# 'normal' transformer and basic center tap transformer

Discussion in 'Homework Help' started by PG1995, Apr 16, 2011.

1. ### PG1995 Thread Starter Well-Known Member

Apr 15, 2011
805
5
Hi

Though I'm posting it here, it's has nothing to do with homework. It self-study. I'm a beginner so please keep your reply simple. Thanks.

Suppose a CTT (center tap transformer) splits the voltage across its two secondaries into 120V each. I want to get combined voltage of both secondaries which would be 240V (120V + 120V).

How do I do this?

I have drawn this diagram, "B" is a bulb:
http://img97.imageshack.us/img97/9539/ctt1.jpg

One things more. Suppose in the primary current is flowing upward at some instant (current keeps changing direction in AC, correct?), in which direction the current (or current) would flow in the secondaries? In the same direction, as is shown in the below diagram, or in the opposite direction.

Currents in the primary and the secondaries:
http://img194.imageshack.us/img194/6163/ctt2.jpg

Regards
PG

2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,618
1,088
I Simply cannot register to view ur image.
Try photo bucket for a change

3. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
784
To PG1995:

Your schematic (ctt2.jpg) shows one half of the secondary (the top side) shorted out from 0V to Line 1. That would eventually destroy the transformer or (hopefully) activate whatever primary side over-current protection exists. To obtain the full 120V across the load you would leave the 0V terminal disconnected (open) and connect the load between Line 1 & Line 2.

Your other schematic (ctt1.jpg) also shows a situation where the secondary is short-circuited. Lines 1 and 2 connected as shown are effectively a short. Unless the two secondary windings are completely independent (2+2=4-wire) you can't connect them in parallel. You can't connect the outside ends of a center-tapped (3-wire) winding. The "polarities" are not compatible with this connection.

PG1995 likes this.
4. ### PG1995 Thread Starter Well-Known Member

Apr 15, 2011
805
5
Hi R!f

I don't know what's the problem. It's a direct link. You don't need to register to view any of the images if you have a direct link. So, please try to check it out and let me know what the error is. Thank you.

Regards
PG

5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
784

"To obtain the full 240V across the load you would leave the 0V terminal disconnected (open) and connect the load between Line 1 & Line 2."

6. ### R!f@@ AAC Fanatic!

Apr 2, 2009
9,618
1,088
Funny..I get a domain blocked error

7. ### PG1995 Thread Starter Well-Known Member

Apr 15, 2011
805
5
Perhaps, it has something to do with your ISP, or your avatar!

Regards
PG

8. ### PG1995 Thread Starter Well-Known Member

Apr 15, 2011
805
5
Thanks a lot, t_n_k. It has been really helpful. I do have some follow-on question on transformer which I would ask soon. And I understood it was just a 'type'.

Best wishes
PG