Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired and if the spec's were avaialbe (24 Volt
center tapped 10 Amp for example) it could be substituted. Aside from
the shielding I can't see any reason it can't be subbed. There is
plenty of room too. I have found several 10 amp tranfromers that are
similar in size. I don't want to buy the wrong voltage transformer. I
have schematics for similar models and it doesn't show voltage /
current ratings, just part numbers. I asked the JVC part supplier if
they could get specs on the transformer, they haven't returned the
information. Thank you in advance !

carneyke wrote in message
...
Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired and if the spec's were avaialbe (24 Volt
center tapped 10 Amp for example) it could be substituted. Aside from
the shielding I can't see any reason it can't be subbed. There is
plenty of room too. I have found several 10 amp tranfromers that are
similar in size. I don't want to buy the wrong voltage transformer. I
have schematics for similar models and it doesn't show voltage /
current ratings, just part numbers. I asked the JVC part supplier if
they could get specs on the transformer, they haven't returned the
information. Thank you in advance !

From one of 2 tips files on my site , URL below

Blown primary, how to determine unknown secondary voltages of a mains
transformer

Simulating a multi-secondary transformer using a known
good one but not using the primary, to get some data.
I used a variac supply near the bottom of its range at 18volts and a 25 ohm,
20W dropper to feed 50Hz (UK)ac into a secondary. Assuming you have a
reasonable idea of the voltage of one 'unknown' secondary.
The transformer I used first was a high grade enclosed Gardners, 1.3Kg but
only 15W combined outputs,
240V (UK) with marked 2 separate secondaries of
6.3V, 0.6A and a 150-0-150 at 25mA.
With 3.43V ac on one '6.3V' secondary there was open circuit 3.40 on the
other isolated '6.3' and 161.4V end-to-end on the '150-0-150' and incidently
116.4 on the primary.
Then loading with different resistors
100K, 161.4 drops to 159.1
5.8K on 161.4 drops to 55.8, 3.43 input drops to 1.64
swapping to 5.8K on 3.4 , no change
1K on 161.4 to 12.1 and 3.43 to 0.771
swap to 1K on 3.4 , drops to 3.39
270 ohm , 161.4 to 3.34V
270 on 3.40, drops to 3.37
56 ohm on 161.4 to .704 and 3.43 to .54V
56 on 3.4 , drops to 3.28 and 3.43 to 3.42
8.2 ohm on 3.4 , drops to 2.55 and 3.43 drops to 2.99V
A bit more generalised.
Noting that for one secondary for this test transformer was rating 300V,
25mA then V/I of 12K and the 6.3V, 0.6 secondary of 10.5 ohm.
Doing as before powering a 6.3V secondary to 3.43V and '300V' was 161.4V
then loading it until the voltage ratio was 80 per cent that is 161.4V down
to 101.5V and 3.43 falling to 2.69V so 101.5/2.69 = .8 then that R is 12K.
So for similar transformer construction and high V, low I then find that
value of R for 80% then if V is known then current rating is V/R.
Doing the same for the low V,high I one then for R=10.5 ohm then
corresponding ratio drops from 1:1 ie ==3.43:3.4 down to 3.03/3.43 is 88%
for high current , low voltage.
So for similar transformer construction and high I, low V then find that
value of R for 88% then if V is known then current rating is V/R.
Other clues would be the gauge of the wires if they can be seen and the
overall size and weight giving an idea of the overall power rating.
Resistance checks would show which are more likely high V or high I.
Second test with a more basic Albion make, .8Kg, 20W open
construction 245V primary, 2 secondaries 17V,1A and 6.3V,.6A.
Again putting current into the lowest secondary giving 5.59V on
'6.3' and 14.52 on '17' (185.8V on 'primary')
6.3/.6 wire was 24thou diameter and 17V,1A wire was 27 thou diameter.
17/1 = 17 ohm. This time loading the 17V secondary with
17 ohm meant the ratio had dropped 69 per cent (15.52/5.59 to 2.778/1.544 )
Usually you would get some idea of one rectified V from max or min, by
capacitor ratings or a regulator voltage etc.
Valve radios would have one secondary connected to the
heaters so usually 6.3V. A vacuum fluorescent
display is likely to have a feed in the range only 2 to 5V
Toroidal transformer 2x 120V to 2x 15V,2A, .75Kg and 2A wires
33 thou diameter. Characteristic R = 15/2 = 7.5 ohm.
Critical ratio in this case was 82 per cent with 7.5 ohm.
15.27 input on '15' giving 15.26 on the other and 108V on
one of the primaries.
With 7.5 ohm 15.27 i/p drops to 3.91 and 15.26 drops to 3.19.
For a large toroidal 500W 2x 35V, 7.1A , weight 4.8 kg
Secondary wires consist of 2 paralled 56 thou diameter wires
per secondary.
Characteristic R= 35/7.1 = 5 ohm.
With 15.16 on one 'secondary' 15.1 on the other and 49.8V on
a 'primary'
15.16 dropped to 2.59V and 15.1 dropped to 2.46
so characteristic ratio is 95 percent for this transformer.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"carneyke" wrote in message
...
Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired and if the spec's were avaialbe (24 Volt
center tapped 10 Amp for example) it could be substituted. Aside from
the shielding I can't see any reason it can't be subbed. There is
plenty of room too. I have found several 10 amp tranfromers that are
similar in size. I don't want to buy the wrong voltage transformer. I
have schematics for similar models and it doesn't show voltage /
current ratings, just part numbers. I asked the JVC part supplier if
they could get specs on the transformer, they haven't returned the
information. Thank you in advance !

Generally, you can take the working voltage marked on the main filter caps,
reduce it by about 1/4 (though note that there are some on here who would
dispute that level of derating) then divide the result by about 1.4 to get
an RMS secondary voltage for the transformer. So, if the caps are rated at
say 63v, it is likely that they have no more than about 45 - 50v across them
in normal use. Dividing this figure by 1.4 - or multiplying by 0.7 - gives
you an RMS figure of around 32 - 33v. You can get a rough idea of the
current rating by looking at any secondary fuses. These will be usually 1.5
to 2x the expected current draw. If there are no secondary fuses, an idea
can be obtained from the input power rating shown on the back, and the
voltage ratio primary to secondary. An efficiency of 90% or better can be
assumed for the transformer.

Obviously, it's all a bit more complicated than that in truth, but you can
use it as a good 'rule of thumb' that I have used for many years to do just
what you are trying to do.

You might try looking at the existing transformer when you have it out, just
to see if the thermal fuse legs are visible, or brought out to tags. In
either case, it can then be bodged with a TEMPORARY short to measure the
transformer voltages.

Arfa

carneyke wrote:

Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired...

So often I see posts like this in this NG and never any suggestion
to use a transformer rewinding house; this is often _more_ cost effective
than purchasing the replacement part from the mfg or even substituting
equivalents. The specifications are contained in the construction of
the transformer; by unwinding and documenting you know what they are.

Please consider it.

Michael

msg wrote in message
...
carneyke wrote:

Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired...

So often I see posts like this in this NG and never any suggestion
to use a transformer rewinding house; this is often _more_ cost effective
than purchasing the replacement part from the mfg or even substituting
equivalents. The specifications are contained in the construction of
the transformer; by unwinding and documenting you know what they are.

Please consider it.

Michael

Have you ever tried unwinding an impregnated transformer ? usually more
often a case of weighing and measuring core and outer sizes and inferring
number of turns.

The other suggestion is trying to excavate around for the thermal fuse,
assuming its failed without the wiring welding together beforehand.
But take variac reading etc before doing so


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

N Cook wrote:
snip

Have you ever tried unwinding an impregnated transformer ? usually more
often a case of weighing and measuring core and outer sizes and inferring
number of turns.

For sure; in one instance I used a slitting saw to slice the windings
into manageable pieces which then permitted me to count turns by viewing
them edge-on. Careful use of flat-blade chisels is often needed to
pry off chunks of potting material and to dislodge the sections of
cut-up windings. It is a lot of work, but even when impregnated, the core
is usually salvageable and can be rewound after prepping. Needless to
say I only resort to such endeavors when options for replacement are
limited.

Michael

On Nov 28, 9:43 am, "Arfa Daily" wrote:
"carneyke" wrote in message

...

Hello All,
This transformer is NLA and appears to have an open primary (internal
fuse) caused by leaky electrolytics. I have exhausted all searches on
the transformer and can't find any specifications. The owner really
would like this repaired and if the spec's were avaialbe (24 Volt
center tapped 10 Amp for example) it could be substituted. Aside from
the shielding I can't see any reason it can't be subbed. There is
plenty of room too. I have found several 10 amp tranfromers that are
similar in size. I don't want to buy the wrong voltage transformer. I
have schematics for similar models and it doesn't show voltage /
current ratings, just part numbers. I asked the JVC part supplier if
they could get specs on the transformer, they haven't returned the
information. Thank you in advance !

Generally, you can take the working voltage marked on the main filter caps,
reduce it by about 1/4 (though note that there are some on here who would
dispute that level of derating) then divide the result by about 1.4 to get
an RMS secondary voltage for the transformer. So, if the caps are rated at
say 63v, it is likely that they have no more than about 45 - 50v across them
in normal use. Dividing this figure by 1.4 - or multiplying by 0.7 - gives
you an RMS figure of around 32 - 33v. You can get a rough idea of the
current rating by looking at any secondary fuses. These will be usually 1.5
to 2x the expected current draw. If there are no secondary fuses, an idea
can be obtained from the input power rating shown on the back, and the
voltage ratio primary to secondary. An efficiency of 90% or better can be
assumed for the transformer.

Obviously, it's all a bit more complicated than that in truth, but you can
use it as a good 'rule of thumb' that I have used for many years to do just
what you are trying to do.

You might try looking at the existing transformer when you have it out, just
to see if the thermal fuse legs are visible, or brought out to tags. In
either case, it can then be bodged with a TEMPORARY short to measure the
transformer voltages.

Arfa

Thank you ! I already tried taking it apart and finding the internal
fuse. I felt it would be destroyed taking it apart. The option on
getting it rebuilt is good too. I am not aware of any places doing
that anymore. Any places in the USA ? Thanks.