| TomWaits |
I have some 39-0-39 (625VA) toroids and I'm looking for 29-0-29. I have never unwound a toroidal and I don't want to wreck them. I was wondering if yee all have some insight or procedure to do it right the first time. Also, the procedure to re-wrap them back up nice?
I'm fishing for all input as I will give it a shot in the next day or so.
Cheers,
Shawn. |
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| TomWaits |
Also, will the VA change?
Shawn. |
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| poobah |
As far as unwrapping them is concerned... you'll have to use the Armstrong method... the trick will be in spotting how the center tap is created. This may not be possible if the secondaries weren't wound bifiler (two wires pulled at the same time side by side).
The VA rating of the primary will not change... strictly speaking. But the VA rating of the secondary will... keep in mind, this is applying the definition of VA somewhat wildy. The botton line is you must (should) keep you secondary current within it's original rated value. The wire size chosen for the secondary was based on amperage.
:) |
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| Christer |
If one just unwinds a couple of turns, the winding will no longer be evenly distributed around the core, but cover only some percentage of its length. Will that make any difference, or doesn't it matter if the secondaries cover the whole 360 degrees or only, say, 90 degrees?
I think this has been asked before, but I don't remeber it being answered satisfactorily.
An analogous case is where we add some extra secondaries, typically with lower voltage and current draw. Will it matter if these are evenly distributed around the core or just wound more tightly locally somewhere along the core? In this case I primarily assume these extra windings use only a small share of the total VA capability. Of course, the total power draw of all secondaries must still be within the VA rating.
Actually, this latter method is also an option for the original question. Instead of unwinding turns, you could add a suitable number of turns that cancel the corresponding number of turns of the original secondaries, and connect these new secondaries in series (in the right direction) to the original ones, so you subtract the voltages. |
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| poobah |
Partial layers can have a minor impact on leakage inductance... very minor... especially on a 'roid.
:) |
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| Christer |
| quote: | Originally posted by poobah
Partial layers can have a minor impact on leakage inductance... very minor... especially on a 'roid.
:) |
So, nothing to worry about then?
No problems with local heating of the core or anything like that? (Maybe a stupid question but the magnetic fields and I have never been quite friends with each other. :) ). |
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| poobah |
naw... just a little leakage flux.. therefore inductance... no biggy.
:) |
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| I_Forgot |
If you want to lower the voltage you can do it by adding wire, a much easier process than removing it. You simply wind additional wire in the opposite direction of the existing windings. Put equal no of turns on either side of the center tap and you will have equal voltages.
I_F |
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| TomWaits |
Thanks PoobaH, it sounds like it could be easy depending on the method the manufacturer used to wire it. But either way, can it still be unwound or only one way?
| quote: | Originally posted by I_Forgot
If you want to lower the voltage you can do it by adding wire, a much easier process than removing it. I_F |
I find this counter productive and likely to reduce the VA rating. Have you done this and can you show more input with pictures and a Toroid model this worked on? What size was it? What size was it when you were done? What was the application?
I looked but only viewed content regarding "variacs". Is there some hidden content regarding un-winding toroids or are you just taking a **** on this thread?
Cheers,
Shawn. |
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| poobah |
You'll just have to pull the tape off and see how the center taps and windings were done. Hopefully, the secondaries are wound bifilar... that would make your task simple.
As far as over-winding bucking coils... sure, it would work I spose. Seems like like installing a drain pipe on a drip bucket instead of fixing the roof though. If your secondaries are layered, it may be your only option. It won't reduce the VA rating... at least no more so than removing turns in the first place. Remember, you can't pull more secondary current just because you knock the voltage down.
:) |
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| TomWaits |
| quote: | Originally posted by poobah
You'll just have to pull the tape off and see how the center taps and windings were done. Hopefully, the secondaries are wound bifilar... that would make your task simple.
As far as over-winding bucking coils... sure, it would work I spose. Seems like like installing a drain pipe on a drip bucket instead of fixing the roof though. If your secondaries are layered, it may be your only option. It won't reduce the VA rating... at least no more so than removing turns in the first place. Remember, you can't pull more secondary current just because you knock the voltage down.
:) |
JAH :cool: I'm gonna do it and post pics, that way if I hit the wall I may get some help? ...few days...
Shawn. |
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| I_Forgot |
| quote: | Originally posted by TomWaits
I find this counter productive and likely to reduce the VA rating. Have you done this and can you show more input with pictures and a Toroid model this worked on? What size was it? What size was it when you were done? What was the application? |
I have no pictures to show you, however, the technique is an old, common one and is fully in compliance with the operating mechanism of the transformer. A voltage will be induced in any coil of wire that surrounds the magnetic field in the core. The phase of that voltage depends on the direction of the winding. If you want to increase the voltage from an existing winding, you wind the coil in the same direction as the existing winding and connect the new coil to the original. The voltages will add. To decrease the voltage, wind in the opposite direction. A few turns of wire and a volt meter will tell you which way is the right way to wind to achieve the desired effect.
Low voltage transformers don't have so much wire wound on the secondary. That means it doesn't take many turns of wire to shift the voltage up or down a bit. Of course, you can't do it if the transformer is potted, or if there is insufficient room inside the core for the new windings.
I merely suggested it as a major time and effort saver. There is a lot of tape covering the windings on a toroid, and it is a lot of work to take it off and put it back on after you're finished unwinding a few turns of wire. It is also difficult to match the original neatness of the tape winding and the security of the coil winding - maybe you're going to loosen the wire up and its going to start to vibrate and buzz.
I'd rather do it the quicker, easier way that doesn't risk compromising the existing windings.
To each his own...
I_F |
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| Variac |
| quote: | | especially on a 'roid |
Watch out for 'roid rage though
Just love that site.... |
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| TomWaits |
| quote: | Originally posted by I_Forgot
There is a lot of tape covering the windings on a toroid, and it is a lot of work to take it off and put it back on after you're finished unwinding a few turns of wire. It is also difficult to match the original neatness of the tape winding and the security of the coil winding - maybe you're going to loosen the wire up and its going to start to vibrate and buzz. |
Points noted. I will try to be careful. I especialy don't want to losen the windings . :eek:
| quote: | Originally posted by Variac
Watch out for 'roid rage though |
Is that when I swing the damn thing around the room smashing stuff off the shelves as the secondary rapidly unfurls? I have done these things before. ;) Three months ago I stabbed my LG LCD in the face with a screw driver :eek: It was a bad scene and I wasted $400. I kinda felt better afterwards but perhaps I should have gone for a bike ride or a little jog?
Back to trannies...Shawn. |
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| I_Forgot |
| quote: | Originally posted by Variac
Watch out for 'roid rage though
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They have "preparations" for that, don't they?
I_F |
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| poobah |
What have I started?
Anyone ponder the physical similarities?
:eek: |
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| TomWaits |
| quote: | Originally posted by poobah
What have I started?
Anyone ponder the physical similarities?
:eek: |
OMG, I am unwinding a giant sphincter muscle...yikes. Poobah's fault.
BTW I don't think I'll do this (unwind) again to save quid as it is tedious work. I think I'm making progress, just taking a beer break...more to follow.
Shawn. |
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| TomWaits |
Well if you look at the attached image you will see the orriginal and the "other" after wrecking it by removing all of the secondary windings. As you can see the secondary winding has very few turns in comparison to the primary inductor (coil) . I over did it by not knowing anything about the winding method. It cost me $20 and two beers. :bawling:
I estimate if I pull 10 turns off each 39v tap I will be very close to 29v. Pulling ten turns for each tap is easy compared to unwinding the entire secondary. I now know for certain tension must be held and lots of patience. I just went in there like a bear at a BC salmon. It was fun but I am lucky there are more left at the surplus joint.
I am determined to post good results as I can be very stubborn. Or I can drop the Visa at Plitron for $500 and wait 7 weeks...no way man. DIY baby! :cool:
Shawn. |
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| poobah |
| You did count the turns now... didn't you? |
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| TomWaits |
| I blame it on the Staropramen. |
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| TomWaits |
| quote: | Originally posted by poobah
You did count the turns now... didn't you? |
Yeah but it won't help me much as I don't know how many turns are on the primary. I will be cautious knowing not much wire need be undone.
Shawn. |
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| poobah |
You don't needs da know the turns on the pri...
:rolleyes: |
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| AndrewT |
Hi Tomwaits,
I suppose you will rewind the toroid that you took off ALL the secondary from?
If you go and buy some enamelled wire of a thickness one or two sizes up from the one you took off you will get back the VA you lose by just removing some wire.
A second advantage to all this work you are doing is that you can create a custom wind to suit ALL the voltages you need in the amplifier you are building. Normally this is almost never considered due to the cost of a custom wind.
Is this a two channel amplifier? Then wind on four 29Vac secondaries. Then you can create two completely separate dual polarity supplies rather than dual rectifiers from a single pair of secondaries. This time you can use wire that is one size smaller than the original since you are theoretically drawing only half of 6.9A from each. But there is a cheat you can use here. The sum total of the secondary VA can be MORE than 100% of the primary VA. This is done by winding some or all of the secondaries with thicker wire than needed for the 100% case.
Custom is the way to go , if you have the time and patience.
Careful with the primary. Do not damage it while the secondary is off.
Finally, use flexible cord (multi cored wire) for the leadouts. Saves breaking them due to fatigue in single cored copper. |
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| richie00boy |
| quote: | Originally posted by TomWaits
Yeah but it won't help me much as I don't know how many turns are on the primary. I will be cautious knowing not much wire need be undone.
Shawn. |
No you made a grave mistake not counting.
New sec turns = (old secondary turns / old sec volts) * new sec volts
Although I have to say I would not like to wind a toroid myself, it's not very easy and really you need a special bobbin to carry the wire.
Coming from somebody who made transformers for a while. |
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| AudioFreak |
| He knows the turns on the secondary just not the turns on the primary. He's got all the info he needs to figure the new number of secondary turns required. |
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| 405man |
If you wind a few turns, say 10 and then measure the voltage you can calculate the volts per turn and you will then know how many turns are required
Stuart |
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| I_Forgot |
Wouldn't it have been easier to just wind 10 turns on each side of the center tap and save all this time/effort? Sure, you've learned something about toroid transformer construction, and there's no doubt you'll learn more by the time you get it put back together (like how big a pain in the *** is is to wind a toroid transformer and retape the windings!), but some learning experiences are not worth the effort- i.e. some things can be learned and are in fact best learned by just reading about them.
The reason humans develop theories and models of the behavior of things is so that the behavior can be predicted without having to build and try every single time. Hopefully you'll come away from this experience with a better understanding of how transformers work and that they do indeed behave according to theory. Next time you can use the theory to figure out what to do and save yourself a lot of time and trouble.
I_F |
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| AndrewT |
Hi,| quote: | | Next time you can use the theory to figure out what to do |
and then build a custom wind that is better than available retail. |
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| richie00boy |
| Not really sure how you would make something better than retail unless you unwound the primary. And that would really be an absolute **** to rewind. |
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| AndrewT |
Hi Richie,
post24 lists some advantages and describes how to go about improving on a two secondary transformer without touching the primary windings. |
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| I_Forgot |
There's a myth that is very popular on these forums, that amateurs can make everything better than commercial, mass manufactured products. In most cases I'd say it just isn't so. It is hard for an amateur to compete with teams of engineers who have large budgets for equipment, more experience, and better tools. Most manufactured products are made to pretty tight quality standards, and ALL mass manufactured products have been through accelerated life testing, etc.
What an amateur can do is make something that suits his specific needs, and/or make something that performs a function that is not readily available in commercial products, or duplicates a commercial product at lower cost. For example, if you need a transformer that has some voltage that is not commonly available or is expensive, and you can modify an inexpensive one to provide the desired voltage, you can come out ahead on the deal economically.
Most of the time, expecting the amateur result to be better than a commercial product will leave you disappointed. You can get a lot of satisfaction from making things yourself, but don't kid yourself about performance.
I_F |
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| poobah |
For sure... if you are going to peel the whole secondary, why not kick up the wire size a gauge or two?
He'll be fine... not that many turns on this anyway... |
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| EC8010 |
| quote: | Originally posted by TomWaits
... just taking a beer break... more to follow. |
Was that the Staropramen you were referring to?
I used to rewind EI transformers. All that was necessary was to count the secondary turns as they came off (not trying to rub it in, really), to give the volts per turn ratio. Then measure the wire diameter with a micrometer and calculate the cross-sectional area to determine the current density per square mm. From that, you can work out what gauge of wire and how many turns are needed for any given secondary within the original VA rating of the transformer.
I still do it for the transformers you just can't buy. Suppose you wanted to build a PP 2A3 amplifier with cathode feedback in the output stage that didn't hum. When did you last see a commercial transformer with 2 x 2.5V 2.5A CT? |
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| poobah |
I used to build alternators for wind turbines that had 3 separate stator windings... so they could operate efficiently over broad ranges in speed. We finally found a woman who was thrilled to wind them for us for $50 apiece (she got it down to about an hour!).
I believe until just few years ago, most tape heads were still wound by hand.
All kinds of little RF couplers, mixers, etc.. are done by the Armstrong method.
While most would prefer giving breech birth to a porcupine over winding a toroid... it can be done. There is no honor lost.
'sides, Shawn has the proper beer for it...
:) |
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| TomWaits |
Stripping the entire secondary and rewinding it for full custom effect would certainly be amazing. I don't do this for a living and with out the proper set up it is tedious to say the least. I would never wind a toroidal transformer as $500 for two 500VA 30-0-30 is very fair.
If I was a transformer maker, then I would make transformers.
This business of counting does not help. I counted and ended up with 35-0-30 on my second try ( the one that counts because I was more familiar with the winding). Why didn't it work?
The wires, not including the core (primary), are overlapping and interweaved. I believe this is done to get the peffect balance. I ended up taking 6 more turns off one side than the other. But it did matter counting as I reached a perfect 30 volts on one side. So it is a yes but no kinda of thing.
Now having the experience close up on these transformers, I believe it to be possible that a patient DIY enthusiast could wind better secondaries but great skill and some kind of machine would most certainly be required. I don't see the bennefit from doing this type of work unless your best friend does it for a living and he/she is willing to show you how.
I am not going to use the "naked" core that I stripped but I will pick up one more toroidal today and get my number 2 set up. Then I'll start wrapping them and I'll post some more picks. BTW I will never do this again as it is not very fun and it is not worth it. I am certain others will disagree and that's cool cause they have different skills and tools. Or mayby some are just more stubborn. ;)
If one of you chaps has the skill to wind, I'll mail you the toroidal primary for free. You gotta promise to use it.
Shawn. |
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| TomWaits |
The core is wound so well and looks so hot that I imagine company's purchasing cores and winding the secondary themselves, hence the not so perfect secondary winding.
I bet Plitron would sell toroidal primaries? Someone should send them an email and ask.
Wind you own at home! Just ask us for our free brochure. You can do it, we'll show you how! :clown:
Shawn. |
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| poobah |
Tom,
$500 for 1000VA worth of transformer is a screaming rip-off.
Send both your cores to me with $150 and I'll return them hand wound.
This is easy...
:rolleyes: |
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| TomWaits |
Well I called Plitron just now. 2 pieces of
757017201
400VA
30-0-30
5% regulation
$246.49 including taxes. No shipping fees as they are 15 min drive from my home.
Plitron does not make cores, they purchase them and they will not resell them. I asked. I regret my price estimate was a little off. Poobah that is a fantastic offer but with my updated pricing, much lower than I thought, and shipping costs, it would neutralize the deal.
More so than the offer is the gesture! It is very nice to hang out with real dudes at the DIY! :)
Shawn. |
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| poobah |
Well,
I would leave the primary in place on your existing cores and just pull about 22 turns bifilar over them for the secondaries.
Take ya 'bout 20 minutes... |
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| Tweeker |
You might want to get a couple quotes from Toroid Corporation of Maryland and Avel.
PE has 625VA 30+30 VAC Avel toroids for $83.18. 4.3% regulation. |
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| poobah |
Now you're talkin...
I think Shawn is wealthy though - :D |
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| TomWaits |
| quote: | Originally posted by Tweeker
You might want to get a couple quotes from Toroid Corporation of Maryland and Avel.
PE has 625VA 30+30 VAC Avel toroids for $83.18. 4.3% regulation. |
Don't forget, duty, exchange and shipping. Great deal @ PE! For approximately same price including extras but way more VA.
Shawn. |
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| poobah |
Are you committed to using toroids? At that VA you're going to get into "inrush" / turn-on problems.
:confused: |
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| TomWaits |
| quote: | Originally posted by poobah
Now you're talkin...
I think Shawn is wealthy though - :D |
I buy everything surplus and still this is an expensive game to play! :eek: I wish Texas Instruments were buying my pattents, if I had any that is. :xeye:
Shawn. |
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| richie00boy |
| quote: | Originally posted by AndrewT
Hi Richie,
post24 lists some advantages and describes how to go about improving on a two secondary transformer without touching the primary windings. |
No offence Andrew, but other than gaining an extra pair of windings I don't see any advantages to rewinding the transformer. Certainly any toroid I've bought (and not that expensive either) has had flexible leadouts. |
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| richie00boy |
| quote: | Originally posted by TomWaits
This business of counting does not help. I counted and ended up with 35-0-30 on my second try ( the one that counts because I was more familiar with the winding). Why didn't it work? |
No it helps perfectly. The mistake you made was winding a centre tapped transformer and not accounting for the ever-increasing turn length as more wire goes on the core. If you had wound bifilar (two wires at once) you would have obtained the correct voltage.
| quote: | Originally posted by TomWaits
Now having the experience close up on these transformers, I believe it to be possible that a patient DIY enthusiast could wind better secondaries but great skill and some kind of machine would most certainly be required. I don't see the bennefit from doing this type of work unless your best friend does it for a living and he/she is willing to show you how. |
I still say you will struggle to beat a commercial one. Especially once you start trying to wind bifilar it becomes a real pain to keep the wires tight and maintain neatness. It's certainly damn tedious and frustrating.
For a start you really need a special bobbin to hold the wire or it becomes a scratched, tangly mess.
| quote: | Originally posted by TomWaits
If one of you chaps has the skill to wind, I'll mail you the toroidal primary for free. You gotta promise to use it.
Shawn. |
That is a very kind offer. Just keep it as a doorstop ;) |
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| poobah |
Well Shawn,
Buy a little magnet wire and try it... really it's easy!
Lot of non-sense here: the windings don't need to be super tight, they should be fairly uniform but not "art", you don't need to wrap them up with anything special.
I ask again... do you have to have toroids?
:confused: |
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| Tweeker |
| quote: | | Don't forget, duty, exchange and shipping. Great deal @ PE! For approximately same price including extras but way more VA. |
I forgot that PE can suck for foreign shipping. It really isnt bad at all using USPS, but alot of others rape you on brokerage fees etc. |
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| TomWaits |
| quote: | Originally posted by richie00boy
No it helps perfectly. The mistake you made was winding a centre tapped transformer and not accounting for the ever-increasing turn length as more wire goes on the core. If you had wound bifilar (two wires at once) you would have obtained the correct voltage. |
Nope. I pulled in a bifilar fashion as it is obvious 2 wires per tap and a common 4 wires for center. The wires are interleaved in a strange way on one part of the winding. But counting got me one of the 30 I was looking for. Still it all worked out fine.
Poo, I was looking at some winding wire this afternoon but I'm not going there. For now I stick to peeling a few back as it works. I broke down a payed a visit to plitron. I ordered some toroidals for September.
Do I have to use toroidals? No but I can get them $20 each up to 800 VA 39-039 so I gots to have them. Surplus still has some and they seem to have a steady flow comming in.
I will keep the old core as Plitron will wind it for me and give a big discount.
Time for a new thread...I got layout some power supplies;) |
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| richie00boy |
| That is a great price on those surplus ones, would be perfect for some of my projects. |
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| tomtt |
Originally posted by TomWaits
I looked but only viewed content regarding "variacs". Is there some hidden content regarding un-winding toroids or are you just taking a **** on this thread?
Cheers,
Shawn.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
hidden content revealed-
no need to un-wind,
vari' the voltage instead |
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| TomWaits |
| quote: | Originally posted by tomtt
hidden content revealed-
no need to un-wind,
vari' the voltage instead |
Ya know, your are right. I see now that most good power amps use Variacs instead of transformers. It seems to greatly lower the cost ;)
Tom, you crack me up. :)
Shawn.
Some of the Toroidal's I've been collecting. I have several of each. See pic. |
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