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Re: Ballasting the secondary side of transformers



Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Aaron,

On the LV side, many have built current limiting in many different ways. So, thinking of the low current on the HV side, I had to wonder (spur of the moment thought). That's why I thought HV ballasting might be interesting to look at. However, I just made a few calcs to answer my own question. For a 10KVA pig, the inductance method of ballasting on the hv side turns into a 1 to 20 Henry value which is an ugly thought. One could of course R ballast the hv output, but then for 20A LV side current, were looking at a 900W dissipation need. The HV side does have some qualms I didn't realize at first glance (which is what happens when you express an idea prior to doing the math). One thing about LV or HV side, power is the same (neglecting internal losses), so there is still a price to pay. The bottom line for me from an inductive standpoint is that it is just easier to form a uH large wire ballast on the LV side rather than form an extremely high turn small wire ballast on the HV side (and of course dealing with the HV standoff).

Thanks for your input.
Take care,
Bart

Tesla list wrote:

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

But what are the costs of making a LV ballast?  I've
made two:  My first was a 30 gallon garbage can full
of water with 1/2" copper pipes immersed, one of which
had a PVC sheath I could raise or lower to adjust the
current.  Spent about $20 on that thing, including
brand new plastic garbage can from Home Depot (but I
already had the copper pipe).  The other is a ~24"
long ~5" OD piece of PVC with two layers of #6
stranded on it filled with steel ceiling wire gotten
from the local industrial surplus joint.  Steel gets a
little warm after long runs.  Big deal.  Same with the
water :-)  This latter ballast cost me $35 or so.
Granted, if you go and buy a big variac, you'll be out
$100 or more real quick!

I have a hard time believing high-side ballasting is
going to make things cheaper, and making a variable
high-side ballast (that you can vary while running!)
poses greater health risks, I think!

Regards,
Aaron, N7OE

--- Tesla list <tesla@xxxxxxxxxx> wrote:

> Original poster: "Barton B. Anderson"
> <bartb@xxxxxxxxxxxxxxxx>
>
> Can someone please tell me why we are still
> ballasting on the LV side
> of Pigs and PT's? This should be easy enough to do
> for a fixed
> current limit. The costs associated with a LV
> ballast almost demands
> we do this. The LV side is starting to appear very
> silly to me at the
> moment. Granted, there are HV concerns, but is it
> really a big deal?
> I get the feeling LV ballasting is simply
> convenient. However, it is
> also expensive (unless one builds a ferrite
> ballast).
>
> Just curious is anyone else has contemplated a high
> side ballast.
>
> Take care,
> Bart
>
> Tesla list wrote:
>
> >Original poster: "Gerry  Reynolds"
> <gerryreynolds@xxxxxxxxxxxxx>
> >
> >Hi Harvey,
> >
> >>Original poster: Harvey Norris <harvich@xxxxxxxxx>
> >>
> >>How can you even ascertain what a resonant cap
> value
> >>would be if you are not using a current limited
> >>secondary?  Can a pole pig for example have a
> current
> >>limited output measurement made by shorting out
> the
> >>secondary outputs, simply by ballasting its
> primary?
> >
> >
> >Primary ballasting current limits the same as
> secondary ballasting.
> >Only the needed value of the ballast is different.
> If ballasting on
> >the seconary, the inductance needs to be n^2 larger
> than if
> >ballasting is done on the primary, yes??
> >
> >Gerry R.
> >
> >
> >
> >
> >
> >
>
>
>
>
>