Simon
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Re: Energy Consumption During Preheat

Fri May 09, 2014 9:29 am

I got the following answer on the question why the battery is not 100 full at departure after preconditioning and why it is not taking power from the charger at all times: (it came from BMW headquarters)

” Required precon. power can be higher than charging power, depending on temperature, SoC and charging supply. Thus SoC can go down even if the vehicle is plugged in! … but will be recharged. some details: at cold temperatures (<0°C), a precon. power of up to 5kW is required. Charging with the standard cable at charging power “low” only delivers ca. 1,4kW, even at “high” only 2,8kW. And: at nearly full SoC, charging power goes down <1kW, no matter if plugged in to a AC 7,4kW charger or even DC charger. This is part of the charging characteristic of every Li-Ion battery.

- SoC can go down up to ca. 10%, if it is very cold/hot and charging power “low”.

- Timing: e.g. at -10°C, preconditioning will start ca. 30min before departure time with 5kW, then go down to 3kW and keep the vehicle warm 15min after departure time. Charging will proceed afterwards (if still plugged in) until the battery is fully replenished.

- All this is independent of automatic preconditioning at departure time or manual activation and charging timer / immediate charging etc.

- Exception: at public charging stations which unlocks after full charge, charging cannot be restarted.

MikeS
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Re: Energy Consumption During Preheat

Fri May 09, 2014 10:35 pm

But is this true if you have the 7kw EVSE?
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Gonville
Posts: 400
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Re: Energy Consumption During Preheat

Fri May 09, 2014 11:36 pm

MikeS wrote:But is this true if you have the 7kw EVSE?
Is this bit the answer to your question? (Continental "," Is a decimal "."?)
BMW Technical Centre wrote:.....no matter if plugged in to a AC 7.4kW charger...

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RJSATLBA
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Re: Energy Consumption During Preheat

Sat May 10, 2014 1:05 am

To my relatively non-technical mind this seems to be saying that the power for pre-con is taken from the battery, regardless of whether the car is plugged in; then because the charging characteristics mean that the charge drawn by the battery reduces to a pretty low level as full SoC is reached, regardless of current being drawn, the current draw exceeds the charging current. If so it sounds as if the Winter pack, with HV preconditioning will cause even greater depletion during charging, so may not have as much of a beneficial effect on the range as one would have hoped, if any.

I wonder how this reconciles with the way the REx works and perhaps explains why it can't be invoked until down to 80% (or is it 75%). However, I would have expected that the motor would draw direct from the REx, not via the battery, but would draw additional juice from the battery if the load caused the requirement to exceed the max available from the REx. The latter situation would be the point at which the REx isn't able to maintain the charge level, ie uphill at speed.

So if the motor can draw from the REx and only deplete the battery if the motor needs more than the REx can provide, why can't the power users during pre-conditioning draw direct from the EVSE and only deplete the battery if they require more than the EVSE can provide?
Roger

i3 REx ordered 7 Feb 2014, delivered 8 Oct 2014

MikeS
Posts: 713
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Re: Energy Consumption During Preheat

Sat May 10, 2014 1:33 am

Gonville wrote:
MikeS wrote:But is this true if you have the 7kw EVSE?
Is this bit the answer to your question? (Continental "," Is a decimal "."?)
BMW Technical Centre wrote:.....no matter if plugged in to a AC 7.4kW charger...
Yes it was! Too early this morning at 0635 for my brain to register the info!
BMW 3 Series 2005 - Aug 2014
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Bunter
Posts: 372
Joined: Sun Nov 17, 2013 3:41 pm
Location: South Central England

Re: Energy Consumption During Preheat

Sat May 10, 2014 2:09 am

Simon wrote:I got the following answer on the question why the battery is not 100 full at departure after preconditioning and why it is not taking power from the charger at all times: (it came from BMW headquarters)

” Required precon. power can be higher than charging power, depending on temperature, SoC and charging supply. Thus SoC can go down even if the vehicle is plugged in! … but will be recharged. some details: at cold temperatures (<0°C), a precon. power of up to 5kW is required. Charging with the standard cable at charging power “low” only delivers ca. 1,4kW, even at “high” only 2,8kW. And: at nearly full SoC, charging power goes down <1kW, no matter if plugged in to a AC 7,4kW charger or even DC charger. This is part of the charging characteristic of every Li-Ion battery.

- SoC can go down up to ca. 10%, if it is very cold/hot and charging power “low”.

- Timing: e.g. at -10°C, preconditioning will start ca. 30min before departure time with 5kW, then go down to 3kW and keep the vehicle warm 15min after departure time. Charging will proceed afterwards (if still plugged in) until the battery is fully replenished.

- All this is independent of automatic preconditioning at departure time or manual activation and charging timer / immediate charging etc.

- Exception: at public charging stations which unlocks after full charge, charging cannot be restarted.

Thanks for that information, it's very useful and makes complete sense of what I've been noticing and struggling to understand.

If your EVSE cannot supply sufficient power for the pre-conditioning phase the power extra is drawn from the battery.
- When preconditioning my standard UK EVSE draws the maximum 10 amps, the rest is coming from the battery

The consumption during pre-conditioning when cold is likely to be much higher than can be supplied from a standard charging connection.
- That fits, most mornings so far in my ownership the ambient has been below 10 C and the battery is not full when leaving.

If you do draw from the battery, because the SOC is nearly 100 %, charging rate is low, so the energy drawn from the battery takes a long time to replace.

Seems like another good reason to have a 7kw EVSE.

Bill
Born Electric 15.03.14

RJSATLBA
Posts: 292
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Location: Pool in Wharfedale, W Yorks, UK

Re: Energy Consumption During Preheat

Sat May 10, 2014 4:00 am

Bill

First can I add my thanks to Simon.

It looks like I'd read BMW's reply differently from you and re-reading it I think there is some ambiguity. The opening statement 'Required power can be higher than charging power' implies that precon juice is taken from the EVSE and only if the required power is greater than the EVSE power will power be drawn from the battery. So given their example of 5kW at 0C, a 7kW charger would mean that nothing would be drawn from the battery.

But if so, why the comments ' standard cable at charging power “low” only delivers ca. 1,4kW, even at “high” only 2,8kW. And: at nearly full SoC, charging power goes down <1kW, no matter if plugged in to a AC 7,4kW charger or even DC charger'. Surely these would only be relevant if precon juice is taken from the battery, which would immediately start to draw from the EVSE for replenishment but the rate of draw would be limited to the low rates taken when the battery is close to full charge. Then, given the comment that charging power goes down to <1kW, regardless of whether hooked up to a 7kW charger or DC, this seems to be saying that a 7kW EVSE wouldn't confer any advantage over a 3kW EVSE or even a basic 3pin 13A mains lead set-up.

I think the ambiguity is that they keep referring to charging power, which for a 7kW EVSE is always 7kW, when they should be referring to the power drawn by the in car charging controller, which falls as the SoC approaches 100%. Hope the layman's terms make sense.
Roger

i3 REx ordered 7 Feb 2014, delivered 8 Oct 2014

ultraturtle
Posts: 439
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Re: Energy Consumption During Preheat

Sat May 10, 2014 5:24 am

RJSATLBA wrote:So if the motor can draw from the REx and only deplete the battery if the motor needs more than the REx can provide, why can't the power users during pre-conditioning draw direct from the EVSE and only deplete the battery if they require more than the EVSE can provide?
Because the pre-conditioning power comes only from the battery's DC output, and is not capable of bypassing the charging circuit to use the EVSE's AC output. At high battery states of charge, the charging system protects the battery by limiting current to less than 1 kW, regardless of the power demanded from the battery.

Bunter
Posts: 372
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Location: South Central England

Re: Energy Consumption During Preheat

Sat May 10, 2014 6:24 am

ultraturtle wrote: Because the pre-conditioning power comes only from the battery's DC output, and is not capable of bypassing the charging circuit to use the EVSE's AC output. At high battery states of charge, the charging system protects the battery by limiting current to less than 1 kW, regardless of the power demanded from the battery.
Oh I'm confused again? Mainly because during pre-conditioning the car draws as much as the UK EVSE can deliver (10 amps), even though the car battery is close to 100%.

Bill
Born Electric 15.03.14

MikeS
Posts: 713
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Location: Brighton UK

Re: Energy Consumption During Preheat

Sat May 10, 2014 7:37 am

Bunter wrote:
ultraturtle wrote: Because the pre-conditioning power comes only from the battery's DC output, and is not capable of bypassing the charging circuit to use the EVSE's AC output. At high battery states of charge, the charging system protects the battery by limiting current to less than 1 kW, regardless of the power demanded from the battery.
Oh I'm confused again? Mainly because during pre-conditioning the car draws as much as the UK EVSE can deliver (10 amps), even though the car battery is close to 100%.

Bill
Then again a 7kw Uk EVSE should be able to draw about 16 amps.
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