Conclusive guide to: Mild hybrid operations in the D5
06-01-2019, 01:27 PM
#1
AudiWorld Super User
Thread Starter
Conclusive guide to: Mild hybrid operations in the D5
After 4 hours of data collection today, I am pleased to report back some conclusive learnings about the operations of the DC DC converter, the 48V mild hybrid battery, and the Belt Starter Generator (BSG). I decided to start a new thread on these topics to combine all of these topics, and to also now do something I was unable to do before, which is to post actual scientific findings.
TLDR: Just drive your D5, the Audi engineers have figured it out.
Couple of great findings today.
1) The 48V battery is kept at a charge of between 50% to 68%. It was absolutely impossible for me to force more power into the 48V battery even when holding the brakes and going down a long long hill. After the 48V battery hit 60-68%, the battery stopped accepting charge. This is absolutely fantastic as lithium ion batteries age significantly if you charge it above 70%, with a realistic suggested max of 80%. Seeing the 48V battery in this 50-70% state constantly makes me ecstatic!
2) The BSG actually assists the ICE in almost every single condition. If you floor your D5, it'll go into overdrive and shove more than 100 amps of current into the BSG versus when it's assisting the ICE from a standstill, it shoves about 20 amps of current in.
3) If you are idling for any substantial amount of time, you are drawing about 7-15 amps from the 48V battery as it charges the 12V battery. This depletes the storage rather quickly. By pushing the drive mode to Sport, and leaving it there, or by doing so and then Parking the vehicle, the idle will remain high, and thus short of turning AC on max, the BSG is able to generate enough electricity such that the 48V battery does not go "into the red". I calculated a depletion of the 48V battery from 60% to 50% when idling when the car was in the Comfort Drivetrain setting in about 15 minutes.
4) No matter what I did to charge my car with my battery tender, the 48V battery SOC was unaffected. I don't know if a lengthy plug in duration would change this, but ultimately the DC DC converter was constantly in step down mode as OBDEleven cannot connect unless Terminal 15 is on (the car is on without the engine running). Even with the engine off and the tender on for hours, the 48V battery after the fact had the same SOC. So either the DC DC converter is preventing the 48V battery from getting charged (NOT in line with documentation), or the fact that if the DC DC converter does eventually step up from 12V to 48V to charge the 48V battery, the current is so minuscule that it's pointless. Remember, a 12V 5A battery tender is what I am using and what most people use, so by the time it does step up to 48V the current is probably so miniscule that it doesn't really affect the SOC of the 48V battery. At times when driving around, the BSG would regenerate up to 125A of current for brief moments to charge the 48V battery. Thus, a battery tender doesn't do much...
These are my top of mind findings thus far. I really need to sleep now. - exhausted after a whole day of collecting data
TLDR: Just drive your D5, the Audi engineers have figured it out.
Couple of great findings today.
1) The 48V battery is kept at a charge of between 50% to 68%. It was absolutely impossible for me to force more power into the 48V battery even when holding the brakes and going down a long long hill. After the 48V battery hit 60-68%, the battery stopped accepting charge. This is absolutely fantastic as lithium ion batteries age significantly if you charge it above 70%, with a realistic suggested max of 80%. Seeing the 48V battery in this 50-70% state constantly makes me ecstatic!
2) The BSG actually assists the ICE in almost every single condition. If you floor your D5, it'll go into overdrive and shove more than 100 amps of current into the BSG versus when it's assisting the ICE from a standstill, it shoves about 20 amps of current in.
3) If you are idling for any substantial amount of time, you are drawing about 7-15 amps from the 48V battery as it charges the 12V battery. This depletes the storage rather quickly. By pushing the drive mode to Sport, and leaving it there, or by doing so and then Parking the vehicle, the idle will remain high, and thus short of turning AC on max, the BSG is able to generate enough electricity such that the 48V battery does not go "into the red". I calculated a depletion of the 48V battery from 60% to 50% when idling when the car was in the Comfort Drivetrain setting in about 15 minutes.
4) No matter what I did to charge my car with my battery tender, the 48V battery SOC was unaffected. I don't know if a lengthy plug in duration would change this, but ultimately the DC DC converter was constantly in step down mode as OBDEleven cannot connect unless Terminal 15 is on (the car is on without the engine running). Even with the engine off and the tender on for hours, the 48V battery after the fact had the same SOC. So either the DC DC converter is preventing the 48V battery from getting charged (NOT in line with documentation), or the fact that if the DC DC converter does eventually step up from 12V to 48V to charge the 48V battery, the current is so minuscule that it's pointless. Remember, a 12V 5A battery tender is what I am using and what most people use, so by the time it does step up to 48V the current is probably so miniscule that it doesn't really affect the SOC of the 48V battery. At times when driving around, the BSG would regenerate up to 125A of current for brief moments to charge the 48V battery. Thus, a battery tender doesn't do much...
These are my top of mind findings thus far. I really need to sleep now. - exhausted after a whole day of collecting data
Last edited by angrypengu; 06-02-2019 at 06:18 PM.
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06-02-2019, 04:08 AM
#2
AudiWorld Member
Valuable info, Angry. I appreciate your hard work! Although I’m not in the market for a D5 at this time, there will be other family vehicle needs on the horizon , and now that I know something about the 48 volt system concept, I would feel more comfortable going that route. Mike
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angrypengu (09-02-2019)
06-02-2019, 07:26 AM
#3
AudiWorld Super User
Let me second that “thank you.” Really appreciate Angry’s deep dives into the tech aspects of this vehicle. There’s much to research and much to be a bit apprehensive about the new Audi “D-Class,” but posts like this thread from Angry have gone a long way to smoothing out the D5 purchase decision for me. Perhaps we should refer to angrypengu as “Mr. D5” ��. Seriously, thanks angry!
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angrypengu (09-02-2019)
06-02-2019, 08:48 AM
#4
AudiWorld Member
Let me second that “thank you.” Really appreciate Angry’s deep dives into the tech aspects of this vehicle. There’s much to research and much to be a bit apprehensive about the new Audi “D-Class,” but posts like this thread from Angry have gone a long way to smoothing out the D5 purchase decision for me. Perhaps we should refer to angrypengu as “Mr. D5” ��. Seriously, thanks angry!
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angrypengu (09-02-2019)
06-02-2019, 11:21 AM
#5
AudiWorld Super User
Thread Starter
I appreciate the support everyone! It's been an interesting ride and it is very helpful to know that it is beneficial to the community! 
Sometimes I wonder if I'm actually being helpful or just geeking out at the expense of readers. This is helpful to know! I will keep on trucking!
Sometimes I wonder if I'm actually being helpful or just geeking out at the expense of readers. This is helpful to know! I will keep on trucking!
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radders57 (07-27-2022)
06-06-2019, 06:00 PM
#6
AudiWorld Super User
Thread Starter
I was researching, tonight, the best way to extend the life of AGM batteries (the 68AH 12V battery) and inadvertently came across this Youtube video which helped summarize some concepts I have been learning which, I will be the first to admit, I sort of understood but didn't understand fully.
Audi essentially programmed the 48V battery to exist in this state:
(Skip to 6:05 in case my copy+paste did not work).
The D5's 48V battery literally stays within about 50-70% SOC, which as I alluded to before, is fantastic! The D5's SOC range is in between the purple and the orange line, which if this is to be believed (which it should be as this information comes from batteryuniversity which is a highly reputable source), we're good to go.
I will say I still do take the temperature variable very seriously, as well as humidity, but all things being equal, I will respectfully like to say that my fear of all things MHEV are basically gone. FWIW for anyone else - I figured I'd bury the hatchet once and for all
Audi essentially programmed the 48V battery to exist in this state:
The D5's 48V battery literally stays within about 50-70% SOC, which as I alluded to before, is fantastic! The D5's SOC range is in between the purple and the orange line, which if this is to be believed (which it should be as this information comes from batteryuniversity which is a highly reputable source), we're good to go.
I will say I still do take the temperature variable very seriously, as well as humidity, but all things being equal, I will respectfully like to say that my fear of all things MHEV are basically gone. FWIW for anyone else - I figured I'd bury the hatchet once and for all
Last edited by angrypengu; 06-06-2019 at 06:28 PM.
07-12-2019, 01:28 PM
#7
AudiWorld Super User
Thread Starter
Some interesting information published by the Society of Automotive Engineering which I missed until now (sorry, a few months delayed). There's no reason to pay the $30 for the full article, as this preview already has the info I've been curious about.
Before you read this, please keep in mind:
1) None of our cars have the VH3 cooling package for the 48V battery. This is a fact, sadly. That said:
2) There is an air inlet and air outlet reading in OBD11. So I would guess there is "Active" cooling of some sort on the 48V battery, although it's not pulling air from the back seats as we don't have the VH3 battery.
3) Everything in the article about highway driving causes elevated battery temperature due to active assist and recuperation is absolutely bang on. I saw these values myself. (elevated versus city driving)
4) At no point, have I ever, ever seen the 48V battery on the D5 in excess of 32'C, and we are in the dead of summer right now.
5) The tests done by the SAE are for the India region where it is insanely hot. These tests are helpful for us as they represent an extreme, but it is not likely for us to see.
The nuggets I wanted to read about were near the end of this article where they investigate active/passive cooling and looked at typical EOL (End of life) durations for these 48V batteries. The one tested by the SAE came out to a little under 3 years of extreme testing.
The article can be found here: https://www.sae.org/publications/tec...-1001/preview/
There is a lot of information in there that is definitely applicable to the D5. The article was truly a fantastic read for a geek like me.
Before you read this, please keep in mind:
1) None of our cars have the VH3 cooling package for the 48V battery. This is a fact, sadly. That said:
2) There is an air inlet and air outlet reading in OBD11. So I would guess there is "Active" cooling of some sort on the 48V battery, although it's not pulling air from the back seats as we don't have the VH3 battery.
3) Everything in the article about highway driving causes elevated battery temperature due to active assist and recuperation is absolutely bang on. I saw these values myself. (elevated versus city driving)
4) At no point, have I ever, ever seen the 48V battery on the D5 in excess of 32'C, and we are in the dead of summer right now.
5) The tests done by the SAE are for the India region where it is insanely hot. These tests are helpful for us as they represent an extreme, but it is not likely for us to see.
The nuggets I wanted to read about were near the end of this article where they investigate active/passive cooling and looked at typical EOL (End of life) durations for these 48V batteries. The one tested by the SAE came out to a little under 3 years of extreme testing.
The article can be found here: https://www.sae.org/publications/tec...-1001/preview/
There is a lot of information in there that is definitely applicable to the D5. The article was truly a fantastic read for a geek like me.
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07-12-2019, 03:43 PM
#8
AudiWorld Super User
Interesting. I'm still curious to see what a non m-hybrid D5 A8L 3.0T would have been like. A dream I know cause it will never happen. But hear me out... Since the first sentence of that article states m-hybrid is designed to meet fleet CO2 emissions targets...that usually is of no benefit to the end user...like stop-start or other CAFE requirements which means 0.01 mpg improvement but over 100000 cars it is significant for the manufacturer only. You have already proven there is significant complexity in the system so to eliminate it all-together seems like one less headache, but alas...never to be.
I mean even on the EPA site the D5 get 2mpg WORSE highway mileage than the supercharged 3.0T D4 when things like mild hybrid, turbo, and 7-8 years of evolution should have improved that...
It is great there is progress, but I feel like it should be leaps and bounds, not stop-gaps. If you told me the introductory D5 was a 3.8L turbo V8 with a mild-hybrid that got 21 city/ 30 highway then I'd say that is real progress but otherwise you can see they are abandoning things for all-electric.
When the A8 E-tron comes out that should be interesting...
I mean even on the EPA site the D5 get 2mpg WORSE highway mileage than the supercharged 3.0T D4 when things like mild hybrid, turbo, and 7-8 years of evolution should have improved that...
It is great there is progress, but I feel like it should be leaps and bounds, not stop-gaps. If you told me the introductory D5 was a 3.8L turbo V8 with a mild-hybrid that got 21 city/ 30 highway then I'd say that is real progress but otherwise you can see they are abandoning things for all-electric.
When the A8 E-tron comes out that should be interesting...
07-12-2019, 04:23 PM
#9
AudiWorld Super User
Thread Starter
Interesting. I'm still curious to see what a non m-hybrid D5 A8L 3.0T would have been like. A dream I know cause it will never happen. But hear me out... Since the first sentence of that article states m-hybrid is designed to meet fleet CO2 emissions targets...that usually is of no benefit to the end user...like stop-start or other CAFE requirements which means 0.01 mpg improvement but over 100000 cars it is significant for the manufacturer only. You have already proven there is significant complexity in the system so to eliminate it all-together seems like one less headache, but alas...never to be.
I mean even on the EPA site the D5 get 2mpg WORSE highway mileage than the supercharged 3.0T D4 when things like mild hybrid, turbo, and 7-8 years of evolution should have improved that...
It is great there is progress, but I feel like it should be leaps and bounds, not stop-gaps. If you told me the introductory D5 was a 3.8L turbo V8 with a mild-hybrid that got 21 city/ 30 highway then I'd say that is real progress but otherwise you can see they are abandoning things for all-electric.
When the A8 E-tron comes out that should be interesting...
I mean even on the EPA site the D5 get 2mpg WORSE highway mileage than the supercharged 3.0T D4 when things like mild hybrid, turbo, and 7-8 years of evolution should have improved that...
It is great there is progress, but I feel like it should be leaps and bounds, not stop-gaps. If you told me the introductory D5 was a 3.8L turbo V8 with a mild-hybrid that got 21 city/ 30 highway then I'd say that is real progress but otherwise you can see they are abandoning things for all-electric.
When the A8 E-tron comes out that should be interesting...
I'm sure in time people will figure out a way to bypass all of that. There is a build for the D5 that does not have the 48V battery/systems at all. I see it all over OBD11, and even in the SSP there is mention that in some markets the D5 exists in 12V form only....
Man....if only it was procurable by us!!!!!!!
-------------
I caught an interesting nuggets and I think I may have misread originally and may be slightly wrong in my first post about this article
So in their testing, they are assuming a distance of 75,000KM a year and the battery is rated at a service life of 10 years. I believe what they are saying is that they killed the battery in 2.8 years, which is equivalent to almost 225,000km of driving. Again, they define the useful life of a battery as one having only 50% of the original capacity. If that's the case, I mean, that's a long amount of distance travelled or close to 1250 hours/year so they killed it in ~3750 hours.
Quoted below
I snipped parts of it to combine the below)
All in all as I mentioned before and the article confirms, highway driving is the worst for a mild hybrid battery. I certainly avoid driving on hot summer days, try to do groceries and such when it's cooler, and I do everything I can to keep the mild hybrid battery cool. I also don't do much highway driving, so I'm confident my battery pack will last a very long time.
To reiterate all of the testing are a confluence of worst case scenarios. Everyone's driving situation will be different, but for now, at least in the summer months, I'll continue my 5x ice pack regime of swapping it out every 24 hours and keeping it on my trunk floor to keep the mild hybrid battery at a cool 20'C even when the garage/ambient temperature is 32'C+.
It's not that back breaking.....and I have the routine down!
Last edited by angrypengu; 07-12-2019 at 04:33 PM.
07-13-2019, 09:49 AM
#10
AudiWorld Super User
Thread Starter
After a few headaches later, I have found some conclusive new information!
I have been trying to figure out why some 48V mild hybrid batteries are actively cooled. In fact, even on our A8's (55 TFSI) if you open either of the rear doors and you look at the rear seats where the airbag of the seat meets the door...follow that to the bottom of that airbag. There is a gap between the bottom of the seat airbag and the bottom seat. Why? This gap is fitted (on some cars) with an airvent that carries cool air to the mild hybrid battery and is actively cooled. For those that have been following my tireless quest to understand that system, vehicles with that feature are denoted as a vehicle with VH3, or active air cooling for the mild hybrid battery.
I have been trying to figure out why some cars have the VH3 designation and thus active air cooling, and why our A8s don't have it, and are classified as VH2 instead (which means they have the 48V system and the mild hybrid battery but no active cooling is available for the hybrid battery). Early on in my quest, I was trying to see if it was a matter of "hot climate" versus "cold". So I looked at the parts list of my A8 which is configured as a "mild hot country" build versus that of a "hot country" build (e.g. Texas). Much to my surprise the Texas hot country builds were also designated as VH2 which baffles me.
Well, I finally figured out which cars have the VH3 designation and it is not specific to the A8. It would appear that ALL S model mild hybrid VAG vehicles have active cooling.
How can I confirm this? Well, here we go:
A6: Ctrl F VH2. https://audicentrumgdansk.pl/wp-cont...5/AF6ZGQ9E.pdf
A8: Ctrl F VH2. https://www.wirkaufendeinauto.de/aut...-391c3d861050/
S6: Ctrl F VH3. https://www.motor-talk.de/forum/akti...hmentId=769753
S7: Ctrl F VH3. https://www.motor-talk.de/forum/akti...hmentId=770826
I would suspect the S models have more aggressive utilization of the BSG for added grunt/boost and thus the battery runs at a hotter temperature. Once the 48V system hits a certain temperature, it enters a reduced power mode to cool off. I believe there is still a fan in the regular mild hybrid battery (VH2) as NMC batteries have a higher internal resistance than LFP or other LI ION batteries and in OBD11 there is an air inlet and air outlet temp specific to the 48V battery. However, the VH3 builds get the coldest of air using those air ducts that draw cool air from the rear cabin down into the cavity where the battery is housed and then blown through the intakes of the mild hybrid battery assembly due to extensive charge/discharge and high current output to assist with acceleration as they are S models.
Once the A8 60 TFSIs roll off the line I will be able to run the VINs of those cars to see if the 60 TFSIs get the VH3 designation too, but at this point I'm 99.99% sure the S8 will get them.
For me, in the summer, I have the middle vents in the rear seat blasting towards the pass through which I leave open. For the rear vents in the doors, I now have them pointed towards those gaps mentioned in my first paragraph. Does it help? Probably, but if not, it won't hurt anything as lithium ion batteries are like humans in that they don't like hot temperatures!
So that's a conclusive find today to a question eating at me for a few months now. Off to bed (and very happy right now!). Knowledge is king!
I have been trying to figure out why some 48V mild hybrid batteries are actively cooled. In fact, even on our A8's (55 TFSI) if you open either of the rear doors and you look at the rear seats where the airbag of the seat meets the door...follow that to the bottom of that airbag. There is a gap between the bottom of the seat airbag and the bottom seat. Why? This gap is fitted (on some cars) with an airvent that carries cool air to the mild hybrid battery and is actively cooled. For those that have been following my tireless quest to understand that system, vehicles with that feature are denoted as a vehicle with VH3, or active air cooling for the mild hybrid battery.
I have been trying to figure out why some cars have the VH3 designation and thus active air cooling, and why our A8s don't have it, and are classified as VH2 instead (which means they have the 48V system and the mild hybrid battery but no active cooling is available for the hybrid battery). Early on in my quest, I was trying to see if it was a matter of "hot climate" versus "cold". So I looked at the parts list of my A8 which is configured as a "mild hot country" build versus that of a "hot country" build (e.g. Texas). Much to my surprise the Texas hot country builds were also designated as VH2 which baffles me.
Well, I finally figured out which cars have the VH3 designation and it is not specific to the A8. It would appear that ALL S model mild hybrid VAG vehicles have active cooling.
How can I confirm this? Well, here we go:
A6: Ctrl F VH2. https://audicentrumgdansk.pl/wp-cont...5/AF6ZGQ9E.pdf
A8: Ctrl F VH2. https://www.wirkaufendeinauto.de/aut...-391c3d861050/
S6: Ctrl F VH3. https://www.motor-talk.de/forum/akti...hmentId=769753
S7: Ctrl F VH3. https://www.motor-talk.de/forum/akti...hmentId=770826
I would suspect the S models have more aggressive utilization of the BSG for added grunt/boost and thus the battery runs at a hotter temperature. Once the 48V system hits a certain temperature, it enters a reduced power mode to cool off. I believe there is still a fan in the regular mild hybrid battery (VH2) as NMC batteries have a higher internal resistance than LFP or other LI ION batteries and in OBD11 there is an air inlet and air outlet temp specific to the 48V battery. However, the VH3 builds get the coldest of air using those air ducts that draw cool air from the rear cabin down into the cavity where the battery is housed and then blown through the intakes of the mild hybrid battery assembly due to extensive charge/discharge and high current output to assist with acceleration as they are S models.
Once the A8 60 TFSIs roll off the line I will be able to run the VINs of those cars to see if the 60 TFSIs get the VH3 designation too, but at this point I'm 99.99% sure the S8 will get them.
For me, in the summer, I have the middle vents in the rear seat blasting towards the pass through which I leave open. For the rear vents in the doors, I now have them pointed towards those gaps mentioned in my first paragraph. Does it help? Probably, but if not, it won't hurt anything as lithium ion batteries are like humans in that they don't like hot temperatures!
So that's a conclusive find today to a question eating at me for a few months now. Off to bed (and very happy right now!). Knowledge is king!
Last edited by angrypengu; 07-13-2019 at 09:54 AM.