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
"mowhoong"
** Measure the resistance of the primary winding and post it.... Phil
Weigh it, and look up similar style transformers of similar weight in catalogs.
John
Hi Phil thanks for your prompt response, the resistance of the primary is 691 ohm .
"mowhoong" "Phil Allison"
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
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
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