Buck Boost Transformer

[Little Bill]

If you fed a 240V/120V 24V/12V BB transformer with 208V, what would the boost voltage be?
The transformer was mounted on the side of an air compressor but neither the air compressor or transformer were hooked up.

 

[wwhitney]

Depends on how you wire the transformer. The split primary will presumably be wired with both coils in series, since 208V > 120V.

If you wire the split secondary with both coils in series (nominal 12V configuration), then the turns ratio will be 240V:12V = 20:1. So with 208V on the primary, the secondary will be 208V/20 = 10.4V. Wired in a boost configuration, the boosted voltage will be 208V + 10.4V = 218.4V.

If you wire the split secondary with both coils in parallel (nominal 24V configuration), then the turns ratio will be 240V:24V = 10:1. So with 208V on the primary, the secondary will be 208V/10 = 20.8V. Wired in a boost configuration, the boosted voltage will be 208V + 20.8V = 228.8V.

Cheers, Wayne

 

[Little Bill]

Depends on how you wire the transformer. The split primary will presumably be wired with both coils in series, since 208V > 120V.

If you wire the split secondary with both coils in series (nominal 12V configuration), then the turns ratio will be 240V:12V = 20:1. So with 208V on the primary, the secondary will be 208V/20 = 10.4V. Wired in a boost configuration, the boosted voltage will be 208V + 10.4V = 218.4V.

If you wire the split secondary with both coils in parallel (nominal 24V configuration), then the turns ratio will be 240V:24V = 10:1. So with 208V on the primary, the secondary will be 208V/10 = 20.8V. Wired in a boost configuration, the boosted voltage will be 208V + 20.8V = 228.8V.

Cheers, Wayne

Thanks, I knew it was close to 230V but didn't know how to figure it.

 

[wwhitney]

Oops, I swapped the series/parallel descriptions for the two possible secondary configurations.

Thanks, I knew it was close to 230V but didn't know how to figure it.

Hopefully I elaborated the steps of the computation sufficiently for you to be able to duplicate it in the future.

Cheers, Wayne

 

[Little Bill]

Oops, I swapped the series/parallel descriptions for the two possible secondary configurations.


Hopefully I elaborated the steps of the computation sufficiently for you to be able to duplicate it in the future.

Cheers, Wayne

You mean the 12V configuration should have said parallel, and the 24V configuration should have been series?

 

[wwhitney]

You mean the 12V configuration should have said parallel, and the 24V configuration should have been series?

Precisely. Two 12V sources in parallel give 12V; in series they give 24V (or 0V if the polarity of one is reversed).

Cheers, Wayne

 

[LarryFine]

Oops, I swapped the series/parallel descriptions for the two possible secondary configurations.

Yes, you did. I was about to point out that the greater boost requires the greater secondary voltage.

 

[LarryFine]

Easy to remember that 240 to 24 is the same ratio as 208 to 20.8

 

[wwhitney]

I was about to point out that the greater boost requires the greater secondary voltage.

I got that part right, just transposed the words series and parallel.

Cheers, Wayne