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Does braking in freezing temperatures damage batteries?


Skeptikos

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I'm just trying to think this through. I've read that lithium ion batteries shouldn't be charged below 0°C/32°F. However it's OK to discharge the batteries at lower temperatures.

So it almost seems like riding in freezing temps is OK-- except that braking charges the batteries. That seems to imply that we shouldn't be riding when the battery is freezing.

Do I have this right? If I'm riding in the cold, should I be checking to make sure my batteries don't reach freezing temperatures?

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On 2/1/2022 at 3:55 PM, Tawpie said:

In general, one doesn't want to charge a frozen battery. But internally it warms up some when it's discharging (who knows how much, this is a singular case where a crappy battery with high internal resistance is an advantage). Is it warm enough? @winterwheel rides at -35C, but I'm certain he's pretty careful to start with a room temperature battery, and doesn't dilly dally around sipping beverages or taking in the scenic (frozen) vistas. In the ice and snow, one tends to go slower too, and I at least avoid hills... regen will happen, but not like slamming on the brakes from 40 mph.

To echo this, as long as you are riding hard enough and don't take extended breaks, your batteries should not cool to freezing temperatures since discharging and recharging the batteries keeps them warm. 

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Imagine someone that keeps their wheel in unheated space (not good for moisture intrusion) and they take it out for joyrides. That's going to degrade the battery faster yes. Starting at temperatures below zero. I don't think you can heat up a battery that's already below zero, by discharging it and not accelerate wear.

If you start with a warm wheel and return home after the ride without parking, I don't see much risk.

However people often don't realize how cold it can get in some places. If it's minus 10C and the wind absolutely slaps with a vengeance, it will freeze that wheel in minutes. After any ride basically you'd return home with a wheel well below freezing. 

The OP has a very good point. The currents we charge wheels with these days, pale in comparison to the currents experienced under braking. If the pack is not room temperature then you're (temporarily) exceeding the maximum currents set by the cell manufacturers.

Edited by alcatraz
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On 2/6/2022 at 12:03 AM, alcatraz said:

However people often don't realize how cold it can get in some places. If it's minus 10C and the wind absolutely slaps with a vengeance, it will freeze that wheel in minutes. After any ride basically you'd return home with a wheel well below freezing.

I'm guessing the shell is an important consideration here. If you have a shell that's mostly enclosed then it probably insulates the batteries to some extent. Maybe you should be more careful if you have a wheel with a more open design, like a King Song S18 or S20.

Edit: I can tell there's some insulation because my temperature sensor, wherever it is, still shows temps that are pretty warm. There doesn't appear to be much wind chill inside the wheel.

Edited by Skeptikos
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Good point @Skeptikos. Most of my cold weather riding has been on my 16x which is further protected by a roll.nz so there are a couple layers of (poor, but real) insulation from ambient. The totally exposed metal battery compartments of the S18, S20 and Ex20S are going to change the equation quite a bit.

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On 2/1/2022 at 4:55 PM, Tawpie said:

In general, one doesn't want to charge a frozen battery. But internally it warms up some when it's discharging (who knows how much, this is a singular case where a crappy battery with high internal resistance is an advantage). Is it warm enough? @winterwheel rides at -35C, but I'm certain he's pretty careful to start with a room temperature battery, and doesn't dilly dally around sipping beverages or taking in the scenic (frozen) vistas. In the ice and snow, one tends to go slower too, and I at least avoid hills... regen will happen, but not like slamming on the brakes from 40 mph.

I use the app to watch the temperature on the wheel, if and when it gets into single digits I start looking to end my trip.

The exercise I recommend people to do on a new winter wheel is to monitor the temperature for a known ambient riding temperature to see what point the wheel temp drops while riding. On my ACM2 the temp would stay stable to about -18c so I knew above that I could take long trips, below that I'd need to be careful to avoid riding too long.

On the -37c commute with that wheel it dropped to 7c by the end of my 6km trip; I wouldn't have wanted to ride it much further.

 

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On 2/5/2022 at 10:03 PM, alcatraz said:

If it's minus 10C and the wind absolutely slaps with a vengeance

Maybe worth noting that the windchill is always extreme with winter riding. On the -37c commute I was at times riding at around 40kmh. That puts the temp with windchill down to -56c, even on a totally calm day. Not sure how much that matters to the wheel, but it definitely means you need to be careful to leave nothing exposed.  

https://www.wpc.ncep.noaa.gov/html/windchillbody_txt.html

Edited by winterwheel
typo on the temp
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1 hour ago, winterwheel said:

Maybe worth noting that the windchill is always extreme with winter riding. On the -37c commute I was at times riding at around 40kmh. That puts the temp with windchill down to -56c, even on a totally calm day. Not sure how much that matters to the wheel, but it definitely means you need to be careful to leave nothing exposed.  

https://www.wpc.ncep.noaa.gov/html/windchillbody_txt.html

Very true. I was once over 3 minutes in -112°C (-170°F) wearing only swimsuit. It wasn't bad at all, but even a slight blow to bare skin felt terrible.

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2 hours ago, winterwheel said:

That puts the temp with windchill down to -56c, even on a totally calm day. Not sure how much that matters to the wheel

The wheel will still only see -37 as its not evaporating anything :)

But still, thats bloody cold for Li-Ions whichever way its sliced.

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1 hour ago, Planemo said:

The wheel will still only see -37 as its not evaporating anything :)

Wind chill factor is a equivalent temperature person would felt without a wind speed. The phenomena behind it is increased heat transfer. Same thing is happening also for machine's. Battery's surface temperature in our case is lower than human skins, so battery's wind chill factor would also be much lower.

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6 hours ago, Eucner said:

Wind chill factor is a equivalent temperature person would felt without a wind speed. The phenomena behind it is increased heat transfer. Same thing is happening also for machine's. Battery's surface temperature in our case is lower than human skins, so battery's wind chill factor would also be much lower.

I sorta get your point but a wheel left in a -37 ambient with even 100mph of wind blasted at it will never get any colder than -37 deg. Therefore 'wind chill' in the traditional sense of the meaning doesn't apply. Granted the wheel will chill quicker if it's own temp is above -37 to start with but when speaking of wind chill it doesn't apply to inanimate objects. I'm sure you know this given where you live but I'm just trying to avoid confusion for anyone else reading.

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@Planemo I think you're adding to the confusion. Earlier you implied that wind chill is about evaporation, which it is not. Wind chill isn't about people sweating or stepping out of the shower, although that can be a bit cold sometimes. The wind chill numbers on the nightly news forecast are human-specific because they're calculated based on human heat loss, but the general concept (that stagnant air is a good insulator, and moving air is not) applies to everything.

 

But what I want to know is how @Eucner ended up in -112°C weather in a swimsuit. It sounds like a scene from The Hangover. How much alcohol was involved in this? Did you calculate beforehand how long you could withstand the cold before freezing or did you just wing it? Does it actually get that cold in Finland or do you work at an experimental physics lab making superconductors?

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5 minutes ago, Skeptikos said:

@Planemo I think you're adding to the confusion. Earlier you implied that wind chill is about evaporation, which it is not. Wind chill isn't about people sweating or stepping out of the shower, although that can be a bit cold sometimes. The wind chill numbers on the nightly news forecast are human-specific because they're calculated based on human heat loss, but the general concept (that stagnant air is a good insulator, and moving air is not) applies to everything.

Well, on second thought, I'm not totally sure about the evaporation part. I guess I'm reading some conflicting definitions. But it's definitely not a factor for the cold temperatures we're discussing, when people aren't sweaty.

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9 minutes ago, Skeptikos said:

@Planemo I think you're adding to the confusion. Earlier you implied that wind chill is about evaporation, which it is not. Wind chill isn't about people sweating or stepping out of the shower, although that can be a bit cold sometimes. The wind chill numbers on the nightly news forecast are human-specific because they're calculated based on human heat loss, but the general concept (that stagnant air is a good insulator, and moving air is not) applies to everything.

Cool (no pun). I'll make this final comment before I call it a day.

The original post was quoting animate wind chill temperatures: that -37 degC ambient at 40kmh = -56 degC. My point is that the wheel won't be seeing anything like -56 degC. As I said earlier, I accept the batts may cool quicker than if left static, but quoting anything in relation to animate wind chill temps is largely irrelevant.

Thats all.

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55 minutes ago, Skeptikos said:

But what I want to know is how @Eucner ended up in -112°C weather in a swimsuit. It sounds like a scene from The Hangover. How much alcohol was involved in this? Did you calculate beforehand how long you could withstand the cold before freezing or did you just wing it? Does it actually get that cold in Finland or do you work at an experimental physics lab making superconductors?

I'm sorry, the story doesn't include any dramatic content or alcohol. Neither was it like in the movie The Day After Tomorrow. The cold room was one of spa facilities. I just couldn't resist to try it out. It was a very nice experience. Skin felt tickling warm whole evening. I would do it again, if had a chance.

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3 hours ago, Planemo said:

Cool (no pun). I'll make this final comment before I call it a day.

The original post was quoting animate wind chill temperatures: that -37 degC ambient at 40kmh = -56 degC. My point is that the wheel won't be seeing anything like -56 degC. As I said earlier, I accept the batts may cool quicker than if left static, but quoting anything in relation to animate wind chill temps is largely irrelevant.

Thats all.

A person’s skin wouldn’t get that cold either despite the “feels like” temperature being so cold. It’s about heat transfer, both with humans and machines. Heat transfer is why people are able to spend a long time in a +100•C sauna, yet their skin doesn’t burn like it would immediately when touching a +100•C frying pan.

The “feels like” temperature is only there to represent the temperature that the wind feels like to us humans due to the more effective heat transfer. It doesn’t represent an actual measurable temperature in any situation.

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9 minutes ago, mrelwood said:

A person’s skin wouldn’t get that cold either despite the “feels like” temperature being so cold. It’s about heat transfer, both with humans and machines. Heat transfer is why people are able to spend a long time in a +100•C sauna, yet their skin doesn’t burn like it would immediately when touching a +100•C frying pan.

The “feels like” temperature is only there to represent the temperature that the wind feels like to us humans due to the more effective heat transfer. It doesn’t represent an actual measurable temperature in any situation.

Totally agree.

Wind chill ('feels like' temp if you want) was invented for humans. It doesn't work or bear any relevance to 'real' temps, let alone with inanimate objects where the ability to wick heat can be vastly different to humans given people wick moisture (and yes, even when they are cold).

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1 hour ago, RagingGrandpa said:

As mentioned above, the cell temperature is what we care about, not the outdoor temperature. Starting a ride with the pack above 0°C should be sufficient, for all but the most severe climates < -20°C.

And, yes, if the cell is below 0°C, recharging accelerates cell aging.

The page below describes it nicely: 
https://dcbattery.tech/charging_your_lithium_battery_below_zero/

Both of those things (capacity and internal resistance) are quite important for EUC's.

I do not bring my EUC indoors, and leave it in a sheltered, but exposed, environment. I throw an old coat over the EUC to keep it warm when charging. I have never seen the temperature go below 40 Degrees F.

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