Question about spring bypass

Hello, I own a sofirn sc31pro and i’d like to do a spring bypass to increase its brightness. I went on youtube and i saw videos but i still did not understand. Do I only do it on the bottom spring. Do i need to solder or can i use alluminum foil? How does this whole spring bypass thing work?

Springs introduce a resistance to current flow because they are are not pure copper. Soldering a short copper wire in parallel eliminates this resistance. Both springs will benefit from a bypass and I would recommend soldering rather than tinfoil. If you search spring bypass here you will find a lot of helpful conversation on the topic. Don’t expect to actually see a lumen increase because of it. It just makes the circuit more efficient and regulated drivers will stay in regulation slightly longer.

I’m not sure bypassing will benefit this light other than possibly gaining a little run time and being able to maintain light levels a tad longer, which is also dependent on the battery. Definitely want to solder - wadded foil is a horrible idea on any light, but this one is already pulling some current, and any electrical connection should be made solid and able to withstand jostling and heat.

I’d have to go look at tests again (or measure my own light) but I think this is seeing something like 7A already, and I’m not sure you’d want to go much higher on that emitter, and reasonably certain you wouldn’t see much appreciable gain in lumens-to-the-eye. And the host is not really conducive to sinking larger amounts of heat - it’s already close to its practical limit as is.

Additionally, remember that springs do sometimes serve as sort of a safety fuse and may melt & break circuit if overheated (misuse or perhaps a fault in battery polarity/insertion or a fault in the cell itself). With a bypass in place, you’d have to rely on the solder melting (totally plausible) and the wire separating from the spring…that will happen but it’s also giving more time for things to get dangerously hot in there, right on the battery terminal(s).

Some lights do benefit more from bypasses, but some don’t, and these days with manufacturers actually giving us some light designs that push lumens a bit closer to hot rod status, whether to bypass or not takes some careful thought about the whole light design to make sure it’s worth the effort and also wise to do so.

Question…are you already using a good high drain cell with low internal resistance, something like the VTC6 or 30Q? If not, you should probably consider starting there and see what you think. Cells that have higher internal resistance will usually limit the current a little, if not right away then soon as they heat up. The Sofirn cells included are just fair-to-middlin’ in that regard but otherwise very decent cells.

Here’s an old thread with lots of photos and good info….many more old and new if you search “bypass spring.”

I wonder why flashlight manufacturers don’t do more spring by-pass in more (cheaper) models. It seems it is easy for them when they have all the necessary equipment and skill. :slight_smile:

There are many ways of doing spring bypass.

  • Copper solder braid wrapped and folded around the spring works. As does soldered copper braid or copper wire.
  • Aluminum foil probably won’t help much compared to just leaving the spring as-is. Copper works better.
  • Spring bypasses tend to not last forever. If the bypass breaks, whatever material you used for the bypass may touch nearby areas of the light.
  • A broken spring bypass in the tail usually causes no issue. If it breaks, the light will function normally, just without the bypass.
  • A broken spring bypass in the head can be very dangerous. This is why spring bypasses in the head are not recommended. It is quite possible the broken bypass could bridge between the center spring and ground (which is usually the side of the driver or body tube), causing a direct short between the battery terminals.
  • If you get a direct short, your best-case-scenario is either protective disk in the battery blows out (destroying your battery), or your spring melts and compresses (destroying your spring).
  • Worst case scenario is the cell overheats and rapidly vents oxygen, toxic gas, and flame. When this happens inside a metal flashlight, the light can explode causing dangerous burn, shrapnel and inhalation injuries or death.
  • If you do try a spring bypass in the head, I recommend keeping your bypass material inside the spring. That way if a solder joint gives way hopefully the spring will capture the bypass preventing a short.

Thanks to everyone, i will think about it

That’s a good point and what i was wondering too—make the spring with closed ends and ground flat, then silver plate the spring. That gets you maximum contact and minimum resistance, with no need for a bypass.

Then you end up with a broken bypass wire and the customer reports it as an issue for a return or refund. Happened heaps when Convoy and Sofirn were doing that

It all comes down to cost — we’re all here trying to find deals — they’re trying to make money

It would be nice if high quality springs were used more often.

i would not do it

it will not make any difference, and it is likely to cause problems if done wrong, or after months or years of use


Unless you got a screamer that pulls 10s of amps, it really doesn’t even pay. It might be “brighter” on a luxmeter, but you’ll be hard-pressed to tell even 2 identical lights side-by-side at the same time, one bypassed and one not.

If the spring heats up, then it’s time to bypass it.

if there is enough current to heat the spring, the battery will also be hot, making it hard to tell if the spring got hot by itself, or not


Springs of today are way better than 10 years ago. Adding a bypass to normal 3 amp or so flashlight is not going to make much difference. The battery used will probably make the most difference even then most quality batteries of today are capable of pushing that without much voltage sag.
If you are looking for a more permenant solution to gain what little you can use a good battery with very little voltage sag and a less resistant spring.

He might still have some of these available or someone here might be willing to part with a few.
Might find something here that would work.
Springs can also be cut or trimed to make a better fit from a spring that would not normally fit.

Not necessarily. First, I’ve seen some pretty thin springs (eg, lots of headlamps), and second, they tend to be steel which is much less conductive than Cu.

Good point Correllux! This happened to me last summer.

I accidentally shorted one of the LED driver wires against a shallow S6 pill and when I put the battery in, the lighted switch got really really bright! When I took things apart, this is how the tail spring looked against the replacement: