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Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160
Posted: 01:00am 25 Jul 2017
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Thanks Oztules. They are curious kids, can be good and bad! They loved unwinding mylar tape buy running up and down the house with a loop of mylar over an arm!
I quickly took some idle load readings with an actual reputable meter tonight.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:47am 25 Jul 2017
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Yes that looks truly excellent.
The magnetizing loss given in the manufacturers loss curve is measured in watts per Kg at a certain specified flux density. So the more massive the core, the higher the no load loss is likely to be. That sounds logical when you think about it, larger transformers have higher idling current loss than really small transformers at the same flux density.
I measured 16.8 watts loss at 230v for one 1.5Kw Inspire toroid, and that is a bit smaller than a single 3Kw Aerosharp toroid. You are running two of the big guys stacked, and seeing only 13.7 watts at 230v which is quite an amazing achievement.
You now have a 5+Kw capable transformer with only 13.7 watts no load loss. That is going to be pretty hard to beat. Edited by Warpspeed 2017-07-26Cheers, Tony.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 03:05pm 25 Jul 2017
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Yes it is one of the sobering things that cause you to try to understand what is really happening in the internals of the torroid.
When your run current is a lousy 56ma, and yet, the start up current can blow the overloaders off the wall..
..........oztulesVillage idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:45pm 25 Jul 2017
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That is caused by the evil "flux doubling effect".
When you switch it off, there may be considerable residual magnetism remaining in the core. That is because of the very high permeability of the steel and there being no air gap. Next time you switch it on, you may be unlucky and be on the same mains half cycle that tries to drive the flux even higher in the same direction. It can theoretically hit twice the normal peak, and of course it then goes into violent magnetic saturation, with almost no dc resistance to limit the current.
It can indeed blow things off the wall, and quite spectacularly.
From the figures I got from testing my "Inspire" toroid a few posts back, saturation begins at about 1.2 volts per turn and rapidly gets more savage above that.
If we run at 1.0 volts per turn, expect some pretty dramatic turn on events, because worst case could be up to twice that, although in practice it will usually be far less than double.
Now Mulver is running a very low volts per turn, so low it can probably almost double without getting into trouble with saturation from flux doubling. So the flux doubling monster will have been tamed. Another big plus will be much more silent operation, even under full load.
The flux doubling problem can easily be demonstrated by connecting a 60 watt light globe in series with the 230 volt winding, and switching both on and off. If there is a massive current surge at turn on, there will be a very bright flash, then the lamp will only glow dimly.
If it just lights up dimly its because there was no transformer core saturation. It just draws 17 watts or whatever, and that will limit the brightness of the light globe to something less than that.
If you get a super bright flash every time its turned on, you know your transformer is operating within a bee's dick of saturation. And that ain't good. Cheers, Tony.
Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160
Posted: 05:13pm 25 Jul 2017
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Awesome and interesting stuff!!
I'm using the 1.6 diameter enameled wire from the Aerosharps.
Do i go 3 in hand (6mm2) or 4 in hand (8mm2)?
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 05:57pm 25 Jul 2017
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Each strand of 1.6mm is worth about 6.4 Amps continuous rating.Cheers, Tony.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 07:38pm 25 Jul 2017
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The other thing to note is the surge will last for less than 5milliseconds.
and the other thing to note, is it is not consistent. It depends where on the sine wave you turn it on.
If you coincide with the peak of the sine wave, there will be NO inrush current.
If you coincide with the zero crossing of the sine wave then maximum inrush current will occur..... and then everything in between those two points.
You can get up in the hundred plus amps, and this shows, as the C curve breakers break "instantly" at 6kva, and at even twice their rated current will still take a second or more to blow so to do it in less than 5 ms, the current must be huge. A typical C curve breaker ( domestic) will take probably 6kva in less than 100ms... and we are doing it in in probably a 4ms pulse.
When we go deep into saturation, the core looks like air, as it can't take any more flux.... so we are looking like a short circuit, and the better we wind the primary in cross section, the lower will be our R... and the bigger the E/R=I so if we have a 1r winding we have a 240v amp surge I guess... if we coincide with the zero point.
Hairy stuff if your not looking for it at the time.
..........oztulesVillage idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:41pm 25 Jul 2017
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The grid will just blink and carry on business as normal.
If you are off grid your inverter might have a heart attack.Cheers, Tony.
Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160
Posted: 01:15am 26 Jul 2017
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I think I'm going to push through and wind 4 times. Gives a nice 25amps!
Thankfully I have a variable transformer. So no big bangs for me!
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 01:49am 26 Jul 2017
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I have 4 X 1.6 in mine, I have had it running at 8KW for 30 minutes which is around 35A. At that load it did not get above 70 degrees from memory. I would think 3 would be plenty unless you plan to run it at 25A for hours on end.
Know what I know now and having a GTI connected as well the inverter rarely gets loaded beyond 5KW.There are only 10 types of people in the world: those who understand binary, and those who don't.
Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160
Posted: 03:30pm 26 Jul 2017
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Thanks Madness, maybe ill make my decision after the 3rd wind! Its unlikely Ill need the 25amps, but maybe the extra work now may be minor in the long run if i decide to use the transformer in a high load task.....
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 04:02pm 26 Jul 2017
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I know Oztules has kept his at 3, both myself and Tinker went to higher numbers and both of us had issues that Oztules never came across.
I put 4 on before considering using a GTI, as we try to run bigger loads during the day the off grid inverter has a bludge and spends most of the time running backwards while the sun is shining.
With the 3KW AC running, 2400W oven and general stuff like fridge and so on the off grid inverter is only running at around 2500W. The smaller inverter I built with a single core toroid would handle that easily. There are only 10 types of people in the world: those who understand binary, and those who don't.
Clockmanfr Guru Joined: 23/10/2015 Location: FrancePosts: 429
Posted: 10:04am 27 Jul 2017
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Hi Mulver.
My OzInverters on the secondary are all 4off 1.8mm diameter.
My Big OzInverters are 6off at 1.8mm diameter.
It all depends on your primary winding and getting everything neatly through that centre hole with space for a 10mm insulated torroid holding down bolt. Everything is possible, just give me time.
3 HughP's 3.7m Wind T's (14 years). 5kW PV on 3 Trackers, (10 yrs). 21kW PV AC coupled SH GTI's. OzInverter created Grid. 1300ah 48v.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:11am 27 Jul 2017
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That hole through the middle of the toriod looks pretty big when you start winding. It shrinks amazingly quickly.Cheers, Tony.
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 11:17am 27 Jul 2017
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Yes and the smaller it gets the quicker it shrinks.There are only 10 types of people in the world: those who understand binary, and those who don't.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 01:23pm 27 Jul 2017
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I think this is where the rubber hits the road....
That toroid hole is only so big, and you may have to make a difficult choice between fitting in one more extra strand of wire, or using one less strand and increasing the total turns count. It depends where your priorities lie.
If its going to be running flat out most of the time, go for the lower resistance winding to reduce the heating effect at very high power level. That might be be a good solution where one inverter only drives one single specific load, where its either running at full normal power, or switched completely off.
If your average power over 24 hours is up and down, but mostly down with only the occasional short term load peak, lowering the inverter idling current as far as possible would be a much better goal.Cheers, Tony.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 02:37pm 27 Jul 2017
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The first thing I do with the inspire trannies, is rip out the center of the torroid from about 85mm to 100mm.... I loose about .2v/turn from memory.
But I have lots of room to add a bit more copper to compensate, and everything is much easier to get down the hole, and it shrinks slower, as the circumference is larger to begin with..... so two x 2mm windings x 120 turns fits on/in without any overlap... thats good for 5kw for as long as my batteries can tolerate it. Then there is mountains of room for the primary. I use mad's system now of 19 or more wires spun together.... no over lap there either.. so neat and simpler.
This is important if your doing more than a single unit. Wholesale suffering if your only doing one is not so bad.
.......oztulesEdited by oztules 2017-07-29Village idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:14pm 27 Jul 2017
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That is most interesting. The extra 15mm diameter increases the area of the hole by roughly 38%.(5675mm^2 to 7855mm^2) But it only reduces the cross sectional area of the magnetic path by roughly 13% (55x65mm to 48x65mm).
I assume you bore out the toroid hole on a lathe ?Cheers, Tony.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 04:47pm 27 Jul 2017
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Yes it gives you much more room to play...... and pretty little drawback.
No, the inner silicon steel "tape" is only spot welded with two or three tiny spots just to hold it until they lacquer it fully.....
So I just release the steel, and unwind the foil/sheet/ (whatever we want to call the silicon steel strip)...with a blade of some sort or very sharp small screw driver will do it just fine to get a purchase, then long nose pliers.... and were done. I use scissors to cut the strip when I get there.
It takes a few minutes, and the dividends are more than significant..... to put it mildy.
.......oztulesVillage idiot...or... just another hack out of his depth
Mulver Senior Member Joined: 27/02/2017 Location: AustraliaPosts: 160
Posted: 06:35pm 27 Jul 2017
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Thanks everyone, the Aerosharps have 100mm internal diameter so I have a bit of space.
In reality Ill only have most of my loads on when the sun is out. The other point is ill probably start with a pretty small bank of batteries. As i do have the grid I'm considering using a grid tie with rectified mains during long dark days and or when I use too much power in the evening. This in my head would be controlled to keep the batteries above a bottom voltage limit.
With all that said Id probably be fine with 3 in hand.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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