Re: [CAD_CAM_EDM_DRO] newbe needs help?

In a message dated 5/30/2003 8:14:41 PM Central Standard Time,
bazo@... writes:

> toroidal type 1000va 11.25A 48V with the secondary winding at 500va . so my
> questions are what does VA stand for, what sort of rectifiers do need and
> what size and sort of capacitors do I need ,for any uk people out there I am
> hoping to bye these from RS

Baz:

"VA" = "Volt-Amps". That is NOT the same as "Watts" except perhaps for
resistive circuits, which transformers and motors are NOT. How can this be a 1000
VA xfmr if the math on the two numbers you give indiates only 540 VA?

You need a "full-wave bridge-rectifier," possibly very-difficult to
impossible to find at 15 amp. Maybe! Or four "stud-mounted" types, preferable two
"normal" and two "reversed" (facilitates mounting, but you have to know what
you're doing in ANY case!)

I'd use 20 amp. silicon stud-mounted diodes, with at least a 100 peak reverse
volt rating.

Capacitors? I generally figure 1000 uF per amp. For motor-powering, not
super-hi-fi audio, that is sufficient. So, you'd need a 11,000 uF capacitor.
There is NO such thing, so, go for 12 or 15K. Possibly, a 10,000 uF might do
"if you never TELL anyone!" (Seriously!)

Nevermind any "part numbers" on stuff like this! YOU are designing/building,
so whatever you find in your hands with suitable electrical characteristics,
no matter WHAT the make of the paint-color, will do fine! Also, there is
nothing nebulous about these parts you need, and RS SHOULD have them at hand, if
not in one of those very-useful bins about the showroom floor with "Misc.
components, marked down" in them! (last I was in an RS store "over there" musta
been '82?)

You are VERY lucky to have a TOROIDAL transformer, as that is a MUCH better
configuration than the "conventional E-I type"! I assume you know the actual
OUTPUT of a full-wave rectified 48 VAC will be in the region of 65 Volts, if
very slightly loaded! Maybe even 70 V. if not loaded much at all! So, be sure
your motor-driver circuits will HANDLE that voltage (and current!)

Lotsa luck! Jan Rowland, Texas Troll


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