Thanks for the clarity
Yes, it's true that the manufacturer gives the "on-load" voltage.
JojoD818 has 2 problems that are clouding the issue:
1 He has low mains voltage (easy to calculate the difference)
and,
2 He doesn't know the true RMS current being taken from the secondarys. We can only guess that it about 1.5 x the DC current after rectification.
Cheers,
Yes, it's true that the manufacturer gives the "on-load" voltage.
JojoD818 has 2 problems that are clouding the issue:
1 He has low mains voltage (easy to calculate the difference)
and,
2 He doesn't know the true RMS current being taken from the secondarys. We can only guess that it about 1.5 x the DC current after rectification.
Cheers,
This may sem like a bit of a crap way to do this, but if you were to conect to high power resistors of around 0.22Ohms in between the transformer and the rectifier diodes (one on the supply for each rail), you could use the AC voltage setting on a multimeter to mesure the voltage drop on the resistors, and try and work back from that to find the current. The only problem with that being the fact the voltage vaveform will not be a sine wave, so the MM might give the wrong reading for the RMS voltage.
This may be redundant as I think someone has already mentioned something along these lines before but.
P=V.I
power(watts)=voltage * current
So the VA is volts times current so is the power in watts. Why they dont just call it power i dont know cause its the same thing and can cause confusion as it clearly did earlier on before.
P=V.I
power(watts)=voltage * current
So the VA is volts times current so is the power in watts. Why they dont just call it power i dont know cause its the same thing and can cause confusion as it clearly did earlier on before.
The reason they don't call it power is that it is actually the current that counts. For example, if you have a transformer with a secondary voltage of 24V and put a capacitor across it that draws 10A, it will use 0W of power (if the cap was ideal), but the transformer would heat up as much as if you put a resistor across the secondary that drew 10A instead.
Well, I checked it again and it really is hot. My rectifier and filters are correctly placed.
At least the amp is up and running, maybe I should buy another transformer and just use this for bench testing future amp projects.
I have learned a lot from this project, a friend told me that the design of a power supply in an amp is as important as the amp itself. That is why I am so concerned with my transformers specs.
Thanks guys!
Jojo
At least the amp is up and running, maybe I should buy another transformer and just use this for bench testing future amp projects.
I have learned a lot from this project, a friend told me that the design of a power supply in an amp is as important as the amp itself. That is why I am so concerned with my transformers specs.
Thanks guys!
Jojo
maybe the transformer has a short inside betwen wire, remember there is only varnish to insulate the wire, if there is a short winding, the magnetising current will rise. magnetising current is the minimum current needed by the transformer wen there is no load at the secondary. to measure it you remove all loads ( disconect the secondary ) , place a small resistor in series with the primary ( 3-5 ohms ) an measure the voltage drop on the resistor. then calculate the current and do the same on a similar tranfo, if the magnetising current of the transfo is really highier it may be defective.
transformerrating for DC power supply is tricky the transformer supply current only wen diodes are conducting ( during the part of the cycle wen the voltage rise on the cap ) so if this par of the cycle is let say 20% of the time during this time the current must de 5 times higher than the DC current out of the power supply 
this is why the manufacturers will tell you that if you build a power supply with a 1 AC amp transformer ( standard bridge capacitor configuration ) you will get a 0.55 DC amp supply. But if you use a bigger capacitor there will be less ripple but the diode will conduct a shorter time an the current during conduction will be higher and you will need bigger diode and bigger transfo. several transfo company have chart on the net..........
this is why the manufacturers will tell you that if you build a power supply with a 1 AC amp transformer ( standard bridge capacitor configuration ) you will get a 0.55 DC amp supply. But if you use a bigger capacitor there will be less ripple but the diode will conduct a shorter time an the current during conduction will be higher and you will need bigger diode and bigger transfo. several transfo company have chart on the net..........
Yes a mains transformer designed for 115/230Vac 60Hz will perform adequately. But has it been designed for universal use?
Will it work within specification if the supply voltage is 120/240Vac?
Will it .... is 127/254Vac (max tolerance of most mains)?
Will it work with 50Hz rather than 60Hz?
Will it still be within specification?
To be classed as a universal transformer it must remain in specification with 127/254Vac 50Hz as the worst case supply voltage.
I would expect it to be labeled:
110/120 or 220/240 Vac 50/60Hz
And for the manufacturer to publish the specification details that apply.
Will it work within specification if the supply voltage is 120/240Vac?
Will it .... is 127/254Vac (max tolerance of most mains)?
Will it work with 50Hz rather than 60Hz?
Will it still be within specification?
To be classed as a universal transformer it must remain in specification with 127/254Vac 50Hz as the worst case supply voltage.
I would expect it to be labeled:
110/120 or 220/240 Vac 50/60Hz
And for the manufacturer to publish the specification details that apply.
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