Do high current batteries make flashlights run cooler?

llmercll

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I am wondering if high AMP IMR batteries will make a flashlight run cooler than standard NCR18650B's. I mean samsumg 30q's and sony VTC5's for example. A light that requires high draw batteries for turbo mode, would be there be a difference between a 10A sanyo 3500mah and a 15 amp samsung 3000mah?

I ask because I can't help but notice my standard lights run cooler with IMR batteries in them.
 

emarkd

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I can't think of a single reason why this would be true. A regulated light will only pull the amperage they need and should generate the same amount of heat no matter what type of cell is inside - amps are amps. An unregulated light will pull as much current as it can and therefore should run hotter with a high-drain cell, because more amps.

You say you "notice" it, but have you measured it? Got an infrared thermometer or something you can use to get actual data?
 

parametrek

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A regulated light should run ever so slightly cooler with a high current battery. Usually high current batteries have a lower internal resistance. The IR is why batteries get hot. Lower IR means less heat generated by the battery.

An 18650 might have an IR between 12mΩ and 150mΩ. At 5 amps (close to the max drain for a high IR 18650) that would be 0.3 watts for the low IR battery and 3.75 watts for the high IR battery.

The driver and LED will be consuming around 18 watts at the same time. Maybe 4W of that is turned to light and the other 14W is heat. With a low IR battery there will be 14.3W of heat. 17.75W for high IR. Or 26% more heat because of the battery. 26% might be enough to produce a measurable difference in temperature.

This is ignoring voltage sag because sag complicates matters for the type of driver. Linear vs buck vs boost will behave very differently. What the heck let's add sag into the calculations....

Assuming 3.6V nominal. In the above example the sag drops the voltage on the low IR battery by 0.6V and the high IR sags by 0.75V. This reduces the driver/LED power slightly. Low IR falls to 17.7W and the high IR falls to 14.25W. That huge drop in power to the LED eats up nearly all of the extra heat from the battery.

Though it only acts that way with a linear driver. As the voltage sags the linear driver gets more efficient and burns off less excess voltage as heat. The current remains constant and the overall heating is nearly identical. The only difference is that the excess voltage is burned off inside the battery instead of inside the driver.

A switching driver is going to draw a constant wattage (let's say 18W) from the battery. As the voltage sags the current draw increases. This is when the math get fun. For low IR it works out to 5.086 amps and for high IR it is 7.1 amps. The battery that I was looking (UR18650ZTA) at has a max current of 5.8 amps so it is not going to be a happy battery. Heating in the high IR battery skyrockets to 7.5 watts. That is certainly enough heat to be noticed!
 
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KITROBASKIN

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Seems like we could assume that if output is fairly similar, then therefore emitter heat will be close for both. If anything, the higher Amp battery would make the LED create more heat. Then the question of heat generated by the battery? Seems like that would be a small fraction of what the emitter is producing. One possibility is to run on maximum for, say, 2 minutes with the 100% charged cells in question. Then remove battery and use an infrared thermometer to measure surface of battery. Thinking the difference would not be significant.
 

mattheww50

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The heat generated by a battery can be substantial. If you care to check the battery tests run by HJK, you will find that many rechargeable batteries do indeed get very hot at very high amperage. The formula for losses is I^2 x R, so if are drawing say 5 amps, I^2 is 25. R can be quite small and still generate substantial amounts of heat. The voltage drop in most batteries as the current rises is due to internal resistance, so if while drawing 5 amps the battery voltage falls from 4.2 to 3.7 volts, that is .5 volts, and at 5 amps, that is 2.5 watts. Small compared to the LED it is probably driving, but there aren't a lot of ways for a battery in the battery compartment to dissipate heat. In general cells designed for high current applications have lower internal resistance, which both helps them achiever higher discharge rates, and reduces the internal heating that results from high discharge operation.
 

old4570

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Hmmmm . Everyone seems to assume a regulated light . ( Even then )

A) Higher current batteries may run cooler at lower current draw
B) Higher current batteries generally discharge at a higher rate ( they are capable of discharging more )
C) VARIABLES , oh those nasty variables ( Comparing what to what in what , under what conditions )

The variables in themselves would be so vast as to make this discussion almost pointless .
 

InvisibleFrodo

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Sounds like the group consensus is that the high current capable battery itself will likely generate less heat when under the same wattage/amp load as another less capable cell would.

But theoretically the lower internal resistance of the battery will lower the resistance in the circuit, and thus could actually lead to greater output / heat generated by the driver and LED.

As has also been pointed out, I'm sure it depends on exact specifics. What batteries are being compared in what kind of host running what kind of power?
 

bykfixer

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Can definitely see how the fuel cell would run cooler. Therefore the body of the light would perhaps seem to run cooler.

But the business end running watt for watt, nah I don't see how that would run cooler.
 

llmercll

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This is all very interesting. Here are some more details

The light:
https://www.imrbatteries.com/xtar-h3w-warboy-headlamp-flashlight-cree-xm-l2-u2-led-950-lumens/

When using a protected NCR18650B on max brightness the head of the light became uncomfortably hot. Protection I guess would be another variable however. When I Switched to an unprotected NCR18650GA, the head of the lamp is significantly cooler. It's literally the difference between me feeling comfortable using the light at that brightness or not. I'll get an IR thermometer and get some numbers.

My curiosity resulted in me using an even higher current rated battery, a Samsung 30q. When I used that however, the light began flickering and smoking. It smelled like a hair dryer. I quickly turned it off and both the battery and light are still working, which is nice =p. This makes me think it's an unregulated light however, and the 30Q put too much current in the driver. The 30q works fine in one of my zebras though, since I guess it's regulated. What's interesting is that the 18650GA improved performance, but the 30Q nearly fried it. This experience almost makes me feel like unregulated lights are dangerous.
 
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old4570

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This is all very interesting. Here are some more details

The light:
https://www.imrbatteries.com/xtar-h3w-warboy-headlamp-flashlight-cree-xm-l2-u2-led-950-lumens/

When using a protected NCR18650B on max brightness the head of the light became uncomfortably hot. Protection I guess would be another variable however. When I Switched to an unprotected NCR18650GA, the head of the lamp is significantly cooler. It's literally the difference between me feeling comfortable using the light at that brightness or not. I'll get an IR thermometer and get some numbers.

My curiosity resulted in me using an even higher current rated battery, a Samsung 30q. When I used that however, the light began flickering and smoking. It smelled like a hair dryer. I quickly turned it off and both the battery and light are still working, which is nice =p. This makes me think it's an unregulated light however, and the 30Q put too much current in the driver. The 30q works fine in one of my zebras though, since I guess it's regulated. What's interesting is that the 18650GA improved performance, but the 30Q nearly fried it. This experience almost makes me feel like unregulated lights are dangerous.

NOPE !
The unprotected cell is probably running much lower current ...

Get out the Multi Meter - And start checking current !

I have owned batteries that were simply not capable of delivering more than 2 amps , I think one was limited to 1.5 amp ..
My guess would be that that cool running battery is not delivering current ... ( For what ever reason )
 

lumen aeternum

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Very interesting. Could you estimate internal resistance by measuring temp while charging ( in some particular manner) ? Could you do a side by side test of two batteries in the same charger (but on different charging circuits)?

How can you shop for a low IR battery? Presumably higher draw batteries will have less than a lower draw, but for the same discharge rate how do you figure out which has a lower IR when shopping?

If a battery is protected (ie discharge rate capped ???) then wouldn't there be some point at which a lower IR becomes irrelevent (ie don't pay extra for it)?
 

lumen aeternum

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there aren't a lot of ways for a battery in the battery compartment to dissipate heat.

So having a heat sink contact the full surface of the negative side of the battery might be a good thing? Instead of just a bit of spring.
And removing the wrapper so the metal casing contacts something... say a metallic sponge to prevent rattling.

A casing that is conical could fit snugly into a conical battery housing, making lots of heat sinking contact.

A spring-metal battery holder for a cylindrical battery could have fins that are triangular, thus imparting a conical shape that would slide into a conically bored body to make lots of contact.
 

WalkIntoTheLight

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So having a heat sink contact the full surface of the negative side of the battery might be a good thing? Instead of just a bit of spring.
And removing the wrapper so the metal casing contacts something... say a metallic sponge to prevent rattling.

A casing that is conical could fit snugly into a conical battery housing, making lots of heat sinking contact.

A spring-metal battery holder for a cylindrical battery could have fins that are triangular, thus imparting a conical shape that would slide into a conically bored body to make lots of contact.

But, for what purpose? We already have 30 amp 18650 cells (like the Sony VTC5A). Sure, you can run it at 35A if you keep it below a temperature of 80C, but is more really necessary for a flashlight? Even at 30A, a flashlight will have a run-time of a few minutes at most. Besides, the problem with heat will not be from the battery, it will be from the driver and LED. Batteries aren't the problem with heat; it's the electronics of the flashlight.
 
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Cheers to parametrek.

After reading parametrek's response (dated 5.21.2018 at 09:39 a.m.), I can't help but feel like an amateur. I'm awfully glad there are folks like him (or her, as the case may be) on this forum, to help educate those of us (like me) without a technical background in the electronics of flashlight engines.
 
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