RE: Dual layer primaries

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>

I found no way to calculate it, so I built one.  Two 1/4" diameter
copper tubes, 13 turns per layer,  1/2" ctr-ctr spacing, flat spirals,
8.5" ID, 21" OD, 1-1/8"  vertical separation between the two coils,
connected in the center.  The following inductance measurements were
made with a Wavetek model 27XT inductance meter.  Measurements above
100uH are known to be quite accurate.  I have no real reason to suspect
lower measurements, but these are unverified.  Bn refers to tap on
bottom turn "n", Tn to top turn "n".  Example: From 12th turn on top to
10th turn on bottom measures 161uH.  From B12 to T10 "should" be the
same, but measured 168 uH, due to experimental error (close enough IMO).

B13	B12	B11	B10	B9	...	B0
T13	250uH	223	205	175	168		81
T12	228	204	187	161	152		71
T11	208	185	170	147	138		59
T10	189	168	154	134	124		50
T9	171	150	138	121	110		42
T8	154	134	124	108	98		34
T7	139	120	110	96	86		28
T6	125	107	97	85	75		23
T5	112	95	85	74	65		20
T4	101	84	76	65	56		16
T3	92	76	67	57	49		14
T2	84	68	60	51	42		12
T1	78	63	55	46	38		xx
T0	74	58	51	42	34		xx

I have a 1/4" Lexan sheet between the two coils, with no holes outside
the 8.5" circular cutout in the middle, extending about 1 inch beyond
the outermost turns.  This has proven to be inadequate to prevent
surface arcing between the ends of the two coils, I would suggest at
least 2 inch outer margins to the insulating sheet from each coil.

Regards, Gary Lau
MA, USA


>Original poster: "Jason Johnson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" ><hvjjohnson13-at-hotmail-dot-com>
>
>Hello,
> 
>Does anyone have any idea as to how to calculate inductance for a two
level
>primary? I'm talking about a primary coil that is wound with two layers
both
>going the same direction and seperated by an inch or so, inner turns
connected
>together, and tapped in two places, one on the bottom half, one on the
top
>half. I know that I can't just calc. for one primary and then double
it,
>because the halves are going to have some mutual inductance, resulting
in a
>higher overall inductance than just doubling one of half the size,
right? Does
>anyone get what I'm talking abut here?
> 
><<Jason Johnson>>