Powerstar W7 Inverter modification

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Re: Powerstar W7 Inverter modification

Postby Andrew_electrix » Thu Feb 02, 2012 12:35 am

I have been writing this in the past tense because this inverter modification project has been happening over the last 6 months not the last 6 days... ;)
It's been abit of a marathon project, but i've working on getting it all working properly before publicising any info...

Good guess Tracker - but the inductors in the last photo are actually the final ones.
Also regarding just reducing the 4.7uF cap, by all means try it, but i don't think no load current will drop that much as poor design of the original transformers mean the magnetising inductance is not enough and they draw to much current...

To fill in the background:

I worked out by experimentation and calculation that approximately 60uH would do the trick in terms of filtering the switching waveform before the transformer.

My first attempt was actually this:
3x 2.5mm diameter enamled copper wire wound on an F6 neosid ferrite, which is a low Mu ferrite that is specifically used for filtering and power suppression applications. (We use them at work for loudspeaker crossover inductors)

High power 50uH inductor.jpg
50uH inductor

Actually this worked fine with the reduced 0.47uF capacitor the inverter could easily carry a 1kW load without any problems and the no-load current was about 0.34A (approx 18W)

The next refinement was to try a 110uH inductor on each of the 30V 50A winding which would reduce the current and losses thorugh each inductor (approx 2x 50uH)
Such that now i could use the inverter to charge the battery at full power (70A) using 3100W from the grid supply.

Actually these inductors were not too bad. However they buzzed quite badly at full power and because the magnetic circuit is open on these inductors the radiated field was quite large and the metal case was would affect the inductance, vibrate and buzz ect

The resistance of these inductors in critical as it directly eats into the voltage delivered to the transfomer reducing the headroom available to the inverter to regulate it' output voltage as covered previously.
Also the inductive reactance at the fumdemental frequency of 50Hz also does a similar thing but slightly differently

Z = 2 x PI x F x L

= 2 x 3.1416 x 50 x 50E-6
= 0.0157 Ohms

The voltage across the inductor at full power is then V= I x Z

= 0.0157 x 50

= 0.785V

Howvwer this voltage is at 90 degrees to the voltage across the transformer and has to be added as a vector wise

Pythagoras theorem http://en.wikipedia.org/wiki/Pythagorean_theorem another brilliant mathematician from another time...

= sqrt (30^2 + 0.785^2)
= 30.0102
So this doesn't really effect the voltage overhead too much

Anyway wondering where i could find some 50A inductors that were appropriate i found this site:
Which are designed for power applications like welding output ect using the similar types of low Mu ferrites that specifica to these applications.

At the spec'd resistance of (only) 4 miliohms will have a voltage drop of 50 x 0.004 = 0.2V at full power which OK and won't compromise the inverter's ability to regulate it's output voltage

I ordered 2x of the 110uH 60A units part No:ES55246-111M-60AH

These work superbly allowing the toroidal transformer to perform correctly, i have made an aluminium bracket to hold them in place to ensure there is no magnetic interaction with the inductor

The last piece of the puzzle is some final output filtering, as any additional capacitance place on the output (say the power factor correction capacitor in a fluro lamp) of the inverter would serve to short circuit the switching harmonics increasing the current draw

Basically a 0.82mH inductor in series with the output and another 0.47uF capacitor across the output form a filter whose pole is tuned BELOW the switching frequency of 20kHz.

F = 1/(2 x PI x sqrt (L x C))
= 1/ 2 x 3.1416 x sqrt (0.82E-3 x 0.47E-6)
= 8.1kHz
This is very important, if the filter happened to be tuned near the switching frequency large currents would flow, large voltages appear across the filter, and nasty things might happen :!:

With this filter any additional capacitance or inductance placed on the output of the inverter will mean the filter pole is moved down increasing the filtering effect.

In other words, at the switching frequency the filter remains inductive blocking any switching harmonics and delivering a smooth sine wave!! :D :D

The 0.82mH inductor is another Harbuch product, actually a 1.6mH filter inductor wound for use in a lighting dimmer rack, that i unwound a few turns off to get the desired value.
This only has to handle 12.5A which is max output current of the inverter at 240VAC

Lastly Grounding the negative terminal of the DC power connection to the metal case and adding ferrite chokes to the mains output leads keep the radio interferance under control, which is actually quite bad without those measures.
Here's a pic of the approximately finished unit:
inverter completed_RS.jpg
Inverter with all modifications

The last checks i did on this unit was to load test the unit with different loads:
1500W heater - OK
700W transfer pump - OK

Lastly our 2600W Grunfos CR4 high head pump located at the dam down 100m of 6mm2 cable, this is a SERIOUSLY taxing load, the 2 pole induction motor uses 12A when runnning but least 3X the current is required to start it.
When i switched on the overload light flashed and the inverter beeped but it just kept going, let it go for a couple of minutes and all seemed to work fine, although the fan on the MOSFET heastsinks turned on the keep things cool.
So you can't argue with that

The final result is good all round:

Cost: Approx $1800
Loads: 3kVA + more short term
No load power: less than 20W

Here a pic of inside a LATRONICS PVE 1200 (my grid tie inverter) that uses a toroidal transformer.

Latronics PVE1200.jpg

Guess what that other small looking toroid is below the main transformer is?? (filter inductor)!!
I'd done all this modification development on the POWER STAR W7 before i brought the PVE1200, when i took the lid off i was veeeery happy to know that i was on the right track... ;)

Basically a now V12 motor that idles using only 0.2L of fuel an hour but can deliver 3000hp when required.


PS: i might try to put together a more concise list of the changes so that anyone can follow them
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Re: Powerstar W7 Inverter modification

Postby Helipos » Thu Feb 02, 2012 10:03 pm

One of the most interesting threads on here in ages.

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Re: Powerstar W7 Inverter modification

Postby WALL-E » Fri Feb 03, 2012 6:56 pm


You are an absolute genius, I can't believe I just stumbled across this, I now feel like I have a brother who I can relate to.

I also have the the Powerstart W7 inverter 6kw 48W (non lcd version) and have observed to the exact same measurements as yours in no load draw/ power wastage.
I have been testing the performance of the inverter thoroughly and also had a brief moment of research into replacing the existing transformers with toridials. I bailed on this idea due to lack of deep technical electrical knowledge and the fact that I couldn't find any toridials large enough for the application.

I am in contact with the manufacturers of these units trying to problem solve and get some answers however they are absolute pelicans and have no idea how a light bulb works, Will post email correspondence later!! :roll:

Fantastic job with checking the waveform and identifying that it is clapping generating all that heat.

Other problems I have identified with my unit are as follows...
Maximum battery charging voltage is 57amp which should be 70amp.
Battery type selector which should set the battery charge / float voltage is wrong, I currently have mine set to 15.1 volts but it actually produces the 14.0v which is what I require to get 57v for charging. changing this to the displayed 14.0v only produces 13.0v, all other settings produce under voltage than what is selected.

I would like to preform that exact modification to my inverter as what you have done in your blog. the only issue I have is 3kva is only 2.4kw and some, I would like to try maintain a minimum of 5kw output, does this mean I would need to purchase 2 toridial at $900 each? I paid $950 for my unit, blowing another $1800 on what potentially is my sheds electric bar heat at the moment seams silly.

Can you also comment on the performance of the battery charger after the toridial swap out.

Once again fantastic write up!
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Re: Powerstar W7 Inverter modification

Postby Tracker » Fri Feb 03, 2012 9:14 pm

Helipos wrote:One of the most interesting threads on here in ages

Here, Here.....

When the results of the first small toriod were mentioned, my first response was to think... "..but a big one will not be the same.."
Well, I was wrong.. Very wrong, and pleased to admit it..

NOW - Do I rip mine apart..

I would like to know how the results would translate to my situation with the Re-Charge overhead of 100%..
ie for every 1kw of battery power I use, I need 2Kw to recharge those batteries FROM/VIA the W7..
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Re: Powerstar W7 Inverter modification

Postby WALL-E » Sat Feb 04, 2012 12:00 am

Measurements taken from my inverter whitest charging batteries at 29.4amps / 56.0v = 1652W, on the AC side it was draining 2057W. this makes it about 75% efficient. it was wasting 405W of power in heat!
The above measurements do not include the inverters load that is transferred to mains charging power, it is important not to include these loads as they are easily forgotten when reading scroll meters. the mains feed was supplying around 500w to running house appliances at time of measuring

Inverter Mode
4.3amps @ 52v =223.6W loss while turned on with no load. 223.6W loss is also evident at all times with any size load, in other words while the inverter is on its there!

I would love to see how the toroidal preforms in this situation.
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Re: Powerstar W7 Inverter modification

Postby Tracker » Mon Feb 06, 2012 4:25 pm

As impressive as the project has become, I suppose the bottom line is now, that it can be done, but at what cost..

I admit that I had thought about it, but when I think more deeply, I will take a 6000/18000W device and convert it to a much smaller device, but with grander performance.
For this, it will cost something like $1000 extra.. (total about $1800)
8000W 48v SOLAR pure sine wave Inverter 60A battery charger + 50a SolarChargeController

and for about $1800, I can have a device that does much more, delivered to the door...

FULL MARKS for the effort and the project -- Most impressed.. :!:
BUT - Unless we can find a far more economical toroid, then it's not all that practical..

Please do let us know what you eventually manage to drag from the unit..

BTW - In the final picture, there are three chokes.. One toroial and two E cores... What are the three used for.. Tow for INPUT and one for OUTPUT.. :roll:
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Re: Powerstar W7 Inverter modification

Postby Andrew_electrix » Tue Feb 07, 2012 12:39 am

Hi All,
I'm glad this thread has generated some interest, i'm glad i havn't wasted my time writing this stuff up :)

Regarding the Charger performance of the powerstar W7 with the modifications - It is improved by the same sort of margin.
When i've used to to charge my 48V battery, it has done so without generating the same amounts of heat and power wastage as the original transformer(s)
Now i've got may DC power board up and running with 100A current shunts in place, i'll do an actual Pin vs Pout measurement to characterise the efficiency.

Regarding the kVA rating of the transformer 3kVA is 3kw at unity power factor and most domestic loads are not that bad in this regard. Our grunfos CR4 pump probably runs at about 0.8 PF lagging drawing 12A from the inverter which would be an average worst case.
You could go for a 4 or 5kVA transformer but useless there is really a need to deliver massive amounts of power i think the extra expense would not be justified.
Keep in mind this replacement toriodal transformer is conservatively rated for continous opperation at 3kVA, in other words it could easily do more for short periods - I have connected a 40deg N/O thermal switch to the 120mm AC fan such that it will come on if thing really start to get hot.
Also the charging voltages as spec'd int he manual seem to be fairly close, but that's NOT to say that
other units might not have problems or be out of calibration...
Also very interested to hear that you are in contact with the manufacturer!

THe magnetic components are as follows:
2x 110uH E-core chokes
1x 0.82mH AC output filter inductor
2x ferrite suppression chokes - one on transformer output leads, that other on the inveter AC output leads

Also i strongly suggest that you DO NOT buy one of those other inverter/charger units off EBAY!!!
One of the guys at work has been putting together a camper trailer with a 12V inverter system it and we bought the 12V 1200W version from Altronics (as i suggested it):
Howvwer the performance left us more than slightly disapointed here is a list of the problems we encountered:

>All test were done with a brand new century N200 excavator battery.
> 1. Inaccurate sensing of the battery voltage – The battery voltage was being overstated by almost 2V. As >a result the inverter would think the battery was fully charged before it actually was. I took the lid off the unit >and found the battery voltage adjustment, carefully adjusted this down and this largely resolved the issue.
> 2. Battery voltage display has no decimal places – The battery voltage varies by only a small amount so a >precision display is important and this contributes to the problem in Pt 1
> 3. Charge current into the battery approx 10A NOT 40A when on line with 240VAC input is as claimed by >the spec, resulting in very slow charging of large 200-400Ah batteries. Is the spec referring to the charge >current from the solar input?? This is not clear from the specs.
> 4. Incoming line voltage understated on the display - This had other implications, See Pt 1 below.
> 5. The charging process is not adjustable. The end point ABSORB voltage of 14.7 V is OK for flooded >(wet) batteries. But this is NOT suitable for GEL, AGM or any other sealed battery contrary to what the >spec’s state. The RICH ELECTRIC unit was great in the regard, fully adjustable BULK charging rate, >ABSORB and FLOAT voltages, meaning any flooded or sealed battery could be accommodated.
> 1. The Nominal 240V 50Hz setting on the LCD resulted in 262VAC at the output of the inverter, >DANGEREOUSLY HIGH!!!, By adjusting the LCD setting down to 220V 50Hz the output came back to >nominal 241V. This calibration error is consistent with pt 3 in charging mode and is unacceptable. Couldn’t >see any internal adjustment to correct this problem.
> 2. No load current draw is too high approx 4 amps (50W or 1.2kWh energy loss per day). Before any >loads (lights fridge ect) are added this energy loss need to be recovered. The daily output from 2-3x 180W >solar panels including 80% charging losses would cover this wastage. This makes the product totally >unsuitable for any solar power system.
> 3. Inaccurate sensing of the battery voltage – As mentioned above because the battery voltage was being >overstated, the unit would shutting down unnecessarily thinking the battery was flat when this was not the >case. Once the internal voltage adjustment was set more accurately the unit would work as intended under >load.

I'm will to bet that the 24V and 48V versions are much same as the above, for the same reasons the stock powerstar W7 is no good - they use an E-I transfomer that is poorly designed but additionally poorly engineered electronics as well.

As for the cost really $1800 is not too bad considering a brand name inverter would cost at least double this!!


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Re: Powerstar W7 Inverter modification

Postby Privatteer » Tue Feb 07, 2012 2:15 am

Can't help but think spending a bit more on the inverter, ie brand name is going to save you more in the end.
By the time you take into account the high standby current and other issues. Then allow for cost of additional panels/bigger battery bank to cover the inefficiencies.
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Re: Powerstar W7 Inverter modification

Postby Tracker » Tue Feb 07, 2012 6:20 am

Andrew_electrix wrote:Now i've got may DC power board up and running with 100A current shunts in place, i'll do an actual Pin vs Pout measurement to characterise the efficiency.

and, thanks again..
I too would like to set up the experiment of Pin/Pout, but have not had the time.
I know that just running for demand and charging for a fixed (Off-Peak) period, the power overhead is 100%.. ie. I use twice what is generated..
I'm confident that I would find that it's a bit higher with LOW usage, and again this is what I expected..
Again - I have only done the Pin/Pout at a KwH level, simply measuring the AC power by spinning meters..
That IS the ultimate test.. Determining what is the Cost benefit..? and so far it's halving the cost of PEAK power costs for refrigerators and one Air-Cond, so that we have a "Refuge" if needed..

Something that intrigues me, is the thought that there must be thousands of Grid-Connected inverters out there that might like a make-over to improve their eficiency.
That is naturally NOT ON, from a practical and a legal perspective.. You would not want the drama of a law suit..

3Kw with some extra, would be AOK for my needs, I must admit..
With my house Cct and a simple clamp-meter, I have found the MAX current to be 6Amp, but start up compressor currents could be higher, especially if a few fridges START at the same time.. I would like a PF device, to see just how I could help the highly inductive circuit of various compressors.

Andrew_electrix wrote:Also i strongly suggest that you DO NOT buy one of those other inverter/charger units off EBAY!!!

This is the BIG issue with ALL this stuff.. What is good value.. Which device actually does what it says..???
We have seen some pretty average performance from some very reputable inverter names, and no one questions them..
You would hope that just because it's sold on EBAY, does not mean that it's crap..
BUT - How do you find out ?

PS -
our 2600W Grunfos CR4 high head pump ...... the 2 pole induction motor uses 12A when runnning but least 3X the current is required to start it.

Interesting how you see new relevance when re-visiting past posts.. 12A = Double what I "Feel" I need.. :lol:
As one IN the industry, have you toyed with the thought of correcting PF for that motor..
Is there anything to be gained in doing so.. ( I do admit that AC Power is NOT an item in my resume )
What ultimate effect would a corrected PF have for the W7..AND battery drain.. :? .. :?:
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Re: Powerstar W7 Inverter modification

Postby WALL-E » Tue Feb 07, 2012 2:26 pm


I have contacted Peter Terlich at Harbuch Electronics regarding a 5000va Toroidal transformer, I mentioned about your toroidal and this thread you have created, regardless to say he was much impressed.
The Toroidal he quoted me PN# HS2417XFA cost $1300+GST this is a 5000va with 30 + 30 / 240v with flexible leads. At this price I am seriously considering performing the modification you have listed, As I have nowhere near the technical understanding as you with sizing correct capacitors and chokes are you able to provide assistance with getting this to work? Or do you think that the parts you have used on your 3000va toroidal will work the same with the 5000va?

Regarding the powerstar W7, besides the fact that it wastes allot of power in no load draw and has small problems with battery charging voltage settings, value for money it’s a good machine and good foundation if you can perform your mods and have them work reliably. The grid/generator power automatic switching works perfect and once you get your charging voltage set correct it charges my batteries no problem.

In order to purchase a brand name inverter which will perform the following at a power rating near 6000W your looking at spending between $5000~$7000.

If you can get the W7 working efficiently and still maintain the same power rating for under $2500 it’s still a bargain.

As for performance of the W7 my inverter easily pumps out 5500W no problem.

Please see attached image
Powerstar W7 pumping out 5482 no problem
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