# Transformers

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#### the fuse

##### New member
On a typical buck/boost transformer the power across the primary and secondary windings is equal, ie. 1920 watts on the primary windings is also 1920 watts on the secondary windings. If, for example, I'm installing undercounter low voltage (12v)lighting and my load is 1920 watts, why isn't my current at 160 amps? Using P=I*E for my primary, current is equal to 120v*16a=1920watts, my secondary should equal 1920watts = 12v*160a. What gives?

#### hurk27

##### Senior Member
Re: Transformers

theroreticly it would be. But you have to take into account the amount of loss accross the transformer. which can be as high a 40%

#### cote

##### New member
Re: Transformers

We need to know a little more. What wattage are the 12v lamps that are you using and how many are you installing?

#### bennie

##### Esteemed Member
Re: Transformers

Please explain how you determined the wattage.

#### charlie b

##### Moderator
Staff member
Re: Transformers

The thing that determines the secondary current is the load on the secondary. As Cote says, start by adding the wattage of the lamps. Is this where you got the number 1920? Or did the 1920 come from the rating of the transformer? Once you know the total wattage of the total number of lamps, divide that by 12 and you will get the total current. Then divide the result by 10 and you will get the current on the primary side.

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