zybitx Posted February 12, 2005 Report Share Posted February 12, 2005 Hi!How do I get the VA of a transformer with the output:4,3V.. 42,5V.. 9,7V.. 19,7V.. 16,1V? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 12, 2005 Report Share Posted February 12, 2005 Hi Zybitx,Welcome to our forum.VA is the power that the transformer is rated to deliver to a load.Power is Volts times Amps. You show only five unusual voltages without any current (A). Usually a power transformer has only one output and its voltage is rated with a rated current or VA rating:30VAC at 2A, or30VAC 60VAThe above transformer ratings are the same. Quote Link to comment Share on other sites More sharing options...
zybitx Posted February 12, 2005 Author Report Share Posted February 12, 2005 Hi!The problem is that the transformer was removed from an old TV and is unmarked. I have measured out the secondary windings.The plan is to use the transformer in a powersupply-project and I need to know how much current the other components must be able to handle...By putting a load on the output I know I measure the maximum outtake, but I need to know how to calculate the total VA of the transformer... Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 12, 2005 Report Share Posted February 12, 2005 Hi Zybitx,When you load the transformer, you will find out its power-handling capability when it burns-out or over-heats.If you know the size of the TV it was in, look at the power rating label on a similar TV. Or go to the electronic parts store and see the rating for a similar-size transformer.But you know that its outputs probably have different power ratings.Try loading an output, one at a time, measuring its output voltage. Stop when the output voltage drops about 10%, I would't load it any more for such a big transformer. You will see by your measurements which output is its most powerful one. Quote Link to comment Share on other sites More sharing options...
Ldanielrosa Posted February 14, 2005 Report Share Posted February 14, 2005 Does the transformer have standard E-I laminations? If so then with the dimensions of one of the outer legs (cross-section) and the power frequency I can give you a guess as t o the total VA rating.If the outputs are the wire they're wound with (not terminated to a terminal strip or spliced internally to more durable wire) then you can divvy up the output current according to the wire cross-sections. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted February 14, 2005 Report Share Posted February 14, 2005 The VA rating is not nearly as important as the current rating. The VA rating is apparent power. In fact it can be difficult to decide what the power requirement is because of the reactance involved. My guess is that you would use a special meter to measure apparent power. Anyways, if you stay within the current rating, you will most likely be okay when it comes to power. But you will never be sure without the special meter. I like to say that if the load consumes equal to the apparent power your close to the limit. Add in there some reactance and it will be too much. Just keep the load beneath the apparent power rating. Quote Link to comment Share on other sites More sharing options...
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