Steve,
Q: Are you saying that you are blowing a 30 amp fuse in the variac that is
supplying your NSTs?
A: Yes, the fused variac is connected to the NSTs. The srsg motor is
plugged directly into the wall, no phase controller has been built yet. I
am phasing by hand for now.
Q: 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.
A: Yes, I have noted the same startup and run current draw as you.
Q: I don't use fuses on my variacs.
A: The AGC glass fuse is built in on my unit. Unless I bypass it with a
solid bus, removing it is not an option.
I do plan to do more testing with different NST configs and different PFC
caps as well. I am also going to remove some uF from the tank cap and
increase to 240 bps.
Thanks,
~Dan
On Mon, Nov 19, 2018 at 11:33 AM Steve White <steve.white1@xxxxxxxxx> wrote:
> 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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