Need some help about transformer rating for amplifier

[sanbadgujar]

hello friends

I have simple question about transformer selection for
amplifier, i have amp which required single 60vdc and 1.2 amp current for
operate .currently i have tranformer 22-0-22 CT with 5 amp current in secondary .can i use this transformer for this amplifier or it will blow amp.

 

[JonSnell Electronic]

If you work backwards. 60V at 1.2A is 72VA.
44 x 1.414 = 62.216.
If the total secondary current is 5A then the power available is 44 x 5 = 220VA.
Plenty of power but will your project stand the extra 3Volts or so, ( not allowing for mains fluctuation)!

 

[sanbadgujar]

If you work backwards. 60V at 1.2A is 72VA.
44 x 1.414 = 62.216.
If the total secondary current is 5A then the power available is 44 x 5 = 220VA.
Plenty of power but will your project stand the extra 3Volts or so, ( not allowing for mains fluctuation)!

HI Jonsnell

What do mean This transformer is OK for my project even if it have nearly 5 time more current in it. please clarify that to me because I am confused. Thanks

 

[Juhleren]

HI Jonsnell

What do mean This transformer is OK for my project even if it have nearly 5 time more current in it. please clarify that to me because I am confused. Thanks

I believe he means that while the trafo seems juicy enough (from a VA perspective) it gives a slightly higher secondary voltage which might be a problem -especially if your mains voltage varies...

For example, I bought a 120VA r-core claimed to have 2 sets of 32VAC secondaries. In my actual application it gives me 54-56VDC due to regulation compensation and higher than usual mains voltages (measured 125-126VAC!). This was a problem due to my amp being limited to 56VDC...

Another issue to consider is what kind of rectification your amp works best with. If you have two sets of secondaries, you should be fine. But if you only have one set of 22-0-22, you have limited options when using the full 44-0 swing.

best,

 

[JonSnell Electronic]

HI Jonsnell

What do mean This transformer is OK for my project even if it have nearly 5 time more current in it. please clarify that to me because I am confused. Thanks

It is acceptable to have more current available than is ever going to be used, in fact, a good thing. The only issue is the voltage supplied.

 

[sanbadgujar]

I believe he means that while the trafo seems juicy enough (from a VA perspective) it gives a slightly higher secondary voltage which might be a problem -especially if your mains voltage varies...

For example, I bought a 120VA r-core claimed to have 2 sets of 32VAC secondaries. In my actual application it gives me 54-56VDC due to regulation compensation and higher than usual mains voltages (measured 125-126VAC!). This was a problem due to my amp being limited to 56VDC...

Another issue to consider is what kind of rectification your amp works best with. If you have two sets of secondaries, you should be fine. But if you only have one set of 22-0-22, you have limited options when using the full 44-0 swing.


Hi Juhlern

Do you mean that the output current of transformer is not matter
Even if my amplifier required just 1.2A but transformer have 5A at secondary.

best,

 

[sanbadgujar]

Hi Juhlern

Do you mean that the output current of transformer is not matter
Even if my amplifier required just 1.2A but transformer have 5A at secondary.

 

[sesebe]

Hi Juhlern

Do you mean that the output current of transformer is not matter
Even if my amplifier required just 1.2A but transformer have 5A at secondary.

Yes.

If the transformer it is rated at 5A this means that can supply anything from 0A to 5A. Because you need only 1.2A, this transformer will work cooler and will be verry happy with this. The only problem can be the physical size but I suppose that is not the case now.

 

[Juhleren]

Yes.

If the transformer it is rated at 5A this means that can supply anything from 0A to 5A. Because you need only 1.2A, this transformer will work cooler and will be verry happy with this. The only problem can be the physical size but I suppose that is not the case now.

+1

And yes as JonSnell say, its the voltage that might be a problem. If you hook up the supply, then try to test its unloaded rail voltage and compare it to the max safe rail voltage of the amp.

Unless your mains run high, its probably not an issue...

best,

 

[sesebe]

If only 2-3V in plus are a problem then the design is not so god.

A schematic that it is projected to work from an unstabilised power supply must accept at least +/-10% but if it is well engineered will accept over +/-15%.

From my point of view the transformer it is perfect for this job.
Keep in mind that they lose about 1.5V on the bridge diodes.

(44v-1.5V)*1.4142=60.1V

 

[sanbadgujar]

thanks for all to help me

 

[esgigt]

Please keep in mind that the VA number after rectification ought not to exceed the transformers VA rating. So 44v x 5A = 220 va. Therefore 220va/63v = 3.5A.

Which indeed is plenty for your application.

 

[Juhleren]

If only 2-3V in plus are a problem then the design is not so god.

A schematic that it is projected to work from an unstabilised power supply must accept at least +/-10% but if it is well engineered will accept over +/-15%.

From my point of view the transformer it is perfect for this job.
Keep in mind that they lose about 1.5V on the bridge diodes.

(44v-1.5V)*1.4142=60.1V

Trouble is that all trafos and especially small ones have been designed to compensate for a load and thus produce more voltage unloaded than what they are specified to. If the amp is energy efficient, you can experience a lot more voltage than you opted for. It is not unrealistic to get 10-15% higher rail voltages.... Then you can add mains variations :/

 

[AndrewT]

Regulation can approach 30% for small EI transformers.