LCD monitor help; DC into the monitor????

[simple_gifts]

So I bought a not used 19" LCD monitor from a friend who needs the cash. Rush home, tear the box open and find out it uses 12VDC into the monitor and there is no power adapter. Back of the monitor says "12VDC 3.3A" and it is one of those circular plugs that most DC stuff is powered by.

Not an issue, rush down to RS and of course I don't have the monitor so I can't tell which size circle thing to buy and apparently it doesn't matter since they don't have a unit that can supply 3.3A; all the other adapters are < 3A and cost about $40. Too much for me.

Back home, i remember that I have a Micronta power supply unit I bought for my CB radio back in 1984 and it still works,(the PS) but can only supply 2.5A. If I find the correct adapter (round thingy only) @ RS can I hook up the DC power to it and find out if it will drive the monitor. More importantly do I have to get the + and - correct and if so what is the + and what is the - on a DC adapter?

Also, do any of the computer guys have one of these adapters in their junk pile?

Thanks.

 

[javacontour]

I think most of the time the - side is the exposed contact and + is the inside, but not always. Hopefully you have a multimeter so you can test the polarity of the plug.

I'd suggest looking up the manual for the monitor to see if it provides any information about the polarity of the power connection contacts.

You might be able to get away with the 2.5A power supply. The 3.3 probably gives some leeway for startup. I don't think a monitor will have high initial current like a CRT, but there probably is a small period of time of higher current until the monitor is started.

I guess you've called the friend and asked if he forgot to put the power brick in the box already???

 

[javacontour]

I don't know these folks, but they seem to have a number of such adapters and for less than the $40 rat shack wants.

They and others like them may be able to provide the proper brick.

http://www.unitedsale.com/LCD-Monitor-AC-Adapter_c_17-4-0.html

 

[PandaBear]

if you can wait for a few days, probably cheaper to buy a power brick on ebay than building your own.

 

[JustinH]

Ask the friend to mail you the power brick?

 

[StevieC]

From my computer engineering days I can tell you that the center pin is almost always the positive in DC powered devices. Some cheap chinese manufactured goods switch them around but the standard is supposed to be the center pin.

I would bet on the center pin being positive.

As for getting it right, most manufacturers build in a safety because it's so easy to do that if the polarity is wrong it will either switch it around for you or it will just not work but it won't do any damage. (This is a nice feature but some MFG's are lazy and don't do this)

As for the amperage you could probably get away with 3amps (less .3 of amp) but 2.5 is cutting it too short and although the monitor might fire up you could cause damage to the processor and other components if its not getting enough current.

You could also cause the power supply to overheat (Micronta) if not careful.

I'm not sure where the place is charging $40 but I can buy a power supply like that around my area for $15 CDN. You just gotta know where to look.

Steve

 

[brianl703]

Most of those devices use a 5.5x2.1mm plug. Some of them might use a 5.5x2.5mm plug, but that is very rare.

You can get a 5.5x2.1mm plug from radio shack. The center is almost certainly positive, as mentioned before.

 

[simple_gifts]

Thanks brian, I picked up the adapter @ RS. 5.5x2.1 was the one; only $7. lol. Another wire adapter and I'm up and running with my Micronta 12VDC unit for about $16 We'll see if it holds up to hours of use. Frankly I have more confidence in a 20+ year old supply overstressed than a factory fresh new one from last year....

To all; my friend lives near by. This LCD monitor has been sitting around her house for years and the power brick is nowhere to be seen. I was surprised by the number of places that could supply one; I just typed in the monitor model # and the words "power supply" into google and there were plenty to choose from. Odd I never even thought of that, a market for odd monitor PSUs.