Transformer question

[Keith Rowland]

Hi Mark:  The volt-ampere rating is always equal to or greater than the
load.  Transformers are often rated that way becuase, depending on the
DC filtering (capacitor or choke input), the transformer has to handle
the power consumed by the load, but the reactive power in the filter
capacitors as well.

Technically, when using a voltage-doubler, the transformer will still
handle the same amount of POWER, but this means if you go to 250-volts,
you can only draw half the current as at 115-volts DC. This would not
suit your purpose.

I suspect, tho, that your transformer rating is probably CCS )Continuous
Commercial Service), so depending on whether your load is continuous or
intermittent, it MIGHT do the job.

I would suggest breadboarding your circuit, hook it up to whatever you
want to power, and see if it overheats.  If it gets too warm to touch
comfortably, it's probably not adequate.

If you have an ARRL Handbook, look in the Power Supply section (in the
1997 Handbook, there's a discussion of this beginning on page 11.3).

Good luck with your project.

73, Keith

Mark Dittmar wrote:
>
>         Hi-
>
>         I am trying to construct a 250 VDC @ 130 mA power supply.  I have
> an isolation transformer,  115/115 rated at 35 VA.  I would like to
> voltage double the output of this transformer up to the required 250 VDC.
> How do I determine if this transformer can handle the job ?  250 VDC*130
> mADC = 32.5 Watts,  not really the same as 32.5 VA, which holds for AC
> values of voltage and current,  correct ?  Should I being thinking in
> terms of average values ?
>
>         What numbers should I be using in my calculations ?
>
>         Thanks,
>
>         Mark, AB0CW
>
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