Powerstar W7 Inverter modification

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Re: Powerstar W7 Inverter modification

Postby brucedownunder » Tue Dec 10, 2013 12:39 pm

Am I "out of order" here ,in thinking this modification subject has been hijacked ?

Could the "powerstar W7 inverter modification " be condensed to it's pure and original subject ,please. That way , it would be a step by step proceedure for interested members to follow.

Thanks,

Bruce

[Moderator- yes it was hijacked, but has now been split into 2 threads]
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Re: Powerstar W7 Inverter modification

Postby Tracker » Wed Dec 11, 2013 6:05 am

oztules wrote:......... this unit can run backwards with synchronous switching so that putting a grid tie on the output will see the grid tie drive the house loads AND charge the batteries at the same time if solar permits, and the inverter picks up the slack when cloudy... handy when the hot water or oven is used in the daytime, and loads may exceed 5kw or more. The grid ties can drive this, while the inverter just provides the timing for the grid ties. ( I have up to 6kw of grid tie I can connect up to it).


An interesting revelation ... but given all the discussions about why a grid tie can't be used off grid, I am left scratching my head as to how it all works... perhaps the devil is in the detail..
Ie.. it will work when there is sufficient load in excess of GCI production.. but my limited experience with the PS would suggest that it could not generate and charge at the same time, and if it tried to charge, then it would cause the GCI to desync.. and drop out..

Again, your suggestion seems to contradict all I have previously taken as fact..

As for fridge discussions .... that definitely needs to be cleaved off..
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Re: Powerstar W7 Inverter modification

Postby Garyho » Wed Dec 11, 2013 7:00 am

I have a trace inverter and according to it's manual the way it uses power from the grid or charges is controlled by voltage. It synchronizes with the grid and by regulating the voltage controls whether power is used for charging or running loads from the batteries. Batteries remain at float voltage and if the DC voltage rises the inverter uses this to power the load. As it is synchronised with the grid it can supplement or take the full load depending on DC voltage. There is an option to sell power to the grid but it is not approved for this.
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Re: Powerstar W7 Inverter modification

Postby davidg » Wed Dec 11, 2013 7:01 am

Tracker wrote:
oztules wrote:......... this unit can run backwards with synchronous switching so that putting a grid tie on the output will see the grid tie drive the house loads AND charge the batteries at the same time if solar permits.
An interesting revelation ... but given all the discussions about why a grid tie can't be used off grid, I am left scratching my head as to how it all works... perhaps the devil is in the detail..

Tracker he has not invented a magic solution, it's just AC coupling on one of those horrid PSW7's which I think has been modified with a "round" (toroidal) tranny, picked out of an inspire grid inverter that was broken anyway. it has then had 75C PVC based wire wrapped around the tranny for the ELV side so it can retrofitted. If I have the key points right.

I've said the PSW7's were not designed to have power shunted backwards through them, I'll stick to that. It appears it is able to from the statements, that it can do it at all is interesting indeed. I stand corrected on that point :shock:

The PSW7 inverter is providing the sync signal for the GCI, I wonder what happens to either the batteries of the inverter when the batteries get towards fully charged, I'm assuming the unit is not able to export excess to the grid as it should be isolated, I really hope it is. I also wonder what happens to the batteries when the power output from the inverter is no longer able to be absorbed by the batteries and there is not enough load to absorb the excess power. They don't have the ability to frequency ramp, control a relay directly, etc.

Now there's an issue, how to get enough smarts to deal with more power than you can use, transparently. I'll stick with Selectronic SP-pro thanks, it can export the excess to the grid etc, or push it elsewhere or with Kaco Grid Inverter's control power output, and if all else fail's kick the GCI off one way or another. I've had thousands of kWh's shunted through the one here. 8-)
Last edited by davidg on Wed Dec 11, 2013 7:45 am, edited 2 times in total.
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Re: Powerstar W7 Inverter modification

Postby oztules » Wed Dec 11, 2013 7:11 am

Hi Tracker.
I use from 1 to 3 grid tie inverters on this unit.
I have to drop some of them off if the sun is out properly, as they can between them provide over 6kw of solar power into the inverter.... which is too much to handle for long, as the battery bank is only 750ah or about 36 odd kwh.

The inverter acts the same as the grid. If the solar input is say 3kw, the house loads 1kw, then 2kw will travel back through the mosfets into the battery as they switch.

We can't control the amount of power going backwards to the batteries.... thats the down side. You need to switch out the inverters if the battery voltage gets out of hand (>60v). If you don't, then the unit will turn off form over voltage anyway and so save the system from damage.

It is easy to run the house, and charge the batteries at the same time... just like the grid. With the grid, someone else uses the excess, here the batteries soak it up instead... no modifications are required.. it just works.

If the solar sags from cloud, the power is supplied to the house from the batteries. The amount coming from the batteries will be the house load, minus the grid tie power, so the batterie just make up the difference when the solar dies away a bit.

SMA have an island inverter product that works with their grid tie units, and they solve the over battery voltage problem by varying the inverter frequency slightly, the grid tie see's the drift away from 50 hz, and throttles back the grid tie unit by changing the mppt up the pv curve.. ie let the panel voltage rise above the mmpt point until in the end, it is so high that the current component is nil, and the voltage of the panel is max... ie the further the frequency drifts, the further it shuts down the solar component. A very neat communication system between the inverter and the grid tie.

So it is commercially available with the SMA island units. In our case a dump load on the batteries would so the same thing, but stress the components more than throttling back.

It is a happy coincidence that the inverter part of the charger uses to the same effect. When you go to "shore power setting), it simply uses that to feed backwards through the fets and transformer to charge the batteries with it's 70 amp charger. It can control this though, as it uses the shore power to run the loads, and so can switch the fets according to their battery charging algorithm.

So rest in peace, the grid tie does whatever it can, and the power star will either make up the difference for the load, or if the load is small, then charge the battery as well. I have seen over 70 amps going into the batteries while the grid tie is powering the house. It seems to be more efficient than it's own charger if transformer temp is anything to go by.

So I can't claim the idea as my own,... it's not, but I use it extensively, as it allows small wiring to HV arrays over long runs..... thats a good thing as well.

I suspect all Low Frequency inverters will do the same thing, as they don't get a choice really because of the synchronous switching H bridge.. so it should work on any LF unit...... but unlike the SMA, they probably won't have a communication to the grid tie unit to thottle it down when the batteries are charged. This could be as simple as a comparator turning off a ac relay between the grid tie and the inverter output.


Happy to answer any questions about this if I have not been clear in any part of it. For once a too good to be true is actually true..... but I have noticed the grid tie likes to see some load, or it makes odd noises. I use the shed light (40w flouro), and then the units can drive many kilowatts without making a sound, without it turned on, they make silly noises that I don't much care for. So a 40 watt load seems to be all thats needed to keep the system stable as a brick..... not sure why.


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Re: Powerstar W7 Inverter modification

Postby oztules » Wed Dec 11, 2013 8:00 am

Hmm Just read Davidg... didn't see that before.

Yes this is a horrid power star inverter. They are reasonable built, and very tough. I quite like them.

You are welcome to sneer at my humble conversion, it was an experiment that worked so well I have not rewound it properly, nor will I ever as there is no need for my circumstances.

Too many arm chair experts form opinions that are based on agreed facts... which when tested are shown to be wrong in the physical world.

Are they designed to be run backwards..... of course they are. Thats their battery charging part... this is just a logical extension of looking at the circuits... it is not rocket science.

The circuits are provided. The fets don't care what goes on when they are hard switched. The N channel is no longer a block to the current flow... ie ceases to be a semi conductor, and becomes a conductor.

The transformer cares even less which one the primary is or the secondary is, so thats not an issue... where do you see the problem.

I agree that classy inverters are classy inverters, but I have had to repair a few of those selectronic units too. They are robust and well engineered. I quite like them, and if I didn't have this self sufficient streak in me, would probably have settled for one of them.... but I like a challenge from time to time.

No the real grid does not interact with this system, so rest easily
The inspire was not broken, I bought 12 of them for peanuts... to get the case and transformer really, but they are pretty good grid tie inverters too.

The usual crowd of brand oriented ( read safe sheep) experts will pooh pooh them, but I know where there is a glut of australian built and designed blown up grid ties too... and the inspectors will tell you the inverters that fail most at the islanding tests are of German origin, and the Chinese ones seem not to fail this most basic of requirements... interesting.

I note Aerosharp got a caning in this country as well, I have 2 of them also ( driving the real grid over here... if you can call it that ), and after over 10 MWH each, have yet to see them fail. I suspect it is from cut price solar designers, rather than the units themselves. I have seen the reports on whirlpool, and I suspect nearly all can be attributed to poor understanding of solar variability verses the manufacturers stipulations.

"I've said the PSW7's were not designed to have power shunted backwards through them, I'll stick to that. It appears it is able to from the statements, that it can do it at all is interesting indeed. I stand corrected on that point"
What bought you to that conclusion. Did you research it to come to that opinion, or did you just take a stab at the result and run with it? Please explain how you reached that rock solid conclusion, that has now shocked you. You are a senior forum member, I am the village idiot on a remote island in the middle of nowhere. I did not reach the same conclusion based on the facts before me.

"Now there's an issue, how to get enough smarts to deal with more power than you can use, transparently. I'll stick with Selectronic SP-pro thanks, it can export the excess to the grid etc, or psh it elsewhere, and if all else fail's kick the GCI off one way of another. I've had thousands of kWh's shunted through the one here. "

This is a 5 minute problem I have been too lazy/busy to address, but a simple lm324 and a relay would suffice.... maybe 5 dollar solution for starters..... Interrupt the grid (relay), and it will turn off for 5 minutes while it follows the design rules before trying again.... give you decent hysteresis for pennies, but there are very many ways to achieve this regulation from simple that works to complicated arduino solutions.

It works, it is not for everybody, but please check your facts before making sweeping statements that you are unable to support with practical experience or experiment.

sincerely


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Re: Powerstar W7 Inverter modification

Postby davidg » Wed Dec 11, 2013 8:47 am

oztules wrote:Hmm Just read Davidg... didn't see that before.
Yes this is a horrid power star inverter. They are reasonable built, and very tough. I quite like them.

Oh I did not say they were built badly, but in their default form they're dreadful with power consumption, I have a couple of dead ones here, cascade fet failure everytime.I even converted one properly using an imported custom wound toroid x 2 (good after that for off-grid). I have killed several of them and had them replaced under warranty each time till the warranty ran out one I had one replaced 4 times in a year, I bet that killed any profit on the original sales of the unit. They do have at least one real design flaw in them though destroyed 2 of them figuring it out > transfer from grid to battery flaw.

oztules wrote:You are welcome to sneer at my humble conversion, it was an experiment that worked so well I have not rewound it properly, nor will I ever as there is no need for my circumstances.

No it was not a sneer, it was a compressed version into a one post , along with wondering how one might really control the rest of the possible issues and fail safes. I did see the dump load mentioned.

I think you would need something along the lines of a pentametric style system to really cover and control the excess power, etc. I'm not an electronic designer, I can build circuits, I can even fault find them sometimes as long as I have a proper guide to what is what and the rest of the details on what should be going on where plus complete circuit diagrams. I'm slow at it though.

oztules wrote:Too many arm chair experts form opinions that are based on agreed facts... which when tested are shown to be wrong in the physical world.

I stated "I stand corrected" :oops:

oztules wrote:The circuits are provided. The fets don't care what goes on when they are hard switched. The N channel is no longer a block to the current flow... ie ceases to be a semi conductor, and becomes a conductor. The transformer cares even less which one the primary is or the secondary is, so that's not an issue... where do you see the problem.

Good excess power control and battery temp compensated charge control, just to name two. However it's still impressive, and I will still stick to Selectronics SP-Pro's or SMA and the like for supplying to possible customers. As a home project fantastic, if you supply and install systems, you could not use it ............ Australian Standards and all that.

oztules wrote:I agree that classy inverters are classy inverters, but I have had to repair a few of those selectronic units too. They are robust and well engineered. I quite like them, and if I didn't have this self sufficient streak in me, would probably have settled for one of them.... but I like a challenge from time to time.

Yes it can be interesting, and while I have converted one, I'm no expert in electronic circuit board fault finding, I'm pretty good at breaking electronics like though, having destroyed a number of them.

oztules wrote:No the real grid does not interact with this system, so rest easily

I expected it wasn't.

oztules wrote:The inspire was not broken, I bought 12 of them for peanuts... to get the case and transformer really, but they are pretty good grid tie inverters too.

I made an assumption they were broken, because there were a heap flogged off one place or another that were. Apart from that I have never made a comment about them, never having used any at all.

oztules wrote:The usual crowd of brand oriented ( read safe sheep) experts will pooh pooh them, but I know where there is a glut of australian built and designed blown up grid ties too... and the inspectors will tell you the inverters that fail most at the islanding tests are of German origin, and the Chinese ones seem not to fail this most basic of requirements... interesting.

What caused so many of the inspire (klne) inverters to "fail" out of interest. :?:

oztules wrote:I note Aerosharp got a caning in this country as well, I have 2 of them also ( driving the real grid over here... if you can call it that ), and after over 10 MWH each, have yet to see them fail. I suspect it is from cut price solar designers, rather than the units themselves.

I installed a couple of them, never had problem with them.

oztules wrote:I have seen the reports on whirlpool, and I suspect nearly all can be attributed to poor understanding of solar variability verses the manufacturers stipulations.

Yes .............

oztules wrote:What bought you to that conclusion. Did you research it to come to that opinion, or did you just take a stab at the result and run with it?

broken PSW7's inverters on the floor in my shed, one of which was destroyed testing it with AC coupling it did work for a little while (hours), before a cascade FET failure killed it. (one of the several warranties I took back without saying how it died)

oztules wrote:It works, it is not for everybody, but please check your facts before making sweeping statements that you are unable to support with practical experience or experiment.

As above ..............
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Re: Powerstar W7 Inverter modification

Postby oztules » Wed Dec 11, 2013 12:05 pm

Thanks for your civil response David.
I will try to behave myself with more decorum in future.

Well even the Aussies have their bad days.... have an upmarket Australian charge control box turn up today to fix for a bloke at the top end of the island........

It sports a big torroid (10 kg I guess ) inside, and a nice solid build.
Unbelievably, it was the torroid with the fencing wire size primary that shorted out on the torroid former.

I would not have believed it till I scratched around in the transformer.... looked good on the outside.

We all have our days, but if had been Chinese we would all have said yea of course, but this time we are more inclined to wonder who ran over the black cat, and how could that possibly happen.......... poor workmanship when they were insulating the former or more likely, when they wound the coil.......now if they had used thick plasti.........just kidding .

I guess..... it happens to the best too.


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Re: Powerstar W7 Inverter modification

Postby Gordon-Loomberah » Wed Dec 11, 2013 12:24 pm

Oztules, any chance we can keep this topic on topic, ie "Powerstar W7 modification"?

thanks.
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Re: Powerstar W7 Inverter modification

Postby Tracker » Thu Dec 12, 2013 3:52 am

Gordon-Loomberah wrote:Oztules, any chance we can keep this topic on topic,...

Oi.... :shock: .. it's been a bit more relevant than a mass of discussions about fridge design and consumptions, that would easily warrant a serious discussion in isolation... ;)
"Fridges ain't fridges, Sol"

Both the observations about the W7 are consistent..
They are a pretty wretched device, out-of-the-box, and the entire thread itself has shown that they can be improved, and dramatically..improved at that.
But the bottom line is that David is correct, that only a fool would do a commercial job with one, as they would likely either end up in consumer courts, or gone broke after having to replace units..
I blew my one up, and have no intention to repair it as it is.. I had thought about doing the conversion and replace the fets, but I would really like to be as LEGAL as possible at home..
The Weekender or the boat s another issue.

W7 -- a dark horse indeed...

It's funny how things change .. years ago we were naievly and simplistically asking WHY we could not use our solar GC system in a blackout. (The question keeps arising every other day, even now)
Now we talk about 'AC coupling' like it was old hat..
And continually, designers work on ways of interconnecting these various technologies to complement each other.
Interesting discussions Oztules and David..

I can only wonder at what the Authorities think as they read these discussions, and then think about all the fancy "Standards" and "Regulations" that they write and re-write.. as though they had nothing better to do..
..
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