Tranformer question ?

[mowhoong]

I salavaged some step-down tranformer from pcb which has ac 220 volts
input, ac 23 volts
output.
I want to use them in my hobby electronic, but i do not know how to
find out the output current or KVA of these tranformer.
can any members give me some pointers . Thanks you.

Best Regards

 

[Phil Allison]

"mowhoong"

I salavaged some step-down tranformer from pcb which has ac 220 volts
input, ac 23 volts
output.
I want to use them in my hobby electronic, but i do not know how to
find out the output current or KVA of these tranformer.
can any members give me some pointers .

** Measure the resistance of the primary winding and post it.



.... Phil

 

[John Larkin]

On Fri, 28 Aug 2009 19:11:56 -0700 (PDT), mowhoong
<mowhoong@hotmail.com> wrote:

I salavaged some step-down tranformer from pcb which has ac 220 volts
input, ac 23 volts
output.
I want to use them in my hobby electronic, but i do not know how to
find out the output current or KVA of these tranformer.
can any members give me some pointers . Thanks you.

Best Regards

Weigh it, and look up similar style transformers of similar weight in
catalogs.

John

 

[Phil Allison]

"mowhoong"
"Phil Allison"

I salavaged some step-down tranformer from pcb which has ac
220 volts input, ac 23 volts

** Measure the resistance of the primary winding and post it.

Hi Phil thanks for your prompt response, the resistance of the primary
is 691 ohm .

** That PCB tranny is of about 6VA capacity.

The secondary volts will vary (drop) by about 20% from no load when full
load is applied.

The full load current is about 250mA.

The precise way to measure it is to run it for an hour or so with say a
100ohm, 10watt test load and then measure the primary resistance again.

The rise should not be more than 30% ( ie to 900 ohms) for safe, long term
operation.



...... Phil

 

[mowhoong]

On Aug 28, 7:40 pm, "Phil Allison" <phi...@tpg.com.au> wrote:

"mowhoong"

I salavaged some step-down tranformer from pcb which has ac 220 volts
input, ac 23 volts
output.
I want to use them in my hobby electronic, but i do not know how to
find out the output current or KVA of these tranformer.
can any members give me some pointers .

** Measure the resistance of the primary winding and post it.

...   Phil

Hi Phil thanks for your prompt response, the resistance of the primary
is 691 ohm .

 

[Paul E. Schoen]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:7frl5nF2m3k4mU1@mid.individual.net...

"mowhoong"
"Phil Allison"

I salavaged some step-down tranformer from pcb which has ac
220 volts input, ac 23 volts

** Measure the resistance of the primary winding and post it.

Hi Phil thanks for your prompt response, the resistance of the primary
is 691 ohm .

** That PCB tranny is of about 6VA capacity.

The secondary volts will vary (drop) by about 20% from no load when full
load is applied.

The full load current is about 250mA.

The precise way to measure it is to run it for an hour or so with say a
100ohm, 10watt test load and then measure the primary resistance again.

The rise should not be more than 30% ( ie to 900 ohms) for safe, long
term operation.

That is a good method assuming input and output windings are properly sized
for I^2*R losses. The 30% increase in copper resistance corresponds to
about 75 degrees C assuming a 0.4%/Deg C tempco. This method will also take
into account the overall heating effect of all losses, so actually the
primary and secondary windings will both reach about the same temperature.

Paul