Rewiring a Transformer

Thread Starter

spike1947

Joined Feb 4, 2016
383
I wish you success in the unwinding and rewinding, that can be very tedious indeed.
Hi
Thanks for your reply, yes very tedious, have removed the Secondary, so now down to the Primary which is a single core wire far easier than the multi core Secondary, then to find the fault !.

cheers
Spike
 

MisterBill2

Joined Jan 23, 2018
9,797
Transformer outputs:

1st Sec 1.0 - 420v @ 3A
2nd Sec 2.0- 6v @32A
3rd Sec 3.0- 13v @ 400mA
I see an interesting problem with those numbers. This transformer is, I think, physically rather small. When I consider the voltages and currents listed: 420 V x 3A =1260 watts, +6V x 32A =192 watts +13V x 0.40A = 5.2 watts, a total of about 1450 watts, that transformer is not close to large enough to supply that much power. So I am guessing that secondary #1 is really 420 volts at 0.03A =12.60 watts. And looking at the wire sizes that is more reasonable.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
The stranded wire counts as a single conductor, but single core will not carry HF as well as the stranded.

I would rewind it the same way you found it...there is probably a reason.

Distribution of flux...whatever.
Hi
Thanks for your reply, I can't source that size wire to make up the 9 core bundle, looked everywere , that is why I asked could I use a single core instead of the same total mm2, and of course I would need 9 bobins to do the rewind ! .

cheers
Spike
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
I see an interesting problem with those numbers. This transformer is, I think, physically rather small. When I consider the voltages and currents listed: 420 V x 3A =1260 watts, +6V x 32A =192 watts +13V x 0.40A = 5.2 watts, a total of about 1450 watts, that transformer is not close to large enough to supply that much power. So I am guessing that secondary #1 is really 420 volts at 0.03A =12.60 watts. And looking at the wire sizes that is more reasonable.
Hi
Thanks for reply , yes you are correct, my bad, 1st Sec 1.0 - 420v @ 3mA .
cheers and thanks for noticing that mistake .

cheers
Spike
 

MisterBill2

Joined Jan 23, 2018
9,797
Hi
Thanks for your reply, I can't source that size wire to make up the 9 core bundle, looked everywere , that is why I asked could I use a single core instead of the same total mm2, and of course I would need 9 bobins to do the rewind ! .

cheers
Spike
For a mains transformer working at either 50 or 60 Hz the stranding or lack does not make any difference. at all.
AND I have figured out that if those two leads are really for the high voltage winding, that really they are just the connection to much finer wire that is the actual 400 volt winding. So be careful when you get that close. It will probably be about #36 wire by our wire gage, perhaps 0.02mm. At any rate, very thin and rather fragile.
 

MaxHeadRoom

Joined Jul 18, 2013
23,909
@spike1947 I would be curious to know how the winding went open?
It does not seem to have suffered any overcurrent, and as it appears to be a 400v megger application, it should be well protected.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
For a mains transformer working at either 50 or 60 Hz the stranding or lack does not make any difference. at all.
AND I have figured out that if those two leads are really for the high voltage winding, that really they are just the connection to much finer wire that is the actual 400 volt winding. So be careful when you get that close. It will probably be about #36 wire by our wire gage, perhaps 0.02mm. At any rate, very thin and rather fragile.
I think the secondary windings I marked down has 400v is actually 6v @ 25A !, am just guessing, see my revised schematic just sent, may help, I think the 400v winding is the one laid on top of the primary !
 

MisterBill2

Joined Jan 23, 2018
9,797
I think the secondary windings I marked down has 400v is actually 6v @ 25A !, am just guessing, see my revised schematic just sent, may help, I think the 400v winding is the one laid on top of the primary !
That would be reasonable, since it is rather fine wire, even for a 220 volt primary. In the one photo it looked like the bobbin may be split, which is sometimes done to provide more isolation between the mains winding and all of the other windings.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
Just noticed , the Neutral Phase feed #16 has a "silver colour" (going into the winding, not solder) to the wire unlike the others that are the brown lacquer colour !.
Also #16 Neutral wire and #17 120v tap, are 0.060mm, not 0.028 has in the revised drawing. (Sorry), so the Primary winding seems to start of on the Phase feed ( Brown) has a 0.028mm wire then it changes to a 0.060mm !.
cheers
Spike
 

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MaxHeadRoom

Joined Jul 18, 2013
23,909
Just noticed , the Neutral Phase feed #16 has a "silver colour" (going into the winding, not solder) to the wire unlike the others that are the brown lacquer colour !.
Also #16 Neutral wire and #17 120v tap, are 0.060mm, not 0.028 has in the revised drawing. (Sorry), so the Primary winding seems to start of on the Phase feed ( Brown) has a 0.028mm wire then it changes to a 0.060mm !.
If this is on the winding that shows open, it could well be one lead of the buried thermal fuse I mentioned earlier.
 
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Thread Starter

spike1947

Joined Feb 4, 2016
383
If this is on the winding that shows open, it could well be one lead of the buried thermal fuse I mentioned earlier.
Just thinking if the P2 ( 120v tap) to P3 ( Neutral) have a larger wire , that will be because using a 120v supply the amperage will double !.
 

MaxHeadRoom

Joined Jul 18, 2013
23,909
If one primary is dedicated to 120v then that winding could be larger Ga but that would apply to both ends as well as the winding itself.
Any other configuration, the neutral would not be used.
 

Thread Starter

spike1947

Joined Feb 4, 2016
383
Hi
Thanks for your reply, I thought that if the load was 3A for 230v feed to phase 1 brown and the Neutral, then the 120v feed
Is there a circuit drawing of this tester available so that we can see l how the different windings are used?
Hi
I have looked and can’t find anything, also have asked the maker but no reply up to now, will be unwinding the Primary today to see what I can find under there !.
Cheers
Spike
 
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