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Help regarding Transformer current rating..:-):-

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ramshkrish

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Hi friends.. I need a small clarification regarding transformer.. I have an old AC transformer and it reads as 7.5V.. Please let me know how to find out the maximum current that the transformer can deliver.. I dont want to connect it to a circuit which needs higher current and spoil my whole day..:):):):)...:-D:-D:-D
 

There are lots of factors governing the "rating" of a transformer. the best way is to test it. Load the secondary with a resistor until the measured voltage falls by 10%, this is a good basis of its current rating. Run it like this for 30 minutes and make your mind up if it is overheating (depends on the temperature rating of the insulation another unknown!). In general transformers under 40 mm cubed have a regulation of 15%, greater then 100mm cubed have regulation of 5% or better. Your transformer is what size?
Frank
 
Thanks friend.. It is under 40mm... Can you tell me the rating of the resistor value... I want to connect it to a speaker.. It doesn't have a manual or the transformer rating.. Pity thing is the transformer is not working and blew up.. So i want to connect this old transformer and check...:):)
 

One minute you say it produces 7.5V , from 230V mains?, the next you say its connected to a loudspeaker. Which one is right?, if its a mains to 7.5V transformer and its under 40mm cube then its ratings are likely to be about one watt. So 1 W @7.5V = a load of 54 ohms. So start at 100 or 68 ohms and see what is required for the voltage to drop to 7.5 -10% = 6.75. leave it running at this current and check it is not over heating.
If the transformer really is connected to a loudspeaker and it burnt out, there is something seriously wrong with the amplifier and replacing the loudspeaker transformer is the least of your problems.
Frank
 

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