How-To: Add Copper Braid to Springs

I have been meaning to do this post for a while, so here it finally is. How to add copper braid to a tail (or driver) spring.

This mod reduces the resistance of the spring significantly, especially steel springs. This may not make a big improvement on a brass spring, unless you plan to push some real serious current. J)

OK, Here's what you need:

  • Tailcap with a spring in it (driver springs need love and attention too).
  • Side-cutters
  • Tweezers
  • Copper braid, the type with no flux is best (1.5mm to 2.0mm, wider might be difficult to work with)
  • Needle-nose pliers
  • Solder
  • Soldering iron (not shown)
  • Helping Hands (not shown, optional, but highly recommended)

First, open up the tailcap using the needle-nose pliers. Insert the tips into the ring holes and turn counter-clockwise (if you have a press-fit tailcap, usually they need to be pushed out from the switch boot side).

Here's the victim patient:

Prepare the braid by bending the end a little:

Note, if the spring is only soldered in one spot, it is best to solder it on the other side as well. This will prevent the spring from falling off when you melt one of the solder spots.

Position the braid on the bottom of the spring just over one of the solder blobs.

Hit the solder blob with the iron and fresh solder. As soon as the solder spreads to the braid, remove the heat. You want to prevent the solder from 'climbing' too far up the braid.

Now that the bottom is secure, snip off the top of the braid with enough excess to allow the braid to wrap around the spring. Leave a little slack inside the spring.

Now we pre-tin the top of the spring so the bonding occurs quicker when we solder the braid onto it. I tin where the spring top is lowest, so the braid doesn't stand up higher than the spring. This prevents a potential 'hotspot' where all the current flows through a tiny contact point.

Wrap the braid around the spring end:

Solder the braid on with heat and a small amount of fresh solder.

Trim the end as necessary to reapply the spring cap

Replace spring cap, ensuring it slides down all the way. Some prefer to leave the cap out as it adds another contact point, but in my testing it is negligible. Plus, it looks better.

Reassemble the tailcap and you are done! Doing the driver spring is virtually the same. Really short springs may be a little trickier, but can be done.

NANJG 105C springs do not need copper added, but I recommend replacing them with real springs (mounted upside-down) to add some shock absorption. It prevents inadvertent mode changes.

I hope this has been helpful. Happy Modding! searchID8936

Thanks relic. A much talked about mod with some excellent pictures.

Great tutorial with excellent photos, thanks for sharing!

Thanks relic may be able to so that much appreciated

Attach the braid to the top of the spring between the top coil and the one below it. This will allow the top coil of the spring to make full contact to make full contact with the battery. Otherwise, the only point that makes contact will be the braid/solder blob.


I should have pointed out where I specifically solder it. Right next to the end of the spring wire, in the depression it makes. You can see that in the picture. That prevents a raised portion. I’ll edit to make that clear.
Thanks pyro!
Edited too :wink:

Thank you relic38,

So reducing resisitance will make the light brighter or give longer runtime?

I’m curious how much resistance is being reduced in a light with steel springs on both head and tail end.

The reduction in resistance depends on the spring itself. In my experience, I’ve noticed a significant reduction in almost every case.
I measure the tailcap resistance by applying a known current using a power supply (usually 3A or 6A). I measure the voltage drop and from there I can calculate the resistance.
Most tailcaps measure 200mV-400mV at 3A. After the mod, this usually drops to 80mV-150mV.
In a linear driver, this translates to longer runtime at max output. In a boost or buck driver, it has a small effect on run time. In all cases, it’s an improvement in efficiency.
Edit: if there is still a higher resistance, it might mean there is a bad connection in the tailcap or the switch itself is not that great. I’ve fixed bad switches as well, ususally the tiny metal plates inside have a thin raised edge that limits contact area.

Thanks for sharing.
Have any lux readings (before and after) been done for this mod ? To see what if any gains are made. Seems like eliminating the resistance would give a slightly better current rating on a multimeter, (more accurate) but is there an actual benefit that can be measured otf ?

Gains at the lux meter will depend on the driver. If it is an unregulated driver, then there are gains to be had. Otherwise, the gains are mainly to runtime and efficiency.
Edit: I’ve had significant gains on unregulated (DD) drivers by making this mod. On an East-092 driver in an HD2010, the current jumps a lot.

Thanks for the great write-up Relic!

With plunger/nub equipped tail assemblies, Ive been spreading and flattening the braid at the top of the spring before folding it over to increase the surface contact area and keep pressures symmetrical. No solder required on that end before I slip the brass plunger over the top. Protected in dielectric grease, so far no hints of galvanic corrosion (brass/steel/gold plate/copper contact).

People with the HD defiant lights should take heed for max lumens!… hint, hint… :bigsmile:

Great post. I wish I run into it when I first started modding, it would have saved me a lot of time. I got a roll of copper braid when I bought my soldering station. Just a weller but it does the job. I bought it used and he threw in a bunch of stuff. I never knew what the heck that stuff was for until somebody mentioned it. I just managed to go through what was left of the roll and need to buy more. Where do you buy yours from? Or should I say who sells it the cheapest?

Very nice “how-to” relic38!
Thanks for sharing!

I don’t know if it’s the cheapeast, but FT sells some:

Also, you can get it on Amazon:


Cool thanks.

Thanks Relic. I’ve been waiting for this. Since you’ve been tardy in your “how to” postings I had to figure it out myself. Fortunately, I seem to have done it correctly.
A couple of times I folded a piece of braid in half, soldered the vee to the base and the two ends on opposite sides of the spring at the top. I don’t know if it helps, but it can’t hurt.

Great explanation, appreciate it!

EDIT: Is it safe to assume then with this lower resistance there will be less heat no matter how little?

After an XM-L2 or XP-G2 copper star upgrade, I put a lot in the light box, remove the tailcap, jumper the neg. batt to the host with a heavy gauge wire, check the reading. Then, assemble it with the stock tailcap, take a reading. Most lights of single cell, nanjg driver of 3.5A or higher variety will read lower with the stock tailcap and will benefit in lumens from this mod. Usually I get almost all the lumens back from the mod.

Sounds definitive to me.
Do you recall the percentage of increase?

Regarding heat reduction, potentially. To many factors to be sure. One thing is for sure, there is less heat in the tailcap end which increases the chances of that energy being dissipated by the emitter.