Instability between a 16A triac 'dimmer' and 3300uF caps.

Linear and non linear

Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby Doug Coulter » Mon Feb 20, 2012 11:50 am

Let me hazard a definition - I have no idea what the "official" guys are using, but this makes sense with their terminology.
Let's suppose we have a circle, with some sort of absolute phase or time reference, zero at the top. We're now going to draw phase angle arrows from the center to the edge (assuming the radius represents voltage). Either half of a split phase winding will be vertical - the only difference is one is inverted and points down, the other goes straight up.
Now, imagining Jerry's wye - meaning we have a neutral, we can draw the three phases on our circle. They're 120 degrees apart. No two join up to make a straight line across the diameter. There are three distinct lines here. That's why we call it three phase. A two phase system might have two lines 90 degrees apart on the circle (or 270 if you're upside down).

Now, the reason we don't call split phase two phases is there's no phase angle not a integer multiple of pi. You can change the "other" phase into the original simply by reversing the wires. It's one single line or angle on our circle.

Note that while yes, connecting between two phases of a 3 phase (delta or wye doesn't matter here) - you don't get the same voltage as between either of those phases and neutral would give you. That's because while they aren't the same phase, they aren't in or 180 degrees (pi) out either - and this is another key distinction. In a split phase system, the voltages add or subtract just like regular arithmetic numbers. But in a 3 phase or other multiphase system they don't due to the non integral phase difference between all the legs. Thus, if each phase of a 3 phase system is 120v to neutral, I see 208v between any pair - not zero or 240v.

Sigh, I wish I could get people to read the old books more. This stuff is covered in excruciating detail in say, Terman's EE book, as it was important when trying to get the very most of out things like mercury vapor rectifiers used at lower voltages and higher currents than they really like, before there were fat semiconductors. All sorts of tricks for doing things like having the filament be at a zero crossing whilst the plate current was peaking and so on (there's your two phase), Voltage multiplying, getting 6 phase ripple out of a full wave rectifier - also very important at high powers when capacitors weren't as large and cheap as they are today....for me, it's just kind of fun to know that stuff.

I was going to work on the solar system today, but sigh - 9" or so of late season snow put a stop to that idea. At least I can reach the ones leaning on the wall to scrape them some, but that pile of snow in front has to move too - real work. I tried putting the small generator so that its exhaust would blow up behind them, we'll see if I can get some use out of its waste heat!

Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby chrismb » Mon Feb 20, 2012 1:30 pm

Doug Coulter wrote:Now, imagining Jerry's wye - meaning we have a neutral, we can draw the three phases on our circle. They're 120 degrees apart. No two join up to make a straight line across the diameter. There are three distinct lines here. That's why we call it three phase. A two phase system might have two lines 90 degrees apart on the circle (or 270 if you're upside down).


OK, so you've just run into a definition-conflict with 6 phase (60 degree) and 12 phase (30 degree) systems!

http://dl.acm.org/citation.cfm?id=1503732

..and would 4 phases, each at 90 to the cycles either side of each, not then also be a "Two Phase" system by your definition?
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby Doug Coulter » Mon Feb 20, 2012 2:06 pm

By Termans definition, yes (without reading that link, of course). Anytime you can dupe one phase by reversing wires (eg straight line across the circle) it's not really another phase. He shows how to get 6 and 12 phase ripple off 3 phase, for example, just as you can get 120hz ripple off 60 hz mains (that'd be 100 and 50 where you live) with full wave rectification. So at least in the definitions I've been taught since around 1960 (Termans from 1944) - yes, the number of phases is the number of things that don't all peak simultaneously. For example, in split phase, both wires hit the peaks (one positive, the other negative) at the same time. In true two or three phase, this isn't so. However, just like with a single phase, you can split those with a centertap and have full wave rectification of each, and increase the ripple frequency (and decrease dip amplitude, things don't drop to zero when there's more phases overlapping) your filter has to handle. For example, a full wave rectified singe - or split - phase rectifier drops to zero at the zero crossings of the input. In a two phase (90 deg) system, there's a peak on the other phase at that instant - so the output of a rectifier never goes to zero even without a filter. More phases, less unfiltered ripple of higher frequency.

The problem of course, is these days we're a couple generations into the blind leading the blind, specs and salesmanship rule - and the paper WILL still take ink if it's dead wrong or let's say "highly optimistically spun".

In other words, just because I read the other day where a new type of plasma based transistor had been invented (on one of those science press release hype sites, physorg), didn't make it disappear from the Phillips tube book we've had online here since the beginning, that was published in ~1950...going in circles! I guess we just wait for the inventor to die, and we can claim we invented it again, patents notwithstanding.
Phillips wanted to use this as the output tube in car radios - low voltage, high current, but they were on the flakey side due to sputtering - and transistors were only a couple years out at that point.

Of course it's not that bad - it's worse, because I'm sure they really think they did invent it. We've lost that advantage humans had over the animals or are losing it - the ability (willingness?) to pass knowledge down so later generations don't have to find it again.

It's probably a losing battle....
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby chrismb » Mon Feb 20, 2012 2:27 pm

Well, we're not debating any physics here [I believe], just terminologies. As long as it doesn't lead to a misunderstanding, it's the physics that counts rather than what someone has chosen to call it. If you have 6 phase lines each at 60 deg phase generated by a generator with 6 windings instead of 3, and you want to call that 'super 3 phase', or whatever, I don't believe it matters a hoot.
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby Doug Coulter » Tue Feb 21, 2012 5:58 am

Yep, not worth the hassle I suppose. FWIW, a +/- 15v supply is also called a split supply, even though DC. But of course, in a finite duration universe, DC doesn't actually exist - just some really low frequencies. :D
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby Jerry » Wed Feb 22, 2012 7:00 am

Doug Coulter wrote:
Sigh, I wish I could get people to read the old books more. This stuff is covered in excruciating detail in say, Terman's EE book, as it was important when trying to get the very most of out things like mercury vapor rectifiers used at lower voltages and higher currents than they really like, before there were fat semiconductors. All sorts of tricks for doing things like having the filament be at a zero crossing whilst the plate current was peaking and so on (there's your two phase), Voltage multiplying, getting 6 phase ripple out of a full wave rectifier - also very important at high powers when capacitors weren't as large and cheap as they are today....for me, it's just kind of fun to know that stuff.



You should check out the patents for the solid state drives that were installed in Monarch lathes like the one I have. Mine was one of the last Ward-Leonard motor-generator drives before they switched to the WIAD design C.E. Greene came up with in this patent:

http://www.google.com/patents?id=bg5cAA ... &q&f=false

Video of the tubes glowing in the WIAD drive, the big tubes being a pair if C16Js, can't remember what the little thyratron in the middle is.



The drive was updated to the Module version below:

http://www.flickr.com/photos/signalcycles/5740748045/

This version of the drive stayed in production until 82/83 when it was replaced with a fully solid state drive. But the new drive required true three phase where the old thyratron based drive ran off of single phase.

An even bigger version of the drive was built for my lathe's big brother, the 1000EE.

http://www.google.com/patents?id=F7tkAA ... 47&f=false
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Re: Instability between a 16A triac 'dimmer' and 3300uF caps

Postby johnf » Thu Feb 23, 2012 1:47 pm

In all of this you have to go to the flash of brilliance that was Nicoa Tesla
In one synaps he theorised the polyphase system with its inherrent rotating magnetic vector decided on 60Hz as a good compromise against motor / alternator speed and eddy current losses in stator and armature iron
The way I see this is all in the word "Phase"
single phase motors will not start without a second winding that is either mechanically phase shifted or electrically phase shifted (capacitor)
whereas the 3 phase motor is one of mans simplest machines -of incredible importance during the 20th century
PS
all even phase systems have a problem where there are rotor positions that will not let the motor start
and now we have BLDC motors where the use of solid state drive electronics allows true variable speed and yes these are wound with varying number of phases {nearly always an odd number}
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