Hello Dan,
I am a little confused about your setup. Are you saying that you are blowing a 30 amp fuse in the variac that is supplying your NSTs? Or are you referring to a 30 amp fuse in your SRSG phase control variac? Does this problem occur if you have the phase control circuitry by-passed? Have you confirmed that the phase controller does indeed change the phase? You also shouldn't engage the phase controller until the motor is up to speed from what I have read. If you use the phase controller from stall, the motor can spin up very slowly drawing an excessive amount of current. To prevent these potential problems on my phase controller, I use a relay and switch to allow the motor to spin up before engaging the phase control circuitry. I also have a relay that disconnects the phase control circuitry when I switch off the motor. This is to prevent excessive braking of the motor which some have reported.
I have a very similar SRSG setup as yours (11" G10 rotor, 1/2 HP motor) except mine uses 4 flying electrodes (240 bps). I do know that my SRSG motor will draw about 40 amps during spinup which takes 3 or 4 seconds, and it will then settle to about 8 amps which is the same as yours. This is even without the phase control circuitry. This is not unusual for an induction motor startup. My SRSG motor is powered from one leg of the 240 volt power. Did you test the phase controller independently and insure that the voltage does not exceed about 130 volts into the motor? If it does exceed that, then you need to adjust the capacitance. I don't use fuses on my variacs, I use slow-blow circuit breakers. My SRSG phase controller also has voltage and current meters for the motor input so that I can constantly monitor those parameters.
Since NSTs are inherently current limited, you should not be blowing a 30 amp fuse if I am understanding you correctly even if the secondary terminals were tied together into a short circuit. A 15 KV, 60 ma NST should only draw about 900 watts of power which would translate to a maximum current of 7.5 amps. So that would only be about 15 amps for both NSTs. Maybe one of your NSTs has developed an internal short. If you know what the primary resistance should be, try checking it with an ohm meter.
Make things even more basic. Connect one NST at a time and see if you can draw an arc between the secondary terminals with 120 volts input. You should be able to do this without blowing any fuses. If you are still blowing fuses with this simple test then there is something wrong with your NSTs.
In answer to a previous comment, 1/2 HP is not overkill for a G10 rotor of this size. I use the same thing and it seems just about right. Plus, the power is slightly reduced due to the synchronous operation.
Steve White
Cedar Rapids, Iowa
----- Original Message -----
From: "Daniel Kunkel" <dankunkel@xxxxxxxxx>
To: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Monday, November 19, 2018 8:21:58 AM
Subject: Re: [TCML] Adventures in SRSG
Hello "Liberty Rising",
I have 240vac in my garage. I specifically run the motor and transformers
on different hot legs of the supply transformer.
The disc is 12" G10 with tungsten electrodes and is HEAVY. The motor draws
around 8.5 amps when running.
I normally run it on 120vac, but the fuse pops at 90-100 volts as I slowly
increase the voltage.
The interesting this is. I also tried removing half the NST, and even a
single 15/60 NST will draw the same current and pop fuses at the same input
voltage.
I also failed to mention another interesting clue, in testing my Terry
Filter overheated...the ceramic resistors and MOV's got HOT and I believed
the MOV's are fried. I wonder if 120 BPS is not enough and there are
voltage reversals happening. Perhaps I should add more electrodes to get
240 BPS?
Thanks,
~Dan
Kansas City area
On Mon, Nov 19, 2018 at 7:53 AM Liberty Rising <garretsontech@xxxxxxxxx>
wrote:
> Run the motor on a different circuit. 1/2 horse is kind of overkill to spin
> a little disk. I think my SRSG is only 1/8 hp.
> Also, at what variac setting does it blow the fuse / breaker?
>
> On Sun, Nov 18, 2018 at 9:54 PM Daniel Kunkel <dankunkel@xxxxxxxxx> wrote:
>
> > I finally got my SRSG online tonight. To my dismay I started blowing 30
> amp
> > fuses in my supply variac. I am hoping the list can help me figure out
> why
> > this is happening...we have guests coming over for Thanksgiving and they
> > are expecting a show!!! LOL
> >
> > When I was running the previous setup using a vacuum quenched single gap,
> > my NST bank (15kv @ 120ma) was only pulling 10 amps using a total of 302
> uF
> > in PFC caps. I was expecting similar performance with the rotary gap.
> >
> > Basic specs are:
> > 6.5 x 26.5" secondary with 1,057 turns or 22 awg
> > .033uF MMC
> > 1.8 kva NST's
> > Terry Filter
> > 1/2 HP, 3,600 RPM motor
> > 2 flying electrodes (1/8" tungsten, through disc design), for 120 BPS
> >
> > Thanks for any insight,
> > ~Dan
> > Kansas City area
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