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Re: [TCML] VTTC MOT question

Hi Chris,

Inspired by your mention of power factor correction, today I experimented with improving my power factor. It won't make the sparks any longer but it will improve the efficiency and be kinder to the circuit breaker. I tried a 100 uF capacitor and that must have been too much capacitive reactance because the resulting sparks were much weaker and "snappy" sounding. I then tried a 55 uF capacitor. That was much better and reduced the wall current from 23 amps down to 18 amps in CW mode without reducing the spark length. I will probably stick with that value because I only have room to mount one PFC capacitor in my chassis. Even if it isn't the optimum value, it does appear to improve the power factor considerably.

I moved my feedback coil all the way to the top of my primary former and I am now up to a 21" spark length. I suspect that my grid feedback voltage is still too high. I am probably going to remove another turn or two from the grid feedback coil (currently at 18 turns) and see what that does. If nothing else it should allow me to lower the grid feedback coil.

One other thing I have been wondering about. When using the interrupter, we are always after that helicopter soft "whoosh" sound which also forms the long single sword-like sparks. I can only get that type of spark at certain settings of the interrupter PRF. At many PRF settings, the sparks make a loud snapping sound with a spark quality that is a combination of sword-like and a burst of smaller sparks at the base of the spark. These sparks are not as long as the single sword sparks obtained with the whoosh sound. Does this indicate anything that should be modified? When you adjust your interrupter PRF do you get the single sword-like sparks with the whoosh (helicopter) sound?


----- Original Message -----
From: "Chris Reeland" <chrisreeland@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, March 17, 2018 11:55:58 PM
Subject: Re: [TCML] VTTC MOT question

Hi Steve,

Um, yes I did start to have problems blowing or tripping the circuit
breaker, after 3 times, had to quit and correct this. It was impossible to
fine tune further. Realized I have now run into a poor power factor problem
at the increased power level now. I will give some more details later on
what I did for this to correct this. So currently I have added about 224uF
in PF caps.  Amp draw is now at the current state of tuning, going from 10
amps to 16 amps pulsing. Much better now! Can actually do tuning changes
now no problem.

So if we can eventually find out why your coil is not drawing more amps,
you do need more to get the extra spark length, you may run into this also.
I think you said you are currently at about 15 amps, of course no power
factor correction.

I have not done anything Sat on the coil. I worked very early that day. Was
tired after and need to get other things done.
But I can now try some things tomorrow (Sunday). I hope to give some more
details and pictures.

Also want to say, sounds like the better filament transformer change with
meter and small variac is worth the effort and time. Besides no more surge
problem of course, benefit of being able to manually regulate voltage is a
big plus. I have some line voltage drop from the heavy draw of the coil
running, pulls down filament some. Most tube spec sheets want you to hold
unavoidable fluctuations to a minimum. Typically .3-.4 + or - max. Going
low is worse. You will see where to set it on the plus side so it does not
fall to low. Me when under coil running, I like to keep at +.2 for a slight
safety margin for other possible load conditions.


Sent from my LG V20

On Sat, Mar 17, 2018, 9:44 AM Steve White <steve.white1@xxxxxxxxx> wrote:

> Hi Chris,
> Wow! 23 amps at 140 volts. That is 3.2 KW. I am surprised that your 20 amp
> circuit breaker doesn't blow. I guess the slow-blow action of the breaker
> prevents this especially since you are pulsing.
> I think my next step will be to replace my home-made filament transformer
> (rewound MOT) with a commercial filament transformer, which I now have, and
> a small variac and voltmeter for filament voltage adjustment. It won't make
> my sparks any longer but it will be much more efficient. My MOT-based
> filament transformer draws about 750 watts! It gets quite warm even with a
> cooling fan. I measured the commercial filament transformer under load and
> it only draws about 120 watts and stays completely cool.
> Steve
> ----- Original Message -----
> From: "Chris Reeland" <chrisreeland@xxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Friday, March 16, 2018 3:30:07 PM
> Subject: Re: [TCML] VTTC MOT question
> Hi Steve,
> Yes, I am back to my bigger copper tube toroid again. I have said in the
> past recently that I always find myself going larger especially if pulsing.
> I tried 4 other smaller sizes working back up to this. I have several more
> going bigger, but of course they get too physically big for the size of
> this coil, and then I would run into frequency problems again, which I want
> to also say if you are considering larger, you may want to figure out if
> you are going to have a possible frequency problem of pulling it too low.
> This is why I rewound my secondary for a higher starting frequency. I have
> alot more "headroom" to try various changes.
> Yeah, having the feedback above a fairly tall primary can have some
> problems. I have mentioned this also in the past. You got lucky you caught
> is soon enough and have taken corrective action, I have seen variations of
> what you said you did to prevent this.
> Me, I have stopped a while ago of the "traditional" above the primary. I
> always put it below now. Me, I feel (and some may disagree with me, which
> is ok) that even though in theory, it is only supposed to be affected by
> the primary, it seems to be affected by the higher voltage built up on the
> secondary on the upper end, which happens when you have a taller primary.
> If a short traditional primary, it is ok above.
> At the bottom below the primary, you are of course located at the bottom of
> the secondary, which is mostly current of course, and also has the benefit
> of eliminating high voltage short arcs between the feedback and secondary.
> I would also say this is much healthier for the grid wire of the tube to
> eliminate this from happening.
> I will have more details on this later, but I "was" peaking during the
> pulses about 23+ amps at "140" 100% variac input.
> I have not yet done any changes yet last night or today yet. Kind of taking
> it easy...was tired from work. Going to mess around a bit later I think.
> I should be able to give more details and comments and pictures this
> weekend sometime.
> Chris
> Sent from my LG V20
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