LiFePO's range in different temperatures

[Rifle]

Anyone know exactly how much difference one should see in the performance of Lifepo batteries in different temperatures? I once got almost 32 miles out of a 48v 20ah pack in aboit 80F weather, but now can't get more than 25 out of it, I figure due to having 50 degree weather. Also, I bought a used 48v 40ah used pack for real cheap. It measured 56v after sitting around for a few weeks, so it seems in good shape to me, but when I took it out for a ride I only got about 37 miles out of it. Again in 50 degree weather. I'm wondering what the range will be like in warmer weather. Hopefully I'll also be able to improve the range by pedaling with it when accelerating, quite a heavy battery too. Couldn't do hardly any pedaling when I took it for that ride.

 

[docnjoj]

Those numbers sound about right, Rifle! I accidentally got about 35 miles out of my 20 AH 48 volt Ping cause I thought I was recharging it after 12 miles or so but I forgot to plug in the charger. This was at 85-90F degrees. Most battery chemistries take a fall in the cold! Try to start your car at zero F. Even with an oil pan heater you only get 2-3 tries!
otherDoc

 

[sparky]

I'm sure my range is impacted, but I haven't pushed it that close to the limit. Am still able to do my 14mile round-trip commute on my 48V 16Ah Ping V2 without issue, even tho it's about 30+degrees F cooler here in lovely Minnesota now than in the summer. Also, no perceived power/top speed degradation either. Maybe it needs to be colder... somehow, I know that's on the way! :wink:

I did a quick google: looks like my experiences are in-line with manufacturers expectations: at 0C you can expect about 80% capacity, at -10C (cold!) expect about 50% capacity. Sheet 4:

http://www.batteryspace.com/prod-specs/LFP18650.pdf

 

[Russell]

I use more energy from the battery in colder weather due to increased wind resistance from the extra clothing and I don't perform as well in the cold so the motor picks up my slack. I don't believe you will actually see much less capacity from a lithium battery in the cold especially if you start with a pack that's been stored at room temperature up until the ride. SLA's are the worst in the cold yet when I rode with them at the start of the year I didn't see much if any capacity variation based on temperature but then I always started with a room temperature battery. If you have a wattmeter you can easily verify whether you are getting less capacity or simply using more as it gets colder.

-R

 

[Rifle]

I use more energy from the battery in colder weather due to increased wind resistance from the extra clothing and I don't perform as well in the cold so the motor picks up my slack. I don't believe you will actually see much less capacity from a lithium battery in the cold especially if you start with a pack that's been stored at room temperature up until the ride. SLA's are the worst in the cold yet when I rode with them at the start of the year I didn't see much if any capacity variation based on temperature but then I always started with a room temperature battery. If you have a wattmeter you can easily verify whether you are getting less capacity or simply using more as it gets colder.

-R

I started with the battery inside, but it had no insulation from the weather and the ride took 4 hours. I was under the impression that in cold batteries use some of their wattage to essentially keep themselves warm and functioning. I didn't know a wattmeter would account for this. Looks like it's going to be awhile before I get one anyways.

 

[dogman dan]

Cold does affect range. Even with some insulation on the pack(not the bms) I lost about 25% of my range last winter. Mabye about 30% loss on the below 32 ride in the morning, and about 20% loss on the ride home at 45-55 F in the afternoon. My bike was not stored at room temp, and the charging spot at work is shaded. So the battery would start cold, and gradually warm up when discharging. On really cold (to me) mornings I would put the bike on a bus bike rack for about 6 miles of the trip. Removing the now froze solid bike from the front of the bus, It would trip the bms lvc repeatedly till I got the thing warmed back up. About a quarter mile of low throttle riding would get the electrons flowing in the controller, and I could then ride normaly.

So if it's reallly cold where you are, keeping the battery at room temp is good.

I think some of the cold affect on range is due to cold wiring on the bike too. Ever notice your headlights and wipers work lousy at 0F? Then begin to work better later when the wiring warms up? So some range is lost that way at first I bet, if the bike is really cold.

 

[Russell]

Cold does affect range. Even with some insulation on the pack(not the bms) I lost about 25% of my range last winter. Mabye about 30% loss on the below 32 ride in the morning, and about 20% loss on the ride home at 45-55 F in the afternoon. My bike was not stored at room temp, and the charging spot at work is shaded. So the battery would start cold, and gradually warm up when discharging. On really cold (to me) mornings I would put the bike on a bus bike rack for about 6 miles of the trip. Removing the now froze solid bike from the front of the bus, It would trip the bms lvc repeatedly till I got the thing warmed back up. About a quarter mile of low throttle riding would get the electrons flowing in the controller, and I could then ride normaly.

So if it's reallly cold where you are, keeping the battery at room temp is good.

I think some of the cold affect on range is due to cold wiring on the bike too. Ever notice your headlights and wipers work lousy at 0F? Then begin to work better later when the wiring warms up? So some range is lost that way at first I bet, if the bike is really cold.

The thing is looking at the range you get from a battery is not a direct indicator of the capacity of the battery. I use more Watt-hours per mile when it's cold for many reasons which reduces my range however that does not mean the battery capacity was less.

If you start with a freezing cold battery in freezing cold weather the battery capacity will of course be less. I haven't seen temperature specific data for lithium batteries except that their range is -20C to +60C but for SLA's one manufacturer shows that at a 1C discharge rate their battery will deliver 60% of the rated capacity at 25C and only 40% at 0C, a 33% decrease. In my experience however if you start with an SLA battery at room temperature and ride for less than 2 hours above freezing you will see little temperature effect.

I keep a log of all of my rides so I have lots of detailed data for a wide temperature range (~34-90F) however to draw any conclusions to whether the temperatures had any effect on the battery capacity I would have had to run the battery down to cut-off each time and preferably drained the battery at the same rate each time. Of course that's impossible to do but here's what I can say; I conducted a controlled discharge of my 36V/9Ah SLA battery pack indoors (72F) with the bike wheel spinning a trainer and got 5.7Ah from it before hitting the controller LVC. The maximum I ever got outdoors on the bike was 5.42Ah on a 48F day. Would that have been significantly less at 32F, I can't say, I also can't say if any of the reduced apacity was due to temperature or because of draining the battery at a different rate out on the road. The best I ever got from my Bosch LiMn Fatpacks (theoretically 6.6Ah) was 6.39Ah which coincidently was also on a 48F day.

This would be an excellent experiment to run; discharge a single lithium cell at room temperature then repeat in the refrigerator and then in the freezer...anyone? anyone?

-R

 

[Ypedal]

http://www.endless-sphere.com/forums/viewtopic.php?f=4&t=8452&start=75

See about half way down this review of an e-bikekit.com lfp 36v pack in the COLD...

 

[dogman dan]

Did I say the battery had less capacity? Does the thread title mention capacity? I only have the fact that on a cold morning it took me longer to charge after the ride by about 30%. Capacity may indeed be the same. The important thing was that I could not ride as far on the cold battery as I could on a warm one. The exact reason why would be nice to know.

 

[Russell]

http://www.endless-sphere.com/forums/viewtopic.php?f=4&t=8452&start=75

See about half way down this review of an e-bikekit.com lfp 36v pack in the COLD...

To summarize; you got 9.3Ah from the 10Ah pack when discharged at a 20A rate indoors then starting with a frigid battery at between -5 and -7.5 degrees C you got about 7.5Ah or about a 25% decrease from rated capacity or a 19% decrease from the 20A capacity. It would be interesting to see what the capacity would be starting with the battery at room temperature then going out for a ride, this is where I contend there will be minimal effect.

BTW I did find some temperature data for Thundersky batteries and they show only a 10% decrese in capacity from 25C to -25C, but of course they are a completely different animal.

http://www.thunder-sky.com/pdf/TS-LFP40.pdf

-R

 

[Russell]

Did I say the battery had less capacity? Does the thread title mention capacity? I only have the fact that on a cold morning it took me longer to charge after the ride by about 30%. Capacity may indeed be the same. The important thing was that I could not ride as far on the cold battery as I could on a warm one. The exact reason why would be nice to know.

The title of the thread certainly implies that the author wants to know the effect of JUST the battery at different temperatures. In practice however that is a very difficult thing to do unless a controlled experiment is conducted.

The biggest thing which affects my range in the cold is probably MY output. In cold weather I don’t breathe as deeply because I don’t want so much cold air in my lungs and I put out less power. The second thing is in the cold I wear more clothing. A floppy jacket and sweat pants greatly increase air resistance as does even the denser air. Third the cold temperatures increase the mechanical and rolling resistance of the bike. All of these things PLUS the effects of temperature on the battery will affect range. The best way to find out how much of the decrease in range is due to decreased battery capacity is to run the battery to cut-off and monitor how many Watt-hours it delivers at different temperatures. Only in this way can you try to separate any reduced battery capacity due to the cold from all of the other causes of reduced range in cold weather.

-R

 

[Russell]

I'm still looking for manufacturer data concerning temperature. I found this graph on the Headway-cn.com site for one of their Li-ion ebike packs, it shows good performance at 0C but the output takes a big hit at -20C.




-R

 

[Russell]

Hey I had the info right on my computer all along. This is for the LiFePO4 battery supplied by Fusin.



Zoomed in on temperature data.



The results Ypedal got look very close to the data above.

-R

 

[dogman dan]

I agree with you Russell, but just didn't want you putting words in my mouth. I say plenty of stupid shit on my own just fine.

I suspected, as Ypedals test confirms, that a cold lifepo4 battery does have less capacity. I only knew for sure that my charge time at work increases, and sometimes I trip the bms rolling in the driveway on the coldest days coming home.

In the winter, I have all the things you mention, wind drag, body less frisky, etc. I also have a seasonal change in wind direction. In winter, I often have 50F a mostly uphill ride home, AND a nice headwind. So the battery is sorta cool, though the charger heats it some, then you get wind chill, uphill, and I'm tired at the end of the day. Going home range can really suffer if the headwind is over 15 mph. But commuting all through last winter, I can say that range definitely decreases in the cold. I also see a bit more voltage sag too. It was real nice last spring when it got warm to see my bikes top speed come back to normal. I had gotten used to sub 20 mph speeds on much of the ride all winter.

Starting out with the battery warm can make a huge difference. I did a test on that last winter, and was amazed how much faster the bike was but I didn't test range that day just top speed. The heat of discharging should keep an already warm battery toasty for the full range ride unless you freeze it on the bus bikerack or something.

 

[Ross]

Do a lot of lurking here, not much posting, but I thought I would throw this idea out for those frosty battery days. Add a couple of these to your insulated battery container and away ya go.
Ross

HEAT WAVE Instant Reusable Hand Warmers - 1 pair (Says it stays warm for two hours. Probably really one hour.)

http://www.amazon.com/HEAT-WAVE-Instant-Reusable-Warmers/dp/B002Q6VTJ2/ref=pd_sbs_hpc_3

 

[DerekG]

I have used those before and they work well at first but after a year or two they only hold "warmth" for a few minutes.

Good idea but technology not advanced far enough yet. I think a small 20 watt resistive heater would work... after all what is 20 watts to most who have over 400 watt hours available

 

[Ross]

Two possibilites. Although I am not sure if it would be really worth it.
Ross

STI 6580 12V AC/DC Heater Kit- 24 Volt 12 Watts (.5A)
http://www.totalcomputing.net/index.asp?PageAction=VIEWPROD&ProdID=2951&utm_source=googlebase&utm_medium=freefeeds&utm_campaign=productfeeds

AM-PH 513 Pipe Heater- .5" dia (1.3cm) pipe, 13.5VDC, Length: 12" (30.5cm), Amperage Draw: 2.3 Amps
http://www.ultraheat.com/shop/Pipe_Heaters--AMPH_513_Pipe_Heater.html

 

[dogman dan]

When discharging, the battery actually creates it's own heat, so I just put some insulation around it for winter. Most of my problem is that I don't bring the bike inside, so I start out colder, and the headwind I have a lot in winter. These sort of issues are why I constantly recomend people buy 20% or so bigger than they calculate needing.