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I've been thinking for several days now about running the gap motor and
the transformer from the same vfd. I could vary the frequency from 30hz
to 500hz and get quite a range of effects from the output. Maybe go even
lower with a circuit that drops in between peaks or makes single pulses.
Here's the problem I have with that:
I'm trying to find a voltage transformer that I can set to pull about 14
amps at 110volts. I'll feed that through a big heavy line cord. My spark
gap motor and any other circuitry will pull about 5 or 6 amps and come
through a lighter cable from a second circuit. This way I can get the
most spark from 110v just about anywhere I travel to putting on shows.
If I run both the transformer and spark gap through the same vfd then
I'm pulling 21 amps and that will pop most home circuit breakers. But
this is something I'm determined to try once I get my conventional srsg
design up and running.
On 14-04-23 11:25 AM, Bert Hickman wrote:
> A VFD makes most sense if you use a DC resonant charging system. A
> properly designed DC resonant design will allow you to smoothly vary
> output voltage and power without the need for any phase-syncing, since
> the tank cap is always recharged between firings at any firing rate.
> This approach works especially well for high power systems using 3-phase
> gap motors.
>
> However, A VFD can be used to make an asynchronous variable speed gap.
> Using a VFD in your existing system would work in a fashion similar to
> driving a DC motor from a variable DC supply. You WILL lose the
> capability of truly syncing and properly phasing your motor to the line.
> Also, some speeds near multiples of line frequency have the potential to
> overvolt your tank cap or HV transformer, so make sure you have a safety
> gap bridging your rotary gap or a Terry filter.
>
> I like Jim's idea of driving your HV transformer from the same VFD and
> using a true synchronous motor would permit you to sync the gap to the
> line. I'm not sure just how well the VFD, HV transformer, and motor will
> all play together, and I don't recall any coilers using this technique
> before. If you try this method, you'll probably need to use a fixed
> mechanical phase adjustment on your gap since the Freau controller's
> phase relationship will change with operating frequency.
>
> Bert
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