Re: Instability between a 16A triac 'dimmer' and 3300uF caps
Posted: Mon Feb 20, 2012 10:50 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!
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!