RE: Ballast training 101

["David Dean" <deano-at-corridor-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Sundog-

EXCELLENT IDEA!

I have been working on a "ballasting primer" for several days now, but
probably won't be done with it for some time to come. Ballasting is a tricky
problem and one that solutions do not seem to come intuitively.

Comments interspersed:

> -----Original Message-----
> From: Tesla list [mailto:tesla-at-pupman-dot-com]
> Sent: Friday, August 25, 2000 12:25 PM
> To: tesla-at-pupman-dot-com
> Subject: Ballast training 101
>
>
> Original poster: "sundog" <sundog-at-timeship-dot-net>
>
>
> Hi all,
>
>   Before I dive into pole-pig land, MOT land, etc, I want to learn a lot
> more about ballasting than I do now.  For my "work" I have a 120v
> transformer that steps down to 16v20-30+A.  I feed it 120v, and it'll pull
> up to 4+A from the wall, but the secondary leads start to bubble,
> so I shut
> it down.
>    About a 3" square cube, it's a true beast for small projects.  It has
> proved itself "unbeatable" for low voltage-high current useage.  Normally
> the things I run it with don't pull much (<2A) so a high amount of power
> isn't needed, so it rarely pops the 120v4A fuse I had on it.
>
>    Now, yes, this is a bit silly, going through the hassle of ballasting a
> 16v tranny.  But it should behave just like a pole pig (suck up
> current till
> it pops the breaker), and by using this nifty 3A breaker I found
> at the flea
> market, I can assure I'm actually limiting it.  I frequently feed
> a 4/30 NST
> with it for ~1kv output (hmmmGMHEICSLR range voltage ;), and come to think
> of it, haven't checked the nst's current output.  Good idea there.
>
Nothing silly about that at all, and you are right, it should behave just
like a pig.


> I intend to try and note: seriesing a lower-wattage tranny (5v500ma) with
> the primary (5v500ma sec leads shorted)
>
Usually the transformers used as ballast for pigs, etc., be they MOTs or
welders with the secondary shorted, are shunted transformers, that is, they
are current limited themselves.
You may find that if the ballast transformer is not shunted, and the
secondary is shorted, it will have a tendency to saturate, and may well burn
up. Should prove interesting to see.


                                    resistive ballast (light bulbs
> of warious
> wattages in series /w primary)
>

Just keep in mind that light bulbs are non-linear in their resistance.

> Will a moveable steel core in a selenoid limit primary current?  How do I
> figure # of turns, etc. (will it work for something this small? would it
> work better on the secondary side?) How about winding a plain
> 'ole inductor
> for it?
>
Yes. Do you have a meter that can measure inductance? If so, you are ahead
of the game. You can calculate the required reactance in Ohms to limit the
current in your transformer to the desired level by using ohms law. (you
don't need to worry about phase angle, power factor, etc. just pretend the
circuit is linear and you are using a resistor, all you want is a number, a
magnitude, not a vector.) Then find the inductance from the inductive
reactance at the desired frequency, and find a sol. that is close to that
value with the plunger removed. That should get you in the ballpark.
Just be sure that whatever you use as ballast, should it be a sol. or a
transformer, or even a light bulb, is designed for the full voltage you will
be putting into the circuit. When I was doing the "ballast training 101"
thing on my own, I found a transformer that had the "ideal" inductance to
limit my pig to the same output as a 15/60 NST. It was from a battery
charger for a golf cart. The problem was, it was designed for 120V and when
I put it in series with the low voltage windings of the pig, it would go
into saturation just about as the limiting effect started to kick in, with
some rather interesting effects.

> Again, yes, this seems a bit silly, but it's a *LOT* less dangerous than
> MOT's, and if it does bite me, I 'll only get a nasty,
> substantial jolt and
> live to coil on.  The goal is *not* to get bitten, however.
>
Actually it does not seem silly at all. It does seem safe. And as always,
much better safe than sorry.

later
deano

>  Ideas?  Comments?  Think it'll even work?
>
>   								Sundog
>
>
>