The usual steel springs that are found at the tail and on the driver of our beloved budget flashlights are real voltage eaters, for single li-ion lights that is something you do not want, it means a lower current or shorter regulation periods, depending on battery, current and driver type. If you want to improve your flashlight, one of the most effective ways is to improve the springs. A common and very good way to improve them is soldering a piece of 'copper braid' through the middle of the spring. Although that very succesfully lowers the resistance , it requires some fairly precize work and the end result is always rather ugly.
Today I got a batch of 200 springs that I had custom made by a dutch spring company (not for cheap, small batches are expensive, it was a gamble), it is a robust spring made of phosfor bronze, diameter 10mm, height 15mm. Having high hopes for the performance (and fear for them not performing well) I did some testing today. I chose some fellow contestants:
From left to right: 1)my custom made spring, 2)a small 'carobronze spring' from Fasttech, 3)the new Beryllium-copper driver spring from intl-outdoor, 4)a sturdy steel spring that was on the stock driver of the UF-1405 flashlight, 5)some steel spring from the spare parts box, 6)another spare steel spring, 7)the short spring from a NANJG105C driver, 8)some spring that came with a flashlight host and that I reckoned it could well be a copper alloy.
The plan was to measure the voltage drop at 6A, which is a current that is common among hotrod modded flashlights. I'm sure you can derive the voltage drops for all other currents from that. Of course some springs are longer than others, some are thicker, but since you have the above picture with it you will be able to judge the measurements to value. After some soldering solid copper leads (all solder joints were done well, double-checked for good contact) I made them into this piece of art :-)
I used my power supply and a resistor load (two fan-cooled 100W 0.5 Ohm resistors parallel) to create a 6A circuitry, and measured the voltage over each spring:
I measured every spring twice and got comparable results, I think the values are correct and typical for that spring :
|spring 1||djozz custom phosfor bronze||98 mV|
|spring 2||Fasttech 'carobronze'||101 mV|
|spring 3||Int-outdoor Beryllium-copper '45% IACS'||17 mV|
|spring 4||Uniquefire UF-1405 steel driver spring||228 mV|
|spring 5||some steel spring I||298 mV|
|spring 6||some steel spring II||285 mV|
|spring 7||NANJG105C driver spring||82 mV|
|spring 8||some hopefully copper alloy spring||288 mV|
-my custom spring performs almost 3 times as good as the average steel spring, good enough for a medium driven flashlight but IMO not good enough for a hotrod. Of course I hoped for a lot better, so I lost the gamble here unfortunately :-( I don't think I can sell them to you guys for cost price (1 dollar/spring)
-the carobronze Fasttech spring performs similar as my custom spring, it really helps using a copper alloy compared to steel
-the intl-outdoor spring is the clear winner. It is a short spring, I guess about 3 times as short as my custom spring (both are 1mm wire diameter), but it performs 6 times better. So their special alloy really works, it is about twice as good as the phosfor bronze of the custom spring!
-the NANJG105C spring is very thick and short but still eats 82 mV at 6A, that is significant in a single li-ion direct drive situation!
-steel springs are no good, spring nr 8 is probably also steel
So what does copper braiding do then? I checked that on spring nr. 5, without braiding it measured 298mV. I used rather thin 'Good Wick' copper braid, zigzagged it a bit through the middle of the spring, and got the following result:
As you can see in the picture: 13.7 mV at 6A, that is great! Loosely extrapolating the intl-outdoor spring to the size of spring number 5 it would measure at least 40mV, that is good, but still worse than a copper-braided spring.
Conclusion from this test:
Despite the work doing it and the ugly result, for the moment copper braiding is still KING!