Transformer color code, euro or jap?

[Satamax]

Hi everybody!

Well, most of the guys here don't even know me by now!

I have this transformer that i would like to test. Two primaries, one is 4.6Ω and is has a brown and a yellow wire, the other one, measuring 4.9Ω is white and red. The idiotic question is, obviously i must put thoses two in series for 240vac wall voltage. But which wires do i connect together? Or it doesn't mater and i have no risk of bucking whichever way i link thoses two windings in series?

Thanks a lot.

Max.

[J M Fahey]

Assuming you have two equal 110 (or 115 or 120)V primaries.
Very short and stupid test: put them in series in one way (flip a coin), and connect free ends, one of them through a 40 to 60W lamp, to a 220/240V wall socket.
If lamp shines brightly you are wrong, unplug from the wall, invert *one* pair of cables and retest.
If lamp only shines dull red/orange or none at all, you are set.
BE CAREFUL, YOU ARE WORKING WITH LIVE MAINS.

[Satamax]

Hi JM, thanks for the reply.

Well, i understand how it could glow dimly, but i should admit i don't understand how it could glow bright

Assuming i have à lightbulb's filament of about 4.75Ω i can work out what voltages i would have at the two midpoints, using the voltage divider rule. But that's about where my understanding ends!

[J M Fahey]

Easy.
What's limiting current there is not DC resistance (9 ohms) but coil inductance.
If they are in series and in phase they add up to a high value, very little current passes , hence dim lamp glow.
A 60W 220V lamp passes 60/220=0.27 A (270mA) on full power, weak red/orange glow means it's passing, say, less than 100mA (0.1A).
*If* you connect windings out of phase, inductances cancel, and the around 9 ohms DC resistance will let it pass catastrophic 220/9=24.5A, burning it in seconds.
That is prevented by the couragous little lamp, which limits current to said 0.27A .

[Satamax]

Easy.
What's limiting current there is not DC resistance (9 ohms) but coil inductance.
If they are in series and in phase they add up to a high value, very little current passes , hence dim lamp glow.
A 60W 220V lamp passes 60/220=0.27 A (270mA) on full power, weak red/orange glow means it's passing, say, less than 100mA (0.1A).
*If* you connect windings out of phase, inductances cancel, and the around 9 ohms DC resistance will let it pass catastrophic 220/9=24.5A, burning it in seconds.
That is prevented by the couragous little lamp, which limits current to said 0.27A .

Well, i didn't know that inductances canceled when out of phase. Mind you besides Ohm's law, and 1/2xΠxRxC

I don't know much

[J M Fahey]

Well, remember that they are wound on the same core, where, to be more precise, *magnetic fields* either add up or cancel, depending on phase.
Obviously 0 magnetic field results in 0 inductance.
If you had 2 separate inductors (say, 2 filter chokes) they would always add when in series.

[Enzo]

I don't think inductors so much as I just think transformers. Nothing wrong with inductance, I just visualize differntly. You have two primary windings on the same core. If they are in phase, both make the same direction magnetic fields so they cooperate. If they are out of phase, then one winding tries to make the magnetic field in the core go one way, while the other winding tries just as hard to make it the reverse. The two fight together.

The primary works teh same as a secondary. COnsider if you had two secondary windings of the same voltage. As the primary AC makes and alternating field in the core, the secondaries use that to make alternating voltages. As AC current, that means that the two ends of each winding behave predictably. One end swings positive while at the same time, the other end must swing negative. And they alternate many times per second.

Imagine you connect the two secondaries together. If we take the end of each secondary that swings positive first, and hook them together, (and then the two negative going ends together) both of them move the same direction so they share. But if you connect the positive going end of one secondary to the negative going end of the other, whatever one does, the other does the opposite, and they fight one another. In essence you have shorted across the winding.

Your primary is intended to make a magnetic field to power the secondaries, but it also induces a voltage into the other primary with the same field. If that induced voltage doesn't move the same direction as the voltage applied from the mains, then they fight.

And just a note, transformers work on turns ratios and turns relationships, NOT resistance.

[Satamax]

Cool guys. Thanks a lot for the replies. Nice explaination Enzo.

Well, found this

Finding phase of dual primary tranny - diyAudio

The gaucho guy has a good technique. I hope i'll have time to do mi fiddle before next week. All i need is a 12/18vdc power supply able to cope with 4x45 peak power watts from a car stereo.

[Satamax]

So, i'm back with measurements.

236Vac line in my workshop.

Three secondaries.

7.56VAC
56.36 VAC
68VAC
On the leaflet of the car stereo, they say, 12 to 16 VDC.

Using the 7.56vac would give me 10.58 aproximately. Bit low imho.

Using the two other secondaries out of phase in series would it give me 11.64 vac? Like the bucking transformer trick i've read over here in the past. This could lead to 16.28vdc. Which would be close enough no?

This DIY boombox is gonna run 8 ours five days a week.

What's your opinion guys?

Thanks a lot.

Max.

[J M Fahey]

Short answer: it won't work.
The bucking trick works for *small* errors, say, 10%, but not over that.
Bucking or not, any power on 12V will need a much higher current that a winding meant for 60V .
Transformer design is *always* a compromise, because of window area, so nobody fits more diameter than absolutely necessary.
Sorry.
The good news is that a 12V, 2 to 4 A transformer is *cheeeeaap* []
You'll get 16V no load, falling a couple volts when full power.

[Enzo]

ANother cheap source is car battery chargers. You would have to add a good filter to it, but they produce high current 12vDC, and cheap ones can be had anywhere.

[Satamax]

Hi guys.

Thanks again for your replies. Yep, this transformer won't do the trick. I'll go to the dump, see what io can find. At some point, i was thinking about using a computer power supply that i have. 8 amps at 12v I would not use the other 3.3 and 5 volts circuits. Problem is, i would like to remove the fan, and i wonder if it would still cope with the 60 watts RMS it might draw, if the fan is removed. I know it's doable no prob with the fan, but without it? Actualy, the thing i gonna use, is this Muse - M-100 MR
I wonder what is the equivalent of thoses 4x45 watts peak, in real world RMS watts.

[J M Fahey]

Probably 4x20W RMS. Easy to achieve with a nominal 12V car battery and 4 bridge output chips. In fact there are modern chips which have all 4 into 1 package.
What I found funny was their bulk offer of 6000 , 12000 or 16000 units per container.
All of us making amps by hand are older than dinosaurs.