hi m,
If its ~1mm dia, then its ~18 gauge, OK.
E

 

so my secondary can handle upto 7A?

 

It doesn't say that!....

 

hi again, how much watts is r2?

 

hi,
You work it out and post your answer.

The Maximum current through R2 is 3 Amps
R2 resistance =0.1R

Voltage across R2 = R2 resistance * Max current through R2

So Wattage of R2 = Volts across R2 * Amps through R2

Whatever you calculate the Wattage to be, make it least 50% more.
[look at the preferred resistor values and wattage tables]

E

 

that would be 0.9W

 

hi,
OK,
So what actual value would you choose.
Whatever you calculate the Wattage to be, make it least 50% more.
[look at the preferred resistor values and wattage tables]


E

 

hello again, how can i adjust the amps output? let say i only need 12v @ 2a? am i going to short the ouput terminl and adjust the current?

 

hi muno,
The amps drawn from the PSU will depend upon the load resistance, with a max current of 2.5A.
What do you mean, adjust the current.?
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Update: [adjust U6 10K Pot for 12v]
Like this sim ~12Vout 2Amps into a 6 Ohm load.
Added the TIP Wattage.

 

for example, my power supply can handle upto 3a with max 25v, now i want to set output to 12v 2a or 1a only

 

now i want to set output to 12v 2a or 1a only

hi,
You set the Output Voltage, not the Current.
For a current at 12Vout, the load resistance will be a minimum value of 6 Ohms.

If the load resistance was, 12 Ohms then the load current would be 1 Amp.

The U5 pot sets the Current Limiter, which is used for a different purpose, what is the load you are powering with the 12 Vout.?
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yeah exactly that current limit, let say, i want to limit the current for unknown device which can take 12v, and to be safe i want to set it to 2a at 12v only, so how to do that? i know how to adjust voltage but how to limit current? am i goint to short the output terminal so that i can set the current output to the limit?

 

i goint to short the output terminal so that i can set the current output to the limit?

Hi m,

Don't short out the PSU output.

Connect a 6 Ohm load resistor across Vout, set U6 for 12V, using a Voltmeter on Vout.

Set U5 at 50% rotation.
You will see the Vout drop, then slowly turn U5 until Vout reads 12V

This should give you Vout=12V at a 2Amp current limit.

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Exactly so, turn volts to Max and current to min, connect multimeter on 10A range across supply. Turn power on, adjust current to 2A. Remove meter and reset to volts. Reconnect meter and turn volts to 12v.

 

hi,
This is with the rectifier connected to the power supply.
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Green plot is power in TIP
View attachment 275325

hi, why does the output voltage goes down to 200mV whenever a load is connected? let say i set the output voltage to 12.30V, it goes down to 12.10V when i connect a load, why it is not stable?

 

hi muno,
With no load connected, you are drawing approx 12V/10k [ R10,11] = 1.2 mAmp
I would expect a small drop in Vout from 1.2mA to say 1Amp.

Try adding a small fixed load of approx 500R at a 20mA current and then add the heavier current load, post what you measure.
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you mean like this?

 

hi,
Yes, I would have chosen 500R, but a 220R will be OK.
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ok, thanks. how about the resistor wattage? is it minimum of 2W?

 

hi,
If you use a 220R the current through the resistor would be 24V/220R = 109mA, so the dissipation would be 24V *0.109 A= 2.6Watt, so I would use a 3W or a 5 Watt
at 12V and a 220R = 54mA thats 0.648Watt

I would use a 470R =51mA, =1.22Watt, use a 3Watt resistor.

Do you follow OK.?
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