Winter battery cover FLIR One measurements.

Joergen8

Active Member
#1
So here are some FLIR One infrared imaging photos of my EVO 29er 2015. Maybe this will be of interest to some people, as there have been some questions about the usefulness of neoprene or custom battery covers/jackets.

UPDATED with official BH Easy Motion neoprene Winter Cover measurements:

I've now had the official BH neoprene winter cover for a few months, and here are some results. I've formatted the pictures to be more at-a-glance instead of uploading each FLIR photo individually.

Background for each result:

-Typically 12km (7.5mi) / 30min commute ride, charging right before riding.
-Bike inside before ride, either room temp or lower garage temp.
-Boost or Sport mode (max assist level, 250W Controller, 350W US-spec motor).
-Official BH Winter Cover on during charging and riding, only taking it off to measure battery surface temperature.

The results are far better than I expected. The neoprene cover performs excellently under conditions where the battery is drained quickly and the resulting current draw / resistive discharge heat together with the stored ambient heat is preserved, but the battery still doesn't seem to reach harmful temperatures either. The resulting battery temperature does seem to correlate with outside ambient temperature, but not nearly as dramatically as I expected. The end result between +2 deg C and -19 deg C weather is only 4 degrees C in battery temperature (37 deg F differential yields 10 deg F variance).

Charging with the cover on at room temperature and at 2 Amperes (36V) is perfectly safe, only a minor difference between ambient and battery temperature can be (superficially) observed after hours of charging. So there's no need to take the cover off at all during the winter months, except for washing the bike or to remove the battery.



20th Oct 2016


21st Oct 2016


7th November 2016


7th January 2017

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Older CUSTOM cover measurements:

Using my custom 13mm Armacell cover, +3 deg C weather, 7km trip. Starting temp (ambient) of the bike was about 15 C. Battery at full charge, not charged for two days (so NO residual charging heat or gain). "Sport" assist. After the ride:



Motor temp immediately after ride, outdoor pic. For reference, the bike frame and wheel should be around +4 C here, and the ground is subzero (actually ice). Reading might be inaccurate.


A minute later, bike indoors, cover still on, warming up towards ambient temp (15C). Fenders are matted plastic just like the battery, for emissivity, scale and reference. Though this won't be an exact science.


Cover off, battery temp (gain?) 17.7 C, clearly warmer than ambient. Notice how the underside of the alloy downtube has transferred the outdoor ambient temp almost uniformly down the frame, despite the thick protective cover. So the downtube is a bit of a heatsink for the battery, though the rubber pads on the battery and the gap between the battery shell and the bike frame should help isolate the battery from the cooler frame.

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I let the bike reach ambient temp again between rides. Second ride just like the first (+3C and 7km, Sport assist), but this time without the cover:


Battery temp much lower. Readings not super accurate due to lack of calibration cycles. Battery temp mostly residual indoor thermal energy due to battery mass and short ride, not as much resistive heat? Notice colder section towards the lower end of the battery, this houses the battery management system (BMS) board and circuitry, so mostly empty space, the groups of 18650 cells are above it.


Reticle on plastic fenders, for reference.

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UPDATE: Second day of testing.

I wanted to see if it's bad for the battery to keep the 13mm cover on while charging, causing it to overheat. Keep in mind, the official cover would only be 3mm neoprene, so way less insulation.


So here the battery has been charging for two hours with the cover on, from three bars to five, and is probably trickle charging by the time I took the pictures. Bike is at ambient 15 C. Charger red light still on, so charging.


And here I took the cover off: 17,3 C. Only a 2 degree gain over ambient, so it seems like the battery is OK to charge at mild ambient temperatures even with overkill insulation surrounding it. Though keep in mind, the BH Evo charger is only 2 Amps at 36V for a 430Wh battery which makes for a slow charge, and very little current gets converted to resistive heat inside the cells. A fast charging power tool battery might just burst into flames covered up like that.

I'll have to try room temperatures (22 C) at a later date.

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Longer ride. After charging the battery and letting the bike sit for 30min without the cover, to get rid of some of the charging heat, I took off for a longer 27km ride in +1 C weather, Sport assist. I rode 12km, took a 15min stop, rode 3km, took a 10min stop, then rode back 12km. So the bike was outdoors in +1 C for 27km and ~90 minutes. This would simulate a shopping run etc.


Again, motor immediately after the ride, outdoors pic. Reading is inaccurate, but obviously some heat generated and sustained by the motor even after a long ride, so definitely not just residual indoor ambient heat stored in the dense mass of the motor.
Cool is good for electric motors, but I wonder how the plastic planetary gears do at even lower temperatures, like -20 C.


Still immediately after the 27km ride, outdoors, cover still on. Note the heat transfer towards the headset. The controller, which puts out some heat too, sits inside the frame right where the reticle is (the 13mm Armaflex wraps around it too), and some of the battery heat might be spreading up the frame too, though the "hot" areas are only about 2-3 C. Some heat is pushing through the cover, forming the shape of the battery.


Indoors again, targeting a reference point on the fender. Cover still on. The surface of the cover reaches ambient temperature very quickly, being foam insulation with very low mass and density. The shiny stanchions are not instantly at ambient temp though, but reflect the thermal infrared of the surroundings like mirrors.


Cover off. Almost right on the money compared to my earlier short 7km run: 18,3 C. So stopping briefly or taking a long ride will not kill the battery temperature so long as the current draw (resistive heat), thickness of insulation and outdoor ambient temperature meet optimally, and the battery temperature neither plunges nor climbs. Near 20 C is the optimal operating temperature for many li-ion batteries, and is achieved here by pure coincidence.


The bottom bracket seems to be one of the coldest spots on the bike. Possibly due to mass and the cable holes on the underside that let cold air circulate within the frame.
 
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J.R.

Well-Known Member
#3
This is great information! I doubt BH ever thought a rider of their brand would put this much effort into finding out if a winter battery cover can help. Thanks for posting your findings.

I used a homemade cover last year and guess-timated it helped with range on the coldest days (single digit F°), but was never really sure.
 

J.R.

Well-Known Member
#6
Thanks, good to get real testing. Especially helpful are the charge results, as it has been annoying removing a muddy, salty cover to get a charge, when not prepared to clean everything.

Anecdotally I've found the cover giving me more range this winter over last, without the cover.
 

Joergen8

Active Member
#7
Here's another set I took on the topic of charging with the cover on. Made sure to take the cover off while 3,5 hours had passed but the charging was still steaming ahead, not trickling at the very end of a charge (when the charging light is still red but the charger cools down). The FLIR is incredibly sensitive to temperature differences, which makes the battery look glowing hot when in fact it's only a degree hotter than the room at that height. I can literally walk across the yard in my winter boots and then retrace my steps by following the hot glowing footprints.

 
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#9
Here's another set I took on the topic of charging with the cover on. Made sure to take the cover off while 3,5 hours had passed but the charging was still steaming ahead, not trickling at the very end of a charge (when the charging light is still red but the charger cools down). The FLIR is incredibly sensitive to temperature differences, which makes the battery look glowing hot when in fact it's only a degree hotter than the room at that height. I can literally walk across the yard in my winter boots and then retrace my steps by following the hot glowing footprints.

I'm a bit late arriving to this thread ... but thank you, Joergen8 for sharing your analysis. (For some reason, my browser doesn't show any of your images.)

From what I can tell... I think I should be "safe" to ride in the summer WITH my spare battery carrier strapped on top of the active battery. (See my Avatar). Originally, I was concerned that the carrier might restrict cooling of the active battery and cause it to overheat.
 

Joergen8

Active Member
#10
Thanks for the heads up. Dropbox changed their policy and no longer allow HTML rendering of files on their service. I've now fixed the links.
 

Joergen8

Active Member
#13
Do you recommend a motor cover for mid drives?
A motor cover, absolutely not. Heat kills electric motors and their efficiency, so if anything they'll run better in the cold. Mid drives also usually incorporate the motor (power) controller into their casing, so heat from the motor AND the controller wrapped in a layer of insulation would be doubly destructive. But a battery cover for any kind of battery will boost your range and efficiency in the cold.
 
#14
A motor cover, absolutely not. Heat kills electric motors and their efficiency, so if anything they'll run better in the cold. Mid drives also usually incorporate the motor (power) controller into their casing, so heat from the motor AND the controller wrapped in a layer of insulation would be doubly destructive. But a battery cover for any kind of battery will boost your range and efficiency in the cold.
I am considering a 2019 Trek Powerfly 5 with PowerTube 500 as a car replacement. I sold my car because I only drove it 1,000 miles per year for the past two years. I have two conventional bikes that I ride throughout the Denver winters. I get around Denver so quickly and easily that a car makes little sense to me.

I was truly surprised by the battery estimate of 54 miles per charge. The "Environment" tab did not include a temperature or season parameter. What percentage range degradation should I expect riding in 25F temperatures? I have an unheated, attached garage that get can get cold in winter. I would bring the battery upstairs.

See post #28 and #55 for more detail.

Based on your wintertime riding, is this estimation accurate? Or, is temperature significant enough to include as an Environment parameter?



Do you believe the completely shielded battery is more of an advantage or disadvantage? I was thinking of protection, rather than temperature issues.

I plan to buy a second battery. Do you think carrying a second battery in a carrier on the rack is a bad idea, especially in cold weather?

https://www.bosch-ebike.com/us/service/range-assistant/



https://www.trekbikes.com/us/en_US/...-hardtail/powerfly-5/p/23180/?colorCode=black
 
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Joergen8

Active Member
#15
The range estimates can be way off, since there are so many variables to consider. When asked for real world range estimates, I usually recommend this somewhat pessimistic and not at all scientific formula for various e-bikes: Watt hours (Wh) of energy in battery divided by nominal wattage of motor. So for a 500Wh battery and a 250W motor, you'll get 2 hours of riding at rated nominal power. And assuming the power is going into maintaining maximum rated speed, at 20mph you'll get 40mi (in 2 hours). It's as good a guess as any (without knowing all the variables), and you wont know your real world range until you've done a few round trips on your usual routes.

As for the battery being more protected in the powertube (double encased), it will probably help with wind chill more than you'd get with a frame mounted battery, but usually these bikes are designed with battery cooling in mind, not thermal retention. Some bikes (like the Focus bikes with Shimano E 8000) even have air cooling between the battery and the outer casing. So a downtube winter cover would still be recommended to keep the battery warm (assuming it's at room temp when you go out).

Battery manufacturers use cells with different chemistries, where some can handle freezing temperatures better than others, but still the optimal operating temperature for lithium batteries is usually near or slightly above room temperature. It's difficult to say what percentage of range reduction is down to ambient temperature, but the worst case would be a total shutdown of the battery via BMS, due to voltage drop under load. This can happen at any state of charge, especially at low charge, or not at all if you're lucky. When the BMS shuts off the battery, you can't get it back on until you warm it up again. Thus, carrying a second battery thermally unprotected, will do you no good. But you wont really know what happens until you've field tested your kit.
 
#16
The range estimates can be way off, since there are so many variables to consider. When asked for real world range estimates, I usually recommend this somewhat pessimistic and not at all scientific formula for various e-bikes: Watt hours (Wh) of energy in battery divided by nominal wattage of motor. So for a 500Wh battery and a 250W motor, you'll get 2 hours of riding at rated nominal power. And assuming the power is going into maintaining maximum rated speed, at 20mph you'll get 40mi (in 2 hours). It's as good a guess as any (without knowing all the variables), and you wont know your real world range until you've done a few round trips on your usual routes.

As for the battery being more protected in the powertube (double encased), it will probably help with wind chill more than you'd get with a frame mounted battery, but usually these bikes are designed with battery cooling in mind, not thermal retention. Some bikes (like the Focus bikes with Shimano E 8000) even have air cooling between the battery and the outer casing. So a downtube winter cover would still be recommended to keep the battery warm (assuming it's at room temp when you go out).

Battery manufacturers use cells with different chemistries, where some can handle freezing temperatures better than others, but still the optimal operating temperature for lithium batteries is usually near or slightly above room temperature. It's difficult to say what percentage of range reduction is down to ambient temperature, but the worst case would be a total shutdown of the battery via BMS, due to voltage drop under load. This can happen at any state of charge, especially at low charge, or not at all if you're lucky. When the BMS shuts off the battery, you can't get it back on until you warm it up again. Thus, carrying a second battery thermally unprotected, will do you no good. But you wont really know what happens until you've field tested your kit.
Sometimes, simple algorithms can be very accurate. I buy your reasoning.

You seem very, very knowledgeable. I had not considered the BMS shutting down due to cold. I was concerned about overheating. If the BMS shuts down, the unpowered pedalling is my fallback?

What is a reasonable minimum temperature?

Is there a way to keep a battery warm in 25F weather in a rack carrier? If the battery were put in an insulated container at room temperature, would that be sufficient for an hour in 25F temps?

Seems like the rack carrier also needs to insulated?

Thank you,
MIke
 
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#17
I have put about 15 accessories on the quote. Basically, the bike will be equipped as a european speed pedelec. I travel through a 425 foot tunnel that goes under a highway. I ordered Supernova M99 front and tail light. Will the current drawn by the lights help keep the battery warm, or might lights have an adverse affect in cold temperatures.

I have two conventional bikes that i ride in fair weather. I hope to use the Powerfly as a foul weather bike. Especially, because it can sport 2.4" Schwable Super Moto-x tires with the wide rims.

Mike
 

Joergen8

Active Member
#19
When the bike shuts off, muscle power is all you have. And these mid motors like Bosch, with small front chainrings and an internal reduction of etc. 1:2.5 (where the chainring spins 2.5 times per crank revolution) , can feel somewhat sluggish to pedal unassisted.

I can only say from my own experience, but below 40 F is where things start to get hairy, and you can't trust the BMS not shutting the battery off at random. With a winter cover, never a problem, even at 0 F.

The battery has quite a bit of thermal mass, so if you wrap it up tighter than a cat burrito, it should hold its heat for a good while.

Lights only take up a few watts, whereas to generate any resistive heat inside the battery you'll need at least ten times or more power draw, so riding at a high assist level will generate a fair bit of resistive heat, but low assist or just lights won't. For example, in my posts above I tried charging the battery with the winter cover on for a few hours, and my charger is 2A at 36V, so there's 72W going into the battery, and it received nearly no heat gain above the ambient temp.

These brand name bikes are pretty well protected against software tampering, or even pulling out any usable metrics. A voltage drop would only occur when the frigid battery chemistry can't keep up with the load (Amperage), and the BMS shuts it down since for all it "knows" low voltage equals low state of charge. Low voltage could end up frying something anyway, so it's all for the better, and rather than logging when it happens, you can just prevent it from happening by controlling the operating temperature with thermal insulation.