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Re: [TCML] vfd spikes and high current draw


You mention that the motor is synchronous (SRSG) but it's fed by a
three-phase line. As the unit is a VFD are you varying the frequency and
trying to match the motor rpm speed to the mains frequency to get
synchronous operation that way? If so how are you varying the firing point
as the John Fraeu phase controller is based on single phase working?
On the issue itself, I would look at adding Ferrite cores on the leads, and
the VFD in a shielded box, or better still getting rid of the VFD and just
have a normal single phase motor modified to synchronous.
I blew a switched-off VFD on a lathe once when the unit was inside a shed
around 8 feet away from a 4 inch coil that had a good local RF earth running
outside. That was solely because I left the plug in (UK plugs have an earth
connection from the house earth) so I think that VFD's are always a
liability when around coils.
Depending on the bps used the current draw should be lower, as 120 or 240
bps operation should give a better PF than a static can.

Phil Tuck


-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of teslafirma
Sent: 23 July 2015 12:57
To: tesla@xxxxxxxxxx
Subject: [TCML] vfd spikes and high current draw

I have finally got my tesla coil working and now I can start to
optimize it. My biggest problem is that the 3 phase power line that 
my srsg motor picks up transients and shuts down the 3 phase driver
board. I used a shielded cable but it's still too noisy. When I measure
between the 3 legs my meter shows an uncanny 120.0 volts each. So my
plan is to multiply 120 by root 2 which is about 170, buy 6 tvs diodes
at slightly more, say 172 volts, and wire them up with a load - a small
light bulb. This way, when spikes threaten my driver board, the diodes
will vent them through the light bulb and I can see it flashing. I plan 
to do this on both sides of the wire, next to the coil and inside my 
control box. Does
that sound reasonable?

I can still run my coil without the spark gap motor by turning
the disk to orient the electrodes into firing position and running it as
a static spark gap. I put a small fan for quenching on one side and I
get 4 foot sparks from my pair of 15kv/60ma nst's. The problem there is
that I'm pulling about 31 amps and that's not sustainable. My
transformers have 200 uf of power factor correcting caps and an rf 
filter. If I
clean up the motor line enough to spin the disk I'm hoping that I'll
pull a lot less current. Any advice will be greatly appreciated!

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