Two mode tailcap = resistor? how does it effect runtime?

gratewhitehuntr

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was looking for a simple two mode for the guy next door to leave in his boat with PRIMARIES in it (long term storage emergency use)

I had ordered a Romisen RC-E4 for myself because it is a two mode light.

I was wondering if the two mode tailcap is achieved through use of a resistor or PWM ?

Seems one of the reviews mentioned a resistor....

how does this effect runtime?

I tried searching for the answer but tailcap isn't real specific plus I'm not positive that is it's means of selecting mode


if someone else has a suggestion for another light that is Hi-Lo- maybe SOS that is $20 or less then feel free to suggest. (runs on 2xCR123 or 1xCR123)

thanks guys, sorry about the seemingly newb question
 

LukeA

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Well, two modes in the tailcap is typically accomplished by a resistor. And while the resistor may be a net loss of power, the low mode will still last a looooong time.
 

jbviau

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I've never had a Romisen, so can't help you there, but what about a Lumapower LM33? It's not that much above your $20 price range, which is pretty restrictive given what you want. From what I've read, the LM33's low mode is not achieved by PWM (resistor instead).

http://www.batteryjunction.com/lumapower-lm303.html
 

gratewhitehuntr

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not my $20 limit

we are talking a bout a non-flashaholic here :whistle:

the guy was so impressed with my new D10 that he asked me what lights cost

I asked what kind, we went from there

it is just going to be an emergency boat light for him

you know, something cheap with two modes and primaries
 

precisionworks

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My Malkoff M60/6P has a 2-stage switch from Wayne at Sandwiche Shoppe. With a 60Ω resistor, the light produces 15 lumens. Runtime on the XR-E Q5 should be quite a few days with fresh primaries.

wondering if the two mode tailcap is achieved through use of a resistor or PWM ?
Easy enough to check with a DMM ... a resistorized tailcap will show something around 15-60Ω. I believe most every PWM controlled light has the circuit/driver just behind the emitter, so that some combination of clicks at the switch will bring up level 1,2,3,4, etc.
 

richardcpf

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Any flashlight which has electric circuit and not electronic circuit sounds bad to me.

A resistor will consume power but won't output anything. But it's just me, some people may prefer it to be easily moddable by changin the resistor.
 

sol-leks

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Is it possible to buy a two mode tailcap and put it on another light, assuming it fits to turn it into a 2 mode light? I would love it if something like this existed for my rc-n3.
 

gratewhitehuntr

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Is it possible to buy a two mode tailcap and put it on another light, assuming it fits to turn it into a 2 mode light? I would love it if something like this existed for my rc-n3.

I sure hope so.
that was part of my reason for buying that light, to cannibalize the tail switch

I have a DD SSCP4 light that is over driven with fresh batteries and was planning on using the switch as a current limiter with a fresh battery.

the light only bin shifts :scowl: (that's angry blue) for maybe 3-5 mins of run and then is perfect.

I have been charging the cells and making a 1 minute run in my WF 500 and they come right down to 3.8-3.9v area ad the light is fine then.
 

sol-leks

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it would be really cool if it were possible to turn the fenix e20 into a 2-mode as well.
 

precisionworks

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A resistor will consume power but won't output anything.
While your statement is factually true, it makes it sound as if the resistor is consuming a large amount of power, which it is not in this application.

If you want electronic control, the McC2S (or McE2S for the E-Series) will work.
 

gratewhitehuntr

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I'm not real electronic here so bear with me


my understanding (please confirm or deny) is that a resistor works kinda like the VF on LEDs
in that the resistor raises the required voltage to flow X amount of current

is this correct?

a resistor causes less current to flow at any given voltage?

so although it consumes power through heat loss, it isn't a major amount and works more like a valve


please elaborate if need be (or correct me)
 

MrGman

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The greater the resistance in series with the voltage source, the less current draw there will be and therefore longer run time.

With 6V "ideal" battery pair and 60 ohms in series with it to the LED, current draw is drastically reduced from what it was without it. Regardless of a regulator chip in the pill driving the LED. The so called "ideal" light emitting Diode turns on at about 3V, 6V-3V is 3V, The most current you can get is 3V / 60 ohms which is 50mA. 50mA of current across 60 ohms is of course 3V 3V times 0.050 amps is 0.15 watts. So the resistor is not just burning up the watts that the LED is not, its restricting total current and therefore power to the LED. The actual voltage will not be 3V it will be somewhere between 3.0 and 3.7. 3V was used as an absolute maximum worst case voltage differential. Point is the resistor will make the voltage drop below that of the regulator where it goes into direct drive. So the LED will be running at low power, the regulator will be doing nothing, and hopefully not wasting any power beyond the level of 1 diode drop (0.6V) worth either, and the resistor will not be roasting either.

If the LED was at say 3.3V for 50mA that would only be 165mW or 0.165W for the LED. The batteries still see no greater than 50mA current draw. If the batteries had a 1000mA/hour rating then they in theory could run up to 1000/50 or 20 hours at this level.

So no its not just wasting all of the energy that should have gone to the LED as heat. Its restricting current to everything and wasting only a little (compared to the original power level without it) as heat.

If you look at the ratio of resistor to LED power its almost even. The resistor is about 150mW and the LED is about 165mW (these are not exact numbers). So to reduce the total power to the LED, you are now wasting about 48% of the total power (315mW) presently put forth by the batteries into the new total load; but if the LED was previously running at 800mA and 3.7V (almost 3W) and the driver was 85% efficient from those same "6V" batteries, total power draw was probably around 3.5 watts from the batteries, so you are still saving a lot of power to run the light at much lower brightness for longer time. There would be absolutely no point in making a lower power mode with a resistor if the resistor were simply to waste all of the power of the original drive level as heat so you could have less light.

These are all example numbers, not exact.

This ratio changes with the value of the resistor.

So its not a bad thing to have a low power setting with just an in series resistor in the tailcap. here is the thread where I originally wrote this.

It works more like a current valve and not just a heater wasting power that's not going to the light.

http://candlepowerforums.com/vb/showthread.php?t=203290
 

gratewhitehuntr

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The greater the resistance in series with the voltage source, the less current draw there will be and therefore longer run time.
.......
It works more like a current valve and not just a heater wasting power that's not going to the light.

http://candlepowerforums.com/vb/showthread.php?t=203290

ok so apparently I do actually know how stuff works
cool

thanks for the explanation and link :thumbsup:
 
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