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Forum Index : Electronics : grid tie inverters
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
????? Can't figure out what you mean Bruce. 30 turns (as quoted above) means you have to pull a single wire diameter 30 times through that hole. I do hope you measured the available area against the wire size. Draw a circle of that hole in the toroid center and then draw inside that circle 30 smaller circles of the wire + insulation diameter. If it does not fit you have a problem  .
There is no shortcut, 30 turns means winding a wire 30 times around the core , always going in the same direction around. Klaus |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Klaus. Yes , I did measure it ,thats how I came up with 11 meters for the 30 turns . I also have a meter or so for connecting leads.. She fits,nice and tight on the inside . I followed Oztules example and bought the earth cable as it has thinner sheathing . I've posted Oztules picture below , hope this is OK with him. My idea of "doubling" the 30 mtrs into two lengths of 15 mtrs was so I would be pulling 15 mtrs for the first 15 turns ,then another 15 mtrs for the last 15 turns .. still the same amount of work ,but half the tail to drag through the hole ???. Each turn will have to require some hand bending as the wire is fairly stiff and I'd want to get tight turns ,not wasting any "length" .. Bruce 
Bushboy |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Did you wind it as you had suggested with the wire doubled over, as my gut feeling tells me that is not what you want, as it will do either of 2 things, and i havent got my mind around which one is correct. Either it will cause a opersite coil that will cancel out the other coil, or you will end up with a two in hand winding, so double the amps and half the voltage. Pete. Sometimes it just works |
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BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
As Klaus said above and there is no escape from that. What you could do is double wind it like you said then when done you have a winding with two ends and the middle of your 30 metres as a loop. Cut the loop and then you have two windings. Join it up like a centre tapped transformer winding. Join the end of one winding to the start of the next and you are done. Mark the cable before you wind it so you know better what connects to what. You have to end up with the windings in series. I'm having trouble making this sound fool proof so if there is doubts ... Mark the two ends as A & D and the ends in the middle as B & C. Here is your cable. A ----------------------------B --- C ----------------------------D When you cut the middle join A to C or B to D. |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks guys -- I seem to have got you all confused.. OK, let me "try" and explain . feed half the length of cable through the "hole" ,, start on one side and do the 15 windings, then go back to the remaining "half" and continue doing it's 15 windings. Now you have 30 turns ,all in the same direction and a start and an end .. Bruce. Bushboy |
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| BobD Guru Joined: 07/12/2011 Location: AustraliaPosts: 935 |
As long as the magnetic flux from the whole winding is in the same direction it will work but yeah, you did confuse me. |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
Bruce , Have a good read of this thread on Energy Matters forum HERE , as I mentioned earlier that this mod has been done by quite a few and there is some good info in the Link on these cheap Chinese "Power Star W7" Inverters if you want to go to the effort. Obviously you are in the loop and asking questions on that thread as well , I just checked P16. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Hi Phill and Crew. Yes, I'm well aware of the mods ,have been following Andrew,Tracker and Oztules mod closly. I'm doing this ,knowing there is a possibility of failure , but ,well, that 300 odd watts of wasted idle and RUN power is just not acceptable, . We'll have to get together for a cup of coffee again , Phill . You must be very busy. Having fun in the workshop--it's been busy doing the solar tracker ,finishing off my amateur radio antennas and ,of course the Exmork is still patiently waiting for it's final lift . Have had a bed winter ,sickness and now waiting for my "pacemaker"install proceedure at the new gold coast hospital Bye the way, any one on the forum thats travelling by is welcome to visit,,just cantact me a day before. Bruce Bushboy |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
OK, I've started to wind the 25mm cable,(primary winding) ,of 30 turns. Not easy, using a soft faced hammer with caution, sort of one turn at a time ,dress it , temp. cable tie ,then onto the next turn ,sort of thing . Time off for 2-3 weeks, have had a "pacemaker" inserted in my chest and have been warned not to do lifting or heavy type work.. 
Only 10 turns on there ,but have 18 turns on now and she's looking very tight in the core. Might be "doubling-up" on a few turns to get the 30 in. I've been talking to the "inventor" ,Oztules, on my progress and he reckons I'm on the right track. Hope you are all having fun in your workshops, Bruce Bushboy |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Well done guys, this is all really great stuff. At the risk of making myself unpopular, I very humbly offer a few suggestions. As Bruce is discovering, massively thick heavy single wire is extremely difficult to wind onto any toroidal core. There is a trick to it, start in the middle of the length of wire, and wind on 15 tuns from the middle out towards one end. Then wind the other 15 turns from the middle out to the other end. There will be far less length of wire to drag through the hole each time. Another way to make things a lot easier would be to use a bundle of much finer wire instead of one single heavy insulated wire. Instead of one 25mm^2 wire how about ten strands of 2.5mm^2 wire ? It will be much more flexible and the strands lay very flat with fewer big air spaces that quickly gobble up the available space. Cheers, Tony. |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Tony ,, thats exactly what i've done ,,and tried to explain in earlier posts... 15 turns one way ,,15 turns the other way ... Bundling,,, I actually stripped lots of building wire and got the equevalant of 25mm square section ,,, but,,, it was a lot "Bulk'ier" if thats a word..?? As I said ,, it's sit and look time for another week --under the doctors orders... I'd have a look at using welding cable next time ,, it has 2 insulation covers , so just strip the outer cover off and you then have a very flexable , well insulated, cable mass to wind. Cheers Bruce. Bushboy |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Bruce, some of us have had some great setbacks in life, both medical, personal, and financial. Take care, and take things very easy for a while. Convalescence actually offers a great opportunity to think a great many important things through. I have found that as I become older, projects take much longer to plan, but the implementation usually goes much more smoothly, and with much better final results than in my impetuous and impatient youth. I don't post much on any of the Forums any more, just lurk. Terminal madness (and aggression) is consuming the entire world and especially he internet. We certainly live in interesting times. Cheers, Tony. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Bruce, My only concern is you have used copper for copper in the required size, but have you used a insulation of the wire suitable to the heat requirements. It looks like a general PVC coated wire used, which has a low temp melting point, where most welding cables have a rubber or silicon based insulation, suitable to far higher temp, for longer periods. I really dont know what is required for your build, so its just a general comment, and im sure you have passed it by Oz, who knows much more than me here. Pete. Sometimes it just works |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Hi Tony, thanks mate , I've slowed a lot ,thats for sure. Still doing lots of "backshed" things around here,but at a more controlled way. I'lltake your wise advice ,thats for sure. Thanks Tony , Oz has used the same earthing wire and he tells me he has pushed the output fairly high ,at times. He also has disconnected the original transformer fan ,the one at the rear, because he reckons it does not need it as the toridal coil has not got past warm. He has left the front fan connected,it cools the mosfet area . I've never seen it "on' ,so all in all ,I'd think things up the mosfet area stay fairly cool also. These inverters are built very strong and with this "Oztules" conversion , would fit the bill . remember , we are doing this because of the 250 odd watts just in stand-by mode, the mod will ,might , reduce this to around 30 watts. I have a 1400 watt ups that is allmost silent and consumes just around 20-30 watts in stand-by ,,so it's a winner. I've been using it for weeks now ,silent. Bruce. Bushboy |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its indeed a valid concern, but my own experience with similar things is that a fully exposed to air outer layer (of few turns) will certainly run warm, but not dangerously so. A very tight multilayer winding wound with thermoplastic insulation, would be a very different thing altogether. This toroidal transformer idea is a very good modification. The thin silicon iron strip these toroids are wound from produces a significantly higher inductance per turn, mostly due to the higher permeability of the material. The toroidal shape reduces the magnetic path length, and the continuous strip reduces the cumulative effects of the unavoidable air gaps found in E/I core transformers. All these features combined, increase the inductance per turn and hugely reduces the no load magnetising current, as we already know. Another advantage is the very thin silicon iron strip lowers eddy current loss, compared to the thicker E/I laminations. All a very big plus for us. It would not be practical for a bi-directional grid tie inverter, but for a straight transformer inverter another way to tackle this whole no load loss problem may be possible. Transformer magnetising current has two components, an inductive component, and a resistive loss component. The inductive component is entirely made up of Xl inductive reactance, so the higher the primary inductance, the higher the inductive impedance, and lower the no load inductive current. The resistive (in phase loss component) is made up from eddy current losses plus hysteresis loss in the iron core. The hysteresis loss is roughly proportional to flux density times the total mass of iron in the core. The bottom line of all this, is that all else being equal, a big heavy transformer will have a much higher no load loss than a small transformer, simply because it takes energy to flip all the magnetic domains each way during each half cycle in the iron core. So a 10KVA inverter transformer is going to have much higher no load loss than a 100VA inverter transformer, simply because of the extra mass of iron in the core. What Should work according to theory (?) is that it may be possible to run a large transformer and a small transformer in parallel, provided they have an identical turns ratio. For zero load or very light load the small transformer only supplies the 240 volt output of the inverter. If its a small very efficient toroidal wound transformer, the no load losses could be kept absolutely minimal. Now the interesting thing about transformers is that output current is limited only by heating and voltage regulation, you can safely massively overload any transformer for very brief periods. The idea proposed here, is to run a high power transformer inverter with a greatly undersized and very efficient output transformer to provide 240 volts for zero or very light loads. When something like a huge motor load kicks in, the big transformer is very rapidly switched in parallel with the small transformer (with a relay or a contactor) to supply the higher output load. When the heavy load is removed, the big transformer is switched out. This may possibly cause a brief voltage dip at the switching in point, but it should also be possible to greatly minimise zero load inverter losses if you plan to run a fairly large inverter constantly. This is just an idea put forward for discussion, I live in the suburbs and am 100% grid power here, so its an idea I cannot really try out myself. Cheers, Tony. |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Tony. You sound like a fellow that has eaten a lot of transformers for brekkie . Oztules, sort of reckons it might be OK to put the finished coil in it's own steel box adjacent to the original set-up .In my case it would look a lot better and the leads to the electronics side would only be 200-300 mm longer .. Thanks again for the feedback .. Birthdayboy,,69,Bruce. Bushboy |
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| M Del Senior Member  Joined: 09/04/2012 Location: AustraliaPosts: 155 |
Hope you have a happy  one Bruce.
Mark Mark |
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| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Bruce, It is too late now to save you some loot but big toroidal transformers are available at scrap yards as people throw away their pool chlorinators. Found one at a roadside drop. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Another less obvious source of big toroidal cores that already have a 240 volt winding, would be to strip down an old "variac" variable voltage transformer. 
Ratty old ones often go quite cheap at auctions and on e-bay. They are always clearly marked as to current capacity, and a ten amp one would be sufficient for 2.4 Kva inverter. Cheers, Tony. |
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