Yes, a 3600 rpm motor can definitely work with 4 flats. It might produce
less power and run hotter through. Of course 2 flats is correct
as you said.
John
-----Original Message-----
From: pip <pip@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Fri, Mar 30, 2018 8:57 am
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
Steve, you are missing nothing, 3000rpm (3600 on 60Hz) only needs 2
flats. It may well work with 4 flats but unsure what you would end up
with when twiddling the phase control.
Someone mentioned unbalance: Machining 4 flats is much more likely to
result in unbalance, not so much because there's more 'flats' to
machine, but getting the flats at exactly at 90 degrees to one another.
Really needs a mill for 4 - and obviously preferable for 2.
Phil Tuck
Steve wrote:
Steve you said in your initial post that your SRSG motor was 3600 rpm.
In
your last post you said the motor armature had four flats machined into
it.
I understand that a 3600 rpm motor has only two poles so I would expect
the
rotor to have only two flats.
What am I missing.
Teddy
On 29.03.2018 20:02, Terry Oxandale wrote:
Sounds like Teddy is using a two-&-two configuration, rather than a four-in-one, so I suppose that helps. I also run a two-&-two arrangement (two in parallel for voltage control, and two in parallel for current control) with no balancing choke, with no issues.
Terry
From: Steve White <steve.white1@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Thursday, March 29, 2018 12:02 PM
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
Hi Teddy,
Keeping 4 variacs in balance must be a challenge. Did you use a current-balancing transformer for each pair? They are used to balance the current between transformer pairs to prevent one from overloading the other. If you don't know what that is, look in the Superior Electric catalog. You can make one yourself with a large toroidal core. I originally planned on using two of the General Radio W50 variacs (240 volt, 25 amp) on a common shaft with a current-balancing transformer. I went so far as to make the transformer but I never used it. I decided that a single GR W50 variac would supply all of my power control needs without the complication, size, and weight of 2 large variacs.
I measured the phase shift with the motor running with the load of the rotating disk and electrodes. I used an optical sensor and oscilloscope to measure the phase shift. The phase shift is real. I don't remember what my maximum phase shift was but it was close to 90 degrees. My phase shifter uses a large (20 amps at 120 volts) Superior Electric variac. I can't remember how much capacitance I used. I want to say that it is about 200 uF. I know that I used 4 motor "run" capacitors which I think were about 50 uF each. I kept adding and removing capacitors until I got the maximum RMS voltage into the motor below 130 volts. My motor is a modified 1/2 HP induction motor with 4 flat spots machined into the armature. One thing that I do remember is that when I looked at the power coming out of the phase shifter at the motor input, the waveform was far from sinusoidal with a lot of distortion. This doesn't seem to affect the motor. I even see the distortion without the phase shifte
r.
So that is a mystery.
When you make your SRSG the most important thing is to get that rotating mass VERY accurately balanced especially if you are running at 3600 RPM. The electrode mounting holes must be VERY accurately located and drilled. Any mounting hardware for the flying electrodes must have identical weight for each electrode. The rotor must be perfectly round or as close as you can get it. If not, the whole thing will shake itself to pieces. I now have a lathe and milling machine which I did not have when I made the SRSG. These would have made the job a lot easier but I came up with some creative ways to do this without those machines. I found that building the SRSG was the most difficult part of building the tesla coil because it requires a lot of mechanical precision.
Steve
----- Original Message -----
From: "Tedd Dillard" <tedd.dillard@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Thursday, March 29, 2018 9:42:47 AM
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
Steve thank you for your quick response.
It sounds like we are going down the same road except that you are farther
along than I am and know more about what you are doing.
My transformer is a 10 kva pole transformer, 14.4 kv/ 240v.
I too made a current limiting ballast like Richie's, I used three golf cart
battery charger I E cores with an adjustable air gap.
I have four identical 120 volt 20 amp variacs mounted on a common shaft.
Two in parallel feed one side of the transformer and two in parallel feed
the other side thru the ballast.
I am not done with building the controller but with the high side shorted
on the transformer I have so far adjusted the ballast for 32 amps and I can
put as much as 298 volts on the transformer.
I still have the rest to build and am most concerned with the tank
capacitor. I really want to build a flat plate capacitor but am seeing a
lot of negative feed back on them.
I am also planning on building a SRSG so am very interested in your issue.
I went back and read your first post.
You see no visually apparent effect in spark length from phase shift.
You have verified that you do get effective phase shift, I am assuming that
was done under no load conditions.
The fact that you see no apparent change does not mean there is none.
But I have trouble understanding how you could be changing the phase as
much as you say and that it would have no apparent effect.
There is no change in sound?
I would question if the phase is really changing under load.
And if it is actually changing and having no apparent effect it would
suggest that the thing that should be affected by the change is not
responding for some reason.
That is why I suggest the caps being too small and since they are already
fully charged with even the worst case phase setting there is no gain by
varying it.
I am of course not educated very well on the resonance issue but the
explanations given explain why no improvement with phase shift may occur it
seems likely that there would be some change.
Teddy
On Thu, Mar 29, 2018 at 12:07 AM, Steve White <steve.white1@xxxxxxxxx>
wrote:
Hi Teddy,
For my pole transformer (10 KVA rating) powered system I made the decision
to limit the input power to 4.8 KVA wall power. This is done through the
use of an adjustable air gap ballast that I made which is very similar to
the one that can be seen on Richie Burnett's web site. I can very easily
increase that power up to about 10 KVA by increasing the air gap spacing. I
picked the 4.8 KVA power level because it can almost fully charge my
capacitors: 45 nF charged to 88% at 240 BPS according to JAVATC.
As you may know, pole transformers are not current-limited, so a means
must be provided to limit the current, hence the ballast. The other reason
that I chose this power level is not to push things too hard. When I built
my SRSG (this was my first RSG) I only used 0.125 inch tungsten on the
flying electrodes. Although this seems small, they seem perfectly happy
with the cooling they get at 3600 RPM and I see no noticeable erosion. The
stationary electrodes, which are 0.1563 inches, actually erode more because
the cooling isn't as good and they are fired 4 times as often. If I were to
build this SRSG again I would use larger diameter tungsten electrodes. So I
am not certain how well the SRSG would work with these electrode sizes
above power levels of 5 KVA. The limiting factor in my power cabinet is the
variac. It is a large 240 volt General Radio unit rated at 25 amps but can
be pushed higher for short periods. So my ultimate power limit with this
variac is probably around 7.
2 KVA, assuming 30 amps through the variac. I am perfectly satisfied, for
now, with my 8-foot sparks.
In answer to your question, the capacitance can be made bigger if I allow
more power. I have enough extra Maxwell capacitors to go to 60 nF if I
want. But this would require a power level beyond my current setting of 4.8
KVA to take full advantage of that extra capacitance. For the reasons
mentioned earlier, I don't want to do that right now but I might in the
future if I start to get "spark envy".
Believe it or not this was my first tesla coil. I believe in starting big
if you know what you are doing.
Steve
----- Original Message -----
From: "Tedd Dillard" <tedd.dillard@xxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, March 28, 2018 6:40:24 PM
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
Gentlemen,
I am a newbie just starting my first coil and everything I know comes from
the last several months of reading. The TCML is especially helpful.
Reading Richie's paper on SRSGs and resonate charging it seems that the
main point is to fully charge the caps.
If the simulation says you are getting 88% and that is not changing with
phase shift doesn't that suggest the caps are not big enough?
Teddy
On Mar 28, 2018 6:27 PM, "phil" <pip@xxxxxxxxxxx> wrote:
Steve
As your running the 60Hz equivalent of my own coil setup in the UK (200bps @ 50Hz), you should, when correctly in phase, have four firing peaks of
equal voltage. This gives a very distinct, characteristic sound or 'drone' to the coil, and is what I use to find and set the correct position. (only works on 200bps , and to a lesser extent on 400bps, 100bps always having a 'rasp' sound to it regardless, and 300bps always sounding 'ragged')
Listen to when my coil (deliberately started out of phase) is put onto
phase at 55 seconds in (link starts at 45 seconds):
https://youtu.be/yRBqDZCP0jc?t=45 Also the same later on where I put it out of phase to make it hit the floor more: https://youtu.be/yRBqDZCP0jc?t =234 (it happens at 4:05)
You should be hearing a difference on yours though, if all is correct. You will get some voltage reversal though, as the firing point when all the
caps voltage peaks are equal is after the sine wave peak.
As John says if you tune it enough off phase you can get a 'pseudo' 100bps setup, but having two high peaks and two low ones per 60 Hz cycle. This may over volt the caps though, so I wouldn't recommend it.
I would check with a strobe that you are getting the full 90 degrees shift you need, if not you could find the area you want is just out of reach.
Bear in mind though (or you may have already found out) that getting the
full 90 degree shift is achievable only at the cost of having a higher than comfortable voltage (from the motor's point of view) being fed to it.
On a 240v UK set up I've measured as much as 270+ volts being fed to the
motor with the wrong cap values in place, so that's a good way to kill a
motor if you're not careful.
(Once you do find the sweet spot it's best to move the disc on the motor's shaft so that the best position is midway in the sweep of the phase
controller.)
Phil Tuck
On 27/03/18 04:52, Steve White wrote:
I have had my big SGTC running for about 9 months now. Here are the
salient specs:
* 8.6" x 39" secondary
* 9" x 30" top load
* 45 nF of primary circuit capacitance
* RSG with 4 rotating electrodes and 2 stationary electrodes, 3600 RPM,
240 breaks per second (4 per 60 Hz cycle at 0, 90, 180, and 270 degrees)
* Pole pig as power source
* 4800 watt wall power
* Maximum spark length is about 8 feet
I also built an electrical phase shifter, as others have, based on a
variac and capacitors. I confirmed with my oscilloscope and an optical
sensor that I can get about 0 to 90 degrees of phase shift by turning
the
variac knob. Before I added the phase shifter, I used an optical sensor
and
oscilloscope to accurately set the firing points at 0, 90, 180, and 270
degrees of each 60 Hz cycle.
My question concerns the apparent non-effect of the phase shifter on
spark length. With the coil running, as I adjust the phase shift, I see
no
apparent change in the spark length. Does anyone have any thoughts as to
why this would be? I am perfectly satisfied with the coil's
performance, I
just can't explain the apparent non-effect of the phase shifter.
Steve
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