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Re: Powerstar W7 Inverter modification

PostPosted: Thu Dec 12, 2013 8:22 am
by Garyho
Here is a very expensive way to buy a powerstar inverter, looks well built but why put a cheap inverter in it like that.

Re: Powerstar W7 Inverter modification

PostPosted: Thu Dec 12, 2013 11:35 am
by oztules
I have to agree with tracker and David..... this inverter is not for prime time commercial sale... but it is a nice cheap way to get into playing with inverters..... if your not interested/fully capable in doing a conversion with these things.... stay well away.. they are power hogs to say the least... you will need to be familiar with an oscilloscope to get the gap in the HF inductor sweet.... else it may not be worthwhile..... I repeat it is not for everybody.. ( probably only a few twits like me ), but at least the information is out there.

I am getting the impression that used just as a stand alone inverter, they are reliable work horses, but when we get to folks using them as UPS or AC coupling ( not entirely sure what the connatation of that is... grid coupling, or just ups operation) which I have not done to any extent ( UPS use that is, and never the real grid), I have not experienced any deficiencies.. quite the opposite.

So could it be that the internal change over relay is too fast?, and maybe for this instance another relay with an inductor/choke and timer circuit on the inductor would benefit this set up?

If a choke was inserted in series with the inverter output but before the internal (onboard) change over relay contacts, with another relay in parallel with that choke and with a RC filter driving the relay coil, when it switched from mains to inverter operation, the choke could limit the surge current into the house or whatever circuit, and not be hit in the face with out of phase reactances from the load hitting the inverter output head on. This would soften the change over currents to managable levels, iron out any wave additions that may reflect back through the transformer into the switching fets.

Once the RC across the relay in parallel with the choke allows the contacts to close ( 1/4 second or less should do ), the relay would short the choke and full current would be allowed to flow into the now synced load...

That is if, the primary form of destruction centered around that scenario. There would be a momentry sag in the output as the choke was in circuit, but better than blowing up the fets.... coments from those who have destroyed these things would be useful..... what was going on before it died?

Mine seems tough, the other on on the island has run flawlessly for the last 2 years powering a completly off grid home 24/7...... so for me something just isn't adding up.... We have not used them in the manner of others is all I can work out as yet. I know they run well as inverters, I know they run well as "off grid" grid tied units, I not sure exactly what others are referring to as AC coupling ( have my own ideas, but probably wrong), but it may be the underlying common factor .... can we learn anything from the failure styles.... I hope so........... so I don't do it, or maybe make a simple work around perhaps.


Re: Powerstar W7 Inverter modification

PostPosted: Thu Dec 12, 2013 12:15 pm
by brucedownunder
I'd like to thank the moderators for seperating this from freezers ..

This is a very interesting modification ,indeed. With you guys showing extreme experience in knowledge and actual benchwork,thank you.

I fully agree that these sort of modifications can not be carried out on a commercial basis, thats for sure .

It just goes to show how many of us would like to become more resourceful and do some benchwork instead of just caving in and throwing things in the tip. I'm half way through winding my coil transformer,(been out of work lately with heart pacemaker operation and now a bloody horse fly bite gave me blood poisioning in my leg.)

But I'm watching here every day , and soon will be back at the workbench ,completing my mods.

Thanks you Oz and fellow mates for an excellant contribution - 1st class .


Re: Powerstar W7 Inverter modification

PostPosted: Thu Dec 19, 2013 7:11 pm
by oztules
Stop what your doing and try this first.

Get the e core ferrite you bought, wind 3 and a 1/2 turns on it. Put in 12-15 thousandths of an inch of cardboard ( corn flake pack type) in the gap to stop saturation, and put it in series with the original transformer set up ( hope you have not removed these yet ). You will need to do this anyway , so may as well make it now.

I was idly experienting with the unit ( as I do time to time), and removed the e core to see what difference it made, as I had forgotten...... idiot that I am.

Noticed the idle current jumped up substantially...... tried the grid tie on it and it blew the fuses... why? The 20khz hash is inductor, no grid tie with these units in converted mode, not sure anymore about the native version either.

I am suspicious that I would have done pretty well to just add the inductor, and left the lossy transformers in place, and I am hoping you can prove this one way or the other for other folks... makes it a very easy conversion for next to nothing if it works like that.... I will be miffed as well if it works. May bring the idle current down to respectable levels, never know..

By putting the ecore back in circuit, the grid ties back fed the batteries just fine, without it it blew the fuses and went over 100 amps the wrong way.

That simple inductor may be the elephant in the room, that saves the idle current, and makes the grid tie section work properly.


Re: Powerstar W7 Inverter modification

PostPosted: Fri Dec 20, 2013 6:01 am
by brucedownunder
Thanks John ,( Oztules, I've known him for a long time ,so I guess I can call him my mate).

OK, I've the E core and can do the mod .. Maybe sooner than later ,but with Chrissie around the corner and guests arriving ,I have to mow grass and clean up ,sometimes I wish I lived in a highrise unit again --lol, never !!.

Poisioned leg is getting better,went for a surf yesterday,doctors orders.

Merry Christmas to all you good folk out there.


Re: Powerstar W7 Inverter modification

PostPosted: Fri Dec 20, 2013 7:00 am
by oztules
"sometimes I wish I lived in a highrise unit again --lol"......eekkk... thats sacrilige right there.... I like my tin shed in the middle of the paddock too.

I bought a power jack 8000LF inverter for $600.... it has two very nice 5kva toroids in it. I plugged it in last night... draws 8 amps in idle... sheesh..... dropped on the ecore filter, and it dropped down so low I could not see any sign of it on the 200 amp meter.

So it is beginning to look like the high frequency hash is drowning in the high inductance of the main toroids, and throws away 400 watts for nothing. If they simple added another filter in the primary side of their beaut looking toroids, they would have a very useful machine.... as I do now.

Once again, it would not look at the grid ties without throwing up... when the filter was put in, it ran happily... in fact is is driving the shed ( around -10A Dc, but charging the batteries at + 55 amps at the moment through reverse flow in the switches and transformer from the grid tie units, and the fan only comes on at sensible power flows.... powerjack is looking very very good now to me.

I had expected the worst with the advance publicity, but their LF units are very sturdy, and with a filter in the primary to collect the switching carrier, a very very economical unit to boot.... a 5 min modification that last night saved about 90AH out of the batteries, which would otherwise have been simply wasted.

I will be buying another one of these, as there is no transformer mods to do to get a good unit.... just the ecore filter.


Re: Powerstar W7 Inverter modification

PostPosted: Mon Dec 23, 2013 9:15 am
by astro_optics
Hi Oztules, could you post some pics of the NEW power jack 8000LF inverter with modifications?


Re: Powerstar W7 Inverter modification

PostPosted: Mon Dec 23, 2013 10:50 am
by oztules

Here are a few pics that will allow you to follow what I have done.. it is dirt simple.
It is just a matter of winding the coil aorund the 65mm freeite e-core... and your done... thats it.

Now you can use a grid tie on it,(NOT TO THE REAL GRID) and use less than 25 watts for idle current... mine runs at about 20w.
It is currently running at 55 amps backwards through the unit from the grid tie to replace last nights power.

[Moderator- removed duplicate photo]


And I don't know how or why the pics ended where they did or how one duplicated :roll:

Re: Powerstar W7 Inverter modification

PostPosted: Mon Dec 23, 2013 3:01 pm
by astro_optics
Hi Oztules,

thanks for's brilliant!
Do you have the inverter with LCD...does it have any other function besides showing the stats... can you change any useful settings....the eBay sellers are not that forthcoming when asked that info...

Thanks Again!

Re: Powerstar W7 Inverter modification

PostPosted: Mon Dec 23, 2013 4:33 pm
by oztules
I have the inverter with the LCD display.

It is another one of those things that htye seem to have missed in the design.

It is very good for the first screen, and displays watts pf volts and current, but it needs a next screen thatdisplays simple things like battery voltage, current kwh used etc... but no we have dinky price of power screen.... who cares... and how many KWH used in the AC stage... good, and you can change the setting to set an alarm for when you have used up x amount of kwh.... we don't need that nonsense, we need to know the battery voltage and current loading... and it just dosent have it.

I have to assume it is because they are such power hogs that they don't want to tell the world ... but a simple filter makes it possible to tell the whole world... hey look at this.. I'm really efficient.

The other thing that I don't appreciate, is the screen only lasts for less than a minute... this I will change so that it displays at least the useful first page all the ime, without having to reach over and press the button, and find it has scrolled to the next page.

These are minor things, but the battery voltage is a glaring omission..

Other than that, it really is performing above expectations.. ok they were low, but it really is running beautifully, including running the whole house for the last three day, including the hot water and oven.

I would not want to push the batteries on a regular basis to run the stove for extended periods, but for short runs (1/2 hour or so), it seems not to mind... but I don't like using that knid of current unless I need to.... and been 3 days of 8/8 clouds, so the grid ties cant help very much.

Mine is rated as 8000w, and it will do it too, but I think continuous would be better at less than 3kw or even 2kw.... but if you can run more for a long time you have heaps more battery than I have... and 35kwh is fine for me.

But it is great to drive heaby loads without worring if it will start things.... none of the biggies run for long, but it is a nuiscance if you cant start them in the first place.... and this will for sure.