Hi all,
I want to use a pure copper washer as a contact board for my driver (OD 31mm ID 21MM)
This is how I soldered it:
- It was EXTRA hard to solder on top of the washer)Thanks
I probably would have added more solder including on the back side of the driver mainly because the battery will be pushing fairly hard against the positive post on the driver.
If you drop it once, the battery may push the driver completely through the washer.
Also I’d clean the oxidation off of the washer before installing it.
Electrically this is fine, the vast majority of the current will go through the eleven o’clock joint on the first picture because that’s where the sense resistor and the back of the boost IC are located. It looks large enough and you added a bit of copper wire inside right ?
I agree with @INeedMoreLumens , mechanical integrity is more of a concern, as well as thermal coupling to the body as you suggested.
Thanks guys, I will add some joints on the other side as well.
@thefreeman - I did not add a copper wire inside the joints, pure solder, I must add some copper?
Not necessarily, it just looked like it from the picture.
If you can find a washer with a slightly smaller id that’d be better. There’s no spring to absorb impact from dropping the battery in so you might eventually peel the negative trace off the board the way you’ve done it
That exactly what I was thinking when I mentioned adding some solder to the backside of the driver, to kinda sandwich it in there.
Ah yeh, i skimmed over and didn’t catch that. Good idea 
Another thing I think you could try if you found that wasn’t strong enough, is use two washers with a slightly smaller ID, like 20mm or 19mm, and sandwich the driver in between. So instead of the driver floating in the middle of the washer, with just solder holding it in place, the edge of the driver would be pressed against the inside edge of the washer, just like it would be against the shelf in a 20mm flashlight.
If that works with the flashlight you’re using. You might be able to even just use a thermal epoxy with that, might not even have to solder.
Just throwing out an idea, whatever works.
I would clean the oxidation before trying to solder it too. Solder will not adhere well to oxidized copper. This is likely one of the reasons that the OP had a hard time soldering things to begin with.
Great point!
I’m not a soldering expert, but I’d have thought you need a bit more flux on that to get the solder to flow.
Ya, when you’re soldering copper pipe you apply flux with a little paintbrush and heat with a blowtorch, right? And it’s oxidizes really easily, that’s why you tin copper wire.
So I think, and I don’t actually know, I think, that if it’s pure copper and I wanted it to be as clean as possible what I would do is probably scrub the whole surface a bit first, cover the whole washer in flux, get it to ~200°C with a blow torch or something and put a couple solder blobs on the washer. Then while it’s still hot, but not hot enough to melt the components off, put the driver in there and solder the driver to the blobs. I think that’s what I’d try.
But I think it can be a little oxidized and still be pretty conductive.
Thanks guys!
Unfortunately I dont have smaller id washers, I’ll try to add more solder on both sided, and then test it with some force.
I’ll try to sand off the oxidation once I finish soldering
It would be better to sand it before soldering… at least in the areas where you want the solder to stick well. Flux does help, but if you want the best flow, with the least heat, the copper should be very clean before you start soldering!
I know it is too late now, but it would have been better if you had cleaned the copper before you started the process. I have read that a soak in vinegar (time dependent on the level of oxidation), rinse, and a light sanding with maybe 400 to 600 grit abrasive paper is very effective for cleaning copper.
Like he said ^
The whole point of sanding is so it’s easier to solder
