How to fix this non-contact problem - solder aluminum?

[Bolster]

A Romisen neutral-tint light that I own, became unreliable. So I pulled it apart, and after considerable testing, discovered that my connection problem was between the outer and inner "cylinders" or "tubes" you see that are closest to the viewer in the photo below. You can just see a thin dark line of separation between the outer and inner cylinders. Testing with a wire, I found contact with the inner cylinder (which is immediately adjacent to the PCB) gave me a good bright light; contact with the outer aluminum cylinder (that's surrounds it, perhaps press-fit over it!) gave me a dim flickering light. Yet it's the outer cylinder that completes the circuit.

So I reasoned the "fix" was to solder the outer and inner tubes together. I thought I'd make a neat little circular solder joint all the way around, thereby making a good electrical connection between the two cylinders.

Problem: The outer tube is aluminum (inner I don't know, you can just barely see it or access it, but it appears to have some PCB solder attaching to it), and quite resistant to soldering, even after a good fluxing and thorough heating. After several tries I got a small, unsatisfying, <1mm solder joint (that has fixed the problem...for now) but I would like a much better connection here. Obviously this is not the way to do it. What's the solution for soldering on aluminum? Is this it? I was trying to make your typical 60 tin / 40 lead electrical solder work and it pretty much...didn't.

Thanks.

 

[Thr3Evo]

Take out the driver (if you can) and tin the pill first. Scratch or sand it with something so the solder can adhere better. Also use some flux.
Tin the driver as well, put it back in and bridge the joints.
The pill will require way more heat to be applied since it acts as a heatsink.

And you don't need to solder the whole ring.
I did mine like this:

It's not that pretty but it's effective and it holds the driver in place well.

 

[Bolster]

Thanks!

 

[Thr3Evo]

Good luck

 

[Bolster]

Thanks, and I'm going to try that special aluminum solder I linked above, too.

 

[alexandrul]

What's the solution for soldering on aluminum?

Google: http://www.durafix.com/

An untested way heard from an old technician: scratch the thin oxid layer on the desired spot and then solder as usual, both operations done with the aluminum piece submerged in heat resistant oil. If you're going to try this method (hopefully on another aluminum piece), please share the results as I never needed to solder aluminum, and I don't have any soldering equipment at hand these days.

 

[gradio]

prep & flux is your friend.

Glad your tackling the issue - most I know would replace the batteries if a light doesn't work, some would replace a bulb if easy and inexpensive, many would toss the light (cheap light) and buy another cheap light. Beyond batteries and bulbs, they don't look deeper than batteries and bulbs.

 

[Changchung]

Why no solder a small spring?


Sent from my phone with camera with flash and internet on it...

 

[Thr3Evo]

Why no solder a small spring?


Sent from my phone with camera with flash and internet on it...

Because the object is to bridge the negatives(outside rings) together, the spring (if needed) usually goes in the center(the positive contact).

 

[Changchung]

Because the object is to bridge the negatives(outside rings) together, the spring (if needed) usually goes in the center(the positive contact).

Right, sorry, I dont read all the thread before I respond to it...

Well, the solution will be solder around of the pcb and the copper pill?

Sometimes is hard to the copper pill get solder...


Sent from my phone with camera with flash and internet on it...

 

[Changchung]

I remember sometime ago that something similar happen to me. I solder various wires to the driver and blender it to inside the pill, them press it inside, that way the ground make good contact to the pill...


Sent from my phone with camera with flash and internet on it...

 

[bshanahan14rulz]

I have yet to try this, but I've heard that if you cover the aluminum spot with a blob of molten solder, and while it is still molten, scratch the submerged surface of aluminum to get at the underlying metal without exposing it to oxygen in the air that will instantly oxidize it again.

If the light were a cheapo like most of mine, I'd just crimp the two cylinders together in a few spots in hopes of making an interference contact (which, judging by the pics, should already be made and conducting? weird)

I would say if you already ordered the aluminum solder paste, just wait until that gets there. That is your best bet.