Dual polarity power suppply

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it shows around 18V! Is it dangerous to the load equipment as it requires only 12V?
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Quite likely (but it obviously depends on what the load is)!
Or is it normal as the capacitor being charged? Maybe the voltage will become 12V when it connect to a load
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The cap will charge to the peak voltage (18V in your case). That's normal. It is also normal for the voltage to drop when the power unit is loaded. That's why regulators were invented! Without one you can't rely on it dropping to 12V.
 
so is it important to add a regulator? The powersupply was a switching regulator at output of 12V And 1.2A, but i used a 12V 1.3A Transformer when the switching regulator completely destroyed due to short circuit..moreover the power supply was used to power a small LCD tv.. Any problems? Does that 18V destroy the load? So many questions as this is my first repair job for money..
 
when i added a 25V 2200uf cap it shows around 18V!
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That may be an unloaded voltage.
Cheak it with a load like a car lamp or somthing that 18 volts will not blow
 
this is my first repair job for money
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Then you need a proper regulated supply, or your customer will want you to pay for a new TV if it gets wrecked by too high a voltage .
Do you have professional liability insurance?

If you haven't already done so, check the 'Power supplies' link at the top of this forum opening page.
 
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You never answered my question (or just missed or ignored my post altogether): How much does the TV draw? If it draws more than 1.2A then you obviously can't use that transformer or power supply.

It should say on the back of the TV what its power consumption is.
 

what if i used a 12V 5A Transformer? Maybe the load might needed more amperes even if they have printed 12V 1200mA! the electcronics spare n parts seller told me that YOU CANT REPLACE A SWITCHING POWERSUPPLY WITH AN ORDINARY POWERSUPPLY!!!(Transformer) is he right? Can Any of u experts prove it that he is wrong? By the way, if the Tv draws morethan 1.5A then i must be unable to repair it bcoz of i want to use LM317T!! Any help?
 

You still haven't answered this important question: How much current does the TV draw?

Now, if that wall wart/whatever the old power supply (1200mA) is was made for the TV, then we can deduce that that's what it draws. But you haven't told us this.

You need to know this before you go any farther here.
 
By the way, if the Tv draws morethan 1.5A then i must be unable to repair it
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Was the old power supply the right one for the TV?
If so than the TV must draw 1.2 amps or less.
 
but my customer did't bring the TV and i saw that it is written 12V,1200ma on the powersupply. Today he phoned me the TV blinks when he powered it using the supply that i built for him!! What might be the problem? Pls help..
 
Can you just answer these simple questions?

1. Was that power supply (the 1200mA one) made for that TV? Yes or no.
2. If not, can you tell us what it says on the TV's label about how much current it draws?
 
as i said before, he did't bring me the TV but a switching powersupply(12v,1200ma) i must tell him to bring the TV..
 
Oh, you don't even have the TV. Why didn't you tell us that in the first place?

So are you sure that power supply goes with the TV? or is it just some random power supply your customer tried to use with it?
 
carbonzit said:
Oh, you don't even have the TV. Why didn't you tell us that in the first place?

So are you sure that power supply goes with the TV? or is it just some random power supply your customer tried to use with it?
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Maybe it is.. I am gonna ask him to bring the TV as soon as possible..
 
TV blinks when he powered it using the supply that i built for him!!
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What supply did you make for him? Blinking may be under voltage.
 
Jackdaniel said:
what? Over current? How the heck is that gonna happen as an equipment uses current only it needs to work?
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You don't seem to know what current the equipment will use. How do you know if your power supply can push enough current? You said you designed to 1300mA. What if the equipment requires 1800mA?
 
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