e-Hybrid and 12v battery question

[oldgitdave]

Am I correct in understanding that when I charge my hybrid battery from the outlet, my 12v battery is also charged along with it?

If this is indeed the case, then this changes things radically.

For what reason then was your battery dead one morning if the car was plugged in to charge the hybrid battery?

Well yes is the answer. Cupra's reply confirms it and I've checked it with a multimeter.
My car was not plugged in, it had been stood for 8 days (link here Car Dead) and it seems the rear passenger door was not closed properly. I never had an indication of this in the car or on the Connect app. All very strange I know, but I've had no issues since.

 

[dashnine]

Just to raise this topic again, I'm getting 12v battery low issues (SOS and Travel Assist errors and unable to access the car via the app) and yet the hybrid battery is charged 3 or 4 times a week.

Not convinced the 12v battery is being charged (or charged enough) by the hybrid battery.

 

[LetsForment]

I am fairly sure the 12v is never charged from the high voltage battery, or even on the same circuit. Maybe worth plugging in the obd and driving around a bit and then seeing what voltages are reported.

 

[CupForm]

You're right, the 12V (LV) battery is never directly charged from the HV battery. There was a diagram I saw on the Octavia Forum (same PHEV though) that was showing the LV battery charging scenarios:
- while charging the HV battery from a ch.station (there's a HV->LV converter that provides the 12 V)
- while driving (both on ICE or in EV mode)

 

[LetsForment]

Are you sure about the charging station thing?

Reason I ask is even with the wall charger plugged in, I don't see 14v+ across the 12v battery it stays at the 12.7 odd

If I start the car, goto ICE, boom, 14.2v - even when it's not moving, as long as the petrol engine is running, I see 14v+

With ev mode, if the car is moving I see 14.2/14.1, but not if the car is stationary

As I am sure everyone knows, you need 14.2 to 14.4 for bulk/dump charge and then a 13.4v for float/maintain. If you apply 12v to the battery you are just killing it.

 

[CupForm]

I see what you mean; I never checked the voltage on mine.
Here's where I got the info from:

https://www.briskoda.net/forums/top...ft-to-e-drive/?do=findComment&comment=5684673

It's not clear for me what "Slow and Medium speed charging" means, since this PHEV cannot take more than 3.5kW. However, it is mentioned "Fast speed charging" is not charging the 12V battery...
But again: what is slow and fast charge on this car? Is it referring to the two charging speeds we can set (on Infotainment and App): Reduced and Maximum? You can try to measure while plugged-in, but with Reduced charge setting.

 

[RUM4MO]

You would hope that the traction battery pack and the support 12V battery's charge conditions were both being monitored at all times during fast or slow (mainly traction) battery re-charging - or is this EV stuff still in its infancy as suspected.

 

[CupForm]

It's a bit disappointing, because the PHEV technology is not really young anymore. And the 12V battery discharge seems to be a common issue especially among PHEVs, but not limited to those. I've seen quite a few "dead" 12V batteries - replaced on warranty - on non-PHEV models too.
There's lots of electronics on these "modern" cars and plenty of poor coding/programming - incorrectly managing the low voltage system...

 

[elzo]

Are you sure about the charging station thing?

Reason I ask is even with the wall charger plugged in, I don't see 14v+ across the 12v battery it stays at the 12.7 odd

If I start the car, goto ICE, boom, 14.2v - even when it's not moving, as long as the petrol engine is running, I see 14v+

With ev mode, if the car is moving I see 14.2/14.1, but not if the car is stationary

As I am sure everyone knows, you need 14.2 to 14.4 for bulk/dump charge and then a 13.4v for float/maintain. If you apply 12v to the battery you are just killing it.

I took the car to update and improve the performance of the 12V battery, perhaps this makes a difference in your measurements and that’s why charging from the wall does not charge the 12V battery?!
Have you gone to the dealer for updates related to the 12V battery?

 

[elzo]

I don't remember what update number it was. But this was due to the improvement and preservation of the 12V battery. Read about it on the Internet, other owners discussed it a lot on some forum.

 

[LetsForment]

I will have to get the obd thing going and do some tests this weekend again.