Re: [TCML] DC Coils

[<lightningfor@xxxxxxxxxxxxxxxxxxxxxx>]

Hi bert,
The dc supply is from a 50kva 3phase transformer that gets rectified with
6 HV diodes to give 10kv dc.
The voltage gets doubled via the large inductor 4.5 henries...
I checked my diodes lats night incase some had failed and I wasn't getting
full voltage and all checked out ok.
After further tests, I do think the voltage is lower than it should be
accross the cap.
I stretched the spark gap out a bit and it struggled to jump it.
It is a rotary gap 2800rpm with 4 rotating electrodes and 1 set of
stationary ones so about 180bps from memory.
The gap is about 1.5-2mm each side so total of 4mm max. Even with the high
speed air from the gap I would have expected 20kv to eat it up, but it
behaves more like only a 10kv supply....  it jumps it, but if I open it too
much it starts to splutter.

carlos 

On Wed, 11 Jan 2012 15:21:56 -0600, Bert Hickman <bert.hickman@xxxxxxxxxx>
wrote:
> Hi Carlos,
> 
> Sounds like your DC rail is collapsing under load. Have you tried 
> increasing the values of your doubler and DC storage caps?
> 
> Bert
> 
> lightningfor@xxxxxxxxxxxxxxxxxxxxxx wrote:
>> Scott,
>> I have tried increasing the break rate, and it does increase power
input
>> and to some degree spark length.
>> My inductor is calculated to give a max bps of 500bps, and spark gap
>> works
>> smootly up to that break rate. (below extinction frequency)
>> My inductor is also multi tapped, so I have tried smaller inductances
to
>> allow more current, but this did not help.
>> The only thing I can think of to explain the results is that the 10kv
>> supply is not being doubled...
>> But based on the spark gap I am using, I do not believe that is the
case.
>> Also, back in the early days of coiling when I used to use 10kv AC, the
>> coil would still be drawing more power and producing big arcs with a
cap
>> of
>> this size and similar break rate...
>>
>> carlos
>>
>>
>>
>> On Tue, 10 Jan 2012 15:23:20 -0500, Scott Bogard<sdbogard@xxxxxxxxx>
>> wrote:
>>> Hi Carlos,
>>>       Having never built a DC coil you should probably ignore me, but
if
>> I
>>> had to guess I would say your doubler is limiting your current.  If
you
>> can
>>> vary your spark gap speed you can determine if this is the issue, if a
>>> faster break rate improves performance, current is not an issue, it
was
>> a
>>> calculation error, if it worsens performance, I would guess your
current
>> is
>>> being chocked by the doubler.  Again, probably best to ignore me, I've
>>> never built a DC coil, but you are correct for similar power levels
>> results
>>> should be the same...
>>>
>>> Scott Bogard.
>>
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> 
> 
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