Battery power and cold weather

[flecc]

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 .

Stuart.

It's bound to help a bit, but I doubt if any insulating cover would resist the cold for very long if the temperature gradient was large. There's a bit of "devil or deep blue sea" about this issue. For performance, ideally it's best to start with a battery that's been charged and kept indoors and taken out at 20 to 25 degrees C, then installed with a waterproof insulating cover.

On the other hand, higher temperatures reduce a battery's life through capacity loss, particularly that of Li-ion batteries. So we're beat either way, and I just charge indoors in a fairly cool room and leave it at that, accepting battery limitations.
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[coops]

Actually, I had a feeling that you'd have already made a cover if it was worth it! I suppose then that pedalling more in the cold to compensate for reduced battery performance, and keep warm at the same time, could be one way to go... so I guess it should be 'legpower & cold weather' then?!

Not wanting to drift off-topic, but is it also accurate then to say that in mild/warm weather good battery performance comes at the expense of accelerated battery ageing? The optimum temperature for NiMH discharge has been mentioned here - around 20-25C was it? Is that an optimum for performance only, or for performance and rate of capacity loss?

I must say, I'd not thought much about the ambient temperature when charging and will likewise try to charge in fairly cool conditions .

Stuart.

 

[flecc]

It's a confusing issue! Charging at low temperatures is less efficient and results in reduced charge, so it's an efficiency versus life matter whether charging or discharging. Life loss not too important with NiMh though, it's li-ion that reacts most to temperature.

Hot ambient conditions do indeed shorten Li-ion life, so parking in the direct California sunshine at around midday isn't a good thing. Unlikely to be too important to us in the Uk though.
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[coops]

Too right its confusing! no problem though, so I've decided to just carry on doing things just the way I have been .

 

[prState]

Life loss not too important with NiMh though.

I know in the 4 years, my NiMH has endured a lot of hot weather sitting outside for hours sometimes in the sun, so at least from that standpoint, I feel like it's well tested for durability.

I've never noticed any heat related issues, as far as too hot, as yet.

 

[Jeremy]

Toyota take the cooling air for the battery in the Prius from inside the passenger compartment (there's a small intake grill on the top side of the rear passenger seat), so the same airflow source both cools the battery when it's too hot, and warms the battery when it's too cold. Reading the development book, they hit on this idea after realising that NiMH batteries and people liked to work at about the same temperature!

Jeremy

 

[flecc]

That's the sort of intelligent design I really applaud, taking advantage of natural states and showing a thinking designer.
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[Sector]

Phylion batteries at low temperature

My Ezee battery is marked Phylion and I have found a web page that probably applies:

Product Introduce

I have a problem because I don't have the Chinese character set installed in Windows. Can anyone confirm the charging and discharge temperature ranges given there. I can see "Charge 0 ℃ ～ 45 ℃" and "Discharge -20 ℃ ～ 55 ℃". Do they mean degrees Centigrade?

There are several references on the web to the freezing point for LI+ electrolyte being around -40 degC, so the cells might possibly be rated for storage and discharge at temperatures well below 0 deC.

There are also several warnings on the web that charging Li+ cells below 0 degC will lead to plating of metal on the electrodes, which will destroy the cell. That seems to be confirmed by the above hieroglyphics from the Phylion website. So the advice I've seen previously on the forum to bring the battery inside after a cold ride and let it warm up before charging looks to be well founded.

 

[flecc]

Thats right about the charging, but opinions on the lowest temperatures for storage seem to vary. It's probable that the advice has varied as the chemistry has. It's somewhat academic that discharge may still be possible at very low tempertures though, since our experience shows that performance declines severely as the temperature approaches zero degrees C, the discharge rate too low to avoid cut-outs due to voltage drop.

And of course our experience shows that we know better than Phylion or Lishen on this subject, both previously adamant that their batteries could comfortably exceed any current demands placed on them by our motors, but now tacitly acknowledging that we were right all along.
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[Sector]

Yes, I've also experienced the drop in performance with low temperature, but the effects are not so marked with the relatively level terrain in Leicestershire.

I'm just interested to know whether I can ride the bike to work, leave it outside in say -3 degC for 4 hours, ride it 2.5 miles back home, and still be inside the manufacturer's stated operating conditions.

I no longer have a car. Do I really need to switch back to an ordinary bike when its freezing?

 

[flecc]

In fairly flat terrain you should be ok, and the latest advice doesn't seem to point to any difficulty. Definitely worth trying, and if the performance is adequate, that will be a fair indication that no harm is being done.
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[Branwen]

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.

I dont know if I can quantify how useful the cover has been, except to say I never had any of the problems with lower performance in the winter that other people have complained about, and my battery lasted over 5 years before going from normal performance to a sudden expiration. The pvc layer is definately needed to stop the water freezing fridge effect mentioned by Flecc, with a layer next to the battery that is breathable but treated with something like polar fleece, which expels light moisture such as you might get from splashes. I just happened to have an old fire blanket which has done the trick nicely.