Transformer rewind wire query

[Spike1947]

Hi
I have a Transformer, that needs a rewire on a Secondary windings, the wire that was on it, was a muti-core wire 9 strands, (0.06mm x 9) ( each strand enameled ), soldered together at each end, and laid on top of the primary winding with 175 turns, with a copper tape between the primary and this secondary .

Question: This multi core (Litz) secondary winding is supposed to have a output of 420v, but with only175 turns it will not equate to 420v, but if all the strands of the Litz was classed has a single turn then that will equate to 420v !.

I just don't get it .

Transformer outputs are:

Primary: 0: 0 – 240. V, P1,P2,P3
Secondary 1: 0 – 420. V @ 3 mA , S3
Secondary 2: 0 – 6. V @ 32 A , S1
Secondary 3: 0 – 12. V @ 400 mA, S2

Cheers
Spike
ps: think this might have been posted twice !

 

[Julie.]

?

What query?

 

[Spike1947]

?

What query?

 

[Spike1947]

Hi
The question is asking how can the transformer secondary winding output be 420v using a multi core (Litz) secondary winding with only175 turns , it will not equate to 420v, but if all the strands of the Litz was classed has a single turn then that will equate to 420v !. so does soldering the Litz at each end count has a single turn on the winding, if so how can it produce 420v volts, if they are classed has a single turn for each strand then that would !.

Spike

 

[Spike1947]

 

[Spike1947]

 

[Spike1947]

 

[Spike1947]

Last pic is with the Secondary 420v winding still on Trany

 

[Julie.]

Hi
The question is asking how can the transformer secondary winding output be 420v using a multi core (Litz) secondary winding with only175 turns , it will not equate to 420v, but if all the strands of the Litz was classed has a single turn then that will equate to 420v !. so does soldering the Litz at each end count has a single turn on the winding, if so how can it produce 420v volts, if they are classed has a single turn for each strand then that would !.

Spike

OK, the text is there now, when I asked all that was there was the photo attachment.

To work out how many turns are needed for the 420v you need to know how many are on the other windings.

So if the 240v winding has around 100 turns, then 175 would be correct etc.

 

[Avo Mk8]

Doesn't stack up to me (transformer lamination joke?)
You're thinking 9 x 175 = 1575 turns might theoretically give 425 volts (if the litz wire was all one long single strand?)
That means 0.27V per turn, so the primary has 888 turns?
(Your 175 turns of existing litz would give approx 47V)

If that's the primary on the right in the lathe, that might be more than 888 turns?
Do you know the volts per turn?

The spec you show says 3mA for the litz winding, but its capable of much more current than that.
And why litz? That's for high frequencies - skin effect conduction and all that, not for 50Hz transformers?
Perhaps Lucien can throw light on why litz might be used in a traditional mains transformer ?
I don't understand how you could get 425V from so few turns. Maybe someone has already modified it??

and final comment - nearly double the number of turns wiil be needed for the 425V winding than already there with the primary, (shown as on the same bobbin as the primary) so you might expect it to end up pretty full!

 

[Julie.]

Doesn't stack up to me (transformer lamination joke?)
You're thinking 9 x 175 = 1575 turns might theoretically give 425 volts (if the litz wire was all one long single strand?)
That means 0.27V per turn, so the primary has 888 turns?
(Your 175 turns of existing litz would give approx 47V)

If that's the primary on the right in the lathe, that might be more than 888 turns?
Do you know the volts per turn?

The spec you show says 3mA for the litz winding, but its capable of much more current than that.
And why litz? That's for high frequencies - skin effect conduction and all that, not for 50Hz transformers?
Perhaps Lucien can throw light on why litz might be used in a traditional mains transformer ?
I don't understand how you could get 425V from so few turns. Maybe someone has already modified it??

and final comment - nearly double the number of turns wiil be needed for the 425V winding than already there with the primary, (shown as on the same bobbin as the primary) so you might expect it to end up pretty full!

I am not sure it's litz for high frequency, it could also be for convenience.

The way to check is just wind 100t - then energise the primary - if there is 240v applied and you get 240 on this test winding, then you need 100t x 420/240 or 175t for 420v

If you get a different voltage - so 100v output for 230v input just recalculate accordingly.

 

[Avo Mk8]

I am not sure it's litz for high frequency, it could also be for convenience.

The way to check is just wind 100t - then energise the primary - if there is 240v applied and you get 240 on this test winding, then you need 100t x 420/240 or 175t for 420v

If you get a different voltage - so 100v output for 230v input just recalculate accordingly.

Agreed
Could even do it with say 10 turns if decent measuring instrument available.
Might be a faff putting the laminations back together, depending on type, but that experiment seems a vital next step.

 

[Julie.]

Unless you have the core cross section - assuming 1wb/m^2 flux density the volts per turn will be 1/4.44 × f x x-sectional area ( x flux density if not 1 weber per m^2)

Edit - changed to move to square metres for x-section.

 

[Spike1947]

Doesn't stack up to me (transformer lamination joke?)
You're thinking 9 x 175 = 1575 turns might theoretically give 425 volts (if the litz wire was all one long single strand?)
That means 0.27V per turn, so the primary has 888 turns?
(Your 175 turns of existing litz would give approx 47V)

If that's the primary on the right in the lathe, that might be more than 888 turns?
Do you know the volts per turn?

The spec you show says 3mA for the litz winding, but its capable of much more current than that.
And why litz? That's for high frequencies - skin effect conduction and all that, not for 50Hz transformers?
Perhaps Lucien can throw light on why litz might be used in a traditional mains transformer ?
I don't understand how you could get 425V from so few turns. Maybe someone has already modified it??

and final comment - nearly double the number of turns wiil be needed for the 425V winding than already there with the primary, (shown as on the same bobbin as the primary) so you might expect it to end up pretty full

I am not sure it's litz for high frequency, it could also be for convenience.

The way to check is just wind 100t - then energise the primary - if there is 240v applied and you get 240 on this test winding, then you need 100t x 420/240 or 175t for 420v

If you get a different voltage - so 100v output for 230v input just recalculate accordingly.

 

[Spike1947]

Hi
Thanks all for your replies , I just really want to know how can the spec say that the secondary winding I have to do has a 420v output, when the original winding had 175 turns of Litz wire ( 9x0.06mm dia ) each wire individualy laquered and soldered together at each terminal output lug .
I have spoken direct with the makers Trans Tronic ( UK) to confirm that .

I am not interested in the primary winding that is ok, but I had to remove the secondary winding ( Litz) to get at a thermal fuse that was under the first layer of the primary winding, have sorted that, now I need to replace this secondary winding, but am confused has to how it can give 420v !, maybe I am missing something here .

ps: The primary has roughly about 800 turns, 399 for the first layer !.
pps: Pic of PAT Tester board that the transformer feeds , it does a 500v DC test ! .

Spike

 

[Avo Mk8]

Wow you've got some serious heat damage to the PCB there. Are you actually hoping to repair that!?

Just to be clear, as you know, the volts you get out of a transformer winding is proportional to the number of turns in the coil, not the number of strands in the wire!
So the 175 turns you mentioned are never going to give 420V

Have you got the right information for your particular model/version?
Note the print on the diagram for the 420v is in a different font and size to the rest - did the manufacturers do a change?
Or has someone been at it already?

Just as an aside, one can generate higher DC voltages with a voltage multiplier without having to have a high voltage transformer, but that's presumably not what is going on here.

I have absolutely no idea why there appears to be such a discrepancy between the transformer you have, and the information you have on what it is supposed to be.

Can you get hold of, or find more information on, the 'correct' transformer?

And before you spend too much time on the transformer issue, check out what's happened to the pcb, because that looks a real mess to me!

 

[Julie.]

Without knowing what the exact placement in the circuit is, we could be being sent in completely the wrong direction here.

If it is the supply transformer - I.e. on the mains input then it would give around 50v not 420v with 175t cf 800t primary, if this output is then used to generate 250/500 vdc it would need a voltage multiplier of ~3/6 (plus the 1.41 for rms to peak) which is reasonable.

However if it is actually an output transformer then it could be the 240 winding is the output and the 420v 175t refers to the winding which will generate the ~500vdc after dc conversion on the normally 240v winding - achievable as the frequency would likely be several hundred hertz rather than 50.

Ultimately this transformer looks like a specific design for this product, it may use a standard former normally marked and wound for 240v/420v, but actually wound specifically for the tester with totally different ratios from that implied by the drawing.

Where does the winding connect in the circuit? Looking at this it may indicate a voltage (for example if it goes through a bridge rectifier that has 150v capacitors on it, it clearly wouldn't be a 420v winding)

 

[Spike1947]

Wow you've got some serious heat damage to the PCB there. Are you actually hoping to repair that!?

Just to be clear, as you know, the volts you get out of a transformer winding is proportional to the number of turns in the coil, not the number of strands in the wire!
So the 175 turns you mentioned are never going to give 420V

Have you got the right information for your particular model/version?
Note the print on the diagram for the 420v is in a different font and size to the rest - did the manufacturers do a change?
Or has someone been at it already?

Just as an aside, one can generate higher DC voltages with a voltage multiplier without having to have a high voltage transformer, but that's presumably not what is going on here.

I have absolutely no idea why there appears to be such a discrepancy between the transformer you have, and the information you have on what it is supposed to be.

Can you get hold of, or find more information on, the 'correct' transformer?

And before you spend too much time on the transformer issue, check out what's happened to the pcb, because that looks a real mess to me!

Hi
Thanks for your reply, yes bad design, the glass high amperage resistors are meant to get very hot, will raise and space them a tad more when I sort things out, and a couple of smallish resistors need changing, (looks worse that it actual is) when I can get the secondary winding sorted, I am in a bit of a quandrum, I can get hold of smallish step up transformer 230v to 410v , but I have to be sure that the secondary windings output is 420v, I am going to put the laminates back in and test the out put of the other 2 primary's, just to make sure they are 6v and 12v, then if they check out !.
this is the info direct from the transformer makers Trans Tronic (UK).

quote:Many thanks for your recent enquiry.

Provided that the part is TT1418, the voltages should be:
Primary: 0 – 110 – 240 V
Secondary 1: 0 – 420 V @ 3 mA
Secondary 2: 0 – 6 V @ 32 A
Secondary 3: 0 – 13.2 V @ 400 mA

Please keep in mind that the last drawing we have on record is to issue 9. In issue 7 there is a comment about wind 1 changing; this is the primary winding and may not be so consequential if you are only interested in the secondaries. ;unquote

Spike

 

[Spike1947]

Without knowing what the exact placement in the circuit is, we could be being sent in completely the wrong direction here.

If it is the supply transformer - I.e. on the mains input then it would give around 50v not 420v with 175t cf 800t primary, if this output is then used to generate 250/500 vdc it would need a voltage multiplier of ~3/6 (plus the 1.41 for rms to peak) which is reasonable.

However if it is actually an output transformer then it could be the 240 winding is the output and the 420v 175t refers to the winding which will generate the ~500vdc after dc conversion on the normally 240v winding - achievable as the frequency would likely be several hundred hertz rather than 50.

Ultimately this transformer looks like a specific design for this product, it may use a standard former normally marked and wound for 240v/420v, but actually wound specifically for the tester with totally different ratios from that implied by the drawing.

Where does the winding connect in the circuit? Looking at this it may indicate a voltage (for example if it goes through a bridge rectifier that has 150v capacitors on it, it clearly wouldn't be a 420v winding)

Hi
Thanks for your reply, very interesting, ths is the info from the makers :


quote:Many thanks for your recent enquiry.

Provided that the part is TT1418, the voltages should be:
Primary: 0 – 110 – 240 V
Secondary 1: 0 – 420 V @ 3 mA
Secondary 2: 0 – 6 V @ 32 A
Secondary 3: 0 – 13.2 V @ 400 mA

Please keep in mind that the last drawing we have on record is to issue 9. In issue 7 there is a comment about wind 1 changing; this is the primary winding and may not be so consequential if you are only interested in the secondaries. :unquote

Spike
ps: will send you a pic of were the transformer inputs and outputs go on the board

 

[Spike1947]

Hi
Thanks for your reply, very interesting, ths is the info from the makers :


quote:Many thanks for your recent enquiry.

Provided that the part is TT1418, the voltages should be:
Primary: 0 – 110 – 240 V
Secondary 1: 0 – 420 V @ 3 mA
Secondary 2: 0 – 6 V @ 32 A
Secondary 3: 0 – 13.2 V @ 400 mA

Please keep in mind that the last drawing we have on record is to issue 9. In issue 7 there is a comment about wind 1 changing; this is the primary winding and may not be so consequential if you are only interested in the secondaries. :unquote

Spike
ps: will send you a pic of were the transformer inputs and outputs go on the board

 

[Avo Mk8]

What is needed is the circuit diagram of the equipment. Have you explored obtaining that?
Or failing that, it would be worth you 'reverse engineering' the 400v circuit and drawing it out to see what you've got.
It does superficially look like the transformer is on the mains supply, so knowing how the 400v is obtained might help!

 

[Spike1947]

What is needed is the circuit diagram of the equipment. Have you explored obtaining that?

Yes that would of solved my quandary, have asked the makers, but all they give was the outputs etc that I posted, have asked again but up now no reply from them.

cheers
Spike

 

[Avo Mk8]

Yes that would of solved my quandary, have asked the makers, but all they give was the outputs etc that I posted, have asked again but up now no reply from them.

cheers
Spike

Nothing on the interweb? Is this a Megger PAT?

 

[Spike1947]

Nothing on the interweb? Is this a Megger PAT?

Robin SmartPAT 3000

 

[Spike1947]

Manual Robin SmartPAT 3000

 

[Lucien Nunes]

Well I'm only seeing one diode near the relevant secondary input terminals on the board, so it might even just be half wave rectified, does not look like a voltage doubler despite there being two electrolytics.

Do you know the history of this unit... is it definitely the original transformer? Could someone else have swapped it for an incorrect part? There's nothing special about Litz wire at 50Hz, the turns ratio is the turns ratio.

The splash on the board and vitreous resistors looks like a major arc has occurred, not just heat. Something like the adjacent 30A relay closing onto mains that shouldn't be there and spitting out metal. I presume it's the earth bond test relay.

 

[Avo Mk8]

Well I'm only seeing one diode near the relevant secondary input terminals on the board, so it might even just be half wave rectified, does not look like a voltage doubler despite there being two electrolytics.

Do you know the history of this unit... is it definitely the original transformer? Could someone else have swapped it for an incorrect part? There's nothing special about Litz wire at 50Hz, the turns ratio is the turns ratio.

The splash on the board and vitreous resistors looks like a major arc has occurred, not just heat. Something like the adjacent 30A relay closing onto mains that shouldn't be there and spitting out metal. I presume it's the earth bond test relay.

I wondered if the two electrolytics were in series (with resistors across) to get the voltage rating, as they look quite small!

I'm concerned at the idea of moving/re-soldering the resistors. If they've got really hot, the growth of intermetallic compounds in the solder has made the joints brittle and they will be difficult to work on, and the reliability will just get worse and worse with tinkering!
Am I worrying unnecessarily?
If it's arc splash rather than heat then maybe.

 

[Spike1947]

Well I'm only seeing one diode near the relevant secondary input terminals on the board, so it might even just be half wave rectified, does not look like a voltage doubler despite there being two electrolytics.

Do you know the history of this unit... is it definitely the original transformer? Could someone else have swapped it for an incorrect part? There's nothing special about Litz wire at 50Hz, the turns ratio is the turns ratio.

The splash on the board and vitreous resistors looks like a major arc has occurred, not just heat. Something like the adjacent 30A relay closing onto mains that shouldn't be there and spitting out metal. I presume it's the earth bond test relay.

Hi
Def it is only heat damage to the board, looks a lot worse than it is, relay is ok also, it just a very badley designed board, will alter the Ceramic resistors spacing etc, when I sort out the transformer winding, am sure that is the original transformer for this tester !.
Spike

 

[Avo Mk8]

Hi Spike

I see parallel activity on at least one other forum: allaboutcircuits, pretty well duplicating what's going on here, in the same timeframe!

Someone recently bought this model of tester on eBay for £8 (for spares).
I would keep an eye out for another! ?

 

[Spike1947]

Hi Spike

I see parallel activity on at least one other forum: allaboutcircuits, pretty well duplicating what's going on here, in the same timeframe!

Someone recently bought this model of tester on eBay for £8 (for spares).
I would keep an eye out for another! ?

Hi
Yes you are correct, is that condoned ?, I do keep looking on ebay, but would rather see if I can sort it myself though, bit of a challenge tbh.
Spike

 

[Spike1947]

I wondered if the two electrolytics were in series (with resistors across) to get the voltage rating, as they look quite small!

I'm concerned at the idea of moving/re-soldering the resistors. If they've got really hot, the growth of intermetallic compounds in the solder has made the joints brittle and they will be difficult to work on, and the reliability will just get worse and worse with tinkering!
Am I worrying unnecessarily?
If it's arc splash rather than heat then maybe.

 

[Spike1947]

Hi
I don't see a problem in raising the ceramic resistors away from the board and the relay, the new solder will replace what is there !.

I am wondering if, with the secondary winding that is laid on top of the primary , could it pick up any voltage from the primary !.

Spike

 

[Avo Mk8]

Hi
Yes you are correct, is that condoned ?, I do keep looking on ebay, but would rather see if I can sort it myself though, bit of a challenge tbh.
Spike

You obviously enjoy a challenge - but I was thinking another one for parts might be an overall cheaper and more reliable way of obtaining spares (eg a transformer!).

Do you know if the electronics still works?
If not, have you considered re-instating the transformer without the 425V winding, and seeing if the thing has survived? Or using a bench psu to run it? It would surely be frustrating to rewind the transformer only to find a trail of further issues?

 

[Avo Mk8]

Hi
I don't see a problem in raising the ceramic resistors away from the board and the relay, the new solder will replace what is there !.

You may find the solderability has become very poor, and difficult to get solder to flow to make a proper joint. It may not matter to you, but in the commercial world it's a concern, as the joints become unreliable.

I am wondering if, with the secondary winding that is laid on top of the primary , could it pick up any voltage from the primary !.

'pick up' only in the sense that insulation between the primary and secondary could break down. Thats why you need the layers of yellow polyester tape insulation between the two - as per your pics?

 

[Spike1947]

You obviously enjoy a challenge - but I was thinking another one for parts might be an overall cheaper and more reliable way of obtaining spares (eg a transformer!).

Do you know if the electronics still works?
If not, have you considered re-instating the transformer without the 425V winding, and seeing if the thing has survived? Or using a bench psu to run it? It would surely be frustrating to rewind the transformer only to find a trail of further issues?

No I don't, but that is exactly what I am going to do see post #18., then connect it up if I am getting a reading on the secondarys

Spike

 

[marconi]

If I employed someone to do some statutory periodic PAT testing for a fee and he/she turned up and used a PAT tester which they had repaired themselves after clear and major damage - I would refuse to pay them. And consider what else to do.......

But you may be doing this 'for fun' to see if you can get it working again and then you intend to bin it because the integrity of this test equipment is shot.

 

[Spike1947]

You obviously enjoy a challenge - but I was thinking another one for parts might be an overall cheaper and more reliable way of obtaining spares (eg a transformer!).

Do you know if the electronics still works?
If not, have you considered re-instating the transformer without the 425V winding, and seeing if the thing has survived? Or using a bench psu to run it? It would surely be frustrating to rewind the transformer only to find a trail of further issues?

No I don't, but that is exactly what I am going to do, see post #18, then connect it up if I am getting a reading on the secondarys

If I employed someone to do some statutory periodic PAT testing for a fee and he/she turned up and used a PAT tester which they had repaired themselves after clear and major damage - I would refuse to pay them. And consider what else to do.......

But you may be doing this 'for fun' to see if you can get it working again and then you intend to bin it because the integrity of this test equipment is shot.

Hi
Thanks for your reply, yes it is purely a challenge for me, and believe me I like a challenge , it also won't get into anyone elses hand, so def you won't be paying me to do any PAT Testing for you, actualy they don't use that term now, in the 18th edition it is called "Appliance Testing" , didn't include static Appliances but now does, so don't lose any sleep over it .

Spike

 

[Spike1947]

You may find the solderability has become very poor, and difficult to get solder to flow to make a proper joint. It may not matter to you, but in the commercial world it's a concern, as the joints become unreliable.

'pick up' only in the sense that insulation between the primary and secondary could break down. Thats why you need the layers of yellow polyester tape insulation between the two - as per your pics?

No, I meant any magnetic flux etc !.

 

[Lucien Nunes]

In an ideal transformer all the flux links all the windings. In practice the coupling is not perfect, hence leakage reactance. The physical arrangement thus affects the regulation and efficiency slightly, but not the the transformation ratio.

 

[marconi]

ps: The primary has roughly about 800 turns, 399 for the first layer !.
pps: Pic of PAT Tester board that the transformer feeds , it does a 500v DC test ! .

Spike