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How much power does a standard 14" LCD require?

sygyzy

sygyzy

Lifer
I am working on an "embedded" computing project and would greatly prefer NOT to run a seperate power supply for the monitor. Would I be able to power it from the 12V rail of a standard ATX power supply?
 
How are wattages and voltages related? I was just looking for random specs and found one for a Proview 14" TFT LCD. It says it consumes < 36W. WOW! Does that mean that if it takes 12V input and my PS is somewhat beefy, it should be able to work?
 
If it uses 36W at 12V, it'll need 3A (P=VI, assuming a purely resistive load - the LCD is not really resistive, but 3A is probably a pretty good approximation). So as long as your power supply's 12V rail can supply at least 3A (plus whatever the motherboard & drives need) you'll be OK.
 
***CAUTION***
The one thing that you NEED to be sure of is that the GND of the LCD panel is the same as the GND of the computer. It most likely is, but I have a story to tell.

(the scene shimmers briefly on the screen, and you know that you are going to a flashback scene)

I once had a similar idea as you, and wanted to reduce the power clutter. I decided that I had the following items that ALL ran off of 12V..
1) Speakers.
2) Scanner
3) Sidewinder force-feedback joystick (connected through game port). This was five years ago.

So, I make extra power jacks that ran out the +12V rail of my computer. Here were the results.

1) Speakers -- Worked, but I could HEAR my hard drives working. Obviously, the hard drive put a lot of noise on the +12V line. Not good, but no damage done.
2) Scanner -- worked, but I had to plug it in before turning on the computer. If I didn't the computer would reset itself. Otherwise, OK.
3) Joystick -- FRIED. The nearest that I could figure, the +12V supply to the stick was being split into +6V and -6V. What I had done was to, in essence, hook GND up to -6V. Not good.

My tale just goes to show you that you need to think about these things. I would say that you have a 95% chance of it working. But is the 5% chance of screwing up a monitor really worth it?

*EDIT*
If you REALLY want to do this, connect the monitor as normal, using a separate power supply. Measure the voltage difference between the computer GND and the monitor power supply GND. If you get 0V, or close to it, you SHOULD be OK (but no guarantees). If you get something like 5V or more, then DON"T DO IT!
 
Well here's the problem, I don't really have electronicsd knowledge so I am not sure what to look for. I see that these LDC's require 36W of power or so but it doesn't say what voltage. I am hoping the onboard ATX PS should be able to handle the load. All it'll have to power is the m/b, cpu, USB, and the monitor. No hard drive, I am booting from LCD. No optical drives either.

Edit: I meant to say I am booting from USB.
 
Booting from LCD? Whats that?

The power brick for the display will say what voltage and amps the LCD will draw. My MAG LCD says 12V, 3 amps, which is 36 watts, but others may vary. In theory it should work if your PS is a good brand and beefy, but as harkevv stated, the voltage may be a bit dirty and manifest as noise or something in the display.

What kind of ps and what wattage?

Personally Id only try this if I didnt mind destroying the LCD and/or comp if it goes wrong, especially if you have limited knowledge of electronics. You may set up a ground loop or something.
 
Originally posted by: harrkev
***CAUTION***
The one thing that you NEED to be sure of is that the GND of the LCD panel is the same as the GND of the computer. It most likely is, but I have a story to tell.

(the scene shimmers briefly on the screen, and you know that you are going to a flashback scene)

I once had a similar idea as you, and wanted to reduce the power clutter. I decided that I had the following items that ALL ran off of 12V..
1) Speakers.
2) Scanner
3) Sidewinder force-feedback joystick (connected through game port). This was five years ago.

So, I make extra power jacks that ran out the +12V rail of my computer. Here were the results.

1) Speakers -- Worked, but I could HEAR my hard drives working. Obviously, the hard drive put a lot of noise on the +12V line. Not good, but no damage done.
2) Scanner -- worked, but I had to plug it in before turning on the computer. If I didn't the computer would reset itself. Otherwise, OK.
3) Joystick -- FRIED. The nearest that I could figure, the +12V supply to the stick was being split into +6V and -6V. What I had done was to, in essence, hook GND up to -6V. Not good.

My tale just goes to show you that you need to think about these things. I would say that you have a 95% chance of it working. But is the 5% chance of screwing up a monitor really worth it?

*EDIT*
If you REALLY want to do this, connect the monitor as normal, using a separate power supply. Measure the voltage difference between the computer GND and the monitor power supply GND. If you get 0V, or close to it, you SHOULD be OK (but no guarantees). If you get something like 5V or more, then DON"T DO IT!
Click to expand...

I don't get your explanition of how you killed your joystck. Did you not use the common ground and connected to the wrong rail or was your 12 volt rail so over load that you had an extra 6 volt drop across it.

As for the OP. Don't try it unless you have access to a multimeter. If you do want to try it I would suggest first powering only the monitor from the power supply disconnect everything else. If the monitor powers up measure the voltage on the rails and see if it 12 Volts. Then try it with everything installed except the video card connection. Check all the voltages again. Find out what the specs are for the video input difference and check those to if you want to be extra safe compared to the ground you are using. If everything is with in spec then go ahead and power it plug it in.

If you have noise then you need to put a low pass filter between the monitor and power supply. I think a big capacitor in parallel would do the trick.
 
Originally posted by: Spencer278
I don't get your explanition of how you killed your joystck. Did you not use the common ground and connected to the wrong rail or was your 12 volt rail so over load that you had an extra 6 volt drop across it.

As for the OP. Don't try it unless you have access to a multimeter. If you do want to try it I would suggest first powering only the monitor from the power supply disconnect everything else. If the monitor powers up measure the voltage on the rails and see if it 12 Volts. Then try it with everything installed except the video card connection. Check all the voltages again. Find out what the specs are for the video input difference and check those to if you want to be extra safe compared to the ground you are using. If everything is with in spec then go ahead and power it plug it in.

If you have noise then you need to put a low pass filter between the monitor and power supply. I think a big capacitor in parallel would do the trick.
Click to expand...

My explanation is that the GND of my computer was connected to the "more negative" voltage of the power going to the joystick. Apparently, this was the wrong thing to do. Perhaps it used a "virtual ground" by splitting the +12V into +6 and -6V. So, in reality, I connected GND directly to -6V. Of course, this is just a guess as to what happened. I do know that my computer immediately turned off and the joystick died.

As to your low-pass commend, you would likely also need an inductor. A good pi filter with an inductor and two caps might just do the trick.
 
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