how to specify a transformer for manufacture - Page 1
Forum section: electronics / projects

author: jaunty
author_rank: Regular Contributor
timestamp: December 21, 2018, 04:17:25 am
content: So i have occasion to need to get some toroids built ... I described what i needed in terms of windings and taps on primary and secondary sides - expected voltage and current load on each winding etc and am being told by the manufacturer's sales department that it's simply not enough to base an estimate on ... i think i was rather thorough ... but they are insisting i send in a sample unit before giving an estimated price. What gives?? Is there something i am missing here? I believe i answered all their questions to their satisfaction... anyone here had transformers built for manufacture? One aspect that occurred to me is that there's always a kind of cultural or sociological boundary involved when trying to do business with new people ... a trust has to be built up first (?) (not very professional of them i would say though)

author: jaunty
author_rank: Regular Contributor
timestamp: December 21, 2018, 05:07:36 am
content: well technically i AM trying to 'clone' a product - though in this case the product is just a normal toroidal tansformer - but the manufacturer has been out of business since the late 80s ... i mean LOTS of people make these things right? you can't really patent, say, a toroid with a 110/240v primary and three secondaries at 15/15/5v .. plust a tap ...? i'm also wondering if maybe the quantitiy was too low to be of interest that they were just trying to make it hard for me ...

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2018, 05:50:46 am
content: The transformer place I've dealt with has their own magnetics engineer and can perform these services. When I designed a transformer I provided them with complete specs, core type, wire gauge, turn count, etc. They modified a few mechanical details to suit their manufacturing process but otherwise built it as designed and it worked out.

author: soldar
author_rank: Super Contributor
timestamp: December 21, 2018, 08:39:23 pm
content: Quote from: jaunty on December 21, 2018, 04:17:25 amHow many units do you need? Because I can understand their reluctance if the quantity is small. It is just not worth their time. Or they would have to quote a price you would surely not want to pay.You might need to approach someone who does prototypes and small series.Having said that, there are other red flags in your post. Do you have for them a complete detailed specs of what you want built? Core material and properties, wire specs and properties, insulation, etc. Is it all materials they work with and have in stock?Either you design it completely and take responsibility for the result or you can give them some specs and ask them for a design. What you are asking, it seems, is to give them sort of a rough design (x turns) and then talk about voltage which is your problem, not theirs. So you are kind of asking for them to review your design and I can understand their reluctance to get involved in a project for a small quantity with someone who is not sure of what they want. To them this is a sign of a customer who will take much of their time and give them much trouble and little profit.If the quantity is small you might want to wind them yourself. If you want to order them I would advise you to go to some place where they do small orders and can help you with the design.If you post your requirements in detail maybe we can help further.

author: Benta
author_rank: Super Contributor
timestamp: December 21, 2018, 09:56:08 pm
content: This is complete BS. Mains transformer companies do this every day.You specify primary voltage(s), secondary voltage(s) VA, operating temperature, isolation class, form factor/shape and that's it.My feeling is that you're trying to get some Chinese super low cost offer, which explains the reaction from the manufacturer.One-offs cost a bit.

author: jaunty
author_rank: Regular Contributor
timestamp: December 22, 2018, 01:05:54 am
content: Quote from: soldar on December 21, 2018, 08:39:23 pmyes well my methodology as originally planned was to describe the beast - approximately - (i.e.- number of primaries secondaries and V/A for each) and then ask for an APPROXIMATE PER UNIT price for quantities of 1, 10 and 100. I could well easily go 100 units if i get this off the ground - or more - but i thought it would be good to ask for pricing on those quantities because it gives me a quick indication of their 'pricing curve' you might call it ... certainly there are a FEW companies that told me to go piss up a rope as they weren't interested in quanitities under 5000 or so, say ...but the company i'm dealing with in particular was recommended BECAUSE they do low quantities - or at least dont' mind ... and they are close tooi tried to explain that I really DON'T need a very accurate price but maybe within 20-40 dollars per unit would give me an idea whether i should go this route or go overseas ...etc - so from that perspective wire gauge etc seems kind of niggling

author: jaunty
author_rank: Regular Contributor
timestamp: December 22, 2018, 01:10:08 am
content: Quote from: Benta on December 21, 2018, 09:56:08 pmhow so? i am only trying to get a ballpark estimate of what it's going to cost me ... if they are 500 each then forget it ... not worth my while ... but 100 i can deal with and sure... hell yes i wouldn't mind the lowest price possible but this is new territory for me ... i don't expect them to be cheap ... but i am not really sure WHAT to expect. I also don't want to get ripped off because i'm not a 'respected' corporate entity or someone they want to be in bed with but 'just some crazy guy' who imagines he wants to have transformers made (?)

author: soldar
author_rank: Super Contributor
timestamp: December 22, 2018, 02:02:02 am
content: jaunty, you do not say where you are located and I am sure there may be someone who just does not know how to run a business and who turns away potential customers. It is possible and in that case you can just try other places.On the other hand you might be giving the wrong vibe. You might give the impression that you don't know what you want, that you are going to take up a lot of their time and that they probably have better things to do with their time.Write precise and concise specs and ask for a quote and send it to at least three manufacturers. It should be something precise and clear. If they see something which raises a ton of questions and which looks like something which was put together by someone who is not clear then they prefer to leave it aside and go on to clearer pastures.You need to have it clear what you want and make it clear to the possible supplier so that he can feel confident that he can give you an estimate in very short time and not waste time asking questions of someone who looks like he might not know the answer.Another idea is to try to find commercial, ready-made, transformers which can do the job, even if not perfectly. You will save a lot of money that way.Anecdote time: I was the purchasing manager for a manufacturer and I purchased line transformers from a supplier with whom I had a good working relationship. A guy from the lab told me a transformer from some instrument had burnt and he gave me all the info so I could order another one built. Core of x by y mm, so many turns of such diameter, so many other turns of such other diameter wire, etc.My supplier said "sure, no problem" and he even gave it to me at no cost, as a gift, on account of our other business. So he had it built and gave it to me in hand in one of his visits. And when they installed it in the lab it blew a fuse. After some investigation and calculation it turned out it was badly "designed" and the core saturated. It turns out the original core, of the same dimensions, was made ofGrain-oriented electrical steelwhich has substantially more flux density while the replacement was made with cheaper, regular, laminations. The lab guy did not think to check and the supplier thought there was no need to check since we seemed so clear in what we wanted.

author: langwadt
author_rank: Super Contributor
timestamp: December 22, 2018, 02:17:53 am
content: Quote from: jaunty on December 21, 2018, 04:17:25 amhttps://toroid.com/Custom-Design/Specify-a-Transformer?

author: coppercone2
author_rank: Super Contributor
timestamp: December 22, 2018, 07:31:49 am
content: a nosy application engineer

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2018, 08:28:41 am
content: No manufacturer will be interested in 1 or 10 - they are probably just fobbing you off as they think you are a timewaster.If you want 1-10 then make it yourself - get an off-the-shelf transformer with comparable VA rating and if possible at least one of the required outputs windings, and overwind anything else you need.

author: soldar
author_rank: Super Contributor
timestamp: December 22, 2018, 08:53:58 am
content: Well, youcanfind a shop that specializes in prototypes and small runs. You just need to know where to look. And know how to approach them. Cold calling on the phone and rambling with unclear specs is a bad idea. Preparing clear specs in writing which the guy can have a quick overlook and realize it has all the info he needs is a much better idea. And I would try at least three possible suppliers before I came to any conclusions.I believe what we have here is failure to communicate.

author: jaunty
author_rank: Regular Contributor
timestamp: December 23, 2018, 09:42:48 pm
content: soldar - i'm in southern california and yes - what you say could VERY WELL be the case ... i just asked them the info they wanted and a pic of the faulty one i'm trying to replace and there seemed to be far too much 'back and forth' going on ... i told them i would send it in when i am ready to go on it ... so they can get all the info necessary when necessary but they wanted it just for an estimate - which seems silly to me .. the quote doesn't need to be so accurate - just 'in the ballpark' .. i.e. $10? $100? 10 000??? i can't be sending it out to 10 different manufacturers just for quotes ... ugh! that will take the better part of a year probably.though reading through responses to this thread makes me think MAYBE i should get an 'off the shelf' unit with the right secondaries (need 2 18V IIRC) and just wind my own extra low voltage secondaries .. an 8v secondary might not take so many turns ...

author: jaunty
author_rank: Regular Contributor
timestamp: December 23, 2018, 09:46:49 pm
content: soldar - i might do that - potentially (though i'm liking the stock transoformer with my own extra windings idea at the moment) - for the current rating on each winding i've just been basically mulitplying the fuse amperage times 1.5 or do you think maybe that's too close and they might get too hot? I really don't have a proper spec and just been having to guess ... but for the purposes of the estimate i dont' see how that might be an issue ...

author: jaunty
author_rank: Regular Contributor
timestamp: December 23, 2018, 10:02:58 pm
content: PS - does anyone have a good technique for removing the epoxied cloth wrapping on one of these? it's an absolute BUGGER to get through - i was only able to dig through with an x-acto in one spot - i'm not worried about damaging the secondaries so much since two are already shorted and i may try my hand at rewinding all four (only tricky bit is that one has a tap and i'm not sure how to do that - i guess solder another wire on and feed it out) ... I suppose i could just dremel through it - i tried soaking the cloth in acetone but that did nothing really

author: james_s
author_rank: Super Contributor
timestamp: December 23, 2018, 10:21:33 pm
content: I've bought cores and supplies for winding my own from here:http://www.bridgeportmagnetics.com/index.htmlAt the time at least they also sold toroid cores with pre-wound primaries over which you wind your own secondaries. They may do prototyping as well, I don't recall.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 23, 2018, 10:52:10 pm
content: Quote from: mikeselectricstuff on December 22, 2018, 08:28:41 amJust ask the right place. We ask one or two transformers varying from several kVA to several VA all the time.Quote from: jaunty on December 23, 2018, 10:02:58 pmYou need strong acids to remove polyurethane based epoxy resins. This requires chemical ppe! In short, it's destructive to all non-metals.Although it does get brittle when hot, so you can try that.If it isn't potted, regular thinner with toluene (poisonous) should work (slowly).For larger potted transformers, to know whats inside, use pyrolysis.

author: Globe Collector
author_rank: Contributor
timestamp: December 23, 2018, 11:09:35 pm
content: Rewinding toroids of 2-300VA or bigger with voltages less than 25 or so is not too difficult.As the VA rating, (and core size) increases the number of turns per volt decreases, so the winding gets easier.One point of note....in professionally would transformers with multiple secondaries the total cross-sectional-area of copper in the primary will be equal to the sum of total-cross-sectional-areas of all the secondaries and each secondary will possess a fraction of the total VA rating which is proportional to its cross-sectional-area divided by the cross-sectional-area of the primary.For example, imagine you have a 180VA transformer with two 18v secondaries...if the wire gauges of those secondaries are the same, then each should have half the cross-sectional-area (or ampere-turns) of the primary and each will deliver 90VA or 5A RMS. However, imagine that (although the number of turns are the same) that one winding is wound with thick wire and the other with thin wire....then the thick one will deliver most of the power...say 9A (162 VA's worth) of the total, whereas the other winding will only have 18VA's worth available.If you "lash" an extra secondary onto an existing design, you have to bear in mind that you are increasing the total cross-sectional-area of the secondaries over and above that of the primary, so you may need to de-rate the loads on the existing secondaries, particularly if your new secondary draws a significant proportion of the available VAs (I'd ball park 10% of the total VA rating or more on your overwind) .If you simply need a few VA for some 5v DC for some 4000 CMOS or -25v to bias some valve grids or something like that, then don't worry, but if you have a decent solid, low impedance load on your overwind, like a motor or class AB output stage of an amplifier then you will need to do something about de-rating the loads on the existing secondaries otherwise you might "let the magic smoke" out of the Primary liker Dave Jones did with that soldering station.

author: soldar
author_rank: Super Contributor
timestamp: December 23, 2018, 11:51:29 pm
content: Quote from: jaunty on December 23, 2018, 09:42:48 pmThat is not how things work and I am not surprised they just brushed you off. Rather than answer your vague question he would rather spend his time answering the questions of others who definitely know what they want and are much more likely to result in orders which will bring in dollars which he can invest in feeding and clothing his family. Your question seems to him like it might probably result in more confused questions and more wasted time. He has no interest in doing "approximate" studies when it costs him less effort to do an exact pricing on something clearly defined. You might as well ask how much it would cost by weight and it would give you a rough idea.Quote from: jaunty on December 23, 2018, 09:42:48 pmIf you can use off the shelf commercially available units that would be the easiest and cheapest route. Depending on the voltages and currents you can use two or more transformers. You can also combine windings of a transformer with multiple windings. There are many ways of going about this. If your requirements are somewhat flexible, you have a lot of space, etc. then you should be able to find an off the shelf solution. If your requirements are very tight, space is very limited, etc. then the first thing you need to do is determine and write down all those specs very clearly. But don't expect the guy at the transformer place to hold your hand through all this. He has other fish to fry.We're mostly whistling in the dark here. Why don't you tell us what you want exactly? Pretend we're the transformer guy and tell us what you are looking for exactly.

author: jaunty
author_rank: Regular Contributor
timestamp: December 24, 2018, 11:05:52 pm
content: Quote from: james_s on December 23, 2018, 10:21:33 pmMIGHT be just the ticket! thanks

author: jaunty
author_rank: Regular Contributor
timestamp: December 24, 2018, 11:10:23 pm
content: Quote from: Globe Collector on December 23, 2018, 11:09:35 pmvery interesting thank you! I was kind of wondering about related issues ... i.e. if i could simply 'beef up' my secondaries beyond spec to avoid problems ... perhaps i can find a 'stock' prewound with a decent primary ... i don't think my particular transformer is much beyond 100VA - based at any rate on the size of thing (3.5 inches final diameter) ...

author: jaunty
author_rank: Regular Contributor
timestamp: December 24, 2018, 11:19:51 pm
content: Quote from: soldar on December 23, 2018, 11:51:29 pmyes well ... i think i was quite specific - in asking them to 'ballpark' it for me i was hoping that it was an act of consideration toward them so as not to require much time at all - i told them i won't necessarily hold them to a specific price (or that i just wanted something within, say , 25% of the likely final price). The other problem is that i could only 'ballpark' some of the specs too - like the VA (well current) requirement of the windings etc - and because 2 of them are shorted it cant' really be known until the original is taken apart - that;s why i thought i would let them rebuild it first etc ... but boy is this turning out to be a pain in the arse (and yes likely my fault) - i'm not sure what i'm supposed to do in order to win their confidence - pay them a few thousand first? i would think that it's mostly a 'social' issue first ... they dont' know me and (as you said) know if i'm a 'serious' customer or not ... but it's been massively time wasting and irritating for me.SO - well i'm not sure what i should be asking you - though you so gracefully offered assistance ... should i just tell you what i'm telling the manufacturers about what i want? It seems to me I can't really go wrong if I just try to get it disassembled and then just reassemble it with new wire etc (?)PS - does anyone know where i can get new lacquered wire??? i tried searching for it on my usual supplier under 'lacquered wire' and 'transformer wire' etc and got NOTHING

author: jaunty
author_rank: Regular Contributor
timestamp: December 25, 2018, 05:47:02 am
content: ok - it just occurred to me 'enameled wire' i guess too

author: james_s
author_rank: Super Contributor
timestamp: December 25, 2018, 08:11:20 am
content: Magnet wire and enameled wire are the two common terms in American English.