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Re: 180 BPS synch? (fwd)

---------- Forwarded message ----------
Date: Wed, 18 Jul 2007 23:07:15 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: 180 BPS synch? (fwd)

Hi David,

I know you run twice the power I do on your big coils. I'm using 1.5" x 
0.375" pure tungsten electrodes in the rotary and the same electrode in 
the stationary, except that the stationary electrodes are mounted in 
large brass masses. This is something we might have in common. Another 
item in common for probably most rotary's is the disc diameter which 
affects a similar airflow and cooling ability.

I have a 12" disc with a running electrode diameter of 10.6". For my pig 
coil, this equates to about 46ms of mechanical dwell time. 3rd notch 
quenching occurs at 276us. After quench, I have about 2.7ms of charge 
time before the next alignment. It takes 5.76ms for full charge, so I am 
firing at about 18.8kV peak vs 20.3kV peak. Still 92% with a time 
constant of 2.55. That's based on .04uF cap size. My ballast limits me 
to about 7200 VA. My electrodes are as narrow as I can get without 
colliding, thus timing is serving everything. Most likely, few 
misfirings as the voltage is plenty capable of arcing the gap at 
alignment at 340 bps.

The gap should actually do ok at even higher bps from a charge vs speed 
situation (to a degree), but as you and I mentioned, we are seeing 
sparks decrease beyond the 350 mark. So, I expect it's simply down to 
crossing an efficiency barrier with the gap itself.

Take care,

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Thu, 19 Jul 2007 03:06:19 +0000
>From: David Rieben <drieben@xxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Cc: drieben@xxxxxxxxxxx
>Subject: Re: 180 BPS synch? (fwd)
>Hi Bart,
>Funny thing, I've always ran my big coils asynch and I too have
>found the optimum bps rate to typically be in the 300 to 350 bps
>range. I use a variable speed, permanent magnet DC motor for
>my RSG and find that with bps much lower than 300, the out-
>put is not as smooth and at much over 350, the sparks tend to
>get shorter - almost identical to your observations. I am just
>estimating the bps by the motor rpms as well but I come to the
>same conclusion ;^)  My primary cap is .1 uFd, and fired with
>a 14,400 volt 15 kVA pig.
>David Rieben
>-------------- Original message -------------- 
>From: "Tesla list" <tesla@xxxxxxxxxx> 
>>---------- Forwarded message ---------- 
>>Date: Tue, 17 Jul 2007 19:34:58 -0700 
>>From: Barton B. Anderson 
>>To: Tesla list 
>>Subject: Re: 180 BPS synch? (fwd) 
>>Hi Phil, 
>>No, the modeling does not. I expect others have noticed similar optimum 
>>bps rates when running in this mode and I expect they found their 
>>optimum in the 300's somewhere (if they used a variable speed drive of 
>>some type). This is not a synchronous motor and that should be inserted 
>>here. This is simply an arsg using a VFD to control the speeds, 
>>direction, torque, etc. 
>>I have noticed that if I begin going too fast, the spark lengths 
>>decrease rapidly. It doesn't take much more. It also runs more 
>>erratically at lower speeds but the spark lengths are still pretty good. 
>>There is simply a speed at which the sparks are good and the spark 
>>operation is "really" smooth. It's at that point where you can't hear 
>>the spark gap at all and all you hear are the sparks themselves. When 
>>running srsg, I could run good, but I was still stuck in one domain or 
>>another. By varying the bps to whatever I wanted, with the help of a VFD 
>>maintaining a constant speed at whatever I set it to, I could find the 
>>best possible bps, at least for this coil and gap setup. I'm sure others 
>>would have better performance at other bps ranges and I'm sure it's 
>>based on gap efficiency and coil parameters. 
>>I determined the bps not through measuring, but by calculating the bps 
>>based on the speed of the VFD reading. So, the number is based on a back 
>>calculation. If there were a great number of misfirings, I would be off 
>>by whatever margin. So, as I am big into measurements, I want to make 
>>sure that is clear. 
>>Take care, 
>>>Very interesting! Does the modeling explain this in any way? Have you 
>>>noticed any tuning that significantly affects this sweet spot? 
>>>I may have to try a variable-speed setup with my pig coil when I get it