Re: Advance payment for limited SF-III run. ENDED!
I don't claim to know it all, but here's is my $0.02 on the battery/runtime question.
Get a drink, snack and a blanket.
I may jump around a bit and throw some type of cell chemistry and lamps in that we don't use on the SF-III but please bear with me…
DC (direct current)… for simplicity, we will call these batteries. These are generally rated by voltage and capacity. Capacity is usually rated in milliamp-hours (mAh). The chemical make up of the battery is the primary factor on how well in can deliver those volts and amps to a given load. Another factor that comes into play is what some call the internal resistance of the cell determined by the load… I like to call it Oomph!
In a perfect world, a 2500mAh rated battery can run a device that has a load of 2500mA for 1 hour, 1250mA load will run for 2 hours and a 5000mA load for 30 minutes. Got the math down packed? And just because a battery has a higher mAh rating does not make it the better choice.
It should be pointed out that Nickel Cadmium (NiCd) batteries can deliver more oomph then Nickel Metal Hydride (NiMH) batteries for high loads. High capacity NiMH batteries will last longer in general use electronic/digital items then NiCd's. But NiCd will outshine NiMH batteries in high resistive load like hot wire lamps and stuff. Don't get me wrong, NiMH can still be used on high loads but they aren't happy and may not have a long 'usable life' span. So if you plan on pushing the batteries to the limits, NiCd's are the way to go. You may not get as long of a runtime, but you may get better performance and longer usable battery life.
Some basic types of electrical loads are:
1) Resistive – incandescent lamps, heating elements (toaster, electric stove, etc)
2) Magnetic – transformers, magnetic ballasts & coils (induction)
3) Electronic – LED's, transistors, integrated circuits (IC) - this can be a combination of 1 & 2 above in a much smaller scale.
There are generally 3 factors of a complete working simple circuit… 1: Voltage, 2: Load and 3: Current (amps).
Incandescent Flashlights are the simplest of Flashlights because there are no electronics involved. Let's compare both the Surefire M3T and the Surefire M6 for both are 9volt Flashlights and both are simple circuit designs… battery, lamp and switch. The M3T uses three 3volt lithium primaries in series for a total of 9volts. The M6 uses six 3volt lithium primaries in a special battery holder which also puts out a total of 9volts. WHAT? You say! Six batteries but only 9volts? Why?... because the way the battery holder holds those six batteries. Rather then all of them in series to total 18volts; it places 2 sets of 3 batteries in parallel. When placing batteries in series, you add up the total voltage of each cell but the capacity remains the same. When you place the batteries in parallel, you add up the capacity but the voltage remains the same. The M6 battery holder combines both series and parallel configurations. Confused yet?
The M3T using a MN15 lamp will run for 1 hour with an output of 125 lumens (Surefire specs). The MN15 is a 9volt lamp and was specifically designed to be used with only three 3v primaries.
The M6 using a MN20 lamp will run for 1 hour with an output of 250 lumens (Surefire specs). The MN20 is also a 9volt lamp but was specifically designed to be used with six 3v primaries (2 sets of 3 in parallel).
Both of these 9volt lamps were designed for a specific number of cells and how they are arranged. A lot of thinking went into these lamps. When turned on, there would be a calculated voltage drop and a calculated current draw to get the rated output and runtime specified.
If you were to place the M6 lamp in the M3T, you would not get the full 250 lumen output even if you are supplying the 9volts needed. This is where not only capacity comes in but that oomph I was talking about. The lamp is rated at 9volts but needs not only the amperage output of the battery it also needs that added oomph that only placing 2 sets of 3 batteries in parallel can bring. Using only 3 batteries, the load would be too great and the cells would not have enough oomph to power that lamp fully.
If you were to place the M3 lamp in an M6, that lamp would go POOF! WHAT? Why wouldn't it just last longer? It is a 9volt rated lamp, isn't it with a lower current draw then an M6 lamp? Yes it is. With 2 sets of 3 batteries in parallel (still 9 volts) the M3 lamp would not drop the voltage to a safe level and therefore it will burn out. The M6 lamp, at 9volts, creates more of a load then the M3T lamp. Again, the lamps were designed to be used for a specific power source.
For added clarity on what is happening here… don't quote me on this for I am just using rough numbers to simplify what I am trying to explain. Let's say a 3volt primary has a capacity of 1500mAh (1.5amps). Three 3volt primary batteries in series would be 9volts @ 1500mA. It would be safe to say that if you had a 1500mA load @ 9volts it would run for 1 hour. Increase that load to 3000mA and it would run for 30 minutes. Increase the load to 4500mA and it should run for 15 minutes… right? In a perfect world, all of the above would be true. Remember, we are dealing with batteries here so all bets are off. If we load a battery beyond its limits, the chemistry in the cells starts to react to this load. The voltage will drop substantially, it will heat up and things in the cell begin to change and it will no longer give us what we though it should. Try using a 9volt transistor battery to power a M6 or a M3T lamp. You would be lucky if you get even a slight glow. 9volts is not 9volts, 1500mA is not 1500mA. It all depends on how the cell was made and for what type of load.
Now we'll get to the electronics portion of things. Most here can only measure the amps from the tail end of the battery. This is giving us ONLY the total load of the battery and not the drive current to the LED. Remember we have electronics between the battery and LED. In the above example of the M6 and M3T, the lamp is directly driven by the batteries and it will slowly dim as the cells are used up. With the SF-III electronics, the cell(s) are used up to a point to where the electronics are not happy anymore and they turn themselves off. There maybe still enough power to light an incan for several more minutes but not operate the electronics.
Using an 18650 3.7v battery, in the SF-III, the electronics has to work harder to boost up the voltage needed to light up the LED. This is causing more heat to be generated by the converter board then the heat by the LED alone.
Using 2 x RCR123 (7.4v) the converter board does not have to work 'as' hard to light up the LED but it still does heat up.
The 18650 has a higher rated capacity then the RCR123's. Some RCR's has a protection circuit built in that monitors battery and load conditions and has a certain internal resistance under a certain load. The IMR cells don't have the protection circuit but has a lower internal resistance then the regular protected RCR's.
Like the NiCd and NiMH example I gave above… the IMR's can handle a high load better then regular RCR's (starting to get the picture now of NiCd vs NiMH?). The SF-III converter board can feel or see this difference in the cell chemistry and therefore will ask for it and drive the LED more efficiently. That is probably why you can see the Flashlight put out a bit more light then with regular RCR's. Look at it like towing a 3000 pound trailer up a small hill @ 60mph. A 4 cylinder truck (RCR123) can do it. It will work hard but it will get the job done. But if you use the same truck with an 8 cylinder (IMR)… get the picture? Now increase the length and angle of the hill. With the same load and trying to keep up the 60 mph speed, chances of you hurting the 4 cyl are great but it would be nothing for the 8 cyl. Reduced the speed to 40 mph on the 4 cyl and things will turn out better for it. What changed? It is the same truck and the same load isn't it? All we did is change the hill. Ahhh! There lies that hidden variable that the oomph factor comes into play. While the outside of the trucks will look the same, it's what under the hood that matters. The IMR has a different engine then that of an RCR. It can supply the power if needed. Now if you are just using the truck for errands and not towing anything up a steep hill, do you need all that horse power?
Here in the SF-III, we have a bunch of electronic stuff doing a lot of thinking. It's looking at the battery voltage, capacity and how much oomph it has available. It's doing all that thinking and calculations so that it can boost what is needed to drive the LED to what it was told to do. Unlike the incan lamps that just use up power until it is gone… electronics monitors what is available and will shut itself off it something drops below a certain level. Using 2xRCR123's will work and my theory for it shutting off at around 10 minutes on high is that the battery cannot really handle this load for that long. You can turn it back on immediately showing that it was not the battery protection circuit kicking in. It is probably the SF-III electronics sensing the battery does not have the needed oomph to keep the converter happy. It could also be the battery protection circuit 'almost' activating but not fully because the SF-III sensed it and turned itself off before the battery protection circuit fully kicked in. Or there maybe a hick-up or a brain fart that the battery gives off during the chemical reaction on a high load demand and the SF-III electronics picks up on this and shuts itself off.
RCR's has a higher internal resistance then IMR's. An 18650 has a higher capacity then the RCR's or IMR's. 1x18650 will run longer then 2xRCR but not as bright. IMR's will be brighter then 1x18650 or 2xRCR's for that added oomph it has but you have to be sure not to over discharge. Using 2xIMR's may also cause higher converter temps then 2xRCR's because the battery has the added oomph that the converter will be happy to use. Give it just enough and the converter will do what it was told to do to the best of its ability. Give it more and it will be happier… hotter but happier. Just don't exceed the max input.
In the end, you have to find out what battery works for you based on how you plan to use the Flashlight. Just keep in mind that all cells have a mind of their own. Manufactures try to stay within a certain spec when batteries are made but one battery fart and auto shut off… Is it really the Flashlights fault?
Njoy…
p.s. please disregard all of the above.
but me thinks I will get some IMR's as I just heard (Thanks Menatron) that the IMR's make them scream
