"GregS" wrote in message
...
In article , "Arfa Daily"
wrote:

"Andre Majorel" wrote in message
...
On 2008-09-23, Arfa Daily wrote:
"GregS" wrote in message
...
In article , Andre Majorel
wrote:
I'm trying to get a rough estimate of the rating of a
transformer.

It comes from an AKAI AT-M670L tuner. Transformer part number is
ST41007 TW; L350Y197H01; T 982 TK. No luck searching the web for
these.

Primary: 220 V / 50 Hz.
Secondary #1: 2 x 16.8 V loaded (2 x 5.75 ohm)
Secondary #2: 1 x 3.07 V loaded (2 x 1.5 ohm) (I guess for the VFD).
Fuses on secondary #2: 2 x 315 mA T
Weight: 252 g.
Windings size: about 25 x 25 x 15 mm.
Core size: about 42 x 33 x 22 mm.


I can't find where its in the S.E.R.

You find the voltage drop as you load the outputs
individually. The total load of all outputs will cut down on
the added individual outputs. Measure the output from no load
to drop voltage 10-20%, then measure or compute current.

Given that the transformer is likely to be over 85% efficient,
the input power consumption rating printed on the back of the
unit will give you a good idea of the VA rating of it

Well, there is none !

I expected you'd all take from the fuse rating. Interesting that
you didn't... (I made a mistake, BTW : the fuses are on the 16.8 V
windings.)

The measure-current-at-10-to-20%-lower-voltage-than-unloaded
method seems a little vague to me, not knowing what the V vs. I
curve looks like (I know very little about transformers).

Think I might as well increase the load until the transformer
becomes "too hot"...

--
André Majorel URL:http://www.teaser.fr/~amajorel/
"Je regrette le Concorde. Au moins il vous amenait directement à
l'hôtel." -- Cyrano


If you do that, it might be the only time that you do, as it may well have
a
thermal fuse embedded in the primary winding, which will likely fail. Open
circuit. Forever ...

What exactly is the issue with knowing the rating of this transformer ?
Apparently, it is working, as you are able to measure voltages. Worst
case,
you could just measure the primary current with it running the tuner. If
it's a 'typical' little red transformer that is normally to be found in
such
items, then just multiply the power consumption calculated from measuring
the input current, by about 1.5 to get a ballpark figure for the
transformer
rating. When I say "ballpark", I actually mean in the same county, but
maybe
not the same town ...

Arfa


Knowing the total rating gives little help determining individual
windings.


In theory, that may be largely true, but in practice, it will get you in the
area. The winding for the VFD heater can be largely ignored in the
calculation, as it will only be good for the few mA that the heater needs.
That leaves the two identical 'main' windings, and you wouldn't be too far
wrong, given what I said about ballparks, towns and counties, if you just
took the figure calculated from the primary current, and split it between
the two windings, half each.

Arfa