid inverter when I move it to the cabin... I suppose a Sunny Boy service manual would be helpful in such a conversion project.

Has anyone here attempted such a conversion, or had any luck obtaining a service manual for the Sunny Boys?

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Old 10-02-10, 04:37 PM   #2
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That sounds pretty technical. If you think about the very large differences in a basic
MPPT battery charging system/inverter, and a GTI.. They GTI is clearly more complex.

It seems like your best bet is looking around for a swap deal or a trade-in.
Maybe a GTI costs more and you could go off-grid at no extra cost.


I have a cheap Chinese PowerJack 1200w GTI that I would like to use off-grid. (During long power failures).
I will use a fake grid (AC power source) to trick the GTI into thinking it's connected to the real grid.
Plan A is to use my 5kW gas generator to act as the source..
Plan B is to buy a 'pure sinewave' inverter to act as an AC source.

I'm not sure how well this would work, but it's on my list to check out
the PowerJack this fall when I test the 5kW gas gen..

The pure sinewave inverter idea isn't too complex, you just need
a battery pack to power it. The battery could be fed by a PV charger unit
or just a plain old plug-in charger. You could size the battery to provide
a source all day or into the night, running lower AC power..
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Old 10-02-10, 04:56 PM   #3
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Howdy...

Well, I'm pretty sure it's easy... probably a single jumper wire across an IC... it's just knowing which IC/component to jumper.

You don't need to trick the entire system... you simply need to put +5vdc on the right line which is the signal that tells the inverter to go on-line.

So for the cost of 1 inch of wire and 60 seconds of soldering, one should be good...

A schematic / svc manual should do it.
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Old 10-02-10, 06:24 PM   #4
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Because of safety issues (and being sued) I'm wondering if a GTI chipset
might be running self-testing during operation, to insure that a single
point logic level failure isn't keeping the unit running, when it should have shut down.?.
It might be harder to trick the GTI with a jumper wire, than you think..

But, if it's really just a standard Inverter with a GTI controller added on,
there might even be a factory test jumper to check the inverter without
the grid wired in.

Are their any schematics on-line? Or do they keep them locked up?
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Old 10-02-10, 07:49 PM   #5
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Well, at some point there is a contactor or solid state switch that is activated... and getting that device to close is all it really takes... logic or no.

I have no idea how hard it would be to get a schematic... but I expect that only authorized service centers would have them... perhaps only them.

It would be good to find someone who has tinkered around with them a bit...

R
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Old 10-02-10, 10:00 PM   #6
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I don't think there is a contactor or SSR (SolidState Relay) in standard 12vdc to 120vac inverters,





and I have not seen anything like that in the 1200w Power Jack GTI.
They might be using MOFETs as off-on relays, but that seems unlikely.

This 1200w PJ GTI board doesn't have any relays anyways.. But with no circuit diagram???


As a matter of fact, I want to add an AC SSR to the AC connection,
to keep it from drawing power when there isn't any sun on the panels.
I would tap some voltage off the PV DC input to switch on the SSR.
These things are night-time power leeches..
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Old 10-05-10, 02:01 PM   #7
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Default Add a Sunny Island

The Sunny Island will work in conjunction with the Sunny Boy. It will supply the sine wave signal. It will handle the connection to the battery pack.

If there is more power being generated by the Sunny Boy than the house is using, the Sunny Island will use it to charge the batteries.

If the batteries are full, the Sunny Island will instruct the Sunny Boy to cut back on its power production.

I believe this is called AC coupling.
lses.org/version1/AC%20Coupling%20WHT%20Paper%20(2).pdf
(sorry I can not post links yet)

Last edited by cbarbie; 10-05-10 at 02:06 PM..
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Old 10-05-10, 04:48 PM   #8
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It kinda looks like the Sunny Island goes between the Sunny Boy and the grid.
Or your gas generator.



Logically, it seems like the DC line (in blue) is a DC source for making AC to pass up
to the AC line (in red), to feed the loads and provide the AC (fake grid)
source to the GTIs on top (Red GTIs).
Also on the bottom is another PV array connected to a battery charger.

Price wise, it looks like a 5kW Island unit cost double a regular 5kW Sunny Boy.


~~~~~

I was thinking about using a GTI off grid a while back, because of the low cost of Chinese GTIs..

Off-the-grid with grid-tie inverter?




I'm not sure what size the 12vdc to 120vac Pure Sinewave inverter should be, but the block diagram shows the general idea.

Seems like I could use something like this $220 PSI,
Samlex PST-60S-12A 600 Watt Pure Sine Wave Inverter
With my small 500w array w/ 1200w GTI.

The PV-GTI could provide around 400w and the PSI could provide extra power during peaks,
like a compressor start up maybe.?.

The PSI shuts off when the battery starts getting low, which would kill
the power from the GTI. So the PV feeding the PSI should be substantial.

It's all just a theory. But I think it has a good chance of working with Chinese made GTIs anyways..
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Old 10-05-10, 05:13 PM   #9
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The reason that the sunny boy takes more then just a jumper wire to produce A/C without the grid is that it uses the grid A/C and fallows it, where a normal inverter has a sign wave generator to help produce the sign wave, it's also part of the safety of grid tie inverters is that they have that missing link so they can not work without the grid.
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Old 10-05-10, 07:51 PM   #10
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Quote:
Originally Posted by Xringer View Post
It kinda looks like the Sunny Island goes between the Sunny Boy and the grid.
Or your gas generator.


Logically, it seems like the DC line (in blue) is a DC source for making AC to pass up
to the AC line (in red), to feed the loads and provide the AC (fake grid)
source to the GTIs on top (Red GTIs).
Also on the bottom is another PV array connected to a battery charger.

Price wise, it looks like a 5kW Island unit cost double a regular 5kW Sunny Boy.

If your Grid tie inverter is large enough, all you need to add is the smaller 4k Sunny Island and batteries (and cables, disconnects). You do not need a separate array or charger for the batteries. This assumes 4K is enough to power your loads when it is cloudy and at night.

The Island includes a battery charger as part of the package (part of the reason it is more expensive). If the Boy is producing more power than is being used by the AC loads, the excess power is sent to the battery charger. If the loads exceed the capacity of the Boy, then the Island draws power from the batteries to make up the difference.

If the batteries get low and it's cloudy, then it is time to fire up the genny.

The nice thing about AC coupling is that everything occurs at a higher voltage and less amperage (less voltage drop). You can use smaller diameter cables and save a lot of money. Copper is not cheap around here.

You can add additional arrays later that may run at different voltages, different orientation, (or a wind driven generator). If they are connected to a Boy, they can be connected at the AC panel.

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