Battery power and cold weather

[prState]

Around winter time the local news oftens runs battery tips -- like the first cold snap, a weak battery won't start the car, etc., So, the other day, they mentioned that SLA batteries lose 35% of their power in freezing weather.

If true, that's a pretty big chunk! But at least on combustion engines the battery eventually will get the benefit of a very warm engine compartment.

So, anyway, is the same true for our NiMh, & li-pos? 'Cause not only is your battery cold, it's not getting any warmer while riding. And such a drop would certainly affect riding and test results.

 

[Ian]

The cold will affect all battery types to some degree prState, but your definition of cold in Nevada might be a little different to ours in the UK!

Some users here are reporting slightly reduced range but it's only really likely to be a problem in ambient temperatures approaching freezing.

 

[prState]

hah, on average, we don't have many cold days, but right now it's 4 C outside which is cold enough for me.

 

[Ian]

4 deg C is cold enough, even by UK standards. I didn't realise it got that cold over there, it didn't when I was over there in December a few years ago.

 

[semmel]

Lithium characteristics are too different to speak in general

Kokam a LiPo Manufacturer has some interesting Informations on there Website.
KOKAM Infopage

If you download the E-catalog from Kokam
KOKAM E-info-catalog
you see different Diagramms for different Types (High Power Type, High Energy Type..).

See Page 8:
For a High Power Type the temperature is not so important.
For a High Energy Type the temperature is very important.

We can not speak for all Lithium batterie types !!
With lithiums batteries every manufacturer has the possibility to select production parameters which changes the characteristics of the battery completely.

This makes it very complicated if we like to speak about lithium batteries.


Luke

 

[Branwen]

I made a cover for the battery on my Lafree from pvc lined with an old fire blanket which I used in the cold weather in the days the bike was parked outside. It slings over the top of the battery and hangs down each side like saddlebags do. It has a pocket on one side for the pump and the other for the puncture repair kit, and hid the fact it was an electric bike from casual observers too. It didnt even get in the way and could be left on when riding, though I took the precaution of copying the ventilation slats on the motor cover into the pvc cover too.

 

[Ian]

I made a cover for the battery on my Lafree from pvc lined with an old fire blanket which I used in the cold weather in the days the bike was parked outside.[/COLOR][/FONT]

Good idea Brawen, in normal use the battery will generate heat, and if that heat can be from escaping then the battery should remain at a reasonable temperature.

 

[BBB]

Batteries in the cold

I have had a few customers in with LA batteries that are only 3 months old running low in half the time as normal. Could this be due to the cold or a bad batch of replacment batteries!
And it there any way to really check how good a battery is with out a complicated dischaging system.

 

[flecc]

Lead acid suffer just as much as any other type from cold, and one only has to hear the winter car starting struggles that occur to know that. I'd bet winter car battery sales are at least double the summer ones.

Older type car batteries were easily checked cell by cell using a simple heavy discharge tester to detect dud cells, but modern SLAs can't be checked like that. Tests on a whole battery aren't as accurate.
.

 

[silversurfer]

4deg. in Las Vegas !!! I was there a few years ago late October and it was 24+ 0n the strip and one foot of snow on the tracks on nearby Mt Charlston ! amazing climate changes (at least to us Brits!). One point with temperature, only living thing (to the best of my knowledge) suffer from wind chill. So 4deg for the battery is 4deg. even if you are whizzing along at 20 mph. Not sure if the battery would generate any measurable heat with a 'tea cosy' on it, that might maintain its efficiency ? silversurfer.
Oh a happy,cut out free 2008 to flecc and all his little advisors who provide such good unbiased advice.

 

[Jeremy]

One point with temperature, only living thing (to the best of my knowledge) suffer from wind chill.

Almost. Only things that are warmer than the surrounding air suffer wind chill. Wind chill is really just accelerated convection; moving air takes more heat away than still air. It's how car radiators work, amongst other things.

My guess is that an ebike battery in use suffers slightly from this effect, as internal resistance heating from discharge will tend to warm it up. Air moving past it would then tend to make it lose heat more quickly than if it were in still air.

Jeremy

 

[keithhazel]

i bought my powerbyke from a gentleman in peterborough 6 months ago, he had looked after it lovingly, i doubt he ever left it out in the cold, not so sure he would have been able to lift the battery out every night and take inside though as they so heavy and its a right squeeze to get out,but will have gararged it, i have never left the battery out either,always bringing it inside the house, thinking about selling now as will get my new quando any day now, i took it out 2 weeks ago to test the battery , i used power only, i did 12 miles befor being down to last flickering 2 of 5 bars..i have the receipt for this battery and its 10/06/04....so with looking after and a bit of luck i think its in pretty good shape, im not sure how far he rode it as bought from new but either way i think care and respect of battery has paid off.

 

[silversurfer]

Thanks for the clarification Jeremy, I forgot about the car radiator and the amount of heat it has to dump.
I have never felt any noticable heat in my Torq lithium battery when in use during late summer/autumn but now, in winter I do notice the range is less. It is about 8 months old and in the last two months only used once or twice a week for a 12 mile round trip, restricted other than a half mile pull on a reasonably steep hill (I guess 8/10%)on the home stretch that I switch to de-restrict, now it usually puts the amber light on, then red towards the end of the climb. It is charged immediatly I get home. Perhaps a slim insulation sleeve would conserve any heat it might generate, better get the sewing machine out ! SS

 

[alex]

insulation

People considering knitting teacosies for their batteries or sewing wee covers might investigate some of the modern materials used to insulate buildings. There is a robust polythene material like bubble wrap which includes a metalic reflective layer. Another product has numerous layers of a shiney reflective material similar to the 'space blankets' we see around collapsed marathon runners, this is interspersed with this fleecy stuff. Total thickness around 25mm yet the insulation value can be equivalent to 200mm of glass fibre quilt. There are also some amazing handwarmers which consist of a plastic sachet with a gel like substance inside which can produce considerable heat for about half an hour & are re-useable, pop one of those into a space age hot-box & your battery will think it is on holiday in Las Vegas

 

[Jeremy]

A bit of good insulation might work to improve battery performance in cold weather. Looking at typical ebike batteries, they seem to have an internal resistance of perhaps 0.1 ohm or so. At an average current of perhaps 5 amps for a 36V system, then the battery would generate around a couple of watts or more.

Whether this is enough to do any real good on it's own is debatable, but if the battery was charged just before setting out (so warmed up a bit), then covered with some insulation, it might well be enough power to keep the battery at a reasonable temperature for a modest journey.

It might be worth a try, although you'd have to not be too concerned by the "tea cosy" look...................

Jeremy

 

[silversurfer]

Sounds like windchill will not be a problem as it will never rise above ambient temperature. Pehaps just a bit of modern thinsulate material to keep the freshly charged battery out of direct airflow.
Bit worried now.... is my 8 month old lithium battery starting to develop efficiency 'droop' or is the long period/s of inactivity and cold weather the cause ? and what's the cure ? SS

 

[flecc]

Inactivity doesn't hurt a lithium battery if it's less than about 2 months at a time, but the performance does drop off rapidly in cold weather. I had the last one at 10 months running fine into the start of the winter, but when the first very cold snaps arrived it started cutting out under load.
.

 

[coops]

I've wondered before about whether some insulation might help battery performance in the cold, and it seems like it would (I like the sound of your multi-purpose warmer/mini-pannier Branwen, & the vents sound very sensible! ), but are there any risks to be careful of like overheating the battery - I'm aware some controllers require wind cooling, might this apply to Ezee controllers too?

Might a lightweight, thin & breathable insulating material might also work well - similar to clothing materials one might wear for warmth (& even windproofing too) but still breathable - thinsulate etc. or even wool or polyester fleece - since that would also reduce any condensation risk in extreme cold: I'm quite sure batteries & trapped, condensed water would be a bad mixture: anyone wearing windproof outers in the cold will be aware how water vapour can condense on the inner layer of such due to the temp difference & lack of vapour diffusion through the material (e.g. on your back which doesn't get directly air-cooled) though much of tat is from sweat I guess & for batteries the main factor would be moisture in the air already i.e. the humidity level, which is usually low (i.e. it is quite dry air) in very cold weather.

I should think the risk is small then & the heat problem less than for the body analogy (at least batteries don't sweat! ), but I just don't want to risk wrecking my battery to get better cold weather performance from it .

Since the battery case also seems have quite good waterproofing, I'm not too concerned about adding waterproofing to a cover, especially as that is unlikely to breathe much, but then again it would be good I suppose if a cover doesn't absorb much water or dries quickly if it does get a little wet for whatever reason, to reduce risk of water ingress to the battery/controller.

What does anyone else think?

Stuart.

 

[flecc]

But remember that if a cover gets wet early in a journey, as the water subsequently evaporates, it turns the cover into an efficient fridge, freezing the battery. Years ago, cheap evaporative fridges working on this principle were quite popular.
.

 

[coops]

Thats a good point and would certainly be counter-productive! .

Do you think insulation with a water/windproof outer layer would be best then? On reflection, I think the risk of condensation is lower than I first thought .

How much do you find your warmer helps battery performance with your Twist, Branwen, aswell as being a handy carrier?

Stuart.