understanding how transformers ratings work

[pompeiisneaks]

I've been often confused about this, I swear I've read about this before and can't find anything now.  There are several terms that are used that confuse me. 

Some transformers are rated like 6.3 - 0 - 6.3
others say 6.3 V
other say 3.8 VA (volt amps right?)  (this is a triad one with just 6.3 V @0.6 amps so I guess taht's the VA? see below)

I think I get what the first means, it means it is AC varying from - 6.3 to 0 to positive 6.3  and that 0 means center tapped?  so technically it's a 12v sweep.  If you want 6.3 volts you'd connect the 0 (CT) to one side and the other two together to the other end and get 6.3 V.  On the other hand, if you wanted 12.6 V you'd connect the 6.3 each to the ends and ground the 0 or not connect it,

Are these different from one listed simply as 6.3?   does that mean it's more technically 3.15 - 0 - 3.15 with no real 0/Center Tap?

And are Volt Amps a wattage rating?  volts X amps = watts right?

~Phil

[sluckey]

If you want 6.3 volts you'd connect the 0 (CT) to one side and the other two together to the other end and get 6.3 V.

No! You cannot connect the two ends together because they are out of phase. This would put a short across the two 6.3v windings and quickly melt the transformer.

Are these different from one listed simply as 6.3?   does that mean it's more technically 3.15 - 0 - 3.15 with no real 0/Center Tap?

A bit of clarification... Your 6.3-0-6.3 is the same as a 12.6 w/CT. A 3.15-0-3.15 is the same as 6.3 w/CT. A 6.3 is just two wires with no center tap and there will be 6.3v across the two wires.

And are Volt Amps a wattage rating?  volts X amps = watts right?

Yes to both questions.

[HotBluePlates]

... 6.3 - 0 - 6.3
...  If you want 6.3 volts you'd connect the 0 (CT) to one side and the other two together to the other end and get 6.3 V.  ...

You just use center-tap to one end (from 0 to 6.3v), and not use the other end.

And are Volt Amps a wattage rating?  volts X amps = watts right?

No, but yes.  Volt-Ampere

Watt is "Real Power" and sometimes implies direct current where volts & amperes are same-phase.

Volt-Ampere Reactive is the part of AC power stored in the reactances of a transmission system, where volts and amperes are not in-phase.  Also called "Reactive Power".

Using vector algebra, real power is on the X-axis, reactive power is on the Y-axis, and the vector sum of the two is "Apparent Power", has a magnitude (greater than either real or reactive power on their own) & also a direction (or phase angle).

Volt-Ampere is Volts RMS times Amperes RMS, and is also called "Apparent Power".  We might mentally cheat and treat VA same-as Watts, but they are not because of volts & amperes being out of phase.

Power Factor is (in simple terms) a measure of how far out-of-phase voltage and current are, as it is the ratio of real power to apparent power.  In a d.c. circuit, there is no phase difference between volts & amps, so apparent power is the same magnitude & direction as real power, and the circuit has a power factor of 1.

[pompeiisneaks]

excellent info from both of you as usual, thanks, that makes perfect sense now, I was like "THIS" close to getting it on my own but just wanted to be sure I understood.  Sluckey, especially that part about the out of phase, makes perfect sense now. 

Cheers.

~Phil

[kagliostro]

Sometime an image can be of some help to understand and reassume a verbal explanation





Franco

[pompeiisneaks]

Ahh so VA is a measure of the Watts AND what's lost to say heat in the laminations etc?  Cool. Thanks!

~Phil

[Steve_P]

Newb question. What does the part you lose in the men's room represent?

Sometime an image can be of some help to understand and reassume a verbal explanation





Franco

[kagliostro]

The usable .... used 


Franco

[pompeiisneaks]

That's the return on the beer lease dontchaknow.

~Phil

[pompeiisneaks]

Or if you meant literally from this graph in electronics terms, my statement "I think" explains it, losses to heat in the wires/laminations.  If you push a PT hard, you can feel it, but even if it's not being pushed hard, it still loses some power to heat, nothing is a perfect conductor.  (unless you get near absolute zero I gather?)

[HotBluePlates]

Newb question. What does the part you lose in the men's room represent?

Dissipation (waste heat), because you already got the buzz (action in the load) from that part of the beer.

The part the bartender pours off into the grate/drain is "heater power".  Ya gotta do it to get the beer in the mug (warm the tubes to get them to function), but neither your brain nor your bladder (useful electrical circuits) will ever see that beer/foam that got poured off...

[PRR]

If we were to get real pissy....

Water sloshes from Bud to you to the piss-pot and ultimately back to Bud (hopefully through the full drain dilution evaporation rain filtering cycle) and the same molecules come back to you again. That's Reactive Energy.

You keep the 5% alcohol, and you should pay for that, not the 95% water. But obviously it costs real money to move the water from St Louis to you and back, so you do pay for that in beer-money, and also for "large" electric power bills.

For a better Power Factor, design your drunk for sherry, whiskey, or EverClear. More kick, less water-slosh.

[kagliostro]

For a better Power Factor, design your drunk for sherry, whiskey, or EverClear. More kick, less water-slosh.

 

[drgonzonm]

Why ruin a picture of a  mug of beer to explain VA, Beer's for drinking.

We are talking about guitar amps, running power tubes in Class AB, all heat generators.    Go to RDH 3 or 4, find some Norman Crowhearst read some technical stuff, drink a beer.  Take out an amp, a guitar and enjoy yourself.