# Mag C & D Tailcap Spring - Resistance?



## Bob96 (Sep 20, 2010)

'''




A lot of guys add wire or copper braid as a resistance fix to the tailcap springs of Maglights on high output incans. Looking at these springs the wire diameter is pretty big. Is there really much resistance in the stock Mag C or D springs? Would the bulb really see more voltage if a resistance fix was performed?
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## mrartillery (Sep 20, 2010)

For a short answer yes. If you uncoiled a Mag tail spring it would be probably 10-12 inches, factor that in with the fact that is heavy gauge and you have a lot of resistance and voltage drop across it. A piece of wire or braid soldered in helps counteract this and will make a difference on the amount of voltage the bulb recieves. That's why I have never done a resistance fix to my ROP H with 26500's, the host has enough resistance the way it is to keep from flashing the bulb, reduce the resistance and you can have a  on your hands.


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## fugleebeast (Sep 20, 2010)

A couple of years ago I wanted to see if the resistance fixes to Mags made a noticeable difference. I built two ROP Lows using Kai Domain battery adapters and then did some resistance fixes to one of them.

You can see the thread and pictures here: https://www.candlepowerforums.com/threads/182607

I didn't even solder and you can see that the difference was very apparent in brightness. Well worth the time, if you ask me.


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## alpg88 (Sep 20, 2010)

well if we talking 1-2 amps, stock tail spring needs no mods, for more you want braid soldered.
easy to see, if it heats up, mod it.
my 150w light (12amps) needed that mod, i used c mag spring so i could fit 4x26650, it was getting hot, i install the braid, no heating up.
spring inside the switch (actually inside the tower) has more resistance than tail spring. you might wanna fix that before tail spring.
someone measured d spring resistance, you gain 0.5v by braiding it, at 5 amps iirc.

kd holders are garbage, they even say in description not to use it for anything more than 1 amp.


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## Sub_Umbra (Sep 20, 2010)

Years ago I seem to recall someone selling a low resistance spring for those lights.


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## mrartillery (Sep 20, 2010)

You mean these? They work fine but the solder braid is much better.


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## Billy Ram (Sep 20, 2010)

The springs are made of steel wire. " A poor conductor of electricity " And work like a heater drawing current from your batterys. 
Billy


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## Justin Case (Sep 20, 2010)

mrartillery said:


> For a short answer yes. If you uncoiled a Mag tail spring it would be probably 10-12 inches, factor that in with the fact that is heavy gauge and you have a lot of resistance and voltage drop across it. A piece of wire or braid soldered in helps counteract this and will make a difference on the amount of voltage the bulb recieves. That's why I have never done a resistance fix to my ROP H with 26500's, the host has enough resistance the way it is to keep from flashing the bulb, reduce the resistance and you can have a  on your hands.



The large cross-sectional area of a wire *reduces* resistance. Resistance R is given as

R= rho*L/A

where rho is resistivity, L is length, and A is cross-sectional area. For a steel tail spring, if we assume a diam of 0.1",a length of 12", and a steel resistivity ranging from 1 to 10 x 10^-7 ohm-meter, we get

R ~ 0.006 ohms to 0.06 ohms

As is the usual case, parasitic resistance starts to matter when you start pumping a lot of current.


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## CKOD (Sep 20, 2010)

Ive measured the resistance of one before, it was ~.03 ohms I want to say. I'll measure it again tomorrow to double check if I remember to. It was measured with a benchtop meter with 4-wire resistance measurement so it's much, much more accurate at measuring low resistances then any 2-wire meter could hope to be.


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## Bob96 (Sep 20, 2010)

I am surprised that the resistance mods appear to have effect on voltage output. I was comparing the large wire diameter of the Mag springs against the small dia. wire used on LEd modules - some of which pass 5-6amps. As a comparison the Mag springs look like overkill in reducing resistance. Maybe not?


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## CKOD (Sep 20, 2010)

Bob96 said:


> I am surprised that the resistance mods appear to have effect on voltage output. I was comparing the large wire diameter of the Mag springs against the small dia. wire used on LEd modules - some of which pass 5-6amps. As a comparison the Mag springs look like overkill in reducing resistance. Maybe not?


 
Copper is a much, much better conductor then steel, thats where the difference is. If my above .03 ohm figure is correct, that would be the same a 5 feet of 18 awg wire. ( http://www.cirris.com/testing/resistance/wire.html )


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## Justin Case (Sep 20, 2010)

You may be making the same oversight I've made on occasion. The tail spring is steel; the hookup wires are copper. Steel resistivity can be about 10X to 50X higher than that for copper.

24 gauge is about 0.02" diam, or about 0.0003 sq in cross section.

If the Mag tail spring is about 0.1" diam, that gives a cross sectional area of about 0.008 sq in, or about a factor of 25X larger than the 24 ga wire. Factoring this in, the overall resistance is a wash so far (remember, resistance equals resistivity x length / area).

The LED hookup wire is also probably about an inch long, vs say 12 inches for a Mag tail spring. Thus, overall the hookup wire resistance is thus perhaps about 12X less than that for the Mag spring.


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## CKOD (Sep 21, 2010)

Just double checked, and yep, the spring was .027 ohms from the top to the outside edge of the bottom, and since I had the calipers out it is .075" diameter steel wire. 

7" of #4 "Soder-Wick" .1" wide was .012 ohms, so 2, 2" pieces in parallel would be .0017 ohms. On something with a 10A draw the drop over the spring goes from .27V to .017V, a significant drop, could make quite the difference on something like a DD SST-90 light.


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## bigchelis (Sep 21, 2010)

When I use my ROP's I use them in a 2C Hosts and powered by 2 IMR 18650 cells.

This makes it almost impossible to use a spring, so I use a small magnet.



Does a tiny magnet as fat as a quarter and diameter like a #2 pencil really offer resistance?
Its these magnets:
http://www.lighthound.com/Magnetic-Spacer--16mm_p_1046.html
and sometimes I have to use this one too:
http://www.lighthound.com/Magnetic-Spacer-for-Charging-14quot-x-14quot_p_1047.html

bigC


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## alpg88 (Sep 21, 2010)

bigchelis said:


> When I use my ROP's I use them in a 2C Hosts and powered by 2 IMR 18650 cells.
> 
> This makes it almost impossible to use a spring, so I use a small magnet.
> 
> ...


if it is nickel plated than resistance is negligible, i measured resistance of 10-15 neo magnets (about 1" long stick) my fluke showed as little resistance as 2 shorted probes did. almost 0. 
uncoated ceramic magnets barely conduct electricity. carbon fiber is a conductor too, as i found out the hard way, but has huge resistance thou, but enough flow to short my holder, good thing i noticed soon enough, other ways you'd see new thread in smoke and fire section.

it is the coating that makes the difference, even copper coated nichrome wire will have as little resistance as copper itself, electricity takes the path of least resistance, in case of coatings it works like Faraday suite


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## stinky (Sep 21, 2010)

You could get some of these and bend them. I did it by hand (it's a bit short - I widened a few coils in the middle and lengthened it a bit) to replace the spring in my dd 3D Mag P7. It is noticeably brighter. I would not recommend doing it by hand though; someone must have a better way to bend springs.

Super cheap and resistance is effectively zero (silver-plated 15 gauge copper 172). You could even solder it in for better contact if desired.

Silver-Coated Beryllium Copper Compression Spring .770" OD x .072" Wire Size x 0.690" Free Length (Pack of 10) 
 Buy new: $3.82 

Strangely, if you buy only one it's $7.24. 
Or you could get the same ten pack for 12x the price from the same supplier 
Silver-Coated Beryllium Copper Compression Spring .770" OD x .072" Wire Size x 0.690" Free Length (Pack of 10) 
 Buy new: $47.38


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## CKOD (Sep 21, 2010)

stinky said:


> You could get some of these and bend them. I did it by hand (it's a bit short - I widened a few coils in the middle and lengthened it a bit) to replace the spring in my dd 3D Mag P7. It is noticeably brighter. I would not recommend doing it by hand though; someone must have a better way to bend springs.
> 
> Super cheap and resistance is effectively zero (silver-plated 15 gauge copper 172). You could even solder it in for better contact if desired.
> 
> ...


 
Very nice find there, decent spring rate on that too, much better then I would expect from a copper spring. Beryllium copper is what they use for pins in connectors quite often. Not quite as conductive as pure copper, but much stronger. I wonder how well it handles repeated cycles.


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## stinky (Sep 21, 2010)

CKOD said:


> Very nice find there, decent spring rate on that too, much better then I would expect from a copper spring. Beryllium copper is what they use for pins in connectors quite often. Not quite as conductive as pure copper, but much stronger. I wonder how well it handles repeated cycles.



C172 is physically a very resilient alloy, and very suitable for springs. It's conductivity is roughly equivalent to brass, which is not ideal, but these springs are silver plated to increase conductivity, protect against oxidation, and ease soldering (or so I understand). After bending the bugger with my fingers (not easy) I couldn't imagine wearing one out, although the silver plate could maybe wear through.

Here's far more information on beryllium copper than you could ever care to read: ;-)

ttp://www.rfalloy.com/springs96.htm

Anyway they're way cheap and definitely beat the snot out of steel springs.


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## fivemega (Sep 21, 2010)

Bob96 said:


> '''
> 
> 
> 
> ...



*Biggest resistance of stock M*g is switch spring which will save some bulb from flashing in certain battery options.
For example 2 fully recharged IMR 18650 will flash 3854 HO if above resistance is fixed or lowered while many people use this configuration in stuck M*g without problem.
I have measured some tail current increase with copper plated M*g "C" tail spring compare to non plated stock spring.
So, the answer is yes. copper braid will increase current draw specially in higher current applications and bulb will see higher voltage if it can ever takes it.*


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## stinky (Sep 22, 2010)

fivemega said:


> *Biggest resistance of stock M*g is switch spring which will save some bulb from flashing in certain battery options.
> For example 2 fully recharged IMR 18650 will flash 3854 HO if above resistance is fixed or lowered while many people use this configuration in stuck M*g without problem.
> I have measured some tail current increase with copper plated M*g "C" tail spring compare to non plated stock spring.
> So, the answer is yes. copper braid will increase current draw specially in higher current applications and bulb will see higher voltage if it can ever takes it.*



Nice pics FM!


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## Esthan (Dec 20, 2011)

Is there a chance the pics will be uploaded/fixed in this link ? 





fivemega said:


> *Biggest resistance of stock M*g is switch spring which will save some bulb from flashing in certain battery options.
> For example 2 fully recharged IMR 18650 will flash 3854 HO if above resistance is fixed or lowered while many people use this configuration in stuck M*g without problem.
> I have measured some tail current increase with copper plated M*g "C" tail spring compare to non plated stock spring.
> So, the answer is yes. copper braid will increase current draw specially in higher current applications and bulb will see higher voltage if it can ever takes it.*


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## fivemega (Dec 20, 2011)

Esthan said:


> Is there a chance the pics will be uploaded/fixed in this link ?


*Since those pictures removed permanently, you may look at this picture and solder a copper braid to top and bottom of main (inside tower) spring.*


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## Esthan (Dec 21, 2011)

Thank You.


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