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Forum Index : Electronics : 6Kw Ozinverter build
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Epoxied the inner this morning, this is where you really need to save as much space as possible and not waste it. So decided to try a pumped up baloon to keep the wires pressed up against the inner wall while the epoxy dries. There are two baloons there, one got slid into another so there is a double wall there, might help, dunno, worth a try.  Cheers Caveman Mark Off grid eastern Melb |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Very professional job,Mark. I like following your building .. Q, what is this one for ,just a spare or are you building them for sale? Bruce Bushboy |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Bruce, at least it does show the average mug off the street can do it. This one is a backup, the toroids are getting a bit scarce these days, if you ever see the 3kw one snap them up while you can. Cheers Caveman Mark Off grid eastern Melb |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Good idea Mark, I used a piece of PVC pipe with cloth wrapped around it and inserted in the hole to do the same, but I like your idea better. I have a Toroid sitting on the bench at home at the same stage, been over 2 months since I touched it. I might have to get my finger out and see who finishes first. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Pete Locke Senior Member  Joined: 26/06/2013 Location: New ZealandPosts: 181 |
...The opposite of vacuum bagging. Very creative. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
 Thanks guys, well it did work, very hard to see from pics but you can see with the eye and feel that there is a defined flat surface and there are no loose wires flopping about. Certainly will be doing that again with the next 3 layers. Edit, Forgot to say the epoxy kind of eats away at the balloon, so definitely use two or even three balloons slid inside one another. When they got removed the outer one had got messed up and stuck to the core a bit, but the inner was as new and slid out fine. Cheers Caveman Mark Off grid eastern Melb |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
Mark, that is very creative and original. My experience is that epoxy doesn't stick to oven bags Maybe line the inside of the toroid winding wall with it. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Tiny, balloons are pretty cheap, not too worried about rooting a few. Finished the second layer of secondary winding. The two loose ends were 0.025v between them, last torroid was 0.1v between them. Did the phase and volt test, that was all fine same volts, BUT, when I clamp tested the active line (with bulb shorted) This torroid had 0.048A compared to the last one 0.067A, that's quite a difference, would that be down to the fluctuations in the torroid material? It did look like these ones were from a different supplier. So this one is 11W and the previous one 16W, that's quite different.  BTW that is the exact same test rig I used on the last one. Cheers Caveman Mark Off grid eastern Melb |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
Lucky you put that comma in after Tiny, with talking of rooting and all... (I glanced at it at first and actually read it as tiny balloons are pretty cheap lol)  |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Mark, It depends if the steel alloy in those Chinese toroids of yours were made from crushed Holdens, Toyotas, or Fords, or maybe beer cans from South Africa. And if the subsequent heat treatment was done in a proper temperature controlled oven, or over a bamboo bonfire out in the jungle somewhere. Free is good, but you gotta be lucky too. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Warp, so it's due to the cores itself yeah? Don't get why the loose ends differ? Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The steel does vary from batch to batch and from different suppliers, that is to be expected, and the differences can be quite significant. It only really effects the zero load idling current, flat out at full power it won't make as much difference. The voltages induced in each turn "should" be identical but there will always be some sneaky magnetic lines of flux that take short cuts through the air instead of going only through the steel core. The difference in voltage will be very small, much less than the voltage of one complete full turn, and is quite normal and nothing to worry about. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Thanks Warp, this next one is going to be the backup unit, or maybe make it the primary, since it has a nicer core. Reckon I'll do this one a tad differently and sit the toroid in a tin of oil, that will completely negate any cooling issues, but if there is an internal fire in the case this could be quite spectacular if a tin of warm oil is there too. It will need a different case, possibly like Klaus did, but I have some ex school lockers that could be used. Cheers Caveman Mark Off grid eastern Melb |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Me thinks it would be much simpler to use 90 mm sq wire for the primary and 10mm sq for the secondary than creating some leaking oil contraption. The 29 odd watts of idle power do over time warm the core a little but its sheer size should easily dissipate that. Any additional copper loss heating is minimised by using decent size wire (yes mad - really  ).While you are at the winding stage do re read warps comments about adding a few additional secondary turns to bring the core well into the non saturating range, down from the borderline manufacturers number of turns. Of course, cutting away perfectly good heat sink fins to make room for capacitors does not help with the cooling under high power. Klaus |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Cutting away fins to make room for capacitors has nothing to do with cooling the Toroid in any inverter setup I have seen. The cut down Heatsinks are far more than needed, the fans on the heatsink side of my inverter hardly run at all, certainly far far less than what is required to keep the Toroid cool when the Inverter is working hard. Mark, I had toyed with the idea of putting the Torid in oil and using a radiator like those used for water cooling computers. But in practice the Toroid remains cool enough, they can run at 90 degrees and still be fine. Another thought I had was adding aluminium or copper sheets into the windings to conduct heat out of the core. Fitting in more copper to reduce resistance will help and with the later version of the Nano code you are using you will see the maximum temperature of your Toroid. I suspect it has never been above 50 degrees. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I think Mark has already done the added turns trick to get the idling power down as low as it is. I definitely agree with Klaus, the more copper you can stuff into the thing with fatter wire, the cooler it will run and the more power you will be able to safely get out of the transformer before it gets dangerously hot. Its those 40++C days where the airconditioner burns up your transformer. Power is only limited by safe temperature rise. My mate with the transformer winding business tells me my largest transformer will take about six hours running at full rated continuous power for the temperature to level out at its full rated maximum. Its probably pretty comparable to what you guys have, 50Kg total of steel and copper and a 4.5Kva continuous rating in still air. An oil bath should just about double the possible power rating because the outer exposed area of the metal drum, or whatever you sit the transformer and oil in, will be much greater than the exposed area of just the bare transformer by itself. Air is a pretty good thermal insulator, oil conducts heat away much better, so the heat can get out. Oil has to get very hot indeed to burn, no problems at all with a fry pan on the gas stove, and that will run much hotter than 100C without bursting into flames. An over temperature cutout would be pretty easy to arrange. Its just potentially a very messy thing to do. But there are other advantages such as silent running, and freedom from the effects of damp, humidity, or corrosion if the transformer is in a spare inverter stored for very long periods out in a leaky shed. Its not a solution for everyone, but its something worth knowing about. One final thought. If you use the tunnel heatsink method of construction, the heatsink should be mounted vertical for best convective airflow. That is pretty obvious. Less obvious is that if it gets hot enough to require the fan to turn on, the fan can blow downwards onto the transformer. If the heatsink is struggling, chances are the transformer could do with a little help too. Once you fire up the monster fan, natural convective airflow becomes irrelevant. Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
My current unit has the heatsinks vertical and a fan at top and bottom. The torroid is next to that in a almost separate box, that too has fan at top and bottom, each one is triggered via the temp probes and settings are adjustable via the arduino. The main reason for liking this idea is the lubrication and deadening factor it will give the wires. I just cant help but think even with a small buzz that those wires are rubbing and that will/should cause a short at some point. Maybe I'm worrying about something that may take 15 years to happen though. Edit, BTW still no unwanted restarts since I put the ferrite filters on the on/off switch, so I'd call that a certain fix after one month and no problem. Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I don't know of anyone that has an oil filled inverter transformer. But a place that I worked at had a large three phase variac mounted vertically in a large rectangular fully welded up metal box. On the rating plate it said 15 amps per phase max or 30 amps max if the metal box is filled with oil. That got me thinking... All of the transformers used for mains power distribution are oil filled, even the smaller ones mounted on telegraph poles out in the street are oil filled. Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Hi Mark, I used to re-condition large oil filled transformers years ago when I worked for broadcasting at a high power radio transmitter site. Occasionally they would go bang making quite a mess inside the transformer casing. You need a steel or alloy case with welded seams and a flat right angle section welded around the top where the lid goes; the strong lid sits on this flange on a cork gasket with lots of bolts, the transformer is suspended from the lid and sits in the oil. You will require insulated through connectors (brass threaded rod and a piece of nylon kitchen chopping board would work). There must be an air gap above the oil level with a vent tube to the outside to allow for expansion, a silica gel moisture filter is normally attached to the vent. You probably don't need this with only 240volts. We used to get the transformer oil from Shell depot in large 44 gal drums, its very thin about SAE #5, best local source would be a power line depot or similar. Cheers Mike |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Some of that transformer oil is nasty stuff, I have seen where people have said automatic transmission fluid works well. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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