Has anyone tried a tiered solenoid,helical combination primary for a
larger bipolar coil? For instance, stacked rows of 2 or 3 coils wide and
proper number of coils high for proper tuning.
Doug
On Sun, Oct 18, 2020 at 12:15 AM Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx>
wrote:
> Doug,
>
> Unused primary turns develop an induced voltage, acting like an
> autotransformer. A typical SG Tesla coil may develop 1 - 2 kV per
> primary (and secondary) turn. Unused primary turns (such as the unused
> innermost and outermost primary turns in Mike's proposal) are no
> different. The induced voltage will add to the voltage stress between
> the innermost primary turn and secondary, potentially damaging the
> secondary.
>
> When I built my first coil, I used an oversized 16-turn flat primary
> since I was planning to re-use it on my next, larger coil. With the
> smaller secondary, I only used the innermost 7 or 8 turns to bring it
> into tune. When I cranked it up to full power I got very loud, white-hot
> arcs jumping across the 2" gap between the outermost primary turn to the
> grounded strike rail above. The primary was acting as an
> autotransformer, doubling the primary voltage. Obvious when viewed with
> 20:20 hindsight... :)
>
> Bert
>
> Douglas Johnson wrote:
> > OK Bert, I don't know what " autotransformer effect" is!😉
> > Doug
> >
> > On Sat, Oct 17, 2020 at 3:07 PM Bert Hickman <bert@xxxxxxxxxxxxxxxxxxxxx
> >
> > wrote:
> >
> >> Clever approach, Mike!
> >>
> >> You'd need to watch out for autotransformer effect bumping up voltage on
> >> the innermost turn. You might need to widen the gap between innermost
> >> turn and secondary but otherwise this should work.
> >>
> >> Bert
> >>
> >> mike tucknott via Tesla wrote:
> >>> Hi All
> >>>
> >>> With a bipola coil would having 2 movable tap point work for changing
> >>> the coupling ?
> >>>
> >>> Say the coil need 5 turns to be in tune, you could built the primary
> >>> with 10 turns and you could move the inner and outer taps points in or
> >>> out but still keeping the 5 turns needed to keep the coil in tune, the
> >>> inner and outer turns passed the tap point would be electrialy dead so
> >>> to speak.
> >>>
> >>> Thoughts on this one guys.
> >>>
> >>> Cheers Mike T
> >>>
> >>>
> >>> On 17/10/2020 00:43, Gary Lau wrote:
> >>>> Hi Kurt,
> >>>>
> >>>> Splitting and separating the secondary seems like a great way to vary
> >> the
> >>>> coupling, but one must also bear in mind that doing that will vary the
> >>>> Lsec
> >>>> inductance and tuning. I can't think of a way to vary only the
> >>>> coupling on
> >>>> a bipolar coil, but I have never built one.
> >>>>
> >>>> Regards, Gary Lau
> >>>> MA, USA
> >>>>
> >>>> On Fri, Oct 16, 2020 at 7:15 AM Kurt Schraner <k.schraner@xxxxxxxxxxx
> >
> >>>> wrote:
> >>>>
> >>>>> ...just my 2 cents: cutting the bipolar secondary in 2 independently
> >>>>> movable
> >>>>> halfs could enable the control of the coupling (see the
> ASCII-sketch):
> >>>>>
> >>>>> oooooooooooo
> >>>>> __________________ __________________
> >>>>> I__________________I I__________________I <---->
> >>>>>
> >>>>> oooooooooooo
> >>>>>
> >>>>> ...the primary can be either of a solenoid or a flat spiral.
> >>>>>
> >>>>> Regards, Kurt Schraner
> >>>>>
> >>>>> -----Ursprüngliche Nachricht-----
> >>>>> Von: Tesla <tesla-bounces@xxxxxxxxxx> Im Auftrag von jimlux
> >>>>> Gesendet: Freitag, 16. Oktober 2020 02:15
> >>>>> An: tesla@xxxxxxxxxx
> >>>>> Betreff: Re: [TCML] Coupling
> >>>>>
> >>>>> On 10/15/20 6:50 AM, Douglas Johnson wrote:
> >>>>>> Thank you both, I think I know where to go from here on my current
> >>>>>> build.
> >>>>>> My project is a larger bipolar than I have built to date. Secondary
> is
> >>>>> 3.5"
> >>>>>> dia. X 24" with .015 mag wire. By the time I built the primary it
> >>>>>> was 6"
> >>>>>> long and I was getting "runners" on the secondary. I think my fix
> will
> >>>>>> be going to a flat spiral primary.
> >>>>> On a bipolar, it's hard to control the coupling on a solenoidal
> primary
> >>>>> sliding it one way or the other doesn't change the flux distribution
> >>>>> very
> >>>>> much.
> >>>>>
> >>>>> I'm not sure a flat is any better.
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> >>
> >>
> >> --
> >> Bert Hickman
> >> Stoneridge Engineering LLC
> >> Woodridge, Illinois, USA
> >> http://www.capturedlightning.com
> >> +1 630-964-2699
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