I want to rewind a toroid 12V x2 transformer to 24v x2.
Should I remove the second secondary, wind the first secondary and then wind the second again ?
Or can I just leave those secondaries as they are, solder wire to the output cable and wind some turns for each secondary ?
Should I remove the second secondary, wind the first secondary and then wind the second again ?
Or can I just leave those secondaries as they are, solder wire to the output cable and wind some turns for each secondary ?
yes this
but you know you cant simply get double the VA out, so secondary current is lower than before.
The current will be lower but the voltage higher so the Watt output should be nearly the same (?)
EDIT: I don't want to add another two secondaries. I want to add some additional turns on top of the 12v secondaries to get 24v
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If I understand what you need... and considering that the secondaries are wound "2 cables in hand" on the toroids, you could:
1 - Connect the existent 2 x 12V in serie to obtain 1 x 24 V (take care of the phase) but perhaps it is already done ?
2 - Add a new winding to get an additional single 24 V. It has to be BALANCED both in voltage and resistance with the "stock" winding.
=> First, turn 10 laps of cable, measure the produced voltage and calculate the number of turns required to obtain 24V. And take the opportunity to calculate the total length of cable needed... adding 10%+ is a good precaution, I learned that the hard way ;(
=> As the length of the cable will be increased, you should choice a higher diameter cable to compensate and get about the same resistance between the 24V (12+12V) and your new one...
=> Perhaps you will have better to make and use a special needle. In the case your transformer is >220 VA the cable (diameter >1,5 mm) can become hard to handle.
Thus, an easy way can be to turn 2 smaller cables "both in hand" to be //connected at the end of the job, for the righ Ohm value of course !
I will try to post an excel file (for easy ohm/diameter/length calculation) and also needle pictures...
1 - Connect the existent 2 x 12V in serie to obtain 1 x 24 V (take care of the phase) but perhaps it is already done ?
2 - Add a new winding to get an additional single 24 V. It has to be BALANCED both in voltage and resistance with the "stock" winding.
=> First, turn 10 laps of cable, measure the produced voltage and calculate the number of turns required to obtain 24V. And take the opportunity to calculate the total length of cable needed... adding 10%+ is a good precaution, I learned that the hard way ;(
=> As the length of the cable will be increased, you should choice a higher diameter cable to compensate and get about the same resistance between the 24V (12+12V) and your new one...
=> Perhaps you will have better to make and use a special needle. In the case your transformer is >220 VA the cable (diameter >1,5 mm) can become hard to handle.
Thus, an easy way can be to turn 2 smaller cables "both in hand" to be //connected at the end of the job, for the righ Ohm value of course !
I will try to post an excel file (for easy ohm/diameter/length calculation) and also needle pictures...
But for a perfect balance between both 24 V...
For a perfect balance between both 24 V, I just realize it would be better to wind a new 2 x 12V with "2 cables in hand" !
In fact it is really an easier way, the diameter of the cable will not be so important. You just measure your new cable, you bend it in the middle and just start winding "2 cables in hand".
And at the end - don't forget to cut the cable at the fold - you just have to connect (by twice) "1 stock 12v" with "1 new 12V" and you get EXACTLY the balance, at both volt AND ohm levels ! 🙂
For a perfect balance between both 24 V, I just realize it would be better to wind a new 2 x 12V with "2 cables in hand" !
In fact it is really an easier way, the diameter of the cable will not be so important. You just measure your new cable, you bend it in the middle and just start winding "2 cables in hand".
And at the end - don't forget to cut the cable at the fold - you just have to connect (by twice) "1 stock 12v" with "1 new 12V" and you get EXACTLY the balance, at both volt AND ohm levels ! 🙂
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Thats not a bad idea. But I thought about just extending the existing secondary wires.
So which method will be better ?
Guess how those additional turns are called 😀
And it´s not "some" but as many as you have now .
As a clue, more than you can count with all your fingers 😱
maybe when the transformer starts smelling funny or worse, starts smoking, you will reconsider your advice.
And you will ... but you seem to think it will be only a few turns .... better think as many turns as you already have.
Don´t know your transformer size but think closer to 50 or 100 turns ... *each winding* than 10 or 12 turns.
And in fact the proper way to do it is to pull the old winding,counting turns and measuring wire diameter, and then full rewinding with *twice* the turns and *half* the section.
Meaning: if each current winding is 50 turns of 1mm diameter enamelled wire, now you need 100 turns of 0.7mm diameter one ... for *each* winding.
EI transformers are easy to rewind, because you pull the coil bobbin and wind it on an improvised winder, even a hand cranked drilling machine, but toroids require specialized equipment because you must wind them with the core already inserted.
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Yes, I still don't know how many to add, don't want to unwind it, I'll just check with the multimeter 😀
It's up to you 😉
Now... a late disclaimer : this is a serious job to do, to wind and position correctly the cables, tension them and assembly them and protect the transformer (and the users) with insulation tape... you really need some electrician skills to stay secure and succeed !
I will choose the second one as only the turns number need to be calculated ; anyway, at the end you just will get 2x24V, not less not more... I mean if the job is correctly done 😉
Now... a late disclaimer : this is a serious job to do, to wind and position correctly the cables, tension them and assembly them and protect the transformer (and the users) with insulation tape... you really need some electrician skills to stay secure and succeed !
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Nope... I explained if you add a 2x12V the diameter calculation do not need to be as precise as it is in the first method, when you have to compensate the longer cable. I never said it is OK for 0.5mm²... is my "google translation" English a problem ? 😉
With a toroid its not too hard to figure out how many turns per Volt are needed. Just grab a metre or so of insulated wire and wrap it through the core as many times as it will go. Count how many turns then measure the output with the primary connected to mains. Divide the turns by the volts and you have your figure. For 24V multiply this figure by 24.
As you want a new 24V winding I'd leave the existing 2*12V windings in place, put them in series to create your first 24V winding, add lots of new turns to get your second winding.
As an example I recently disassembled a 30VA toroid, it needed about 9 turns per volt. So for 24V with that example you'd need 216 turns. For higher VA you'll get a lower number of turns per volt.
<edit> Forgot to add - you should factor in the regulation for your particular toroid. To check this measure the existing 12V winding voltage open circuit. Divide reading by 12. This gives you your regulation figure as a fraction. Your turns per volt should be increased by this fraction or your new winding will be too low voltage under load.
As you want a new 24V winding I'd leave the existing 2*12V windings in place, put them in series to create your first 24V winding, add lots of new turns to get your second winding.
As an example I recently disassembled a 30VA toroid, it needed about 9 turns per volt. So for 24V with that example you'd need 216 turns. For higher VA you'll get a lower number of turns per volt.
<edit> Forgot to add - you should factor in the regulation for your particular toroid. To check this measure the existing 12V winding voltage open circuit. Divide reading by 12. This gives you your regulation figure as a fraction. Your turns per volt should be increased by this fraction or your new winding will be too low voltage under load.
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ok the last question : I have 30 meters of AWG10 PVC insulated wire. Can I use it ? Or should I buy magnet wire ?
You'd better give us the mechanical dimensions of your trafo before an answer can be found to that question.
Its a 1000VA trafo diameter is 12cm height is 5cm. If it won't fit that's no problem I'll just buy magnet wire.I am curious if the PVC insulated wire will be ok 😉
What's the external diameter of the PVC wire? With those dimensions I'd guess your core is about 3cm by 5cm so turns per volt will be about 2.5. Hard to believe such a small core is 1000VA.
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I'll estimate your inner diameter as 6cm hence the inner circumference is about 19cm. At 3.2mm you can get 59turns maximum which will almost give 24V excluding regulation. So looks like its too bulky to get to 24V. Better buy magnet wire.
yes magnet wire , its very likely adding double turns of the same gauge magnet wire on the secondary will not fit inside the window. using PVC wire haha good one
I would either unwind and start a brand new secondary with lighter gauge. This is what a professional would do.
OR
Add as many turns in series with the existing pairs with a much lighter gauge (choose about lil more than half of the old cross section area of the existing (magnet )wire ) hoping it will all fit packed inside there and not get too hot inside the primary wire. expect 850VA or 10-15% less than before. and perhaps not as much voltage if you can't fit all the turns planned. this will probably be very bulky and ugly looking.
either way you will need to find out how many volts / turn you will need before starting. Find a magnet wire gauge table ( ask your vendor they have them or google it ) to choose the new wire.
I would either unwind and start a brand new secondary with lighter gauge. This is what a professional would do.
OR
Add as many turns in series with the existing pairs with a much lighter gauge (choose about lil more than half of the old cross section area of the existing (magnet )wire ) hoping it will all fit packed inside there and not get too hot inside the primary wire. expect 850VA or 10-15% less than before. and perhaps not as much voltage if you can't fit all the turns planned. this will probably be very bulky and ugly looking.
either way you will need to find out how many volts / turn you will need before starting. Find a magnet wire gauge table ( ask your vendor they have them or google it ) to choose the new wire.
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