LegendBreath Posted October 24, 2005 Author Report Share Posted October 24, 2005 Don't forget that the 7806 needs at least an 8.5V input, so the 6VAC when rectified and filtered is too low for it. Oh yeah? Well, it's working really fine for me... ??? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 24, 2005 Report Share Posted October 24, 2005 audioguru,LegendBreath is using 7VAC on the input so 7*root(2) - 1.4 = 8.5, I think the LM7806 will output 6V fine afterall. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 24, 2005 Report Share Posted October 24, 2005 Hi Alun,Thanks, I was calculating for 6VAC in error. :-[Actually, his 7VAC will probably be much higher unless he is overloading the transformer or operating it at its limit.You know what? I bet it is a 5VAC winding when loaded, but he measures 7V without a load.Then the DC input to the regulator will be less than its output voltage. A miracle. ;D Quote Link to comment Share on other sites More sharing options...
LegendBreath Posted October 24, 2005 Author Report Share Posted October 24, 2005 Hi Alun,Thanks, I was calculating for 6VAC in error. :-[Actually, his 7VAC will probably be much higher unless he is overloading the transformer or operating it at its limit.You know what? I bet it is a 5VAC winding when loaded, but he measures 7V without a load.Then the DC input to the regulator will be less than its output voltage. A miracle. ;DGeez... you are really confusing me guys! :P Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 24, 2005 Report Share Posted October 24, 2005 What does it say on the transformer's packaging?A 5V transformer might give a higher voltage like 7V when nothing's conntected to it, but 5V when a load equal to its current rating is. This is because the transformer its self has an internal resistance. This problem is generally wors with smaller transformers because they're made with thinner wire and therefore have a higher internal resistance. Quote Link to comment Share on other sites More sharing options...
LegendBreath Posted October 24, 2005 Author Report Share Posted October 24, 2005 What does it say on the transformer's packaging?A 5V transformer might give a higher voltage like 7V when nothing's conntected to it, but 5V when a load equal to its current rating is. This is because the transformer its self has an internal resistance. This problem is generally wors with smaller transformers because they're made with thinner wire and therefore have a higher internal resistance.It's a big transformer taken from a stereo (amplified stereo) it's about 2x2x2inches. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 24, 2005 Report Share Posted October 24, 2005 That explains why it has a 7V output often stereos have weird voltage transformers but there again I can'be sure it's not a 6.3V output unloaded. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 25, 2005 Report Share Posted October 25, 2005 Why is a little 2"x 2"x 2" transformer considered to be "big"?Was it from a 2W boom-box stereo? ??? ??? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 25, 2005 Report Share Posted October 25, 2005 Good point audioguru, I normally think of thins in metric and 2" is only 51mm, this is quite small for a transformer. I would think that the load regulation of a small transformer like the is quite poor so output voltage will drop quite a bit when a load is connected. Quote Link to comment Share on other sites More sharing options...
LegendBreath Posted October 25, 2005 Author Report Share Posted October 25, 2005 Ok... sorry, cuz for me, it's one of the biggest transformer I got here ::) Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 25, 2005 Report Share Posted October 25, 2005 Hi LegendBreath,How much current is your regulated 6VDC output going to supply? What is its load?We are afraid that your big, little transformer can't supply enough current without its output voltage dropping too low. Also it might overheat if it is overloaded.The regulated 6V output might also drop when the 12VAC is loaded.The 12VAC will drop when the regulated 6VDC is loaded. Quote Link to comment Share on other sites More sharing options...
LegendBreath Posted October 25, 2005 Author Report Share Posted October 25, 2005 How can I know what it will give me when it's loaded ???And BTW: Here is some pictures of my "crappy" project :PBTW: I don't have my 12V regulator for now... Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 25, 2005 Report Share Posted October 25, 2005 Hi LegendBreath,You project isn't crappy, but your transformer might be.What is the voltage at the input to the regulator without a load?If you have three 47 ohm/1W resistors, connect them in parallel across the output of the regulator as a load, then measure the input and output DC voltage of the regulator. Don't leave them connected too long or they will get hot and the transformer might get hot too. Quote Link to comment Share on other sites More sharing options...
LegendBreath Posted October 25, 2005 Author Report Share Posted October 25, 2005 Hi LegendBreath,You project isn't crappy, but your transformer might be.What is the voltage at the input to the regulator without a load?If you have three 47 ohm/1W resistors, connect them in parallel across the output of the regulator as a load, then measure the input and output DC voltage of the regulator. Don't leave them connected too long or they will get hot and the transformer might get hot too.Ok thanks audioguru,I'll try to find some 47 ohm resistors. And, without the load it is 7VAC and 12VAC. Quote Link to comment Share on other sites More sharing options...
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