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 Post subject: Secondary Wiring ?
PostPosted: 22 Jan 2010, 16:04 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Hi Guy's
after just too many holiday's and all that c*ap life start to be about the same again with all :idea:
this time i just have to ask before i blow a hole in something.
To a project based on 2*LM3886 that require 28V - GND - 28V in so i looked for a suitable tranny
and after a few days i tripped over a 120VA toroid with 2* 34V but it was no wires on'it just copper
leads and someone had to been creative with a pair of dykes :confused:
so full speed ahead with unwrapping all polyester tape and about 1.5m of copper :censored:
when my DMM showed 29.2V unloaded of course on both windings i felt that my mission was nearly
accomplished and after wrapping all this nice polyester tape back again :censored:
it was ready for a test run as a CT tranny,
now i'm not 100% sure if i connected it right because i have clear 29.2 V - 0V - 29.2V out but when
i measure between Ac/Ac i get 0V it is just between AC and 0 i get voltage whitch is in a way what
i need but in previous attempt's with screwing around with trannys i get "double" voltage between
AC - AC so in this case i should have 58.4V but now i got 29.2V :confused:
Are the winding connected :censored: or is'it right for a change ?

Regards
Kjell.


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 Post subject: Re: Secondary Wiring ?
PostPosted: 22 Jan 2010, 16:51 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
At a second thought ! chance to get the same voltage out on both windings gotta be the same
odds like shooting down the moon with a slingshot,,
either connected like :eek: or it'is a short between sec windings :bawling:
at least with more or less nothing to do i connected this gizmo to a power board and putted on
a 2.5A load on'it and after 30min it was not near warm ( 28 C ) according to my DMM so maybe
even if they are shorted out it may work as planned ( Ac - 0 - Ac ) or ?

Regards
Kjell.


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 Post subject: Re: Secondary Wiring ?
PostPosted: 23 Jan 2010, 06:27 
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Joined: 08 May 2009, 08:20
Posts: 918
Location: Duesseldorf, Germany
Hi Kjell,

i've read the post more than twice, but couldn't get anything out of it...

"It has no wires on it, just copper leads..." That's the way it is. Isolated wires are only used for the transformers output connections and colour codes. The transformer core windings are made of pure copper leads, coated and isolated with polyurethane / polyesterimid varnish.

Which transformer did you buy? A "real" centre tapped or a dual secondary with two seperated windings?

With a real centre tapped xformer you should have the 58VAC at the outer leads. From one of the outer leads to the CT lead, half of the output voltage. With or without load. On a double secondary xformer you shouldn't get a voltage between the outer leads, if it's not connected "in the middle".

How many output leads do you have now? There should be 3 or 4 leads on the secondary side...

_________________
Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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 Post subject: Re: Secondary Wiring ?
PostPosted: 23 Jan 2010, 07:01 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Hi Tom,
Sorry for a foggy description but what i meant was that the colored wires was cut at solderjoint's
so it was no chance to see any coding,
but what i know to a certain degree is that it is a Velleman trafo and a paralell output and according
to size it's a model 12030 ( closest i got ) and i soldered 4 wires to the winding according to that
model ( Sec 1 = Blue - Gray ) Sec 2 = Red - Yellow ) Blue / Red is start on windings.
That way i had'it under test was/is

Red = AC~29V , Yellow/Gray = 0V , Blue = AC~29V

Afaik i should have 58V across Red / Blue but there i have 0V and between AC and 0 i get 29V,
reason i'm pretty sure of it's orign is that i found a small piece of their logo under some taping
That 0 zero null gnd guy seem's to work otherwise i shouldn't have any volt reading ??
like i wrote before so is this perfect for what i need for this amp board ( 2*LM3886 ) that requires
for input 28V - 0 - 28V AC ( built in power board ).
According to my volt readout it can't be wired in serial but gotta be paralell or :confused:
Thnx Tom and good to hear from you again
Regards Kjell.


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 Post subject: Re: Secondary Wiring ?
PostPosted: 23 Jan 2010, 09:30 
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Joined: 23 Jan 2010, 09:17
Posts: 3
The secondaries are out of phase, this is why you read zero volts. If you tie the yellow and the blue together
and measure across the red and the gray you will then measure 56 VAC.


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 Post subject: Re: Secondary Wiring ?
PostPosted: 23 Jan 2010, 11:28 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Couldn't be more full hit an that !
in the battle of heat with my solder iron last night so was 2 colors switched and as you described with Bl / Ye together so was/is output 29V between phase and 0 and 58V between phases :up:


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