12v adapter for lights

[fredinstl]

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:

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

[gfretwell]

PC power supply?

[Tony Hwang]

> - what about the fire hazard: should I replace the whole lighting

Hi, Basically it is a step down transformer. For continuous use the heavier the better.

[mm]

>> - what about the fire hazard: should I replace the whole lighting

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.

[aemeijers]

> - what about the fire hazard: should I replace the whole lighting

Nearest goodwill or salvation army store- look through the row of stuff 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...

[gfretwell]

I doubt you are going to find a 5a transformer at Salvation Army.

[aemeijers]

Those bricks that came with the HP printers for years and years weren't

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...

[gfretwell]

I have an HP500 here and the brick is 20v at 2a. The 690c is smaller than that 30v @ 600ma

[The Daring Dufas]

- what about the fire hazard: should I replace the whole lighting

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

[HeyBub]

- what about the fire hazard: should I replace the whole lighting

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.

[Jim Yanik]

aemeijers wrote in news:b7msl.421981$ [e-mail]:

At Home Depot and Lowes,you can buy the transformers to power these 12V halogens.

[clare]

Get a power supply for outdoor garden lights Constant duty, high output, and readily available (even at the "borg"). AC oputput is fine.

[stan]

Three 20 watt lamps =3D 60 watts. The step-down transformer rated at

57.5 watts. (5 amps x 115 volts =3D 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 =3D 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 =3D watts. (And conversely Watts/volts =3D 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.

[JIMMIE]

The origonal power supply was too small. 57 watts power supply for 60 watt load? You need a 90 watt power supply or larger. If ther is no watt rating on the replacement I would look for 8 amps or better.

Jimmie

[Don Klipstein]

> - what about the fire hazard: should I replace the whole lighting

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 ( [e-mail])

[Tony Hwang]

>> - what about the fire hazard: should I replace the whole lighting

Hmmm, Regulating AC voltage is not easy. You mean under voltage, not underload.

[The Daring Dufas]

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.

Some of the older equipment I've worked on had power supplies designed around ferroresonant transformer circuits.

What do I know, I'm just a trained monkey.

TDD

[JIMMIE]

:

Regulation depends on the quality of the transformer. On a lot of cheap import transformers a 12 volt transformer may put out 18 volts into a light load then drop to 10 when pushed to near there rated capacity. Get a good transformer and you dont have to worry about this. Good transformers arent cheap but neither is replacing cheap ones. My 12.6 volt 10 amp Stancor transformer only varies about 1 volt from no load to full output.

Jimmie

[JIMMIE]

te:

- Hide quoted text -

Depending on how closely you want it regulated a well made transformer goes a long way over the typical wall wart.

Jimmie

[Don Klipstein]

Besides quality, there are 2 other factors:

1. Voltage variation with change of load tends to be less with larger transformers and more with smaller ones. Though my experience is that upsizing the transformer tends to make load voltage more excessive, until the transformer gets so big that open circuit voltage is only a little higher than the nominal load voltage. A 12.6V 10 amp Stancor brand one is a big as well as decent quality transformer as far as ones to find inside a home go - though maybe only mildly oversized for 60 watts worth of halogen lights, probably not especially bad for this job after all. (If voltage runs half a volt high at 5 or slightly more amps, then 60 watts worth of halogen lamps will be supplied 13.1 volts. If the lamps get that much voltage after wiring voltage drops, expect incandescent/halogen lamps rated for 12 volts even to have life expectancy reduced maybe 60%.)

1. Most wallwarts have DC output, and not only the transformer windings but also the rectifier circuit (diodes and filter capacitor) has issues of load voltage varying with load current.

- Don Klipstein ( [e-mail])