# Why don't more people use imr batteries?



## flashlightsarecool (Nov 11, 2014)

This may be a noob question but I'm gonna ask anyway. Wouldn't 1 x 18650 lights like the thrunite tn12 2014, fenix pd35 and zebralight sc600mkii l2 perform better on max output with batteries better able to handle high current? After spending some time on hkj's battery comparator every imr cell out performs its icr counterpart. Am I missing something? Will imr cells over power the LED or circuit?


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## NoNotAgain (Nov 11, 2014)

The light is only going to draw the amperage that is required to run the LED and little more. 

Most single cell lights using XM-L2 leds don't come anywhere close to drawing 5 amps where a high draw cell excels.


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## StorminMatt (Nov 11, 2014)

The main reason why people don't use IMR batteries is because of the lower capacity. It IS true that the voltage will be higher longer with IMR. And the light will remain in regulation for a longer percentage of the runtime. But this is generally not worth it to most people if the runtime itself is shorter. And most mainstream lights (like with your typical 3A XM-L2) really don't need the hugher current capacity. So most people use ICR. With this said, I sometimes wonder why more people don't use HYBRID IMR. Hybrid IMR has close to the same capacity as ICR, yet has somewhat higher current capacity along with better safety. An example here would be the Panasonic NCR18650BD, which, at 3200mAH, is only 200mAH less than the MUCH more popular NCR18650B. Yet, it's safer and can deliver 10A continuous/15A pulse.

Of course, I think another possible reason for people going ICR is that people are generally steered away from unprotected cells, even if the chemistry is actually safer.


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## twl (Nov 11, 2014)

I use IMR batteries almost all the time.
I have small high-output lights that need the current capacity.

However, over my years of flashlight usage, I have found that I almost never need anywhere near the battery capacity that many people want to keep on tap in their lights.
I have NEVER run a rechargeable battery down flat. I see no reason to do it. It's a rechargeable battery.
I don't know what other people do with their lights, but I can't think of anything that I would EVER need 3400mah of capacity for, in a single day's use.
Maybe if you are on some search and rescue missions, where the light needs to be on Turbo for hours at a time, then maybe that might be different.
And maybe if you are out "playing around" trying to see how long you can run your light on Turbo, and impress your friends, that might need a whole battery to do it.
But in "real life", I just don't see it actually happening. At least not in my "real life", in terms of EDC flashlight use.

And so, a smaller capacity is just fine with me, because I never need a large capacity. I generally need less than 15 minutes of flashlight use on any given day, and on some days, I only need 30 seconds of flashlight use. 

I realize that there are a lot of guys out there who are setting up their lights as if they are going to go thru Armageddon at any given night, and will never be able to recharge their flashlight again, and want 87 years worth of battery life on a millionth of a lumen. I'm not one of them.
As long as I can recharge my light at night after I get home, I have all the run time I need. And I do carry a spare battery in a battery container in my pants pocket, just in case I do get some unusual need for light. I never carry more battery than I would be able to use in a night, unless I go camping in some backwoods place that has no electricity for days on end.

IMR is a safer chemistry, doesn't have any protection boards to fail, and has enough capacity for my needs, and offers high current delivery for my little powerhouse lights.
It works for me.
YMMV.


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## ShineOnYouCrazyDiamond (Nov 11, 2014)

Just so you know I only use IMR for my smaller batteries in the 16340 and 18350 size. Under load these IMR cells have an much as, or more, capacity than their ICR counterparts for most any draw over 500mA. I also use IMR for 18500 cells as the capacity is so close to the ICR cells that I prefer the safer high drain version.

For 18650 cells I use ICR cells for many lights that offer good regulation. For other higher draw 18650 lights that have high drain 5+ Amps I always use IMR cells.

Oh - I also use eFest 10440 AAA size cells in my AAA LF2XT lights.

In general I prefer the higher safety margin that the IMR cells provide as well.


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## SimulatedZero (Nov 11, 2014)

Capacity, straight up. That and I've never taken a good look at IMR cells. Once I determined that their advantage was mainly in very high current lights my interest waned. I don't use them as much any more, but I used to go through at least one 3100mah battery a shift when I worked nights. I also used to go through two or three eneloops a day easy when I was doing audio installs and working with a sound crew on my weekends. I had to do a stage set up, tear down a different stage, and then set up a fight cage one day. I went through all four of my spare batteries. :shrug:

I guess it's because I used my lights so much that I was more worried about run time and regulation than I was out put. That's why I'm not a big fan of these modern flash and trash lights. Ultimate cosmic output, for 3 minutes... :shrug:

If I knew more about IMR cells vs ICR cells I would probably be more interested to be honest. But, a lot of that lack in education comes from not taking the time to simply look. Looking at what Matt said up top though does has me very interested in said Hybrid cells. 

Question, if a cell sustains a higher voltage at a higher drain does that give that cell more capacity at said current draws?



Side note: A little irony here is that I have never run through a bunch of cells whenever I've gone caving. Probably because I get so dark adapted that I only use the two lowest modes and generally start cussing whenever somebody flips on anything over 50 lumens. But still, lol.


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## flashlightsarecool (Nov 11, 2014)

SimulatedZero said:


> Capacity, straight up. That and I've never taken a good look at IMR cells. Once I determined that their advantage was mainly in very high current lights my interest waned. I don't use them as much any more, but I used to go through at least one 3100mah battery a shift when I worked nights. I also used to go through two or three eneloops a day easy when I was doing audio installs and working with a sound crew on my weekends. I had to do a stage set up, tear down a different stage, and then set up a fight cage one day. I went through all four of my spare batteries. :shrug:
> 
> I guess it's because I used my lights so much that I was more worried about run time and regulation than I was out put. That's why I'm not a big fan of these modern flash and trash lights. Ultimate cosmic output, for 3 minutes... :shrug:
> 
> ...




These "flash and trash "lights are exactly why I'm curious about IMR cells. The Zebralight seems to be well regulated on max output with ICR. The Thrunite and Fenix seem to be dependent on voltage. After 10 -15 minutes of turbo on freshly charged Eagletac 3100's the beam is noticeably dimmer. After I slap the batteries on the PILA and take them back to 4.18-4.20 we have full brightness again! Seems ICR's have a bit of voltage ED in the Fenix and Thrunite.


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## SimulatedZero (Nov 11, 2014)

Lol, I knew I was going to take some heat on that one. Yeah, that's why I haven't been so keen on those lights, but you're approach with looking at better batteries is probably the more intelligent route.


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## flashlightsarecool (Nov 11, 2014)

SimulatedZero said:


> I knew I was going to take some heat on that one. Yeah, that's why I haven't been so keen on those lights, but you're approach with looking at better batteries is probably the more intelligent route.



Hey, no offense taken. I never would have bought those two lights had I known the batteries would have to be fully charged to achieve max brightness. That's what I get for being caught up in the lumens race. If I've learned anything on CPF its that factory specs aren't always accurate and its a good idea to read lots of reviews here before buying a light. 

Peace


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## GordoJones88 (Nov 11, 2014)

ShineOnYouCrazyDiamond said:


> Just so you know I only use IMR for my smaller batteries in the 16340 and 18350 size. Under load these IMR cells have an much as, or more, capacity than their ICR counterparts for most any draw over 500mA. I also use IMR for 18500 cells as the capacity is so close to the ICR cells that I prefer the safer high drain version.
> 
> For 18650 cells I use ICR cells for many lights that offer good regulation.



Ditto.

Also, just a few years ago, a lot of 3.0v CR123 lights could not use a 4.2v 16340 cell as it would burn out the circuit.

Also, over-discharge protection is built-in to a good ICR cell.
I don't think any IMR cells have over-discharge protection.


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## darkknightlight (Nov 11, 2014)

Yes, imr cells do not have built in over discharge protection, but most led drivers do have low voltage protection. As others have stated, imr cells are able to maintain a higher voltage for longer. With most 7135 based drivers, this means that an imr cell will allow an led to stay in regulation longer because the battery can maintain the forward voltage of the led as well as the voltage overhead of the driver.

Edit: hkj even states in his testing of the 3400 mah Panasonic cells that he doesn't test down to as low a voltage add the cell is rated for since most LEDs could not use a voltage that low.
Take for example his test of the protected Panasonic ncr18650b and Samsung 20r. Under a 5 amp load, the 20r has 500 mah more capacity than the ncr18650b at 3.3 volts, which is the voltage of most xpg2s. At that amperage, the forward voltage of an xml2 is higher; close to 3.8 volts.


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## SubLGT (Nov 11, 2014)

I wonder about this worst case scenario: My 18650 powered budget flashlight has a component failure, resulting in a dead short.
Which battery type is less likely to explode in this scenario?

A. A protected ICR battery with PCB and PTC?

B. A high current unprotected IMR battery that lacks the PCB and PTC?


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## darkknightlight (Nov 11, 2014)

SubLGT said:


> I wonder about this worst case scenario: My 18650 powered budget flashlight has a component failure, resulting in a dead short.
> Which battery type is less likely to explode in this scenario?
> 
> A. A protected ICR battery with PCB and PTC?
> ...


I can't say for sure which chemistry will be less volatile under this particular condition; but I have heard about imr cells having a nail hammered through them without bursting into flames. I cannot say the same for protected icr cells.


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## SimulatedZero (Nov 11, 2014)

So, this thread has got me looking around at various batteries and reading HJK's reviews on them. As a result, I have couple of questions.

1. How much of an advantage would there be using something like an Orbtronic 2900mah Cell instead of the standard Orbtronic 3100mah Cell in a light like the Fenix PD35 2014? 

2. Would the advantage more pronounced in an upgraded version like the PD35vn?

I've found a couple of excellent prices at Orbtronics website for the above mentioned cells. They list the IMR cell as $11.55 and the ICR cell as 11.99, but you can get the newer 3400mah ICR for $14.55. Would the costs be worth upgrading to the 3100mah cell or the 3400mah cell? 

To me, the price difference is negligible between the IMR and the 3100mah ICR. So, the difference between one or the other is which one would give me longer runtimes on a single 18650 light that pulls around 3 or 4 amps. Also, I plan to use mostly the lower modes, so would there be a more pronounced or different performance between IMR and ICR at the lower current draws?


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## Hoop (Nov 11, 2014)

There's another cell to consider as well. In linear regulated single cell lights, the 4.35v 18650's give higher output for more time and are considerably cheaper than higher capacity 4.2v cells. Compare the charts of 18650's on HJK's website. Even the new 3600mah 4.2v 18650's offer greater capacity only beyond 3.2 volts. The 3000mah 4.35v LG D1 cells, which cost like $6 a cell, offer higher voltage through to 3.2 volts. Now, on the lowest output modes the higher cell voltage makes a linear driver less efficient, so there should be some advantage to the highest capacity 4.2v cells here, but capacity isn't much of a concern at the lowest output levels.

Another note about over discharging non protected cells is that, unless the driver is buck boost, a linear light is probably going to be unusable at around 2.9 to 2.7 volts or something, and this is not probably damaging for most cells.


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## ChrisGarrett (Nov 11, 2014)

I use the IMR chemistries in 16340s and in 26650s and I use the LG D1s and E1s for 4.35v in my various lights.

Chris


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## ven (Nov 11, 2014)

I use a mix,imr In high drain devices (mods and flashlights ) ,specific modded lights that thrive off IMR . Also as others I use IMR in smaller cells too,10440 to 16340 to largest 26650.

Most multi cell lights I use higher mah for run times ,even the tk75vn is 4.5A and fine with protected pany B cells . The mm15vn has 4x vtc5 cells in due to being around 6.5A per cell. Although the 30A vtc5 are overkill it does perform its best on those Sony cells. 

Although now a little easier to get,IMR were mainly flat top a while back,now more options of button tops.

As mentioned ,you need to be on the ball with IMR,no running too low where other cells may forgive or even trip with protection. Would not go as far as an advanced battery but some research into the chemistry is advised,more so in high A devices like flashlights and even more so if in a device that sits in your mouth!!! Mods.....


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## BrianHook (Nov 12, 2014)

I use IMR cells although they do not have built in over discharge protection.


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## magellan (Nov 12, 2014)

I'm currently gradually phasing out my ICR use and switching to IMRs because I'm worried about safety and because my IMRs are more than adequate for my needs. The only exception is I have lots of sub CR123A sized lights that use 10180, 10220, 10280, and CR2 batteries which are only offered in unprotected types. 

I usually recharge every night and have set up a side table in the house as a dedicated charging station where I just keep my half a dozen different chargers and batteries. That makes it convenient to recharge often so the extra capacity of the ICRs isn't a factor for me. Since I usually recharge every night I'm not too worried about IMRs not having overdischarge protection as was mentioned previously. If I was a vaper and was running a sub-ohm hot wire customized mech mod with a 10A current draw that would be different.


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## magellan (Nov 12, 2014)

Hi TWL,

You said,

<<I realize that there are a lot of guys out there who are setting up their lights as if they are going to go thru Armageddon at any given night, and will never be able to recharge their flashlight again, and want 87 years worth of battery life on a millionth of a lumen. I'm not one of them.>>

LOL

I suppose it's a guy thing which I have been guilty of too in the past but I've come around to your view recently. It's a saner way to live.  if I were LEO, SWAT, or military it might be different. 

And since I'm usually carrying a 10180, 10280 or RCR2 type light I can easily carry three or four extra batteries in a small holder in my pocket, especially of the 10180 types. Four 10180's or two RCR2's take up less space than the Chapstick I always have with me. Then there's the several small chargers I keep in my car along with a few more batteries there so it's unlikely I'm ever going to run short of juice while I'm out and about. Heck, sometimes I carry a Mophie 6000 mAh dual USB battery in the pocket of my cargo pants which can recharge my iPhone 5C with its 1400 mAH battery four times. The only issue is that these small sub-CR123A batteries are unprotected ICR's.


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## yoyoman (Nov 12, 2014)

I'm with Ven - I use a mix of cells. IMRs in high drain lights, Protected ICRs in multi-cell lights (or single cell lights without low voltage warning/cutoff) and unprotected Panasonic ICR 3400 mAh cells in lights with reliable low voltage warning/cutoff. I use an Eneloop AAA in my pocket carry. And unprotected 10180 cell in my keychain light. Variety is nice.


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## SubLGT (Nov 12, 2014)

StorminMatt said:


> …………….Of course, I think another possible reason for people going ICR is that people are generally steered away from unprotected cells, even if the chemistry is actually safer.



Does the safer chemistry of an unprotected IMR, compared to the "unsafe " chemistry of a protected ICR, actually result in a safer battery for flashlight use? 

I ask again what I posted earlier:

I wonder about this worst case scenario: My 18650 powered budget flashlight has a component failure, resulting in a dead short. A momentary current of several hundred amps will occur.

Which battery type is less likely to explode in this scenario?

A. A protected ICR battery with PCB and PTC?

B. A high current unprotected IMR battery that lacks the PCB and PTC?


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## Capolini (Nov 12, 2014)

I also use both IMR and ICR cells. It depends on the light and what it requires. MOST of my lights are modded and many of those require IMR high drain batteries.


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## funkychateau (Nov 12, 2014)

If IMR batteries are "inherently safe" and don't require protection, does this mean that they can be safely used in 2-cell applications? Are they somehow resistant to damage by over-discharge?


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## darkknightlight (Nov 12, 2014)

Imr batteries are not resistant to over discharge. Like all lithium batteries, if they are being used in multiple cell configurations the batteries must be matched in voltage, capacity, and internal resistance. Multicell flashlights become volatile when one cell is weak and the other cell(s) "compensate." 
The difference in chemistry is that in worst case scenario situations, imr batteries are much less volatile. Iirc, imr batteries do not release oxygen as part of the charging/discharging process, while icr batteries do. I know there are videos on YouTube of a guy creating dead shorts on icr and imr batteries. Might be worth checking out.


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## ven (Nov 12, 2014)

IMR cells are not inherently safe by any means,they are certainly safer in high drain applications where ICR would be susceptible to potential damage by a too high A ask.

IMR should be treated imo the same as any ICR cell,with care and respect with charging /discharging .

The use of IMR cells in mods(ecigs) it is advised to replace every 12 months for example for safety reasons(well it is hanging out of your mouth!!!) but a flashlight could be held at the side of your head too!!.

So with any cell,IMR,ICR/hybrids although some are more stable of course under high loads,they are not without potential risks and could fail.

Just my opinion, treat as with any other 18650 cell in short(no pun intended) :laughing:


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## ven (Nov 12, 2014)

funkychateau said:


> If IMR batteries are "inherently safe" and don't require protection, does this mean that they can be safely used in 2-cell applications? Are they somehow resistant to damage by over-discharge?




I use 4x vtc5 cells as one example in my mm15vn,i still periodically check,use,charge.




They may bounce back a little better than ICR but by no means cells that are safe to abuse,common sense,learn the light and top cells off once down to 3.6-3.8v imo is best practice,as bellow this even though they may power a light,it is better on the cell long term avoiding deep cycles from low voltages.


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## HKJ (Nov 12, 2014)

SubLGT said:


> I wonder about this worst case scenario: My 18650 powered budget flashlight has a component failure, resulting in a dead short. A momentary current of several hundred amps will occur.
> 
> Which battery type is less likely to explode in this scenario?
> 
> ...



A protected battery will not have any problems with a short. Unprotected batteries *may* vent, this is supposed to be fairly harmless, but in a sealed flashlight it can blow the front and tailcap out.


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## SimulatedZero (Nov 12, 2014)

So, reality of IMR safety aside, which cell would give better over all performance in a 3 to 4 amp draw light?


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## darkknightlight (Nov 12, 2014)

SimulatedZero said:


> So, reality of IMR safety aside, which cell would give better over all performance in a 3 to 4 amp draw light?


That depends on the forward voltage of the emitter and voltage overhead requirements of the driver. It's likely that at the 4 amp high mode am imr cell will stay in regulation longer.


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## hazza (Nov 12, 2014)

SimulatedZero said:


> So, reality of IMR safety aside, which cell would give better over all performance in a 3 to 4 amp draw light?



At 3-4 amps I doubt you'll tell the difference between a decent ICR and IMR. However, above 4 amps you're getting towards the territory where you will notice. Some of the vn modded lights that have been measured on this forum have been compared with different batteries and there are slight differences at that sort of current. However, it's often not enough to be noticeable by eye. I definitely have a couple of high drain lights that aren't great with my 18650A's though.


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## hazza (Nov 12, 2014)

ven said:


> I use a mix,imr In high drain devices (mods and flashlights ) ,specific modded lights that thrive off IMR . Also as others I use IMR in smaller cells too,10440 to 16340 to largest 26650.



I do the same. The attraction of IMR is definitely the (sort of) safety, and especially in small cells, the good response at high current.

ICR for most commercially available lights
IMR for small cells (10440, 14500)
Hybrid IMR or IMR for high drain modded lights.


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## SimulatedZero (Nov 12, 2014)

darkknightlight said:


> That depends on the forward voltage of the emitter and voltage overhead requirements of the driver. It's likely that at the 4 amp high mode am imr cell will stay in regulation longer.



In this case the emitter would be an XM-L2 dedomed. I may be getting some triple Nichia or XPL drop-ins in the future though. 

Here's where I keep getting tripped up, does longer regulation mean a longer runtime?


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## SimulatedZero (Nov 12, 2014)

hazza said:


> At 3-4 amps I doubt you'll tell the difference between a decent ICR and IMR. However, above 4 amps you're getting towards the territory where you will notice. Some of the vn modded lights that have been measured on this forum have been compared with different batteries and there are slight differences at that sort of current. However, it's often not enough to be noticeable by eye. I definitely have a couple of high drain lights that aren't great with my 18650A's though.


 
So basically, I might get a slight edge from using a hybrid cell over a traditional ICR, but I wouldn't really notice it in real world use with standard lights.


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## darkknightlight (Nov 12, 2014)

SimulatedZero said:


> In this case the emitter would be an XM-L2 dedomed. I may be getting some triple Nichia or XPL drop-ins in the future though.
> 
> Here's where I keep getting tripped up, does longer regulation mean a longer runtime?


Longer regulation refers to the ability of the driver to maintain output at a given level. Once the battery voltage drops to a certain level, the driver will stop regulating and send the battery voltage directly to the led; direct drive. This does not necessarily mean longer runtime overall. Check out HKJ's battery comparator tool on his website. A graphical representation of voltage under load may be a better way to "see" the difference between batteries at various loads. Also keep in mind than an xml2 and an xpg2 have different forward voltages.

Edit: a light in direct drive is like a traditional maglite for example. Once you turn the light on, it will continue to get dimmer the longer you use it. There is no electronics to regulate the flow of current to the bulb. It's the same with an led that is in direct drive.


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## magellan (Nov 13, 2014)

I just got two 18500 KeepPower Sanyo 1700 mAh IMR batteries in the mail. Assuming the capacity isn't overstated, these are significantly more powerful than my AW IMR cells at 1100 mAH. I'd be curious what accounts for the difference. How can one maker produce a cell that is more than 50% greater than another at a comparable price?

I just checked the prices again on my recent purchase of the AW's and actually the KeepPowers were $20 and the AW's $15 for two. If true I'd rather spend the extra $5 and have the 65% greater capacity of the Sanyo's.

I'm going to put them into service today. If the capacity is overstated I'll know shortly and will post my results here.


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## HKJ (Nov 13, 2014)

magellan said:


> I just got two 18500 KeepPower Sanyo 1700 mAh IMR batteries in the mail. Assuming the capacity isn't overstated, these are significantly more powerful than my AW IMR cells at 1100 mAH. I'd be curious what accounts for the difference. How can one maker produce a cell that is more than 50% greater than another at a comparable price?



I wonder why you call them IMR?.
The ones I have seen had about 1600mAh and a rating of 3.4A

Capacity is very much depend on the actual chemistry in the cell and not everybody has access to the same formulas.


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## magellan (Nov 13, 2014)

HJK,

Oops, I rechecked the description at Illumn.com and you're right, these are protected. It's the Kinoko 18500 at 1200 mAh that are the IMR, slightly higher than the AWs but well within the expected range. That solves that question: the reason is they're not IMRs! This is what happens when I try to order battery/flashlight stuff on four hours sleep after putting in a grueling 14 hour day. LOL

Anyway, these will work well in my Mr. Bulk light which takes 18500's. Next time I'll order the Kinoko IMRs and give those a try.

I did have one technical question though for the experts. Darknightlight said:

<<HJK states in his testing of the 3400 mah Panasonic cells that he doesn't test down to as low a voltage add the cell is rated for since most LEDs could not use a voltage that low.
Take for example his test of the protected Panasonic ncr18650b and Samsung 20r. Under a 5 amp load, the 20r has 500 mah more capacity than the ncr18650b at 3.3 volts, which is the voltage of most xpg2s. At that amperage, the forward voltage of an xml2 is higher; close to 3.8 volts.>>

Okay, given that the XML2 is running 0.5V higher than the XPG2, does an LED emitter really only care about the total wattage and not just total amps? If wattage then the XML2 can pull slightly less amps than the XPG2 at a given output since by Ohm's Law V x I = W. Doesn't this mean the XML2 will remain in regulation longer than the XPG2? But we're taught that semiconductors are current controlled devices unlike vacuum tubes which are voltage controlled devices. So the question is which is it?

Okay, I'm totally confused now. I'm just a biologist after all, not an EE. What the hell am I doing trying to figure sh*t like this out? LOL


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## flashlightsarecool (Nov 13, 2014)

After spending too much time on hkj's comparitor it appear the keeppower imr18650 2500 mah and 3200 mah are the best choices for lights running 3-4 amps that need voltage to maintain output.


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## darkknightlight (Nov 13, 2014)

The forward voltages of LEDs varies from emitter to emitter. So one xml2 may have a forward voltage of 3.8, while another xml2 has a forward voltage of 3.6. What we do know from lots of testing done by members here and in other forums is that the forward voltage of an xml2 is usually a few tenths of a volt higher than an xpg2. LEDs are current controlled devices, but their voltages also tend to fluctuate under different current loads. Typically the more current going through an emitter, the higher the emitter voltage goes (even if it's only a couple tenths of a volt).
The statements I made before we're based on Match's destructive emitter testing charts and HKJ's battery testing charts.
If we assume we are using an led driver that requires no voltage overhead to operate, under a 5 amp load to the led, a Panasonic protected 3400 will run out of steam 500 mah before a Samsung 20r even though the Samsung is technically lower in capacity. This statement is based on using an led with a forward voltage of 3.3.
Don't worry, I'm not an EE either, I just enjoy reading about how this stuff works

Edit: by run out of steam I don't mean the battery is dead and the light turns off, rather that output is less. You may still be in "high" mode, but the output will be less than with a freshly charged battery.


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## ShineOnYouCrazyDiamond (Nov 13, 2014)

I don't think you will see a XM-L2 with a Vf of 3.8v. That's a bit high. I think when you get to the higher amp ranges you are looking close to 3.1-3.3 volts. 

When you look at HKJ's 18650 battery pages be sure to check out this one: http://lygte-info.dk/review/batteries2012/Common18650Summary UK.html. Pay special attention to the sections on Discharge Capacity Down to 3.4 volts and Discharge Capacity down to 3.6 volts. There are really the specs that I use when trying to find a good cell for the application. Just looking at how much capacity any given cell has at a particular current doesn't show you the slope of the discharge curve. When you check out the capacities to a particular voltage you get a great comparison between cells and you start to see that as you get to the 5, 7, 10 Amp range (and even the 3A range) how some cells fall flat on their face during discharge. 

Depending on your use case you then start to see that for high current devices the IMR cells, while still rated lower, will outperform their ICR counterparts at high draw.


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## darkknightlight (Nov 13, 2014)

I agree, 3.8 is high for a forward voltage. I meant led voltage under load; my bad! I hope I'm not the source of confusion 

Edit: that is a good all in one chart to reference as well, just keep in mind that it doesn't show discharge curves, only total capacity down to 2.8 and 2.5 volts respectively.


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## magellan (Nov 13, 2014)

No worries. I think the lesson here is that a little theory is great, but there's no substitute for the sort of empirical testing that HKJ does. 

I now intend to immerse myself in some of those nice charts... 




ShineOnYouCrazyDiamond said:


> I don't think you will see a XM-L2 with a Vf of 3.8v. That's a bit high. I think when you get to the higher amp ranges you are looking close to 3.1-3.3 volts.
> 
> When you look at HKJ's 18650 battery pages be sure to check out this one: http://lygte-info.dk/review/batteries2012/Common18650Summary UK.html. Pay special attention to the sections on Discharge Capacity Down to 3.4 volts and Discharge Capacity down to 3.6 volts. There are really the specs that I use when trying to find a good cell for the application. Just looking at how much capacity any given cell has at a particular current doesn't show you the slope of the discharge curve. When you check out the capacities to a particular voltage you get a great comparison between cells and you start to see that as you get to the 5, 7, 10 Amp range (and even the 3A range) how some cells fall flat on their face during discharge.
> 
> Depending on your use case you then start to see that for high current devices the IMR cells, while still rated lower, will outperform their IMR counterparts at high draw.


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## SubLGT (Nov 13, 2014)

ShineOnYouCrazyDiamond said:


> …………..you then start to see that for high current devices the IMR cells, while still rated lower, will outperform their IMR counterparts at high draw.



 IMR outperforms IMR ???


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## magellan (Nov 13, 2014)

Hi Darkknightlight,

Thanks for the info as that puts a perspective on it. 

You said,

<<What we do know from lots of testing done by members here and in other forums is that the forward voltage of an xml2 is usually a few tenths of a volt higher than an XPG2>>


Interesting. I wonder if it's known why. Is the XML2 die sightly bigger than an XPG2 and so just pulls more juice or is it something more subtle? Now I'm going to have to pull up the spec sheet on the Cree website to find out.


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## darkknightlight (Nov 13, 2014)

I couldn't tell you why some LEDs have a higher voltage resting and under load than others. Fyi, the forward voltage cree lists on their spec sheets are, iirc, listed at 25 degrees Celsius and under a 350 MA load. Happy reading!


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## magellan (Nov 13, 2014)

Thanks SOYCD, some good points there. I was assuming too much linearity, I think, and of course, semiconductors can be very nonlinear depending on where you are on the curve. 

Many decades ago when I was still in grad school I came across a text on semiconductor physics. It was a graduate level text and there was a pretty long chapter, maybe 60 pages, on the physics of the semiconductor junction in a MOSFET. Lots of advanced math and very technical discussions of various phenomena inside a junction as you might imagine. Well, it was actually a physics rather than an EE book. 

Anyway, I was a doctoral student in neuroscience at the time and we had these new brain wave amplifiers based on the new operational amplifier technology and I thought I'd try to understand better how they worked because for one thing their noise characteristics were different from vacuum tube based amplifiers and that could affect our results. Yeah, right. After suffering thru that I wanted to go back to reading about vacuum tube amps which were so much simpler and I felt I understood.

So what can you say. It is the Age of the Transistor, not the vacuum tube anymore but unfortunately transistors and semiconductors aren't so easy to figure out.


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## magellan (Nov 13, 2014)

Thanks, I'm gonna need all the help I can get!



darkknightlight said:


> I couldn't tell you why some LEDs have a higher voltage resting and under load than others. Fyi, the forward voltage cree lists on their spec sheets are, iirc, listed at 25 degrees Celsius and under a 350 MA load. Happy reading!


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## magellan (Nov 13, 2014)

Yes. And total capacity doesn't correlate perfectly with energy density. In fact if I remember right there's almost an inverse relationship, which I still don't understand. But Isidor Buchmann has a good discussion of it and many other interesting topics in his book, Batteries in a Portable World, which I can recommend. I got the Kindle version and it gets good reviews on Amazon. Buchmann is well known for developing the Cadex series of battery chargers. 



darkknightlight said:


> I agree, 3.8 is high for a forward voltage. I meant led voltage under load; my bad! I hope I'm not the source of confusion
> 
> Edit: that is a good all in one chart to reference as well, just keep in mind that it doesn't show discharge curves, only total capacity down to 2.8 and 2.5 volts respectively.


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## ShineOnYouCrazyDiamond (Nov 13, 2014)

SubLGT said:


> IMR outperforms IMR ???



LOL - yeah, sometimes I type too fast and get ahead of myself. I corrected it.


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## ShineOnYouCrazyDiamond (Nov 13, 2014)

darkknightlight said:


> I agree, 3.8 is high for a forward voltage. I meant led voltage under load; my bad! I hope I'm not the source of confusion
> 
> Edit: that is a good all in one chart to reference as well, just keep in mind that it doesn't show discharge curves, only total capacity down to 2.8 and 2.5 volts respectively.



Yes - but keep in mind that when you are looking at the profile curves what you are looking for is to see how long it will sustain voltage better. Specifically, you are generally looking to see how much capacity you will get at a specific current before the cell drops below a certain voltage. I think the graph shows that very clearly all in one shot. They both have their place - I just find the all in one more practical.


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## darkknightlight (Nov 13, 2014)

ShineOnYouCrazyDiamond said:


> Yes - but keep in mind that when you are looking at the profile curves what you are looking for is to see how long it will sustain voltage better. Specifically, you are generally looking to see how much capacity you will get at a specific current before the cell drops below a certain voltage. I think the graph shows that very clearly all in one shot. They both have their place - I just find the all in one more practical.


Agreed! I think we're saying the same thing two different ways [emoji6]


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## ShineOnYouCrazyDiamond (Nov 13, 2014)

darkknightlight said:


> Agreed! I think we're saying the same thing two different ways [emoji6]



Totally!


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