[TCML] Toroid question

Sun May 31 09:59:38 MDT 2009

Hi Jim,

What you mention is very common practice and probably good advice to 
ensure breakout (but not necessarily performance). Coils have been built 
with toroids whose minor diameter is quite a bit larger and they worked 
fine. For example, I use a 6.5" minorD on my 4.5" sec. I also used a 9" 
x 30" toroid on the 4.5" sec when I hooked it up in the hybrid maggy 
configuration. I believe power and bang size are major contributors to 
the performance of a top loads ability to perform well run well. As long 
as the top terminal is sufficiently charged so that the surface field 
strength achieves breakdown in relation to the surrounding.

As Gary points out, we really don't have good hard numbers to predict 
exactly when too big is too big. Considering the cost and/or labor of 
toroids, it is something we should attempt. I personally have an 
academic problem with toroid sizing. To relate a toroid size based on a 
secondary diameter will not be best for all cases. It's simply an 
empirical probability that many coils will do ok with, so it  does 
become good advice from that standpoint only.

Take care,
Bart

Jim Mora wrote:
> Hello List,
> I seem to remember reading 2 thirds the winding length or a bit more as a
> guideline for the major diameter. I have had pretty good results with a
> minor diameter (which has a major effect on the capacitance if the major is
> not oversized) close to the secondary diameter. Can anyone concur with that?
> Jim Mora
>
> -----Original Message-----
> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On Behalf
> Of Lau, Gary
> Sent: Saturday, May 30, 2009 2:37 PM
> To: Tesla Coil Mailing List
> Subject: RE: [TCML] Toroid question
>
> Yes, there surely is a topload size that's too large for every coil.
> Unfortunately no one has yet discovered a means of predicting what that size
> is, so all we have is some very crude rules of thumb and trial and error.  
>
> When a top load is too large, it doesn't just make the sparks smaller; it's
> an all or nothing proposition.  Beyond a certain size, the topload simply
> won't break out - even with a breakout point.
>
> Regards, Gary Lau
> MA, USA
>
>   
>> -----Original Message-----
>> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
>> Behalf Of Dex Dexter
>> Sent: Saturday, May 30, 2009 3:13 PM
>> To: Tesla Coil Mailing List
>> Subject: Re: [TCML] Toroid question
>>
>> John,in your formula
>> Spark lenght = 1.7*SQRT(P)
>> is P in watts power delivered to Tesla coil circuit or total power drawn
>>     
> from the
>   
>> mains?
>> Also,I heard that you developed the formula on the basis of SRSG , 120
>>     
> PPS,and
>   
>> equal bang sizes coils.
>> Does that mean  it is not so accurate for static gap coils,ARSG coils,and
>>     
> higher
>   
>> PPS coils.
>>
>>
>> Gary,there is surely a possiblity of a too big toroid for a power
>>     
> level.Let say ,if you
>   
>> put 48"x12" (with a braekout point on it) toroid on 360 W coil.That would
>>     
> probably
>   
>> decrease a spark lenght output,right?That size of the toroid is optimum
>>     
> for a 1 kW+
>   
>> range coil.
>>
>> Dex
>>
>> --- futuret at aol.com wrote:
>>
>> From: futuret at aol.com
>> To: tesla at pupman.com
>> Cc:
>> Subject: Re: [TCML] Toroid question
>> Date: Fri, 29 May 2009 18:18:23 -0400
>>
>> Andrew,
>>
>> at my website, I show my TT-42 coil with a 4" x 13" spun toroid.  The
>> coil
>> produces 42" sparks using a robust 12/30 NST.  An ordinary 12/30 gives
>> about 38" sparks.
>>
>>  http://futuret.110mb.com
>>
>> Cheers,
>> John
>>
>>
>> -----Original Message-----
>> From: Lau, Gary <Gary.Lau at hp.com>
>> To: Tesla Coil Mailing List <tesla at pupman.com>
>> Sent: Fri, 29 May 2009 9:13 am
>> Subject: RE: [TCML] Toroid question
>>
>>
>>
>> Hi Andrew,
>>
>> As you noted, bigger toroid equals bigger streamers but fewer of them.
>>
>> Personally, between the two choices you gave, I would choose the larger
>> 4.5x18
>> toroid.  I haven't personally built a coil powered by a 12/30 so I
>> can't say how
>> much larger than that one could go.  Do you already own both of those
>> toroids?
>> If so, try stacking both of them and see how that performs, assuming
>> that you
>> have sufficient primary turns to accommodate the lower frequency.
>>
>> The final answer will depend upon how much time and cash you have
>> available.
>> Big spun toroids are expensive.  If cash is limited, you may want to
>> try the
>> custom-made foam toroid that I had made -
>> http://www.laushaus.com/tesla/foamtoroid.htm
>>
>>
>> Regards, Gary Lau
>> MA, USA
>>
>>     
>>> -----Original Message-----
>>> From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com] On
>>> Behalf Of Andrew Robinson
>>> Sent: Friday, May 29, 2009 3:23 AM
>>> To: tesla at pupman.com
>>> Subject: [TCML] Toroid question
>>>
>>> I asked this once before but dont remember getting a very clear
>>>       
>> answer.
>>     
>>> With a 4" x aprox 22" secondary. 12/30 NST what would be an
>>>       
>> appropriate
>>     
>>> sized toroid? I've heard bigger toroid equals bigger streamers but
>>>       
>> fewer
>>     
>>> of them. I guess looking at it from the physics point of view, bigger
>>> toroid = more capacitance = bigger streamer but longer charge times.
>>>
>>> Basically we're looking at either a 3" x 12" spun toroid or a 4.5" x
>>>       
>> 18"
>>     
>>> spun toroid. Also is there a better place to get these other than
>>>       
>> ebay.
>>     
>>> Can someone out there sell us one?
>>>       
>>
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