Rewiring a Transformer

MisterBill2

Joined Jan 23, 2018
9,808
Hi
OK have finished winding the pimary back on, have replaced all the plates to check it out and it is giving 6.7v and 13v on the second bobin secondaries, so that all works ok, I am still left with my original question, is how can the transformer output 420v on the secondary that is laid on top of the primary ?.
I just don't understand how 175 turns on a secondary can produce 420v , the leads joining the board say 400v on the board .

Spike
f the 175 turns is placed in series with the 220 volt winding and correctly phased then the voltage will be close to 400volts. It will not be isolated from the mains but that may not be a problem.
 

MaxHeadRoom

Joined Jul 18, 2013
23,915
@spike1947 I don't recall seeing any confirmation of the turns/volt of the transformer?
Most of the EI 50/60Hz style I have rewound have been around 3 to 5turns/volt.
Toroidal are less, 1.5 to 2turns/volt.
 

MisterBill2

Joined Jan 23, 2018
9,808
I believe that the actual voltage was mentioned at some point after it was rewound, or at least the actual turns count of the primary winding as well. The result was that the "400 volt" secondary produced about 170 volts. What this tells me is that there are quite a few possibilities: There might be a voltage double rectifier circuit, OR it might be used in series with the mains voltage connection of the whole primary (220 V+175V), or that the tag could be wrong, because of being from a prior version of the product.
So it seems at this point that aside from the photos of the PCB we should have the TS trace out the circuit connected to the terminals tagged as "400V", which will let us know what is actually happening.
Or, it may be that the transformer has already been either rewound once, or even replaced. Given that we know nothing about the history of this particular device, any or all of those may be the case.
 
Last edited:

Thread Starter

spike1947

Joined Feb 4, 2016
383
f the 175 turns is placed in series with the 220 volt winding and correctly phased then the voltage will be close to 400volts. It will not be isolated from the mains but that may not be a problem.
No it was not in series , it was a seperate secondary winding laid on top of the Primary winding, the winding's ends terminated at each end to a feed onto the board, pics showing winding soldered to one of the 2 terminal wires, 2nd and 3rd pics are were I cut across the winding to remove it, not possible to unwind it, too many wires had broken when lifting the tape off .
Has it got anything to do with the winding over the primary winding, I know they are not connected but !, I can't even make a new step up transformer, untill I can know how the hell that original winding produced 420 volts, it is driving me crazy .
Spike
 

Attachments

Last edited:

MisterBill2

Joined Jan 23, 2018
9,808
If the windings get connected in series it would be exterior to the transformer when the high voltage testing mode is selected. So there would not be any connection in the transformer.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
If the windings get connected in series it would be exterior to the transformer when the high voltage testing mode is selected. So there would not be any connection in the transformer.
Yes but the manufactures say that the transformer outputs as 420v and the connection onto the board has a 400v warning next to them !
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
I believe that the actual voltage was mentioned at some point after it was rewound, or at least the actual turns count of the primary winding as well. The result was that the "400 volt" secondary produced about 170 volts. What this tells me is that there are quite a few possibilities: There might be a voltage double rectifier circuit, OR it might be used in series with the mains voltage connection of the whole primary (220 V+175V), or that the tag could be wrong, because of being from a prior version of the product.
So it seems at this point that aside from the photos of the PCB we should have the TS trace out the circuit connected to the terminals tagged as "400V", which will let us know what is actually happening.
Or, it may be that the transformer has already been either rewound once, or even replaced. Given that we know nothing about the history of this particular device, any or all of those may be the case.
OK, will see if I can get the trace onto a "Eagle" drawing .

Spike
 

D_racon

Joined Oct 4, 2021
5
Hi
OK have finished winding the pimary back on, have replaced all the plates to check it out and it is giving 6.7v and 13v on the second bobin secondaries, so that all works ok, I am still left with my original question, is how can the transformer output 420v on the secondary that is laid on top of the primary ?.
I just don't understand how 175 turns on a secondry can produce 420v , the leads joining the board say 400v on the board .

Spike
you have to indeed look to all windings, and even half windings. however if you are using a ferite core transformer you can expect quite much self induction. these self induction spikes will peak over the normal voltage. but if you think the windings themselves are off, then you can also just experiment with the windings and slightly reduce the windings of the secondary coil until you get the desired output. you might also want to test the voltage with a load, or see how it responds to other metal objects when they are close by, or not there. but numbers on devices are not always correct. for example there are 3.7v chargers, but they output 4.2 volt when there is little or no load. these are meant to charge 3.7 v batterys but in your case it might expect a high load or some component or inefficiency causing loss. if it is a old device it might even be a normal factory error because realically seen things do not behave as they do on paper. and almost all components will show some minor differences. especially at high power such changes become clear, since the magnetic field gets further, and the device itself uses larger values to measure.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
That is normal shielding between winding's, obviously it is imperative that the ends of the copper strip do not touch. !!

So @spike1947 did you ever confirm the turns to volt ratio?
It is only the secondary voltage I need to sort , have no idea how many turns the primary has, I only un-wound the last layer of the primary !.
spike
 

MisterBill2

Joined Jan 23, 2018
9,808
you have to indeed look to all windings, and even half windings. however if you are using a ferite core transformer you can expect quite much self induction. these self induction spikes will peak over the normal voltage. but if you think the windings themselves are off, then you can also just experiment with the windings and slightly reduce the windings of the secondary coil until you get the desired output. you might also want to test the voltage with a load, or see how it responds to other metal objects when they are close by, or not there. but numbers on devices are not always correct. for example there are 3.7v chargers, but they output 4.2 volt when there is little or no load. these are meant to charge 3.7 v batterys but in your case it might expect a high load or some component or inefficiency causing loss. if it is a old device it might even be a normal factory error because realically seen things do not behave as they do on paper. and almost all components will show some minor differences. especially at high power such changes become clear, since the magnetic field gets further, and the device itself uses larger values to measure.
Looking at the photo of the transformer in post 59, it is very obvious that it is not a ferrite core device, and so none of those words apply.And if a lot of turns were broken while removing the tape, and no count was made of how many that was, then the project is possibly doomed, because without knowing the number of turns it is not possible to know the turns ratio.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
Looking at the photo of the transformer in post 59, it is very obvious that it is not a ferrite core device, and so none of those words apply.And if a lot of turns were broken while removing the tape, and no count was made of how many that was, then the project is possibly doomed, because without knowing the number of turns it is not possible to know the turns ratio.
Hi
I did count the turns of the secondary that was laid on top of the primary, I just counted all the wires ( taped each layer x2 ) before cutting , and then I devided them by 9, tedios yes, but that is what I done .

When I said broken it was just some of the fine ( 0.06mm) wires sticking to the tape has I lifted it .
Spike
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
Have re-fitted the Transformer to the machine and it switches on and tested it and all work ok, apart from the 400v test, not tried that as yet, I still need to know how that transformer give out 420v on that winding, what makes it mpre puzzling is that if you counted all the wires of the Litz wire it would equate to around 400v !.
Attaching drawing of Transformer outputs .
 

Attachments

MisterBill2

Joined Jan 23, 2018
9,808
Because the current needed for the insulation test is very small, a voltage multiplier circuit can easily provide two or three times the peak input voltage. Thus you could get the 400 volts with only a 133 volt peak winding, if a tripler was used, or if a 200 volts peak winding, if only a doubler was used. I have used a doubler circuit off of my 117 volt mains to get about 270 volts for light loads many times.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
Because the current needed for the insulation test is very small, a voltage multiplier circuit can easily provide two or three times the peak input voltage. Thus you could get the 400 volts with only a 133 volt peak winding, if a tripler was used, or if a 200 volts peak winding, if only a doubler was used. I have used a doubler circuit off of my 117 volt mains to get about 270 volts for light loads many times.
Yes, but the manufacturer of the Transformer says one of the outputs is 420v, was thinking of makinga new Transformr just for the 420v outlet but am a bit nervous puting a 420v feed to the machine, can't get a drawing for the machine or the Transformer !

Spike
 

MaxHeadRoom

Joined Jul 18, 2013
23,915
apart from the 400v test, not tried that as yet, I still need to know how that transformer give out 420v on that winding, what makes it more puzzling is that if you counted all the wires of the Litz wire it would equate to around 400v !.
Attaching drawing of Transformer outputs .
Conductors for a winding that are connected in parallel with each other are not going to increase the voltage output.
Have you done the turns/volt test?
It would appear that the 400v (~170v) winding could be connected in the auto transformer mode i.e. in series with the 240v supply. and the total equal to 400v?
 
Last edited:
Top