Transformers 230vac to 9vac

Thread Starter

fredyeah

Joined Oct 18, 2019
9
Hi all,
I am new to transformers and I am working on a power supply unit for an audio mixer. I have a couple of questions about the transformer that I will be using.

First, the transformer has three input pins but only one primary voltage. I am hoping someone can help me determine what all three pins are (I was thinking either +, -, and earth ground?)

Secondly, ideal I would have a 9-0-9 transformer because I need a center tap for my application, but I have only a 230vac transformer with two 9vac secondaries. To my understanding, I can just bridge a + and - from each of the secondaries to create a -9vac, 0v, and +9vac output correct?

Here is a link to the transformer's data sheet.

If anyone has some answers to my questions, it will be much appreciated :)
Thanks,
Frederic
 

ericgibbs

Joined Jan 29, 2010
9,086
hi fred,
Welcome to AAC
The Tag numbers are printed on the transformer, #1 and #7 for the mains input connection.
You can connect the secondary windings in Series, using the connection as a Common for the two 9V windings.
E
AAA 015 13.08.gif
 

bertus

Joined Apr 5, 2008
20,179
Hello,

The 230 Volts needs to be connected to the pins 1 and 7 as @ericgibbs said.
When you connect 10 to 12 , you will have your CT point.
8 and 14 will be the two counterphase 9 volts connections.
To check if the phases are correct, you should measure 18 Volts AC between 8 and 14.

Bertus
 
Last edited:

Thread Starter

fredyeah

Joined Oct 18, 2019
9
hi fred,
Welcome to AAC
The Tag numbers are printed on the transformer, #1 and #7 for the mains input connection.
You can connect the secondary windings in Series, using the connection as a Common for the two 9V windings.
E
View attachment 188265
thanks for the clarification. just for my own peace of mind, is the third pin just not connected to anythings? or what would be a potential use of the third pin?
 

Thread Starter

fredyeah

Joined Oct 18, 2019
9
Hello,

The 230 Volts needs to be connected to the pins 1 and 7 as @ericgibbs said.
When you connect 10 to 12 , you will have your CT point.
8 and 14 will be the two counterphase 9 volts connections.
To check if the phases are correct, you should measure 10 Volts AC between 8 and 14.

Bertus
if the two secondaries are 9vac, shouldn't the measure between the two outer pins be 18vac? where is the 10vac coming from?
 

Thread Starter

fredyeah

Joined Oct 18, 2019
9
Hello,

I have corrected my post.
You should measure 18 Volts.

Bertus
awesome thank you. and then to add an earth ground, my understanding is that I can solder the earth ground from the mains onto the chassis of the transformer. should I ground the 'center tap' to the chassis as well to ground the circuit? will this cause problems and/or is it unnecessary?
 

ericgibbs

Joined Jan 29, 2010
9,086
hi fred,
Checked the 'block-trafo' site for the third Tag [ #2] , no additional info, you can send a request to them asking the question.
E
 

ericgibbs

Joined Jan 29, 2010
9,086
hi,
I would just connect the transformer Frame to the Earth wire of the Mains, keep the centre tap of the transformer secondary windings Earth free.
Use the centre tap as a Common/Ground for the project circuit voltages.

Don't forget the input to the transformer should be fused

E
BTW: do not confuse Earth with Ground/Common.
 

Thread Starter

fredyeah

Joined Oct 18, 2019
9
hi,
I would just connect the transformer Frame to the Earth wire of the Mains, keep the centre tap of the transformer secondary windings Earth free.
Use the centre tap as a Common/Ground for the project circuit voltages.

Don't forget the input to the transformer should be fused

E
BTW: do not confuse Earth with Ground/Common.
Okay and a 250v 1A or .5 amp fuse between the mains positive and the transformer will work, correct?
 

ericgibbs

Joined Jan 29, 2010
9,086
hi,
The Mains do not have a Pos and Neg , its Line and Neutral [ L & N ]
Fuses are in the Line wire side, say a 1Amp fuse.
How is the the input cable connected to the mains supply, is it via a fused mains plug.??

May I ask, what is your country .?
E
 

Thread Starter

fredyeah

Joined Oct 18, 2019
9
hi,
The Mains do not have a Pos and Neg , its Line and Neutral [ L & N ]
Fuses are in the Line wire side, say a 1Amp fuse.
How is the the input cable connected to the mains supply, is it via a fused mains plug.??

May I ask, what is your country .?
E
im going to use this plug for the fuse. im in germany. most of the fuses at the electronics stores are 250v so im assuming thats what most people use for mains applications (mains here is 230vac +/- 10v)
 

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Thread Starter

fredyeah

Joined Oct 18, 2019
9
Hey all,
I am working on a power supply unit. I am in the EU and I'm wondering how to properly add a fuse between the mains and the transformer in the PSU. since the outlets in the EU are non-polarized, I am not sure weather it is better to have two fuses, one fuse, or no fuse? if anyone has an opinion or some experience, please let me know. Thanks :)
-Frederic
 

MrChips

Joined Oct 2, 2009
19,741
Fuse always goes in the LINE feed, never in the NEUTRAL.
You need to replace the non-polarized plug with one that is polarized.
 

Thread Starter

fredyeah

Joined Oct 18, 2019
9
Fuse always goes in the LINE feed, never in the NEUTRAL.
You need to replace the non-polarized plug with one that is polarized.
The issue though, is that european outlets themselves are non polarized. there is not a way to use a polarized plug
 
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