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Forum Index : Electronics : Winding Transformers
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| Alston Regular Member  Joined: 04/04/2021 Location: AustraliaPosts: 63 |
So I am early in the process of my inverter build. I am planning a Warpspeed style with 4 transformers. I currently have a 3KW aerosharp and a 1.5kw SMA (well I will have the core once I finish getting the potting off, probably none of the windings). While I will have lots of questions along the way the first is what are some recommendations for places to buy winding supplies? |
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| Godoh Guru  Joined: 26/09/2020 Location: AustraliaPosts: 458 |
If there is a company that winds electric motors and transformers near where you live try them. Most electric motor winders will have rolls of magnet wire that are not full. You could just buy the weight of wire you need. Best to get it on a spool as it can get in a tangle very easily. They should also have either cotton, fibreglass tape to tape the windings and sleeving for the leads. If you can get hold of some winding varnish while you are at it. Dipping the transformer in varnish will quieten it down and make the windings less susceptible to vibrational damage. Pete |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Look in your yellow pages telephone book for businesses that wind transformers or rewind electric motors, they will have massive spools of wire of every size, and its sold by weight. When you actually have all your steel cores, we can then design and plan the windings, how many turns of what sized wire. Its then possible to roughly estimate the length, and from standard wire tables the weight of copper wire to buy. Cheers, Tony. |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
When hacking the windings off a potted transformer keep all the bits in a bucket. When finished weigh them and you will have an idea of how much to buy. Roughly half primary and half secondary. You will have a little more than you need as the old wire will have potting stuff stuck to it. After determining the turns you can work out the size as noted above. |
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| Alston Regular Member Joined: 04/04/2021 Location: AustraliaPosts: 63 |
Thank you for the responses. I wasn't sure if there was somewhere online people would recommend but happy to support local businesses. I know of some here in Perth I will contact. What is the actual name of the Mylar insulation used on toroids? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Your best bet might be to go around and see what kinds of tape and insulation, and what widths they actually have. Talk to the guy, explain what you are doing, and get some prices. It might also be worth talking to Klaus, he is in Perth and is a toroid winding veteran. He may have cultivated some useful contacts. Cheers, Tony. |
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wiseguy Guru Joined: 21/06/2018 Location: AustraliaPosts: 1156 |
There is a website for Hobby King, they have a warehouse in Australia for local shipping and their pricing for some electrical and electronics stuff is very cheap. If you are into RC modelling it is a good resource but you probably would already know about it. https://hobbyking.com/ They have a High Temperature Polyimide Tape (0.06mm*24mm*33Meters) for around $7 which I think may be suitable but it is adhesive and hopefully the tape former can be squeezed narrower to fit through the centre hole of the toroid. If not maybe 1 metre or so lengths might be workable. They also have polyester wing tapes in various colours ie blue Wing Tape 45mic X 24 Mm X 100m (Narrow - Blue) currently on special for 81cents (not a misprint) for 100m ! I suggest probably not as strong as genuine mylar but maybe worth investigating. Some of their XT60 & XT90 connectors are low cost for 60A and 90A (metric amps not imperial amps....?) They are actually quite good quality & value. The site is worth spending some time looking through for inspirational ideas and repurposing some of their offerings. Just make sure that whatever you order is an Australian stock item or the shipping price might scare you. If at first you dont succeed, I suggest you avoid sky diving.... Cheers Mike |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Yes, if you are located in Perth WA do send me a personal message. I can talk you through the process of winding toroidal transformers by hand. There is quite a bit of stuff that made this task easier cluttering a box here, you are welcome to have it as I'm done building inverters (6 were enough  )Also, keep in mind while winding that toroidal transformer is the biggest task, there are lots of other parts to consider before you start spending money. Its easy to overlook just what else is involved to complete building a working inverter. |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
While winding the transformer you can also embed a thermistor in the winding something like this |
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| Alston Regular Member Joined: 04/04/2021 Location: AustraliaPosts: 63 |
Klaus I don't seem to be able to send you a private message on the forums so wondering if you have it turned off? I would really appreciate the advice and bits you made so thanks for offering the help! I have gone through these forums and complied a document with lots of info on the Warpinverters so think I have a good understanding of how it all works now but was starting with winding the transformers as my first challenge. While I have lots of experience with circuit design, micro controllers and PCB design one thing I have never done is calculate and wind a transformer. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
You will not be flying completely solo Alston. Plenty of help and advise available from Forum members. Cheers, Tony. |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Sorry about that, I seem to have forgotten to 'save' my PM notifications, perhaps that is why it did not work. Yours would have been the first PM anyway. So why not send me an email: az_100@msn.com and we can go from there. I can always block messages if the spammers get hold of this address. |
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| Alston Regular Member Joined: 04/04/2021 Location: AustraliaPosts: 63 |
So since I have unwound my number 2 transformer and have my core, so I thought I would start with that one. I am planning a 5kw 4 transformers setup and will be using a 48V nominal battery voltage. The step voltage I worked out are 229.068v (3375watts), 76.356v (1125watts),25.452(375watts),8.484(125watts) for a total step voltage of 339.36. Transformer 1 will be a 3kw AeroSharp core. The SMA Sunny Boy core is for tranformer number 2 and has an OD of 192mm, ID of 91mm, a height of 52mm and 1 turn is 205mm. The area I calcualted of the core is 26.26 cm2. The rule of thumb for working out how much power the core is rated to I found was the square root of the power. But this would mean a core of this size is only good for about 700watts? I assume since a torodial transformer is more efficient there is a different formula to work this out? Tony I read in another post of yours to wind all transformers as if they were for 50hz. So with that in mind 42/26.26 = 1.59 turns per volt, 1.59x48v = 76.32 turns for the primary and needs to carry 23.43 amps at 48 volts. The secondary is 1.59x75= 121.4 turns and I assume the secondary of each transformers needs to carry 21amps (5000w/240v). Aside from the obvious current carrying what consideration do I need to take into account when selecting the wire guage? When and why would you use multiple turns of smaller gauge wire? Do I calculate my primary with the lowest expected battery voltage instead of the nominal voltage? It seems like transformer design is largely a balancing act, with that said what are some rules of thumb I should follow? Searching around there seems to be more info for EI but not so much toroidal transformers online. Thanks Klaus, I will send you an email! |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
A few rules of thumb about winding toroidal cores. 1. you cannot have a fractional turn, one pass through the hole equals one turn. 2. use the 4 Amps per sq mmm wire area for your current rating. 3. we use smaller gauge wire with turns in parallel because we salvaged the wire and smaller gauge is *much* easier to wind by hand. 4. Yes use the lowest expected battery voltage for your calculations (I used 50V for a lithium battery bank), its less for LA batteries. 5. with warpinverter toroidal cores you will most likely run into trouble with the smallest core. Remember that the secondary must be rated for the full output current so, if the hole is too small it simply will not fit. I ended up using a core much larger than for the expected power rating for that reason. 6. you cannot wind by hand as tight as a machine can so the theoretical number of turns you can fit around the circumference of the hole can be up to 10% less. Lastly, your total step voltage is quite high, I would aim for 230V. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Ah Klaus, you beat me to the draw by a couple of minutes!! Yes, depending on battery chemistry, the lowest voltage the inverter will ever see is your transformer design starting point. The voltage regulation built into the Warpverter can only decrease the inverter output voltage, it cannot increase the output voltage beyond what the transformer turns ratios were originally designed for. So somewhere around 40v to 44v worst case input might be about right. Forty volts sounds pretty extreme, but its better to have a bit extra down at the low voltage end rather than have the output voltage dip under extreme short term surge loads when the battery is down a bit in voltage, which can produce light flicker. The inverter final sine wave output voltages is nominal, anywhere in the 230v to 240v output range will work fine, as the exact output voltage can be tweaked with a potentiometer once its all running. Whole volts are much easier to work with when designing the transformer windings, so the suggested secondary design voltages are 225v, 75v, 25v, and 8.33v. That all adds up to 333.33v which is the peak voltage reached when all four inverters switch on together in the same direction. For a 333.33v peak sine wave the rms will be 235.69v which falls neatly into our desired output voltage range. For 5Kw all the secondaries carry the same current which will be in the region of 21 amps rms. A good design current density for all of the windings will be 4 amps per mm square copper. So around roughly 5mm sq copper would be about right for all of the secondaries. Now the trick is to see if your largest toroid is big enough to fit enough wire on it to satisfy the 5mm sq requirement, with sufficient turns, without using up too much of the hole to do it. If the starting diameter of the hole is 100%, that should shrink to no less than 70.71mm (root two). If the secondary will fit fine, if the secondary uses up too much of the hole, you need to go to thinner wire. Say for example you are forced to use only 4mm sq copper on the secondary to meet the 70% minimum hole requirement. 4mm x 4amps = 16 amp rated secondary, and your inverter will be 3.76Kw not 5Kw. Its how much copper you can fit onto the toroid that determines power capability. Bigger toroid equals higher power rating. Edited 2021-12-29 15:37 by Warpspeed Cheers, Tony. |
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| Alston Regular Member Joined: 04/04/2021 Location: AustraliaPosts: 63 |
Thanks for the advice, I will sit down and digest all of that. I also just came across this topic where you have already given lots of important details so I will go through that https://www.thebackshed.com/forum/ViewTopic.php?TID=11266&P=2 and then get you to double check my work.  |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yup, there is a lot of really good stuff there. Quite happy to talk you through your own transformer design if you require a helping hand. There are at least four Warpverter driver boards now out there, the required waveforms can be generated either in simple hardware, or using a microcontroller. They all plug into the power stage directly with the same identical plugs and pin outs. If you find software a bit challenging as I do, my hardware board works fine as a plain vanilla inverter. If you wish to have all kinds of extra functionality, the more up market microcontroller versions will probably be of much more interest to you. I now have both types here, and cannot tell which type is actually running in my own Warpverter, they all behave absolutely identically. Its your choice, I can supply a circuit board and a pre programmed EEPROM, plus a crystal if you decide to go with simple hardware. Cheers, Tony. |
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| Alston Regular Member Joined: 04/04/2021 Location: AustraliaPosts: 63 |
Thanks Tony. I have been back over your previous post and come up with the following. So for my core of OD of 192mm, ID of 91mm, a height of 52mm the area I calcualted of the core is 26.26 cm2. I have changed my voltages to 40v and the step up voltage to your recomendations and my transformers would be 3375W,1125W,375W and 125W. So to get 1 Tesla of flux density I would need 128 turns (for TX 2 at 75 volts) which works out to be 69 for the primary and 129 turns for the secondary. Does this sound right? I would need 28amps on the primary and 21 amps on the secondary. Since winding thinner wire is obviously much easier by hand as Klaus pointed out what would be recomended in terms of what would fit and be able to be wound? I think I might need some help with working out how much will fit and so on. You mentioned in that previous post that 1.6mm wire is good to 8 amps but the AWG guide says 5.9? As for driver boards I haven't worked that side out yet but I very much like the elegance of your hardware based approach. Writing software isn't an issue for me but I may still buy one of your driver boards as a good starting point. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yup, core cross section 26.26 cm sq Primary voltage 40v, secondary voltage 75v, turns ratio x1.875 step up. And 129 secondary turns comes up with 9,972 Gauss (0.9972 Teslas) 129 x 40v/75v turns = 68.8 primary turns. 69 primary turns with 40v dc would produce 40 x 129/69 74.78 volts which is fine. Now assuming we are going to use several 129 turn secondaries layered one on top of the other. The last layer to go on will have to have a minimum diameter roughly 70.71% of the hole diameter. So assume the diameter of the last secondary layer is 70% of 91mm = 63.7mm diameter. The circumference will be very close to 200mm. The biggest wire that will fit 129 turns around that last layer circumference is theoretical 1.55mm diameter. 1.5mm diameter wire should just fit, remembering that the layers underneath all have increasing circumferences. 1.5mm diameter wire is 1.77 mm sq, and at 4 amps/mm sq is good for 7amps per layer. Now the difference between our final layer (63.7mm diameter) and our first layer (91mm diameter) is 27.36mm. In a perfect world 18 layers should be possible !! But we only need three 7 amp 1.5mm layers to reach out required 21 amps. So there is going to be HEAPS of room on that core. Much thicker wire will be possible, but with slightly greater physical effort to wind. 1.9mm wire would be 2.84mm sq and at 4 amps/mm sq 11.3 amps. only two layers would be required. Our core diameter is 91mm or 285mm circumference. In theory 150 turns should fit. The second layer will only fit 6 turns less theoretical or 144 turns. Two 129 layers of 1.9mm wire should also be possible. So two choices, two layers of 1.9mm, or three layers of 1.5mm with 129 turns per layer. That toriod is pretty big for inverter number two, and its going to look a bit empty. But it will be a very easy wind, and will work very well. Edited 2021-12-31 18:04 by Warpspeed Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
If you decide on two layers, 1.9mm is the biggest wire that will fit. If three layers, 1.5mm is all you need for the current, but there will be plenty of space for larger sized wire than 1.5mm . Cheers, Tony. |
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