VA of unknown transformer

[Andre Majorel]

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.

Thanks in advance.

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

 

[Andre Majorel]

On 2008-09-23, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"GregS" <zekfrivo@zekfrivolous.com> wrote in message
news:gb8e5q$l1s$1@usenet01.srv.cis.pitt.edu...
In article <slrngdfaik.4vn.cheney@atc5.vermine.org>, Andre Majorel
cheney@halliburton.com> 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 ŕ
l'hôtel." -- Cyrano

 

[Andre Majorel]

On 2008-09-24, Arfa Daily <arfa.daily@ntlworld.com> wrote:

"Andre Majorel" <cheney@halliburton.com> wrote in message
news:slrngdk43u.4vn.cheney@atc5.vermine.org...

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

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 ...

Oh. My "too hot" threshold is probably at least 20°C below the
manufacturer's, though. <g>

What exactly is the issue with knowing the rating of this
transformer ?

Partly desire to learn what rules of thumb might exist, partly
that I'm going to reuse the transformer to power a few dual
supply circuits and want to know how much I can count on.

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,

It does have red adhesive tape around the windings.

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
...

Thanks.

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