Re: Constant voltage transformer

Thanks Jon,

That pretty much cleas it up for me.

I'll stash the resistor for 'future' use or dust collecting. and wire
up the transformer so I can use it for testing and not break down my
soon to be completed power supply.

I have to say that over the last few weeks, you guys have steered me
in the right direction more than a few times.

Thanks all.

Dave

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> dave_ace_me wrote:
>
> > Hi all,
> >
> > Thanks to you who advised me that what I have is a constant
voltage
> > transformer or as some called it, ferro-resonant (sp) transformer.
> >
> > In doing some further checking, and going by the size of the frame
> > and using the sq cm as the basis, it is of the same capacity as
> > the 'standard' transformer that was in the same unit.
> >
> > My question is whether there is any plus (or minus) of using this
> > constant voltage transformer over the standard transformer.
>
> They are heavier, dissipate a lot of heat, and sometimes buzz
annoyingly.
> If it produces the correct voltage output, though, it should be
fine.
> One thing to note, ordinary transformers have a large current surge
> capability. By that I mean that they can provide 2 - 5 times rated
output
> for a short burst, which can allow you to use a much smaller
transformer
> for servo and stepper systems. Ferroresonant transformers have a
> LOT of leakage inductance, that is how the regulation is
accomplished,
> and so they have very little surge capacity. If you try to draw
more current
> than the rating, the output voltage drops. This can actually be an
advantage
> in some cases.
>
> > The second question is to the reason why there is a 100 ohm
> > (measured) resistor across the taps of the cap. Does the constant
> > voltage transformer require a minum load or something ? I would
have
> > expected a much smaller bleed resistor over such a large cap.
> >
> > The resistor is a 100 ohm, 55 watt connected directly across the
> > 68,000 / 75 volt capacitor.
>
> No, generally, the transformer doesn't need such a load, but they
may have
> had some reason for this, possibly safety. I suspect you can
replace
> it with a higher value, smaller wattage resistor without much
trouble.
>
> Jon