Changing the Amperage of a Power adapter.

[playman]

Hi there, this might not be the right place for this question, but it felt the right place.
Anyway, as the thread name states, can I change the Amper output of a power adapter?
I have a LCD screen that needs 12v 5A input, I have plenty of 12v's but all are 1.8A and lower.
I tried google but I found nothing regarding my question.
please dont just say no or yes, please tell me why/how etc, I just started in school (after 12 year pause lol) and just started in beginner electronics (soldering, house wiring, control circuits and creation of small PCB's or analogs)
so detailed information would be greatly apreciated

[brethin]

Re: Changing the Amperage of a Power adapter.

It is unlikely you will be able to get one from 1.8A to 5a without a major rework of the circuits. Size will also be a factor unless your going to build your own brick enclosure. To provide you with any detailed information you would need to provide detailed information yourself about a specific brick (adapter).

[mariushm]

Re: Changing the Amperage of a Power adapter.

As above, unlikely. Probably the transformer inside is way smaller than what it should be to provide 60 watts of DC power.

As it's 12 volts, I'd say get the cheapest ATX or AT power supply you can find, cut all the wires except two for the 12v power (black and yellow wires) and the ones that control the start of the power supply (ground and green/ps-on on atx power supplies). Also, as you use so little of its rated power, you can probably get away with running it passively cooled.

Side note: while the adapter may be 5A @ 12v it's unlikely the monitor actually uses that much unless you run it constantly at maximum brightness and contrast.

[playman]

Re: Changing the Amperage of a Power adapter.

Thank you guys for the reply's

Regarding the AT/X PSU I have planty of them around (about 80-100 lol)
of all sizes and shapes, I guess most of them are supplying more then 5A per "expansion/molex/sata/etc." but that should not be of any harm for my screen right?
I could do the AT/X project, but that would look so ugly lol, unless I would box it it.

Is there a chance to take a larger adapter and tone it down?
I have heaps of adapters, of all kinds.
lets say if I found a 19v or even 30v adapter wich would have 5A or more,
could I lower the Voltage down to 12v and use that one for the screen?

[mariushm]

Re: Changing the Amperage of a Power adapter.

Most power supplies out there don't have limits per "cable/molex/sata".

The limits usually are per "rail", each power supply having 1-2 rails for 300-500w power supplies and up to 6 rails for the huge ones (1200+ watts).

When several rails are used, there's generally a chip programmed to cut the power when the consumption goes over a number of amps, but it's usually a high value, like 20-30A on each rail. This is because sometimes molex connectors can be used to power a video card, using a 2 molex to 8pin adapter, and video cards pull up to 150 watts on such 8 pin connector (150w /12v = ~ 12 Amps)

I guess you could use a 19v laptop adapter and get the voltage down using a linear regulator but you'd need big heatsink for the regulator, not to mention one costs 5-10 dollars.
For example, one that can output 7.5A on 12v is 8 dollars : http://search.digikey.com/scripts/Dk...CT-12%23PBF-ND

[playman]

Re: Changing the Amperage of a Power adapter.

hmm, allright I guess i'll use the At/X PSU's then, and try to make a berable looking box

thanks again for the info

[370forlife]

Re: Changing the Amperage of a Power adapter.

Thank you guys for the reply's

Regarding the AT/X PSU I have planty of them around (about 80-100 lol)
of all sizes and shapes, I guess most of them are supplying more then 5A per "expansion/molex/sata/etc." but that should not be of any harm for my screen right?

Voltage is constant (err, regulated as well as it can to maintain a "constant" voltage) but amperage is supplied as it is needed. So if you monitor only uses 2.7A of 12V power, then the power supply only delivers 2.7A of 12V power.