Re: Power Supply Caps and Xformer

--- In CAD_CAM_EDM_DRO@yahoogroups.com, JanRwl@A... wrote:

> In a message dated 9/1/2004 4:08:29 AM Central Standard Time,
> cnc@a... writes:
> Needs to be 50V @ 20A = 1000W
>
> Am I correct in assuming that I need a 2000VA transformer for this,

as 2000VA

> would = 1000W (because of the whole sine wave thing), or would

1000VA =

> 1000W?<<
> No, not correct. If the LOAD is "DC" (not inductive nor highly

capacitive)

> VA=W. Your transformer VA is based upon the sectional area of

the "iron core"

> around which the copper windings are wrapped. As my needs have

always been so

> "intermittant", and "mass-production economies" do not enter into

the

> calculations for one-off home-brew stuff, I never bothered with the

SQR(2)

> relationships of the transformer-VA to the "watts out", etc. I

only remember SEEING

> such in texts, and as it was never immediately really relevant, I

never memorized

> nor learned to "do". (Would one call that "self-replicating

ignorance"???)

>
> I believe a 1000 VA transformer is just fine for a 50V/20A load,

I am by no means an expert on transformers, but the instructions
I received for a 1400 VA transformer kit from Toroid Corp of
Maryland, states the the DC seconday Max Load is 880 Watts. In
all the posts I have read concerning power supply size, no one
has ever stated that power is lowered when rectified to DC. Is
this correct?

Below is a chart from their instruction sheet:

Max Load VA DC Max Load Watts
80 60
200 140
400 260
700 460
1400 880

Thanks: Gerry