Cold charging

apacheguy · Jan 27, 2016

Didn't want to further derail discussion in wk's thread so I created a new one.

Following off of a linked PDF, I found this text:

Hot climates reduce life and cold charging can induce imbalances that also reduce life

Why does cold charging induce pack imbalance? And how do cell imbalances contribute to reduced life? Imbalances are correctable, I thought, by a single range charge.

Source:

http://www.totalbatteryconsulting.c...ort/Extract-from-the-Tesla-battery-report.pdf

Johan · Jan 27, 2016

In cold temps the internal resistance is increased and if different cells in a pack, charged with the same voltage, had very different temps then relatively more of the charge would go to the hotter cells and the pack as a whole would become unbalanced.

OK, so think of two cells in parallell, one hot and one cold. Hook them up one charger. More of the current would flow to the hotter cell as opposed to the colder one (because of lower resistance) and it's voltage would rise faster (=it would fill up faster). So when the hot cell was at 100% SOC the cold cell would be below that = imbalance.

Cyclone · Jan 27, 2016

Could they be thinking that absent an external heating/cooling system, the battery cells can go to different temps and charge at different rates. It sounds weird to me. Sounds like exactly why there is a BMS and it can control each cluster independently.

Johan · Jan 27, 2016

Cyclone said:
Could they be thinking that absent an external heating/cooling system, the battery cells can go to different temps and charge at different rates. It sounds weird to me. Sounds like exactly why there is a BMS and it can control each cluster independently.

Exactly, one of the reasons the Tesla pack has fluid based temperature control.

apacheguy · Jan 27, 2016

Johan said:
In cold temps the internal resistance is increased and if different cells in a pack, charged with the same voltage, had very different temps then relatively more of the charge would go to the hotter cells and the pack as a whole would become unbalanced.

OK, so think of two cells in parallell, one hot and one cold. Hook them up one charger. More of the current would flow to the hotter cell as opposed to the colder one (because of lower resistance) and it's voltage would rise faster (=it would fill up faster). So when the hot cell was at 100% SOC the cold cell would be below that = imbalance.

So really nothing to worry about given Tesla's BMS and thermal management.

CHG-ON · Jan 27, 2016

Li-on hates temp extremes. That's why we need to plan. If you can charge the car in a temperate environment, like a conditioned garage, you are fine. But if you charge outside in either hot or cold, it takes good planning because the BMS will throttle charge significantly to protect the battery and the electronics. It's the nature of the battery.

hybridbear · Feb 1, 2016

CHG-ON said:
Li-on hates temp extremes. That's why we need to plan. If you can charge the car in a temperate environment, like a conditioned garage, you are fine. But if you charge outside in either hot or cold, it takes good planning because the BMS will throttle charge significantly to protect the battery and the electronics. It's the nature of the battery.

We charge in a climate controlled garage at our apartment. I've been able to see this with our Focus Electric. The Focus Electric has liquid thermal management & the cell temperature imbalance is usually relatively small when the car has been parked overnight inside & charged. The biggest temperature differences happen when driving & warming the car after it has been sitting in the cold all day.

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Cold charging

apacheguy

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Johan

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Cyclone

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Johan

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apacheguy

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CHG-ON

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