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This is old hat... everyone's going to say at 6.5% I assume? That's what I thought, as that's what's always happened... until now

Recently (all sing, "driving home for Xmas") starting journey at 100%, we managed a PB of 121 miles on a single charge. 4 miles and 4% left on the GOM/SOC when we arrived at the folks.

Raised as Rex issue with dealer, they said no percentage trigger, it kicks in dependent on conditions. They can't give me a reference for that & Driver's Guide just says "a minimum value" of SOC.

Over to you for answers, Gentle Reader
 

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Nice idea, but not going to waste my time contacting that lot again

I found BMW-i well-meaning but entirely technically clueless regarding my previous i3 information request. Took weeks of phone calls & emails for them to even understand my query, which ultimately they couldn't answer.
 

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I see. So may have tried to start and, still hadn't managed it 3-4 miles (3-4%) later?
So without knowing the conditions its very hard to say but I will give you an example from my usage.

- Bombing down the M1 at 70mph
- SOC hits 7.5% & REX starts.
- Travel for several minutes REX generation hits peak SOC is now at 4%
- As I am demanding more power from the battery due to speed, the REX powers the motor directly and only residual power is sent to the battery SOC remains at 4%
- Slow due to roadworks for 20miles+, the REX now pushing nearly full output to battery to restore to 7.5% (its activation point)
- about 10miles later REX shuts off SOC is at 8%
 

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As @Jack says. Not sure the dealer is giving you a straight answer...
What the dealer is saying is true for PHEV's and was going to be a feature on the i3 after a software update, but CARB deemed that such a feature would warrant the removal of the the i3's BEVx designation and therefore Tax credits so was never put into the wild.

The PHEV's definitely do fire up the engine into charge mode or swap out to battery only depending on context, engine fires up before a long climb, and will disengage in a built up area for example.
 

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I've found that it normally takes the REX about 10-15 minutes to "warm-up" and get up to peak power. During this time you will continue to loose battery charge if you are driving on a motorway (the lowest I've seen it go is 5%)
 

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What the dealer is saying is true for PHEV's and was going to be a feature on the i3 after a software update, but CARB deemed that such a feature would warrant the removal of the the i3's BEVx designation and therefore Tax credits so was never put into the wild.

The PHEV's definitely do fire up the engine into charge mode or swap out to battery only depending on context, engine fires up before a long climb, and will disengage in a built up area for example.
Ah yes, you're right, I have heard this too. Having said this whilst I'm sure you are right Jack I'm not so sure the dealer is right! Maybe I'm being a tad cynical!
 

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I've found that it normally takes the REX about 10-15 minutes to "warm-up" and get up to peak power. During this time you will continue to loose battery charge if you are driving on a motorway (the lowest I've seen it go is 5%)
Ha, lightweight! :)

Managed to get mine down to 1 or 1.5% or so and the car go into reduced power mode and slow right down!
 

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EGGY
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warm up eh, bizarre ? I've not looked at this but I have pondered what the best REX strategy is, so far in my very limited experience I've gone with "turn it on manually in the roadworks as soon as I'm below 75% to turn the red chequered flag off" technique, theory being you're getting more bang for your buck at 40-50 ?
 

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warm up eh, bizarre ?
I believe this is very much a "warm up" in order to extend the life of the engine and allow for the fact that it might not have been run for weeks. The REX keeps it's rev's relatively low at first to let the oil circulate and become more viscous. It then ramps up the revs and load over a ten minute period. Obviously the power output is low at first and then reaches peak capacity.
 

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Thanks for sharing - interesting read.

@Malcom Hedges Section 9.2 explains exactly what is going on with regard to the warm up as well as why sometime you can't hear the engine!

"In order to bring the combustion engine and thecatalytic converter to operating temperature, the combustion engine is operated at a speed of 2,200 rpm-2,400 rpm during the warm-up phase. This is dependent on the speed driven and, at the same time, represents the idle speed of the combustion engine. The period for this warm-up phase is roughly 360 seconds depending on the ambient temperature.
The speed varies accordingly between 2,200 rpm and 4,300 rpm and also the output power of the combustion engine depending on the speed driven and the state of charge of the high-voltagebattery. The resulting acoustics of the combustion engine are regulated conveniently by controlling the speed subject to the speed driven. Inorder to extend the range the engine speed is also influenced by the state of charge of the high-voltage battery"​
 

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EGGY
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thank you, as much as I like a bit of RTFM that was a stretch .... and now we should probably return this thread back to the original subject ! :whistle:
 

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Yes - back to the original topic! The technical doc that Jack posted says that the REX will kick in at 6.5% State of Charge Relative, and “It is important to note that these are relative values and not absolute values.“ Perhaps it is this final point that the dealer is refering to?
 

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Yes - back to the original topic! The technical doc that Jack posted says that the REX will kick in at 6.5% State of Charge Relative, and “It is important to note that these are relative values and not absolute values.“ Perhaps it is this final point that the dealer is refering to?
Hmmm, maybe but still not convinced! Left to its own devices the REx always comes on at about 6.5% charge. I've never seen it behave differently and that's across about 25k of use and 2 different i3 models.
 
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