Re: Passive Ballasting for DRSSTC - My thoughts before Ed Wingates Teslathon

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Dan,

On 27 Aug 2005, at 21:59, Tesla list wrote:

> Original poster: "Daniel McCauley"
> <dhmccauley@xxxxxxxxxxxxxxxxxxxxxxxxxx>
>
>
>  > First of all, I don't see how the drive pulsewidth can be different
>  > than the ON time, especially if you are not using a JK flip flop to
>  > ensure a soft turn off. Even given a constant ON time, there was a
>  > noticable effect. I wasn't claiming that the effect was purely >
>  different ON time, but that if you are gonna try to compare them, you
>  > should at least compare them honestly and not try to cheat a few
>  cycles.
>
> I can't either.  But if i keep drive pulsewidth constant, and simply
> change the wire gauge on the primary, cycles do get cut off in the
> smaller gauge case.  Definitely weird, as i would not expect that to
> change.
>
>  > Do you still notice the effect when you don't change wire length?
>  I'd > find that hard to believe. The only other change is the
>  resistance, > which is a simple ohms law calculation.
>
> Yes.  Wire length can be constant, and the effect is still seen.
>
>  > Not really a 'fluke', just that it works with your coil, with your
>  > tuning. Of course identical set ups will perform identically. It >
>  depends on how you tune the coil in the first place (running a >
>  slightly lower tuning effectively cancels out your 'ballast' >
>  inductance). In other designs, it may not be effective, and in the >
>  case of primary current feedback, it will do nothing, since it will >
>  simply drive it a bit slower, and keep building up current.
>
> What ballast inductance?  Granted, parallel strands of conductors
> (larger wire with more strands) flowing current in the same direction
> will increase inductance, but not enough to make any noticeable
> difference, especially if wire lengths are kept constant.  Also, i can
> tune the coils anywhere (i did that this weekend to further
> investigate this), and it does not affect this ballasting effect one
> way or another.
>
>
>  > First of all, we have to look at the possible effects of adding
>  some > small wire to the setup. The effects can be inductive, or
>  resistive, > or a combination thereof.
>
> No, its not adding any small wire.  Wire length can be kept constant,
> routed exactly the same way, and the ballast effect occurs.
>
>  > The extra inductance both changes the primary resonant frequency
>  (as > does changing the tap point), and reduces the coupling (as does
>  > raising the secondary). Therefore, you shouldn't add thin wire for
>  > the inductive effect, since you can simply retune (and raise the >
>  secondary, although it's probably more about the tuning), and thinner
>  > means more loss.
>
> Again, using identical lengths of wire under same routing conditions,
> the only difference i can see are in the R of the wire, and just a
> slight bit of inductance change due to the variation in parallel,
> current paths from the changes in number of strands.
>
> Thanks for the response.  I'm still a bit stumped.  Even after
> additional tests this weekend, i just can't figure out why simply
> replacing about two feet of 4 AWG connections with 8 AWG connections
> reduced ground strike current by 300A ! ! !  Even when routed
> identically with identical lengths, the change still exists. Oh well .

If that is the only difference then there can only be certain
reasons: higher resistance in the smaller wire and/or higher
inductance in the smaller cable. I know you mentioned more strands in
parallel in the larger one but have you actually measured it? PCbd
ground planes rely on parallel conductors to decrease parasitic
inductances. Even small changes could be significant at high currents.

Malcolm