Replace Low Voltage Bi-Pin Halogens with LEDs

Step 6 Test

With the driver mounted, you are ready to test. You can do this at your bench or installed in the fixture or choice. If you see a lot of flicker then your fixture may not be low voltage DC but rather low voltage AC. You need to modify the circuit to handle the AC by using a full wave rectifier and some capacitors, not too bad but not ideal. Enjoy, and be safe!

Comments

[peterlonz]

Something seems not to add up here: A typical halogen is about 50 watts & its efficiency is not hugely different to LED's as (I understand things), as for example a compact fluorescent is, being 3 to 4 times as efficient as a halogen. So how on earth can an array of three LED's, total 10 watts, be anywhere near the light output of the replaced halogen ?

[jmengel]

The thing that you are missing is that an LED can be hugely different than a halogen in terms of efficiency. Cool white LEDs are available that are rated 100 lumens/watt which is greater than the typical CFL at 50-75 lumens/watt and a typical halogen at 15-20 lumens/watt. Warm white LEDs are not as efficient and peak at around 80 lumens/watt on the market today. Certainly there are less efficient LEDs, and the bulbs out there on the market that use a huge collection of small through-hole lead LEDs do tend to give LEDs a bad, anemic rap. However, the latest high output high efficiency LEDs (Philips Rebel, Cree XR-E, etc) can put out an amazing amount of light. So that is how a 10W LED array putting out 1000 lumens is near the output of a 50W halogen putting out 1000 lumens.

http://en.wikipedia.org/wiki/Luminous_efficacy

[blazingpencilsdotcom]

Thanks, cool instructable. What is the color temperature in this setup, I gather its the bluish light , 6500? and if we wanted the warmer light it would throw off 2-3 times the heat? Can this be dimmed?

[jmengel]

This is a warm white LED, 3000K as noted by CameronSS. I would rate the light as similar to the halogen it replaced in terms of color. I have Rebel stars that put out much more light (100 lumens/watt) but these are the 6500K cool LEDs with bluish tint. The warmer LEDs are less efficient, so they will get hotter at the same luminous output as the cool white LEDs. For example, to get 1000 lumens using a 100 lumen/watt cool white LED would take 10W, most of which would end up as heat. Similarly, with a 60 lumen/Watt warm white LED would require 16.7W, most of which would end up as heat. The difference in heat output is basically the ratio of luminous efficiency, so 1.67 times more heat in the above example.

The driver circuit as shown does not support dimming. The drive IC can support dimming but uses a PWM approach that would not be compatible with the typical triac dimmers found in most residential applications. I am working on a triac dimmable driver circuit based on the LM3445 reference design provided by NSC.

LM3445

[CameronSS]

According to the website to which he linked in the Materials step, it's an average color temperature of 3000K.

[Spokehedz]

Your best bet there would be to use a yellow filter over the light. I personally like the white glow of the LED's, but I can see where some people wouldn't like it.

[jmengel]

Filters decrease efficiency by blocking light, so I can't recommend that approach. The mix of phosphors used in the warm white LEDs gives a warmer look without the use of filters but with less luminous efficiency. An interesting test would be to measure the difference in effective luminous flux of a warm white LED and compare it to a cool white LED with filter. My guess is that the warm white LED without filter would be more efficient. Otherwise, the LED manufacturers would not mess around with making different LEDs, and would just apply different lenses to the LED die. Hmm, maybe a new idea for LED manufacturing...