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Re: 180 BPS synch? (fwd)
---------- Forwarded message ----------
Date: Thu, 19 Jul 2007 00:31:15 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: 180 BPS synch? (fwd)
Hi David,
The 1/16" gap between each stationary gap is about the norm I think.
That's about where my gap is also. Your electrodes are larger than my
own and can handle more power. I'm not a machinist either, but I did
have a machinist do the work (and it only cost me a case of Sierra
Nevada!). You hinted that at higher power, brighter sparks. I can't
really see that as I can't get the power high enough I guess. I've run
my ballast to the point of smoking it, but after that (and a good
cleaning), I decided to keep the power down to 7kva until I get a decent
variac stack. I don't have my large coil any longer so I'm just running
an 8.5" diameter coil with it (and kind of a high turn coil at 1789
turns). Works ok, but nothing like my old 13" diameter coil did.
Take care,
Bart
Tesla list wrote:
>---------- Forwarded message ----------
>Date: Thu, 19 Jul 2007 14:52:18 +0000
>From: David Rieben <drieben@xxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Cc: drieben@xxxxxxxxxxx
>Subject: Re: 180 BPS synch? (fwd)
>
>Hi Bart,
>
>My RSG setup is very similar to yours except that my stationary
>electrodes are 1/2" x 3" long tungsten mounted in brass blocks. I
>believe my rotary disc is actually 11 1/2" OD with about 10 1/2"
>flying electrode centers. My design is pretty much homemade and
>I am NOT a machinist, so I probably can't get my flying electrodes
>as close to the stationaries at each presentation as you can without
>an occasional "tap" - I have to keep appr. 1/16" gap spacing to in-
>sure no electrode tapping throughout the motor's rpm range. Still, I
>don't see ~ 1/8" total gap spacing at each presentation as problematic
>for 14.4 kV. My ballasting allows me up to ~ 20 kVA if my coil can
>stand it ;^) but it seems that after a certain point, the streamers just
>get brighter but not that much longer.
>
>Keep 'em sparking,
>David Rieben
>
>-------------- Original message --------------
>From: "Tesla list" <tesla@xxxxxxxxxx>
>
>
>
>>---------- Forwarded message ----------
>>Date: Wed, 18 Jul 2007 23:07:15 -0700
>>From: Barton B. Anderson
>>To: Tesla list
>>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,
>>Bart
>>
>>
>>
>>Tesla list wrote:
>>
>>
>>
>>>---------- Forwarded message ----------
>>>Date: Thu, 19 Jul 2007 03:06:19 +0000
>>>From: David Rieben
>>>To: Tesla list
>>>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"
>>>
>>>
>>>
>>>
>>>
>>>>---------- 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,
>>>>Bart
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>>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
>>>>>running!
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
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