Hi All,
I am trying to do the age old estimation for a scrap transformer.
Looking around online i have found multiple rules of thumb, however some arent clear if they are meant for 50Hz or 60Hz operating freq and i am getting quite varied results.
The Transformer specs i have:
Only Markings on the transformer are one line stamped into the cover "121-481388-7DR", It was stripped from an old UK Appliance, so expect typical 230-240 rating.
RPrim = 294 Ohms ,RSec = 0.850 Ohms
This means based on 240V Primary, im expecting around a 12V Secondary. (this ties up with the first 2 digits of the markings)
It is an EI transformer, (I believe a EI-48 size based on catalog EI dims also -48 in the part marking) the cross section of the middle of the E is approx 30mm*16mm = 480mm^2 or approx 0.744 Square inches.
Transformer + approx 100mm of connection wires is approx 450 grams (0.99 pound)
So one calc is
A = (VA)^2 / 5.58 (no idea if this is for a 50Hz or 60Hz)
A being Centre CSA of the EI in square inches, VA being the approx VA rating. (From a post by Studiot from 2007 on this forum)
So that would be (0.744 * 5.58 )^2 = 17.24VA
but then according to Wikipedia, for a 12KiloGauss estimate,
a = 0.206*SQRT(VA)
this now gives, (0.744 / 0.206)^2 = 13.04VA
based on the estimate that it is 20W per Pound, at 450grams, 0.99 pounds, so 19.8VA
So i have varying results from 13.04VA, 17.24VA to 19.8VA, my gut would say i am probably looking around 18VA.
But then, looking at RS, UK they sell 12VA Chassis mount transformers which weigh approx 400gram and then 20VA at 550gram. which would then lead me to believe that the transformer is more likely a 12VA rating as its closer to 12VA/400g end of that scale.
Does anyone else have any suggestions? I do have access to a Variac at work (and LCR meter if needed) but its locked away and the guy who has the key works a different shift (I work nights)
Thanks
I am trying to do the age old estimation for a scrap transformer.
Looking around online i have found multiple rules of thumb, however some arent clear if they are meant for 50Hz or 60Hz operating freq and i am getting quite varied results.
The Transformer specs i have:
Only Markings on the transformer are one line stamped into the cover "121-481388-7DR", It was stripped from an old UK Appliance, so expect typical 230-240 rating.
RPrim = 294 Ohms ,RSec = 0.850 Ohms
This means based on 240V Primary, im expecting around a 12V Secondary. (this ties up with the first 2 digits of the markings)
It is an EI transformer, (I believe a EI-48 size based on catalog EI dims also -48 in the part marking) the cross section of the middle of the E is approx 30mm*16mm = 480mm^2 or approx 0.744 Square inches.
Transformer + approx 100mm of connection wires is approx 450 grams (0.99 pound)
So one calc is
A = (VA)^2 / 5.58 (no idea if this is for a 50Hz or 60Hz)
A being Centre CSA of the EI in square inches, VA being the approx VA rating. (From a post by Studiot from 2007 on this forum)
So that would be (0.744 * 5.58 )^2 = 17.24VA
but then according to Wikipedia, for a 12KiloGauss estimate,
a = 0.206*SQRT(VA)
this now gives, (0.744 / 0.206)^2 = 13.04VA
based on the estimate that it is 20W per Pound, at 450grams, 0.99 pounds, so 19.8VA
So i have varying results from 13.04VA, 17.24VA to 19.8VA, my gut would say i am probably looking around 18VA.
But then, looking at RS, UK they sell 12VA Chassis mount transformers which weigh approx 400gram and then 20VA at 550gram. which would then lead me to believe that the transformer is more likely a 12VA rating as its closer to 12VA/400g end of that scale.
Does anyone else have any suggestions? I do have access to a Variac at work (and LCR meter if needed) but its locked away and the guy who has the key works a different shift (I work nights)
Thanks