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AC transformers

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Teletech

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Since regulators, zeners and the like are only used for DC, how can you regulate or reduce AC? In other words, if I need a 12 volt transformer and all I have are 24 volt ones that aren't center tapped what can I do to change it to 12?
 
There really isn't much you can do at the Tranformer.

A Variac on the input would lower the Input as well as the Output Voltage, But the Output Current would Drop Significantly. NOT at All Practical.
 
I use a variac on my homemade soldering station to lower the voltage so the temperature won't be so high...rather crude I think, but it works fine. I was just hoping I could do something with all these 24 volt transformers that I have. Alot of times, I'll dig around looking for a 12 volt one and can't find one.
 
chemelec said:
A Variac on the input would lower the Input as well as the Output Voltage, But the Output Current would Drop Significantly. NOT at All Practical.

You brought up an interesting question about output current.

When the secondary output voltage is say 50% because a variac is used at the transformer input to reduce the voltage by 50%, do we still able to get the same current from the secondary output?

i.e. Can we still get 12V 4A from a 24V 4A transformer?
 
Teletech said:
In other words, if I need a 12 volt transformer and all I have are 24 volt ones that aren't center tapped what can I do to change it to 12?

If you have two exactly similar transformers, you can connect the primary in series and the secondary in parallel. You will get 12V with about twice the current output of each transformer.

There is a 50%(or higher according to Murphy) chance of connecting the secondary winding in the wrong polarity so it is a good idea to test the connection using a series lamp bulb in the primary. If the bulb goes to full brightness, swap one pair of secondary connection.

If you need a diagram, posts back.
 
Hi

Hook primaries in parallel secondary in series in phase or buck out of phase you can get 12 or 48 volts or parallel secondary for higher current 12 volts.
joe
 
chemelec said:
A Variac on the input would lower the Input as well as the Output Voltage, But the Output Current would Drop Significantly.

No it wouldn't. The current capacity will remain the same.


eblc1388 said:
Can we still get 12V 4A from a 24V 4A transformer?

Yes.


Another thing which can be done, if you are keen enough, is to rewind the secondary. (Only really practical with a laminated core though.)
Take the transformer apart by removing any clamp or frame and separate the laminations.
Remove the secondary winding, counting the number of turns.
Rewind with half that number. Re-assemble.
 
jnegowski said:
Hook primaries in parallel

OK. So each transformer secondary now gives 24V.

jnegowski said:
secondary in series in phase or buck out of phase you can get 12 or 48 volts

No. I get 48V for in phase but zero volt out of phase.

jnegowski said:
or parallel secondary for higher current 12 volts. joe

No. I get 24V, but current is sure higher.
 
No it wouldn't. The current capacity will remain the same.

Yes your right, Sorry. I was Thinking about a Resistor in series with the Primary.

Brain Dead.
 
Hi Gary.



What an awful lot of misunderstanding and misconceptions.

The facts are as follows.

We can connect two identical 24V transformers in four ways.

(1) Primaries in parallel.


(a) Secondaries in series.

Output = 48V, current same as one secondary winding's capacity.


(b) Secondaries in parallel.

Output = 24V, current capacity double that of one secondary winding.



(2) Primaries in series.

(a) Secondaries in series.

Output = 24V, current capacity same as that of one secondary.


(b) Secondaries in parallel.

Output = 12V, current capacity twice that of one secondary.
 
Hey Thanks, I have never thought about connecting primaries in any way except parallel. I series and parallel secondaries all the time to get what I want. On the 24volt 40va ones, I parallel the secondaries for more current and sometimes I series two 6 volt ones so I can have 12volts, but duh, I didn't even know you could series the primaries.
 
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