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Date: Mon, 4 Apr 2011 19:46:57 +0100
Message-ID: <BANLkTi=a=W-kayi4CDBib7jiYj8z8716Pw@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: Re: LF: Decca faulty transformer?
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Yes, definitely.

If the transformer were absolutely perfect all flux would be linked,
and your shorted turn intercepts everything.  So you are transforming
a few milliohms though the turns ratio which is probaly not far of 1:1
at a guess, to.... a few mohms.    Which on your LCR bridge woiuld
come out as near-enough nothing.

The very small leakage inductance present is what you are measuring at
1uH.   Which is pretty good, but no more than you should expect from a
closed ferrite core

Anbdy
www.g4jnt.com


On 4 April 2011 19:34, Mike Dennison <mike.dennison@ntlworld.com> wrote:
> Thanks for the suggestion Andy. I did that already using an Atlas LCR
> meter
> (one of the best bits of test gear I ever bought), but didn't believe
> the result.
>
> It showed what looked to me like very low inductance, some 1.3uH on
> the
> =A0'primaries' and 3.2uH on the secondary. The 'monitor' winding is
> much higher
> =A0than this. Would a single shorted turn make all of the inductances
> low?
> The Atlas declined to measure the DC resistances as they were too
> low.
>
> Mike
> =3D=3D=3D=3D
>
>> Disconnect all windings and measure the inductance. =A0 If the
>> transformer is OK, the L will be high - with Xl many times the
>> operating impedance. =A0 A shorted turn - which is what it looks as if
>> you may have - will drastically lower L to a value that should be
>> evident
>>
>> Andy
>> www.g4jnt.com
>>
>>
>>
>> On 4 April 2011 18:56, Mike Dennison <mike.dennison@ntlworld.com>
>> wrote: > I have a fault on my Decca 5501 LF transmitter. It appears
>> that the > main output transformer / combiner is faulty. Each Tx
>> module takes > current when connected to the transformer, even when
>> the output is > disconnected. And there is no power out of the
>> transformer. > > I have some questions: > > According to the the
>> circuit diagram, the transformer's output > winding has a 3.3nF
>> capacitor across it. However, it seems to be > invisible! Does anyone
>> know where it is? Is it inside the pot core? > > Does anyone have a
>> spare transformer for sale? > > Has anyone had a similar fault? > > Is
>> it difficult to disassemble the transformer? > > It is very difficult
>> to test for shorted turns because the resistance > is extremely low. >
>> > Any ideas? > > Mike, G3XDV > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > >
>>
>
>
>
>