RE: [CAD_CAM_EDM_DRO] Re: Power Supply Caps and Xformer

What they are specifying there is not that the power will be lower after
rectification, but that you should take into account about a 20% "loss" due
to power factor of the load(which basically means that the current will not
be in phase with the voltage).The VA is the actual numbers of the current
and the voltage, multiplied. The power is only equal to the VA if there is
no difference in phase angle between voltage and current.


Notice that the VA and Watts specs both refer to the LOAD. I think this
might be caused by the capacitor in the power supply-this will be a big
cause of volts/amps being out of phase.

I would guess that the power of the AC would be equal to the power of the
DC.

Andy

-----Original Message-----
From: kmslinda
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: 9/1/2004 6:33 PM
Subject: [CAD_CAM_EDM_DRO] 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



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