Difference between revisions of "Battery/Temperature Effects"

Latest revision as of 21:31, 4 December 2019

Performance

Battery internal resistance is higher at lower temperatures, which means that while riding, losses to battery internal resistance mean a loss of range at lower temperatures.

Farasis quotes internal cell resistance as <2mΩ but it's not exactly clear how this translates into calculating those losses without some description of how that trends over temperature and charge rate.

The warmer the battery is, the lower these losses will be.

Below freezing temperatures, the battery chemistry will not allow effective charging at all, and Zero provides protections to prevent this until the battery's temperature has been raised sufficiently.

It follows that to get maximum performance, charging and discharging repeatedly at a high rate will raise cell temperature enough to reduce internal resistance so more will be delivered to the motor.

Degradation at high temperatures

Temperature is a bigger factor than state of charge when it comes to aging. Apparently, for every increase of 10F degrees in battery temperature across its lifetime, battery deterioration over that lifetime can double.

Heat Production

It is worth noting though that Li-ion batteries shouldn't generate a lot of heat when charging at normal rates.

On a Zero, charging at or below 4kW will not produce much heat.

Therefore, even if you live in a hot climate and have just been on a ride, the cells should cool down overall even while they are charging (although direct sunlight on the battery will add more heat).

You might want to be a little more careful if fast charging in a hot climate but don't forget that the BMS will either reduce the charge rate or stop charging altogether if the cell temperature exceeds the limits that the engineers have set. They have set these limits on the conservative side to avoid any claims on that five year warranty.

Storage

If you are going to store the bike, it makes sense to store it somewhere cool.

Fridge temperature is probably best but never store below freezing.

If you don't have the option of storing it somewhere cool, then don't worry about it.