centre tapped transformer power supply

[furqankaimkhani]

I have a local centre tapped transformer 12V and 12V. There is no current rating labelled on it. (it is just about a little smaller than the size of a tennis ball). I guess it should be 1 Amp.

Is there a way to find out actual current rating of a transformer?

 

[goldsmith]

Dear furqankaimkhani
Hi
Yes there is a simple way available : your transformer has a core . it can be EI , core . if yes , EI< or = 30 sqrt ( AFE ) and AFE = 1.2 sqrt (P1) P1 =Vin* Iin . so you have vin , and you have vout , you will fine I in from that formula as well , and then you will find iout ( approximately ) with this formula : Vo/Vi = Io/Ii .
Best Wishes
Goldsmith

 

[BradtheRad]

Assuming yours is designed to step down mains AC...

Look up specs on other transformers.
Find one which is similar size and voltage as yours. From its current rating you can estimate that is also yours.

My guess is 2 or 3 amps.

It will depend on what duty cycle you operate each winding.

If it gets too hot to touch, then it's reached its safe current rating.

 

[tpetar]

I have a local centre tapped transformer 12V and 12V. There is no current rating labelled on it. (it is just about a little smaller than the size of a tennis ball). I guess it should be 1 Amp.

Is there a way to find out actual current rating of a transformer?

Yes, like additional to Goldsmith post, you can use nonius instrument to measure diameter of wire on secundar and see what current can be supported by that wire. Sometimes core is bigger and wire diameter is smaller to make lower temperature. ;-)

 

[szhighstar]

measure your diameter of ire, I=A*J, A is across section area of wire, J is current density(3-5A/mm*mm), you can know around Irms.

 

[tpetar]

measure your diameter of ire, I=A*J, A is across section area of wire, J is current density(3-5A/mm*mm), you can know around Irms.

3,5A-mm2 is high (for high temp trafo), better consider 2,5A/mm2 :wink:

 

[szhighstar]

I mean 3 to 5, if you select 2.5, it is better, however your bobbin has enough room to wound wire, if not, your coil is too fat to be assembly with core.

 

[tpetar]

I mean 3 to 5, if you select 2.5, it is better, however your bobbin has enough room to wound wire, if not, your coil is too fat to be assembly with core.

Usually what I know calc is for 2,5A/mm² and 3,5A/mm² over that like 5A/mm² I think we need oil cooling.

I think that is better for existing unknown trafo specification consider lower parameters, based on core square area and wire diameter based on up to 2,5A/mm² amperage density.

Also if density higher per mm² of wire, temp will rise and losses will be higher. Higher amperage per mm² of wire also require better isolation of wires and each turn of winding need isolation resistive on high temp. Wires must be several times protected with special high temp lacquer.

My opinion is to threat unknown trafo as 60-75C temp, not 150C or over.