P60 drop-in: Need alternative for the small spring

I received an empty reflector set from KD and unfortunately the small spring was missing.

I've looked through my dead/discarded lights and other accessories and have not been able to find any springs that are the correct size.

Using rare earth magnets is not an option due to the risk of a short.

Anyone have any ideas on what else I could use as a short spring until I can (hopefully) get the missing part sent?

I've been wanting to do this mod, but I never had the motivation, till' now.

I have suspected the +B springs from the chinese drop in manufacturers suffer from high resistance. I am not sure if its the electrical properties of the spring, or contact resistance with the cell... or a combination. Pics below show that the harder I press down on the -B, the higher the current draw is at the tailcap. Theres also the strong possibility that my +B spring was just part of a bad batch.

Light pressure cell #1:


Heavy pressure, compressing the spring 100%, cell #1:


Light pressure cell #2:


Heavy pressure, compressing the spring 100%, cell #2:


Light pressure cell #3 (IMR-18650)


Heavy pressure, compressing spring 100% (IMR-18650)


Solution was to just replace the suspect spring with copper bar stock, cut to length.






The entire procedure took less than 20 minutes. Tailcap current draw is now a consistent ~2.75A with non-IMR cells. I haven't had it this way long enough to evaluate the durability/reliability but I think if I am careful it should be fine. I expect IMR18650 cells to draw about 3A

Is your LED direct driven in this example?

Bill

Bullzeyebill said:

Is your LED direct driven in this example?

Bill

Click to expand...

I don't know for sure, but I do think it is DD, using the AM radio test I get no RFI noise. I've never had it apart before.

Probably DD. A constant current driver would give the LED consistent current to the LED, and the current at the tail would be more with the least pressure on the spring, dropping as you pressed harder on the spring. Runtime would suffer with high resistance.

Bill

I have used the battery spring from an old TV remote control

Black Rose - I've been wanting said springs for a long time, no luck sourcing any.

There is an item at the Sandwich shope, search for spring, which looks like it might be correct, but their description is lacking. Best and only possibility I've come across.

If they come bulk, I'll split.

In the short term, I can post you the spring from an as-yet-unassembled drop-in, in effect robbing peter to give to paul but I have a few spare units presently. Send your info I can mail in Monday.

I have used a few things for this. A cut off from a 3/8" brass or copper rod will work in most cases, but if you just want a spring you can use a spring from the tower of a maglite. I happened to have several of them so I cut one to length and then bent the end of the spring over to run through the center for the battery pos contact.

kramer5150 said:

Solution was to just replace the suspect spring with copper bar stock, cut to length.

[SNIP]

I haven't had it this way long enough to evaluate the durability/reliability but I think if I am careful it should be fine.

Click to expand...

That's an interesting solution.

The only thing that concerns me is if the light were dropped.
Tailcap springs do not compress as much as the ones on the drop-ins, I wonder if the bar stock could puncture or damage the positive button on the battery.

Black Rose said:

That's an interesting solution.

The only thing that concerns me is if the light were dropped.
Tailcap springs do not compress as much as the ones on the drop-ins, I wonder if the bar stock could puncture or damage the positive button on the battery.

Click to expand...

Doesnt seem likely, but using a slightly larger diameter bar like 3/8" may be better. It would give a larger contact area, so there would be less chance of stabbing that bar into the cell.

Black Rose said:

That's an interesting solution.

The only thing that concerns me is if the light were dropped.
Tailcap springs do not compress as much as the ones on the drop-ins, I wonder if the bar stock could puncture or damage the positive button on the battery.

Click to expand...

Seems unlikely, although it wouldn't surprise me if cell damage occurred on a hard fall with 2x18650. FWIW the brass stock I am using is 5mm.

just a source on pretty hard springs are these switches (dealextreme)

http://www.dealextreme.com/details.dx/sku.5632
http://www.dealextreme.com/details.dx/sku.15879

It looks a little funky but you can sleeve the entire spring with some copper coax shielding braid sourced from a few inches of audio cable to lower resistance. It looks a lot better if you find braid with an ID close to the diameter of the spring wire.

I know, not very elegant. But it works, at least on tailcap springs. YMMV on a module spring.