Transformer wires

[123hotchef]

Ok I have acquired a 16v transformer but I just want to check I have the wires correct.

There are 2 black thicker wires I assume these are the 240V in are they?

Then there are 2 thinner wires 1 blue and 1 brown are these the 16v + and - or have I got it the wrong way round?

Lee

 

[123hotchef]

 

[Seadog]

Brown/blue should be the mains side and have a higher resistance than the secondary.

 

[AdrianH]

I would suggest you have it the wrong way around, but do you have a multimeter to test the resistance of the windings.

The primary or mains winding should be a lot higher resistance then the secondary.

Adrian

 

[123hotchef]

thanks guys I didn't switch it on yet

yes you are correct 4.1 ohm on the blue and brown
and 1.2 on the blacks

 

[Seadog]

4.1 sounds very low. I'd have thought a few hundred into the low thousand. It does depend on the current rating though.

 

[123hotchef]

just plugged it in and measured it 16v Ac on the out

 

[123hotchef]

thanks guys I didn't switch it on yet

yes you are correct 4.1 ohm on the blue and brown
and 1.2 on the blacks

I guess I have to x that by 200

 

[wookie]

There are 2 black thicker wires
2 thinner wires 1 blue and 1 brown

I know you are sorted with this but since it is a step down transformer the output current will be higher than the input current so it should have thicker wires on the secondary/output than the primary/input side, also the thinner wires are blue and brown which are standard colours for mains wiring so that should have given you a clue as well....

 

[voipio]

Not sure why you need to multiply the primary winding resistance reading by 200. It looks like a fairly beefy transformer, capable of delivering possibly 10-20 Amps, so a D.C. resistance of 4 Ohms for a primary is not unreasonable. The effective A.C resistance will be much higher because of the inductive nature of the beast, and also be frequency and secondary load dependent.

 

[123hotchef]

I am not really sorted yet I need to get the AC to DC now via a bridge I do believe

i had the multi meter setting on the 200 setting

 

[skotl]

are these the 16v + and -

I need to get the AC to DC now via a bridge I do believe

I was wondering As you've now discovered, the transformer just changes the AC voltage down, so now you need to change it to DC (which will increase the voltage, by the way; assume around *1.4 so 16VAC will come out around 22VDC).

Quite what kind of rectification (getting from AC to DC) you need depends on what you're going to do with it. You could get away with half-wave rectification with just a couple of diodes and a smoothing capacitor, or you could use a bridge rectifier (which is just 4 diodes in a 4 pin pack) and a cap.
If it needs to be super-accurate then you'll need a voltage regulator like one of the 78xx series (7812 gives 12V DC out) after the rectifier.

 

[123hotchef]

I was wondering As you've now discovered, the transformer just changes the AC voltage down, so now you need to change it to DC (which will increase the voltage, by the way; assume around *1.4 so 16VAC will come out around 22VDC).

Quite what kind of rectification (getting from AC to DC) you need depends on what you're going to do with it. You could get away with half-wave rectification with just a couple of diodes and a smoothing capacitor, or you could use a bridge rectifier (which is just 4 diodes in a 4 pin pack) and a cap.
If it needs to be super-accurate then you'll need a voltage regulator like one of the 78xx series (7812 gives 12V DC out) after the rectifier.

I was going to use it for a rust removal tank so the voltage out is not too critical Skot I have diodes here its like at school when u use 4 in a circle but I have forgot all that now, probably easier and just as cheap to purchase a bridge rated 20amp or so

 

[skotl]

I was going to use it for a rust removal tank so the voltage out is not too critical Skot I have diodes here its like at school when u use 4 in a circle but I have forgot all that now, probably easier and just as cheap to purchase a bridge rated 20amp or so

Yup - one of these will do it for £2.50; http://www.maplin.co.uk/search?text=FULL WAVE BRIDGE RECTIFIERS

 

[123hotchef]

thanks skot do i need a cap with one of those?

 

[123hotchef]

this little baby should do right?


http://www.ebay.co.uk/itm/Single-Ph...756389?hash=item33b7ba0fe5:g:wosAAOSw9etXQXkd

 

[123hotchef]

i sold my old charger and this transformer was free so 99p for the bridge wont hurt me! I could steal a 4 pinned one from a board at work! how do i find out what pin is what?

 

[WorkshopChris]

a bridge will normally be marked with a + and - thats your dc then a ac wave symbol on the other 2 pins.
If not marked 2 legs may be longer or a spot in the corner so you may need the data sheet to confirm.

 

[123hotchef]

i could harvest one of these but unsure what leg is what

 

[WorkshopChris]

Should be (pos ac ac neg) with the 45 deg on the longer positive leg when viewed form the front.
But best to confirm with a data sheet normally it will have the number on it.
If your taking a diode out of an existing circuit can you follow the pcb trace back towards the input and the other way forwards to a voltage reg or cap.