Hold state of charge, question

[125mph]

I just coded my car and tested the HSC feature. I drove and hit the button at 50% and it seem work fine.. Then I turned it off...

WHen I got close to home, the battery was below 10% and I assumed the regular hold state of charge would kick in but it didnt.. So I manually turned it back on again.

When I "check" that box to hold state of charge, am I telling it to hold state of charge starting right now, or what is actually going on. If I dont have that check box checked, will the HSC never kick in?

 

[alohart]

The REx engine typically turns on when the battery pack's charge level drops to 6.5%, so your 10% charge level was too high. This should occur when the HSOC checkbox isn't checked.

 

[125mph]

Ahh perfect.. I thought the default % REX kicks in was 15%.

 

[Deutsch100]

Ahh perfect.. I thought the default % REX kicks in was 15%.

Alohart is right. Whether you have your Hold State of Charge ACTIVATED or not (not coded, LOL! I am going to make sure we stop saying coded...no one is coding anything)..REX kicks on yes, between 6-7%. I think 10% would be better, but obviously BMW thought not

 

[JohnWasser]

I think 10% would be better, but obviously BMW thought not

The firmware gives you a choice in 1/2% intervals. It's the California Air Resources Board that said "The APU (REx) must not be capable of switching on until the battery charge has been depleted". BMW interpreted 'depleted' as 6%. Note: CARB is also why a 64 Ah REx can only access 1.9 of the 2.4 gallons in the gas tank: gas range can't be more than battery range.

Instrument Cluster (KOMBI_I01_F56)
3000/
SOC_HOLD_POSITION werte = hex value xx
Units are 0.5% -- default = 0C

0C = 6%
14 = 10%
28 = 20%
3C = 30%
50 = 40%
64 = 50%
78 = 60%
8C = 70%

 

[alohart]

The firmware gives you a choice in 1/2% intervals. It's the California Air Resources Board that said "The APU (REx) must not be capable of switching on until the battery charge has been depleted". BMW interpreted 'depleted' as 6%. Note: CARB is also why a 64 Ah REx can only access 1.9 of the 2.4 gallons in the gas tank: gas range can't be more than battery range.

Instrument Cluster (KOMBI_I01_F56)
3000/
SOC_HOLD_POSITION werte = hex value xx
Units are 0.5% -- default = 0C

0C = 6%
14 = 10%
28 = 20%
3C = 30%
50 = 40%
64 = 50%
78 = 60%
8C = 70%

Has anyone actually been able to change at what charge level the REx engine automatically starts? I believe that SOC_HOLD_POSITION merely changes the location above the charge level gauge of the white triangle that indicates the charge level at which the REx engine automatically starts..

 

[cdnji]

Would be interested in finding out as well. I tried setting it before but it did not take. At least I got manual HSOC to work.

Also, I found that that it typically takes around 6 mins for the REx to warm up for the catalytic converter to reach optimal temps so that REx can operate at higher RPMs. Max RPM, and resulting higher electrical output from REx is also not achieved until around 85kph. So those combined made me conclude that I should just rely on HSOC only when I have a stretch of highway travel ahead. So no point in having HSOC automatically trigger at 70%; just rely on my read of the current driving conditions and manually turn it on.

 

[RP67]

Great help from

The firmware gives you a choice in 1/2% intervals. It's the California Air Resources Board that said "The APU (REx) must not be capable of switching on until the battery charge has been depleted". BMW interpreted 'depleted' as 6%. Note: CARB is also why a 64 Ah REx can only access 1.9 of the 2.4 gallons in the gas tank: gas range can't be more than battery range.

Instrument Cluster (KOMBI_I01_F56)
3000/
SOC_HOLD_POSITION werte = hex value xx
Units are 0.5% -- default = 0C

0C = 6%
14 = 10%
28 = 20%
3C = 30%
50 = 40%
64 = 50%
78 = 60%
8C = 70%

Thanks for the info, I managed to change the value to 20% (28). Just out of curious, where is the 28 came from? In my case 15% would be better, but I couldn't find any resources or conversion chart to find out the value I need to use. It is surely not Hex (well I think it isn't).

 

[mojo]

Great help from

Thanks for the info, I managed to change the value to 20% (28). Just out of curious, where is the 28 came from? In my case 15% would be better, but I couldn't find any resources or conversion chart to find out the value I need to use. It is surely not Hex (well I think it isn't).

As far as I can see, it's just the hex value multiplied by the increment value of 0.5%.

28hex = 40 -> 40*0.5% = 20%

 

[kd7iwp]

Let us know if it works. I seem to recall a few others who have tried to change the default setting when the REx turns on and people said they could change the number but it didn’t affect the outcome.

 

[RP67]

As far as I can see, it's just the hex value multiplied by the increment value of 0.5%.

28hex = 40 -> 40*0.5% = 20%

So the correct one for 15% would be 1E? (1E=30, 30*0.5=15)

 

[RP67]

Let us know if it works. I seem to recall a few others who have tried to change the default setting when the REx turns on and people said they could change the number but it didn’t affect the outcome.

Wow I wasn't expecting that... I'll let you guys know once it dropped to 20%.

 

[nilknarf]

My high school daughter drives an i3 Rex and freaked out a bit recently when the car told her that it had no more electric range. I am assuming that its ok to use up all of the electric charge and run on the Rex indefinitely (as long as there is gas in the tank), correct?

What is the main benefit of holding your charge at 75% and kicking the Rex in at that state of charge vs just running your charge down to 6% and running the Rex? Is it just so that you have the electric as a backup once you run out of gas?

 

[EvanstonI3]

My high school daughter drives an i3 Rex and freaked out a bit recently when the car told her that it had no more electric range. I am assuming that its ok to use up all of the electric charge and run on the Rex indefinitely (as long as there is gas in the tank), correct?

What is the main benefit of holding your charge at 75% and kicking the Rex in at that state of charge vs just running your charge down to 6% and running the Rex? Is it just so that you have the electric as a backup once you run out of gas?

The car cannot be used indefinitely running the REX alone. Perhaps when new it would work better, but as the years go by, the Computer's idea of how much Battery remains and Reality's version get out of sync. So while the battery level on the dash shows 6%, the computer may think the battery has more than 6% and the REX won't come on. Then you run out of battery and are stranded someplace.

For your situation it might be good to enable HSOC at some level higher than 6% so she does not get stranded by this type of situation.

 

[Wing Pang]

My high school daughter drives an i3 Rex and freaked out a bit recently when the car told her that it had no more electric range. I am assuming that its ok to use up all of the electric charge and run on the Rex indefinitely (as long as there is gas in the tank), correct?

What is the main benefit of holding your charge at 75% and kicking the Rex in at that state of charge vs just running your charge down to 6% and running the Rex? Is it just so that you have the electric as a backup once you run out of gas?

I have always wondered about this as well - is it better for the scooter engine to fully delete and leave charge? I have left mine on the default setting - I assume this is on the basis that the car is designed as an electric car and that the REX is only to be used as a backup?

 

[RP67]

I have always wondered about this as well - is it better for the scooter engine to fully delete and leave charge? I have left mine on the default setting - I assume this is on the basis that the car is designed as an electric car and that the REX is only to be used as a backup?

You are right, the car was designed as full electric and the REX is just an attempt to mitigate the reasonably short range (back in 2013), however the lower limit to allow the REX to start automatically, to maintain the SOC, is rather legislative value, and US specific. Also as far I understand (and it is might not be correct), that is the level when the battery can be called "depleted" and need assistance to get to the next charging spot. So when the battery degradation is reaching a certain level when the lower "buffer" is higher than the manufacturer specs (8% of the real capacity in case of the 60Ah) then the REX start value needs to be adjusted. For example in my case, the HV battery cell voltage start to drop rapidly at 11% SOC (on the display). So no point to wait for the 6% limit, as it never gonna be reached, the HV battery shutting down lot earlier. It isn't a great solution, but hey there is the option to do that, rather than throw the car away... (or delete REX,)

 

[Marscar]

I appreciate that the ability to HSOC at anywhere from 6% to 75% is not available everywhere, but since I've had an 'experience' I thought it might be worth a mention here that if you DO have the option then use it! ... Apart from giving the REX a service run that it might not get because of how you chose to charge and run your car, you don't want to be in the spot I found myself in once where the charge was down to 8%. (longer than usual round trip with, so I thought, the REX in place to finish the journey.)
It was getting dark, and raining, and we were in stop/start, almost standstill, traffic...
The lights and wipers, even though switched manually to reduce drain, took the charge steadily downward to 4%.
Meanwhile the REX was working on the "you're at a standstill so switch off" principle, which in turn meant no charge going to the battery.
No charge point in the area, even if we had been able to go straight to it ...
Messages along the lines of "car will not function" and "charge car now to avoid failure to restart" started coming up.
Let's just say I'm pretty laid back all round but this really kicked in the butt-clenching.
We scraped it to a domestic charge point and proceeded to heat up the socket with a 3 pin charge via the 3 pin cable we always carry plus about 20 metres of scrounged extension.
This is not something I would wish on anyone .......
Do HSOC higher than 6% if you can!
You never know what's "around the corner"!

 

[placetobe]

What is the main benefit of holding your charge at 75% and kicking the Rex in at that state of charge vs just running your charge down to 6% and running the Rex?

Here's one: flexibility.

Imagine you're going on a long motorway journey where you will have to recharge and/or refuel to reach the destination. I have a regular 200 mile journey like this - can't get there on a full battery plus REX tank, so I need to stop somewhere.

If you use up the REX tank early in the journey, then you have three refuel options: charge (slow, but gets you an extra 100 miles of range), petrol (fast, gets you 50 miles) or both (same speed as charging, gets you 150 miles). This gives you much more flexibility, which you can use based on when you reach a good charger that's working and free, when you need a loo break, or when you pass a petrol station.

For example sometimes you plan to charge in one place but can't - never mind, quickly fill up the REX tank and you've got another 50 miles plus what was in the battery to either find a charging station or potentially get to the destination using quick petrol refuel stops. I did a trip around Christmas when the charging stations were completely swamped, so I changed my plan and bought petrol instead.

But if you let the charge run down to 6% then you may end up running it out completely (the REX can't maintain state of charge for motorway driving). Then your only refuel option to get enough range to reach the destination becomes charging. So this means you're forced to find a working available charger pretty soon and then wait while it charges, which is less flexible, riskier and more stressful.

 

[holdenfamily]

Here's one: flexibility.

Imagine you're going on a long motorway journey where you will have to recharge and/or refuel to reach the destination. I have a regular 200 mile journey like this - can't get there on a full battery plus rank, so I need to stop somewhere.

If you use up the REX tank early in the journey, then you have three refuel options: charge (slow, but gets you an extra 100 miles of range), petrol (fast, gets you 50 miles) or both (same speed as charging, gets you 150 miles). This gives you much more flexibility, which you can use based on when you reach a good charger that's working and free, when you need a loo break, or when you pass a petrol station.

For example sometimes you plan to charge in one place but can't - never mind, quickly fill up the REX tank and you've got another 50 miles plus what was in the battery to either find a charging station or potentially get to the destination using quick petrol refuel stops. I did a trip around Christmas when the charging stations were completely swamped, so I changed my plan and bought petrol instead.

But if you let the charge run down to 6% then you may end up running it out completely (the REX can't maintain state of charge for motorway driving). And your only refuel option to get enough range to reach the destination is charging. So this means you're forced to find a working available charger pretty soon and then wait while it charges, which is less flexible and more stressful.

I concur with the option 2 approach, I do a 250 mile road trip in my 2018 REX regularly where I set to charge hold @ 75%, and @ 20% stop at a $0.17/kw dc charger. While charging, I refill the tank w/ a 3 gallon can you eat can I keep in the frunk for road trips, stretch my legs, get a snack & am 20mins later am back on the road w/ 90% charge and full tank. That usually leaves w/ ~75 miles of range on arrival, so no anxiety, and I can run a few errands before home charging/refilling Rex.

 

[Mondomensch]

“…$0.17/kw dc charger…”

I wish we had such here!