12v adapter for lights

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I bought a lighting system from Ikea ~2 years ago, made of 3 halogen lamps, each being 12V 20W. It's mounted on electrical wires. The adaptor died. It is actually a little scary as one wire feeding the adaptor apparently get too hot, and almost melted the adaptor plastic. Looks like a fire hazard to me.
On the adaptor, it says: input: 120V, 60Hz, 0.6A output: 11.5V, 5A, 57.5W
which kind of makes sense from what I remember from school: Watt = Amp x Volt I went to radioshack and the guy said they didn't carry anything like this.
So I the plan now is to buy an adaptor from the internet but not sure what to get: - can I buy any 110V to 12V 5A adaptor ? Apparently, it is easy to find as they are commonly used as a LCD adapters. e.g: (Amazon.com product link shortened) - what about the fire hazard: should I replace the whole lighting system ? or 12V 5A should be fine ? or should I go maybe with more Amps, such as 12V, 6Amp to be on the safe side?
Any feedback much appreciated.
Fred
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On Fri, 6 Mar 2009 17:59:27 -0800 (PST), fredinstl

PC power supply?
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snipped-for-privacy@aol.com wrote:

Basically it is a step down transformer. For continuous use the heavier the better.
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wrote:

For certain fire protection, put the whole transformer in a can of water.
OK, I'm kidding. If you didn't do anything wrong with the first one, you should probably report it to the FTC. These lights may use cheaper ones that expensive electronics.
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snipped-for-privacy@aol.com wrote:

that plugs in, and you can probably find a suitable transformer for less than five bucks. May have to buy the whole item to get it, but at that price, who cares?
If you have your heart set on 'new', try MPJA.com.
Personally, if the thing melted, I'd be inclined to shitcan the whole thing. Who knows what other parts were barely-adequate? At least the sawdust furniture from Ikea isn't likely to kill you.
-- aem sends...
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I doubt you are going to find a 5a transformer at Salvation Army.
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snipped-for-privacy@aol.com wrote:

5 amps? (Don't feel like digging out my crate of mostly-trashpicked transformers to check right now.)
Upon due reconsideration, I now lean more toward just trashing the thing. I may be a cheap SOB, but life is too short (and precious) to try MacGyvering something that can kill you. Fresh puck lamps or whatever with UL stickers just aren't that expensive.
-- aem sends...
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I have an HP500 here and the brick is 20v at 2a. The 690c is smaller than that 30v @ 600ma
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output, and readily available (even at the "borg"). AC oputput is fine.
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On Mar 7, 12:50pm, snipped-for-privacy@snyder.on.ca wrote:

Three 20 watt lamps = 60 watts. The step-down transformer rated at 57.5 watts. (5 amps x 115 volts = 57.5) maybe underrated from the start? Depending on safety factor (if any?) if your voltage sometimes a bit high, say 120 volts (which ours sometimes is) then; 120/115 a 60 = 63 watts approx. That's a 9% overload right there. Other suggestions cut back to three 15 watt amps, or eliminate one lamp, or use LED replacements (if suitable). Better still get rid of the extra 12 volt gadgetry and use 115 volt lighting fixtures. BTW congratulations on the grasp of volts, amps and watts. Using the Formula Volts x amps = watts. (And conversely Watts/volts = amps). Think on this; 60 watts of lamps at 120 volts will need 0.5 amps. That's a relatively small current flow. 60 watts of lamps at 12 volts will conduct 5 amps. That's same amount of power (watts) but ten times the current at one tenth the voltage. Five amps is a heavier current so wiring fixtures, lamps sockets and the transformer must be capable of handling the heavier current flow, continuously.
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wrote:

At Home Depot and Lowes,you can buy the transformers to power these 12V halogens.
--
Jim Yanik
jyanik
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fredinstl wrote:

(Amazon.com product link shortened)
The original transformer would typically be an unregulated AC power supply. The 11.5 volt rating would be under load. No load voltage could be as high as 15-18 volts AC. Any good electronic supply house should be able to sell you a comparable power transformer or one with better specs.
TDD
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fredinstl wrote:

(Amazon.com product link shortened)
If each lamp is 20 watts, you're pulling 60 watts from a transformer rated at 57.5(!). No wonder it croaked.
Confine your replacement search to something rated around twice the anticipated load. Go for 100 watts minimum.
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If the load is far below the load rating of the stepdown device, and the stepdown device is an unregulated type, then such an underload can lead to excessive output voltage - and shortened lamp life.
I would go for either something known to be regulated or something with load capacity only mildly exceeding the actual load.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Don Klipstein wrote:

Regulating AC voltage is not easy. You mean under voltage, not underload.
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Tony Hwang wrote:

Years ago when electronic equipment was even more sensitive to power fluctuations I would install ferroresonant constant voltage regulators on the incoming power. I probably have a few in storage.
http://tinyurl.com/ab9t3k
Some of the older equipment I've worked on had power supplies designed around ferroresonant transformer circuits.
http://tinyurl.com/cxdyz6
What do I know, I'm just a trained monkey.
TDD
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I remember reading that the PC power supplies have some kind of power saving sleep mode. You need to plug in an old drive, in order to get the 12 volts to work. Anyone know for sure?
--
Christopher A. Young
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Stormin Mormon wrote:

That would be a function of the motherboard and it's BIOS program. The motherboard, if so equipped, can control the fan speed of a compliant power supply and when the computer is off but still plugged into line current, there is 5 volts DC coming from the power supply for the quiescent state of the mother board. Some motherboards have wakeup modes that can be triggered by a dial up modem receiving a call, a network card if made for that function, USB port activity and keyboard input. None of the PC power supplies that I've taken apart have had any microcontrollers or memory. It wouldn't surprise me if some expensive server power supplies had brains but I've never come across one that has. Here is a link with some information on APM, Advanced Power Management.
http://tinyurl.com/5m3ah
TDD
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On Mon, 9 Mar 2009 22:29:30 -0400, "Stormin Mormon"

volt, I believe. (could be the 5, but I'mm 99% sure it is the 12 that it regulates from)
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snipped-for-privacy@snyder.on.ca wrote in wrote:

No,it's the +5V;after all,that is what the ICs use,and they don't tolerate over/under voltages well.
--
Jim Yanik
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