Another quick transformer question

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Hiwatt25

So, what do those little dots on the transformer wiring diagram represent? I'm guessing that the have some significance if someone went to the trouble of putting them there. Are they of any concern? I've included a picture below. Some of you will recognize the picture from another thread of mine but hey, it serves to illustrate said "dots"

An externally hosted image should be here but it was not working when we last tested it.

lanchile07

as you can see on the side it says "0" volts.I bet it is the "cold"

hermanv

They are phase dots. If the power fed to the primary side with a dot swings positive all the secondaries ends with dots will also swing positive.

In a practical sense they allow you to connect two secondaries in series so the voltages will sum (hook a dot end to another windings non dot end).

BudP

Hiwatt25,

The dots are absolute physical polarity. Those are the physical starts of the winding. Those leads with dots will be out of electrical phase polarity by 180 degrees, from primary to secondary windings, or the markings do not comply with international electrical standards. This will not change how you use the transformer in any way, just alerts you to the electrical out of phase hook up, across the transformer core barrier.
hermanv is otherwise exactly correct.

Bud

hermanv

BudP said:
Hiwatt25,

The dots are absolute physical polarity. Those are the physical starts of the winding. Those leads with dots will be out of electrical phase polarity by 180 degrees, from primary to secondary windings, or the markings do not comply with international electrical standards. This will not change how you use the transformer in any way, just alerts you to the electrical out of phase hook up, across the transformer core barrier.
hermanv is otherwise exactly correct.

Bud
Now I'm confused. The dots are the start of a winding unless it's a primary winding? If you make the simplest transformer, one primary and one secondary, when the primary start of winding swings positive, so will the secondary start of winding. Assuming both are wound clockwise or counter-clockwise. You seem to say that to conform to international standards the secondary must be wound in the opposite direction from the primary. In the image below the voltage difference between V1 and V2 is essentially zero

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• xformerphase.jpg
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BudP

If you make the simplest transformer, one primary and one secondary, when the primary start of winding swings positive, so will the secondary start of winding.

The dot's are supposed to show the physical start of the winding, turn # one.

Between primary and secondary, the electrical phase, meaning positive going wave form, is 180 degrees out of phase, even though the windings are physically in phase.

This is also true of output transformers etc. For power, phase connections are not always important and I mentioned this just to confuse you..... actually just so you would put that small bit of info into the back brain portion and always think of transformers as *** backwards devices.

Having said all of that, it is a good idea to check for electrical polarity if it is important in the circuit. This because not everyone uses those dots to denote physical winding start and instead use them to show the more intuitive, electrical phase, of positive going wave forms.

Bud

AndrewT

use a mains light bulb tester for first power up.
If you have wired either the dual primaries or the dual secondaries out of phase the light bulb will protect the transformer and save blowing yet another fuse.

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