Re: Terry filter + isolation transformer

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

The filter is really only meant for NSTs.  The filter was never meant 
for any other type of transformer.  I am not familiar with the type 
of transformer you are using.  If it is like a potential transformer, 
it should not need any filtering at all since they are so over-designed anyway.

Cheers,

        Terry


At 11:02 AM 1/7/2006, you wrote:
> Hello coilers, espacially Terry!
>
> Terry's filter is designed to operate with the center winding of an 
> NST tied to RF-ground which is where the center tap should be tied 
> to when using a transformer designed for midpoint-grounded use 
> anyway. But what if the transformer is not an NST but a true 
> isolation transformer? In this case the whole tank circuit can be 
> operated in floating-ground condition which is good for several 
> reasons: You can do measurements of the voltage across any part of 
> the circuit by grounding any point you want and measure the voltage 
> which appears on another point of the circuit. Strikes will not hit 
> the tank circuit since it will not pass current to the ground. The 
> experimenter has a better chance of not being electrocuted by 
> accidently touching a part of the circuit while having low 
> resistance to ground. Possibly there are many other advantages. But 
> how to use Terry's protection circuit in such a floating-ground circuit?
>
> Possible configurations I see:
>
> 1. Just connect the two connections from the transformer's secondary 
> to the "Hot1" and "Hot2" wires on the schematic while leaving the 
> "NST ground" and "RF ground" connection unconnected? That way the RF 
> will still flow through the MOVs/Caps and "cancel itself out" which 
> is what we want. However, "symmetric" interference occuring at both 
> wires will be ignored but it seems like this shouldn't do any harm 
> anyway since it will not cause current to flow through the 
> transformer's secondary. Also the floating-ground condition is preserved.
>
> 2. Connect "Hot1" and "Hot2" to the transformer's secondary and "RF 
> Ground" to RF ground but leave "NST Ground" unconnected? Doesn't 
> seem to make any sense to me since the "Hot" wires aren't in any way 
> related to RF ground during normal operation. Looks like it will 
> just make the isolation transformer effectless since the voltage 
> gets some reference to ground.
>
> 3. Connect one end of the transformer's secondary to RF ground, 
> double the number of MOVs/Caps/Resistors in series in the filter and 
> connect the other end of the transformer's secondary to the 
> connection "Hot1" of the filter while dropping all the parts below 
> the ground wire on the schematic. Sounds very implementable. It's 
> just that grounding the secondary of the isolation transformer kills 
> all of the advantages mentioned above. ;)
>
> So the most logical configuration seems to be the first one. Anyone 
> seeing problems with that configuration or wanting to suggest 
> another one? This question is especially for Terry since I'm sure he 
> will know best how his own filter design works, what it's intended 
> for and what it's not intended for.
>
> Regards, Q.