# Is there any method to get 12V more Ampere from 12-0-12 transformer?

#### Htin Aung

Joined May 29, 2016
36
Hello again my dearest technicians,

I have a 12 0 12 ,2A transformer, I have to use it for 12V DC fan with a bridge ractifier circuit.
So I take 12 and 0 wires from it .But another (12) wire is free and I think just half of my transformer's secondary coil is working.
Is there any method to use free one also to get more amps?

Amyutay
Student
Maymyo, Myanmar.

#### ScottWang

Joined Aug 23, 2012
7,117

#### MrChips

Joined Oct 2, 2009
24,992
Don’t use a bridge rectifier.
Use a full-wave circuit that uses two rectifiers. The 0V tap on the transformer is connected to GND.
This will double your current output capability.

Like this:

#### Htin Aung

Joined May 29, 2016
36
No Sir, I just wanna cooldown my younger sister's old PC.

#### Htin Aung

Joined May 29, 2016
36
Don’t use a bridge rectifier.
Use a full-wave circuit that uses two rectifiers. The 0V tap on the transformer is connected to GND.
This will double your current output capability.

Like this:
View attachment 243301
Exactly it is the helpful one what I need.
Now I'm finished as your diagram and it works fine.
Again , Thank you so much Sir.
In addition, what is the purpose of 1K resistor?
And the capacitor I used is 1000uf 50V and is it suitable value?

#### MrChips

Joined Oct 2, 2009
24,992
The capacitor is fine.
You can remove the resistor. It is shown to represent a load.

#### ScottWang

Joined Aug 23, 2012
7,117
Currently I replaced the capacitor again with 47uf 250V as I think it needs a higher voltage capacitor.
For the Vout = 12Vac*1.414 = 16.968 Vdc = 17V
So you can choose the capacitor as 1000uF/25V or 35V.

If the load is connected to the power all the time then you don't need the resistor, otherwise, you can keep it as a discharge resistor.

#### Htin Aung

Joined May 29, 2016
36
I already unmounted Sir. I carelessly didn't noticed RL and I keep just 1K In my mind.
May be This 1K resistor gave me first swellowed Capacitor after 15 minutes .
So I replaced the capacitor also and after afew minutes, It swellowed again with a Sound(Phoke!)
Currently I replaced the capacitor again with 47uf 250V as I think it needs a higher voltage capacitor.
Now I'm waiting for explode .
May be It works as the capacitor is still not become hot.
For the Vout = 12Vac*1.414 = 16.968 Vdc = 17V
So you can choose the capacitor as 1000uF/25V or 35V.

If the load is connected to the power all the time then you don't need the resistor, otherwise, you can keep it as a discharge resistor.
For the Vout = 12Vac*1.414 = 16.968 Vdc = 17V
So you can choose the capacitor as 1000uF/25V or 35V.

If the load is connected to the power all the time then you don't need the resistor, otherwise, you can keep it as a discharge resistor.
Thank you Sir.
After all ,the reason why my capacitors were explode is just because of my inversely connected rectifiers at low light.
Now I know how stupid I am.

#### ronsimpson

Joined Oct 7, 2019
1,750
Now I know how stupid I am.
You are not stupid. You have little experience. There is a big difference. Experience comes with building many things and reading books. Stupid can not be fixed.

#### Ramussons

Joined May 3, 2013
1,150
Don’t use a bridge rectifier.
Use a full-wave circuit that uses two rectifiers. The 0V tap on the transformer is connected to GND.
This will double your current output capability.

Like this:
Hmmmmmm... How does it double the Current Output capability?

#### crutschow

Joined Mar 14, 2008
28,486
How does it double the Current Output capability?
Well it doesn't double it, but it does increase it.

The 2A transformer limit is basically due to the allowed temperature rise from the winding resistance loss.
Assume each winding resistance to the center-tap is R, then the dissipation in each winding to the center-tap for a 2A maximum allowed current is 2²R or 4R.
For the two diode full-wave rectifier the current is half-wave, so the maximum allowed current is 1/2 I²R = 4R or I = √8 = 2.83A.

So it doesn't double the maximum current but it increases by the √2.