Jamesbeat

The light from my Kenmore's bulb was dim and yellow, and it threw off a lot of heat.

I decided to upgrade to an LED lamp, which will be brighter, whiter, and cooler.
It also has the advantage of having a ~50,000 hour lifespan, which means that it should never 'blow' or need to be replaced.

Here are the old guts:



The led is a Cree (XR-E I think). It is a 'high CRI' version, which means that the spectrum of light it emits is similar to natural daylight.

I'm powering it by USB.
USB is ubiquitous nowadays, so a power supply will always be easy to find. I'm using an old phone charger.
Using USB also has the advantage that it is a standard receptacle and voltage, so it is unlikely that anyone will ever manage to fry it by using the wrong power supply.

I wanted to drive the 3.5v LED at around an amp, so I calculated that I would need a 1.8ohm protection resistor.
I didn't have one that low, but I did have two wire-wound 1ohm resistors. They are a little big, but they are 10w each, so they should run nice and cool. The extra 0.2 ohms is insignificant.

I cobbled together an aluminum heatsink/mounting bracket, and attached the resistors to it with epoxy and a cable tie. The cable tie was really just to hold it together until the epoxy set, but I left it on or good measure.

I then put a dab of thermal compound on the bracket and epoxied the LED to it.
I covered the legs of the resistors with insulation, and soldered them to the pads of the LED.
I didn't use a reflector, because the bare LED gives off a smooth diffuse light.
I positioned the emitter low down, so that it is where the tip of the original bulb was.

The new guts:



All that remained to do was to screw the heatsink to the machine, and solder the original lamp wires to the other ends of the resistors.
I had to use plumber's flux to solder to the original wiring of the machine because the copper was so oxidized.

I disconnected the other ends of the lamp wires from the line voltage connector(!) and soldered them to a USB cable, being careful to observe correct polarity.

The original switch for the light works exactly the same as before.





It works!




I gave it a 'burn in' of a few hours to check that the heatsink is working properly and there are no problems with overheating.
The LED and the resistors were still cool to the touch after being on for around five hours.

The light is MUCH better than before.
It's pure white rather than dingy yellow, and I can actually see what I'm doing now. I can also thread the needle a lot easier.

It looks a little too bright in the photos, but that's just because it's difficult to take a realistic photo of a light source.
In real life it is very bright, but not bright enough to be uncomfortable to look at.

Ok, flame-suit on I guess...

NapaJohn

That's really fantastic. Thank you for posting this.

Mrs. SewNSew

Intersting. It's a bit above my understanding but not out of reach if I need to do that someday. I am a beginner but have had to re-wire lights and so far all has gone well. Its neat to see your work.

Jamesbeat

Thanks

Funny thing; I just looked up the theoretical light output of this emitter @ 1A, and it is 218 lumens.
Incandescent bulbs output around 16 lumens per watt, so the original 15w bulb should have been about the same at 240 lumens (the difference is too small to matter).

I wonder why the LED seems SO much brighter?
I presume it must be the different color temperature (the bulb emitted a yellowish light).

The LED is much more efficient. It is running at 3.5w, which is why it remains cool to the touch

Rodney

Thanks for showing us that. I've toyed with the idea of switching to LED but haven't tried it yet.
Nice job.
Rodney

oldsewnsew

Nicely done, do you have a source for the LED's, or just look on old FleaBay?

Jamesbeat

I believe I bought these from Dealextreme, but I wouldn't recommend them because it can take over a month to arrive!
Ebay is probably a much better bet. I'd definitely recommend a high CRI version, because the cool white versions can be a little harsh looking.
The resistors were from Radio Shack. I only used two of them because I didn't happen to have one of the correct value. The 10w rating of each resistor is uneccesarily high, but does mean that they run very cool

J Miller

No flaming from me this time. I'd love to use cooler LED lights. But I'm waiting till someone produces them as replacements for regular bulbs, at a reasonable price. I prefer not to modify the machine.

I've tried the blue lights as sold by Sew-Classic and my LSMG and they do produce a whiter light. I just wish they'd produce them with screw in bases as well as the bayonet types.

Joe

Jamesbeat

I had the same idea initially, I was going to see if I could remove the glass from a bulb and shoehorn a 110v driver in there. I went back and forth on it for a while, but I had all the parts for this laying around, and it's not like my Kenmore 84 has collector value.
This decision was fueled in part by the realization that the emitter will probably outlast the machine, so the idea of a permanent installation becomes viable, preferable even.

I was as sympathetic as possible with the modification, and it's easily reversible. One bolt and two solder joints, and it would be back to its original condition.
Having said that, I wouldn't have done this to a collectible machine.