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Transformer power?
Transformer power?
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Old 15th November 2019, 02:01 PM   #1
nenad88 is offline nenad88  Serbia
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Default Transformer power?

So I went to local flea market and bought this for $4, ripped it apart and found nice speaker, heatsink and transformer. Transformer was main reason for buying this type of audio systems, name of system was Durabrand 5.1 sp-690w. Heatsink is 9x14cm speaker says 50w 8ohm and transformer is 8x4.5x7cm how can I know how much power can this transformer handle. I will use it only for headphone amps so I know i wont stress him at all but Im curious how to calculate. In this system transformer was powering 7 lm1875t's. Transformer fuse is 250V/1.5A.
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Old 15th November 2019, 02:36 PM   #2
Mark Tillotson is offline Mark Tillotson
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If you measure all the winding resistances you can roughly calculate the dissipation at any given load. You'd want the dissipation to be no more than other transformers with the same physical size, preferrably derated somewhat for uncertainties.
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Old 15th November 2019, 02:56 PM   #3
Galu is offline Galu  Scotland
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A 1.5A/250V primary fuse may suggest a maximum primary current (at 230V) of 0.65A, and a transformer rating of 150VA.

But, don't take my word for it - study the information contained in this source: https://m.littelfuse.com/~/media/ele...hite-paper.pdf
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Old 15th November 2019, 02:59 PM   #4
nenad88 is offline nenad88  Serbia
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Thanks!
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Old 15th November 2019, 03:21 PM   #5
FauxFrench is offline FauxFrench  France
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Really good bargain. And, 7 "genuine" LM1875.
I cannot find any good photo on the Internet of this system. Normally on the rear of the cabinet, near the power input, you have a label stating the maximum power consumption. Do you have such a label?
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Old 15th November 2019, 03:29 PM   #6
DF96 is offline DF96  England
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Weigh the transformer. Compare with catalogue figures.
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Old 15th November 2019, 03:39 PM   #7
nenad88 is offline nenad88  Serbia
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Quote:
Originally Posted by FauxFrench View Post
Really good bargain. And, 7 "genuine" LM1875.
I cannot find any good photo on the Internet of this system. Normally on the rear of the cabinet, near the power input, you have a label stating the maximum power consumption. Do you have such a label?
I throw everything out except radiator speaker and transformer. I didnt want to bother to desolder lm1875t's, speaker was working before ripping apart.

Weight is 1.8kg

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Old 15th November 2019, 03:49 PM   #8
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
With the information you give 150VA, as suggested by Galu, seems a good guess. The power capacity of a transformer is not an exact value but depends on winding resistance and the cooling ability.
Good luck with the potential projects.
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Old 15th November 2019, 03:56 PM   #9
nenad88 is offline nenad88  Serbia
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Couldnt find any better picture so far Click the image to open in full size. I dont see any rating on backplate.
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Old 15th November 2019, 06:50 PM   #10
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
I see "AC power" and then I cannot read the rest.
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