Cold Weather and High Drain cells

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FlyPenFly
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Cold Weather and High Drain cells

So I read somewhere that using a high drain cell like a Samsung Q30 actually does much better than a normal cell like a Sanyo NCR18650GA when it's cold out. Is this actually true and is it true for all high drain batteries when compares to normal drain?

zak.wilson
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Cold weather increases the internal resistance of batteries, resulting in greater voltage sag at the same load. High-drain cells have lower internal resistance to start with, so it takes a greater increase before the battery starts to have trouble with a given load.

The best performing Li-ions in extreme cold are those specifically designed for that purpose like the Panasonic NCR18650F. I haven’t seen anybody selling bare NCR18650Fs in single quantities, but Nitecore and Evva sell wrapped protected versions.

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FlyPenFly
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ggf31416
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zak.wilson wrote:

The best performing Li-ions in extreme cold are those specifically designed for that purpose like the Panasonic NCR18650F. I haven’t seen anybody selling bare NCR18650Fs in single quantities, but Nitecore and Evva sell wrapped protected versions.

See http://budgetlightforum.com/node/65438 for some results in cold weather for high drain batteries. The Nitecore didn’t did as well as expected on HKJ’s tests, so maybe one of the high drain batteries is better after all, the Molicel P26A and P28A particularly have a -40C min operating temperature, the P26A being easily available. I haven’t seen independent testing of it under low temperature, but if its datasheet is to be trusted it should work well.

zak.wilson
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I’d like to see more testing like this. HKJ’s test was colder than maukka’s, so the two can’t be compared directly.

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18650UK
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I covered some aspects of this in a blog post on the website recently, but ill list a few bits here;

Cells being sold a “cold weather” or “low temperature” – If you look at the factory datasheet (in the rare instance they have/will supply one) for the majority of cells used under the wraps of the most common torch battery brands, you’ll find that most have an operating temperature range of down to around -20’C, some as low as -30’C making this a rather pointless selling point…

…unless…

These manufacturers can demonstrate by way of computerised battery analysis in a generated environment (IE, inside an environmental testing chamber) that the cells are demonstrably better than “X” competitor at a given temperature. For example, putting a Samsung INR18650-30Q derived product up against a Sony US18650VTC6 derived one. Both 3000mAh, run them flat out at 15A @ -20’C, track and plot the internal impedance on a graph and see which provides the best in terms of capacity. From my research, no-one is doing this, or at least not providing data to back their claims.

For most cells, the “ideal” discharge temperature is around 25’C and being able to keep to this is the best way to minimise fluctuations in internal impedance and therefore keep the cell as efficient as possible in terms of expending its energy well, and consistently. When i say “well”, i mean, getting the full (or as close to) the full capacity from them.

how crazy is this
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My dog walking lately has been right at the edge of the operating temperature range (near -20C). My 30Q in a C8 has mostly stayed inside a pocket. However I sure see the effects of the cold on the LADA 2450 exposed to the cold on my forehead. After about a half hour walk a fresh good battery will no longer go into turbo at all, high is diminished and it has even dropped out of regulation when trying to reach high — including giving the low voltage warning. After a few minutes indoors, and a power reset to get past the low voltage protection, performance returned to normal.

Not sure how much different the NiMh cells are than the Li-ion but my experience tells me that they definitely have increased internal resistance and voltage sag when they get cold!

18650UK
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how crazy is this wrote:
My dog walking lately has been right at the edge of the operating temperature range (near -20C). My 30Q in a C8 has mostly stayed inside a pocket. However I sure see the effects of the cold on the LADA 2450 exposed to the cold on my forehead. After about a half hour walk a fresh good battery will no longer go into turbo at all, high is diminished and it has even dropped out of regulation when trying to reach high — including giving the low voltage warning. After a few minutes indoors, and a power reset to get past the low voltage protection, performance returned to normal.

Not sure how much different the NiMh cells are than the Li-ion but my experience tells me that they definitely have increased internal resistance and voltage sag when they get cold!

Its certainly more pronounced in NiMH cells than Li-ion, but the effects are there the same.

It might also be down the cells themselves. The Ikea LADDA cells aren’t known for being the_ strongest_ of things. Perhaps give some Eneloop Pro AA cells a go, you should see a marked performance improvement Smile

Valynor
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Yes, it's true. Non high-drain LiIons are only good to about 0°C whereas high drain cells work pretty well down to about -20°C. 

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I once wrote a post on CPF that might be of interest:

http://www.candlepowerforums.com/vb/showthread.php?415498-Cold-temperatu...

I’ve copied it near-verbatim below, with updated links and related text.

——

Lux of Sweden wrote:
I know a CR123a primary battery is the optimal choice in cold weather, but if I for some reason want to stick to rechargeables, is there a general difference (ceteris paribus) between a 1×18650 and 2xRCR123a configuration?

All thoughts welcome.

An interesting question, but not an easy one to answer, I’m afraid. As Chris says, data are thin on the ground.

However, I can give you an idea of what to look for, if you can track down the data sheets for whichever cells you’re interested in.

As examples, here are some data sheets with graphs showing discharge characteristics at various temperatures for three well known Panasonic 18650 cells:

Note that the datasheets are hosted by third parties, not Panasonic directly, because getting them from Panasonic is a pain in the butt and they keep deleting things or moving them around.

Look at the lower left of the page for the -A and -B datasheets, or page 3 of the -GA datasheet. Unfortunately, the -GA graph only covers -10°C to 25°C, where the other two cover -20°C to 40°C. Don’t ask me what Panasonic were thinking there!

You’ll notice that at the lowest temperatures, the cells have trouble getting started, because the cold slows down the electrochemical reactions so much. There’s a large voltage drop at first, followed by a substantial recovery as the cells warm up due to power dissipated via internal resistance.

At -20°C, the -A cell drops to ~2.8V at first, so it has significantly more trouble than the -B cell, which only drops to ~3V. Given a choice between the two, you’d want the -B cell.

At -10°C, the -A cell drops to ~3.4V, the -B cell drops to ~3.5V, and the -GA cell drops to ~3.35V. The -GA cell is actually the poorest performer, which could be very significant, especially if those relative standings carry through to -20°C.

This is why it’s so important to keep lights and cells as close to your body as possible until you use them. Nice and warm inside your jacket is vastly better than frozen in your car’s glove box or at the bottom of your pack. You’ll also want spare lights and cells; that’s practically mandatory in extreme environments.

Another thing to bear in mind is that the cell voltage at low temperatures will only recover if you’re drawing enough current to dissipate significant power via internal resistance. If you’re running your light on a low mode, it may never heat up enough to recover.

I have no idea what capacity you’ll get out of the cell then, because the data sheets don’t cover that case. Those low temperature discharge tests are all performed at substantial currents.

You can also encounter other nasty problems. For example, if you have a light that cuts out at 2.9V to protect the cell from over-discharge, it wouldn’t even turn on using a -A cell at -20°C, because the cell would drop straight down to ~2.8V. This also applies to protected cells, although protection circuits often tolerate lower voltages before they cut off.

You’d also be pushing your luck even with the -B cell. If the temperature dropped just a little further, or the cell happened to be getting a bit old, you wouldn’t be getting any light that way either.

Although I normally like protected cells and lights with cell protection built in, this scenario is one where I’d seriously consider choosing unprotected cells and lights that drain them to the dregs. Of course, the trade off is that you then become solely responsible for maintaining Li-Ion cell safety.

As ever, it’s always a good idea to test the performance of your equipment in safe conditions before you rely on it. Hint: a good household freezer should hit -18°C Smile

On the subject of deciding between 18650 cells and RCR123 / 16340 cells, the first thing I’d say is that Chris is right: 16340s will cost you a lot of capacity, especially in an extremely cold environment. If you still want a two-cell approach, consider 18350s instead. You’ll still lose a lot of capacity compared to the 18650, but it won’t be quite as bad.

The one place a two-cell approach might pay off is if you want to use the light on a low mode where the cell won’t generate enough internal heat to recover a decent working voltage. The extra voltage from two cells might be the difference between a light that works and a light that doesn’t.

Again, this is something you would need to test for yourself.

Whichever way you jump, you’d definitely want to carry some primary cells – CR123As – as your last-ditch backup if your light supports them.

The_Driver
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The Samsung 20S might be the best 18650 cell at extremely low temperatures (under -20 C). It has the highest current rating of all 18650s (30A). Because of its low capacity (2Ah) this effect would only be visible at very extreme temperatures though.

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Where do you live to have minis 40

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