Re: Big Terry Filter Limits?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Matt,

If you run 15kV NSTs at 140 VAC, you may want to add another MOV to each leg. 
Once in awhile the MOV tolerance is on the low side and running the NSTs at
140VAC can start to turn them on.

You may want to push the filter caps up to 1nF on each leg.

The resistor temperature is the main concern.  At 300mA, they dissipate 90
watts which will get them up near their rated toasty 300C operating
temperature.  Simply use the larger 225/250 watt resistors instead.

I rated the resistors to 1/2 their real power so they would not get alarmingly
hot even though the resistors like that.  Several people were concerned about
how hot filter resistors were getting so I only run them at 1/2 power.

So (thinking out load), if you go to 16 MOVs, 1nF per leg, and 250 watt
resistors (still 1k ohm) you should get:

1/2 x 1e-9/2 x 21000^2 x 120 = 13.23 watts dissipated from discharging the
filter caps.

Using 1/2 power:

125 - 13 = 112 watts for the current:

1000 * I^2 = 112   so I = 335mA.

So the filter with these changes would be fine to 335mA.  If you like the
resistors to almost start to glow, you "could" run up to 450mA.

The NSTs should be individually fused and the safety gap will need to be beefy
too.  Note with many NSTs in parallel, if one blows, the others will gang up on
it and really toast it.

Cheers,

        Terry


At 02:00 PM 1/22/2002 -0500, you wrote: 
>
> Hi All,
> A question to the "pro-philter phreaques":
>          My "Big Terry Filter" , built according to specs, works fine at
> 15/60, 15/120, and 15/180. But now that I'm looking at going to 15/240 &
> 15/300  I really don't want to find its limit by the trial and Oh S***!
> method. What modifications to the filter would be recommended?
>
> Matt D.