Transformer rewind wire query

Spike1947 · Oct 3, 2021

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 !

Avo Mk8 · Oct 4, 2021

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. · Oct 4, 2021

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 · Oct 4, 2021

Avo Mk8 said:
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 · Oct 4, 2021

Julie. said:
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 · Oct 4, 2021

Spike1947 said:
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 · Oct 4, 2021

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 · Oct 4, 2021

Avo Mk8 said:
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 · Oct 4, 2021

Spike1947 said:
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 · Oct 4, 2021

Avo Mk8 said:
Nothing on the interweb? Is this a Megger PAT?

Robin SmartPAT 3000

Spike1947 · Oct 4, 2021

Manual Robin SmartPAT 3000

Lucien Nunes · Oct 4, 2021

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 · Oct 4, 2021

Lucien Nunes said:
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 · Oct 4, 2021

Lucien Nunes said:
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 · Oct 4, 2021

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 · Oct 4, 2021

Avo Mk8 said:
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

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