Does the REx engine heat a cold battery?

[BobDowser]

Very helpful, especially if the battery preconditioning is a mere 1.3 kW. My inverter can handle that with ease. And it's nice to hear from someone who knows what cold actually means! One question about that graph, what do the numbers on the right-side vertical axis mean?

 

[3pete]

Very helpful, especially if the battery preconditioning is a mere 1.3 kW. My inverter can handle that with ease. And it's nice to hear from someone who knows what cold actually means! One question about that graph, what do the numbers on the right-side vertical axis mean?

The vertical axis is kilowatts delivered by the EVSE to the car.

That's why I say the battery warming is about 1.3kW because that's about where the rectangle looks to be on the graph.

A few additional thoughts on the i3 in very cold weather in case they haven't already been mentioned:
1) Expect to lose significant range in the cold. The worst case scenario I've seen is about a 30% loss of range. (Preconditioning the battery and cabin can help with that, but just be aware for "unplanned" trips.)
2) Avoid the 20" wheels. The 19" can come with all-season or winter tires, but the 20s are summer only rubber and useless/dangerous in any amount of snow.
3) Leave the car plugged in for extreme cold. That'll let it manage its own thermals to help the battery. IIRC, it will use the battery heater even without a departure time in the event the battery is getting *too* cold (I can't find record of this in my charge logs so maybe I'm imagining it).

 

[alohart]

3) Leave the car plugged in for extreme cold. That'll let it manage its own thermals to help the battery. IIRC, it will use the battery heater even without a departure time in the event the battery is getting *too* cold (I can't find record of this in my charge logs so maybe I'm imagining it).

I have no i3 experience in cold weather, so I'm only expressing what I believe to be true.

The battery heating elements are HV elements that can be powered only when the HV system is on. When battery pack preconditioning hasn't been activated, the HV system and thus the battery pack heater is on only during active charging. They shut off a few minutes after a charging session ends when the battery pack is fully charged. To keep the battery pack heater on as long as possible while charging, I believe that some i3 owners have charged at AC Level 1 (120 V) with the charging speed set to minimum in iDrive (6 A or 0.72 kW, I believe). This is insufficient power for the battery pack heater, so the battery pack would provide some of the necessary power thus reducing its charge level a bit.

Being off-grid, you would probably need to experiment to determine the minimum off-grid power needed to provide the range that you need.

 

[BobDowser]

That's an interesting trick! Can the cabin pre-heat wattage be reduced like the charging rate, or do you just set a cabin temp for it to reach?

 

[alohart]

Can the cabin pre-heat wattage be reduced like the charging rate, or do you just set a cabin temp for it to reach?

The battery pack heater's power can't be reduced. I don't know whether cabin preconditioning (it could cool as well as heat) uses the last climate control temperature setting or whether the temperature is fixed and not adjustable.

 

[BobDowser]

Since the REx engine provides electrical power to the batteries, and since that power is used to provide electrical resistance heating both to the cabin and the battery pack at outdoor temps under 14F, is there an easy way to lock the REx engine ON for at least sufficient time to warm the batteries, to extend battery range, heat the cabin, and to ptreotect the battery bank from cold weather damage? I read a thread on Bimmerpost from 2015 that discussed a $150 flash drive sofware patch that gave control over the REx when the battery SOC was under 75% and the thinking was that this feature would soon make it into production cars right from the factory or in a BMW software update. Is it available for the 2017-2018 REx models?

 

[mojo]

I don't have a REx and so haven't looked in detail, but as I understand it you can code the "hold state of charge" option using Bimmercode - it's just a coding option.

However, I'm not sure it would be much help in the way that you suggest. The highest point at which you can cause the REx to start is 75% battery, but it seems likely to me that you would not want to deliberately start a journey with the HV battery only 75% full, just so that you would be able to force the REx engine to start. In those conditions it seems likely that you would be better served by starting with 100% battery, if at all possible.

 

[EvanstonI3]

Pre-Conditioning/Heating of the HV Batteries does not occur on demand. Only when a Departure Time is set at LEAST 3hrs in the future AND the car must be plugged in to L1 or L2 ESVE. There is no method of simply having the Range Extender come on with the expectation that it will pre-heat the battery pack and the cabin on its own.

Also- the Pre-Conditioning cycle of the HV Batteries will only occur twice in a row (possibly 3X) without moving the car.
After that you must turn the car ON and move it forward or back a small amount to reset the cycle. I'm not aware of any method of keeping the battery pack at an optimal temperature for an extended duration other than making an insulated container for it (a tent or a garage) and then heating that container to 50F so the entire car remains at that temp.