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Charging a 992 via Footwell Socket

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mikegibson
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mikegibson PCGB Member
2021/01/29 18:34:41 (permalink)

Charging a 992 via Footwell Socket

A number of 992 owners appear to have issues using a battery maintainer / charger in conjunction with the footwell accessory socket on the Porsche 992.  In part, the reason that people have issues is caused by the accessory socket automatically turning off 30 minutes after the ignition itself is turned off.

Unlike the earlier generations of Porsche 911s, in which the accessory socket (and cigarette lighter socket) remained live when the car was turned off, the 992 accessory socket (of which there is lamentably only one) comes on when the ignition is turned on and goes off 30 minutes after the ignition is turned off.

Normally this would create an issue in using this for plugging in a battery maintainer.  However, Porsche engineers have incorporated some electronics to allow this to be used for charging BUT you need to follow a procedure to make it work.

The key point is:  If the socket detects a charge voltage/current applied AFTER the ignition is turned off and BEFORE the 30 minute timeout, the socket will remain connected to the battery.  It is that simple.

I have used a CTEK MXS 5,0 without issue by following the steps below which are the steps Porsche document in their Charge-o-mat Pro manual.  If you have a Lithium battery, make sure to use a charger appropriate for that; equally, if it is AGM use an AGM compatible charger.  In identifying the type of battery fitted to your car, make sure you look at the battery itself.  Porsche have fitted battery retaining straps that have a LiPO/Li-ION symbol to all cars; the legend on the strap DOES NOT inform you of the type of battery, it is a warning that a Li-ION battery may be fitted; madness.

To connect your battery maintainer, simply do the following:
  1. Get out your charger, run it to your mains power (leaving this turned off) and open up the car; in other words, get things prepared; you have 30 minutes from the point the ignition is turned off.  Do not plug a powered on charger in whilst the car ignition is on; if the ignition is on, turn it off before plugging in / turning on the charger.
  2. If your car has been turned off (ie the ignition has been turned off) for more than 30 minutes, eg sitting on the driveway for a few days; or if you're uncertain how long it is since you turned off the ignition, simply turn ignition on and then off to reset the 30 minute timer. It is important that the ignition is off before connecting the charger.
  3. Plug the charger into the wall (if you haven't done so); do not turn on
  4. Plug the charger into the accessory socket
  5. Turn on the charger at wall (I suggest powering on charger at this point rather than sooner as some CTEK chargers allow the charging mode to be changed, but only within a short time after the charger was turned on)
  6. The charger will have some kind of power indicator; make sure it is on
  7. In the case of CTEK charger, make sure mode is set to AGM or LiON, if this is selectable; change the mode if you need to
  8. The charging cycle should begin within a minute; on CTEK chargers there is usually a status/progress indicator
  9. If the charging cycle does not start, unplug the charger, turn it off and go back to step 2 and turn ignition on/off to reset the electronics.

A note about batteries
Porsche 992s might be fitted with either a Lead Acid AGM (Absorbent Gas Mat) battery OR a Lithium (Li-ION/LiPO /LiPO4) battery.  The type of battery fitted depends on the Country in which the car was supplied and the equipment fitted to the car; there does not seem to be a definitive statement on what battery is fitted when, but based on colloquial information on various forums, an AGM battery is the default with Lithium batteries fitted to cars with Rear Wheel Steering (RWS) OR in locations where car might be exposed to cold climates (Canada, North America).

In identifying the type of battery fitted to your car, make sure you look at the battery itself.  Porsche have fitted battery retaining straps that have a LiPO/Li-ION symbol to all cars; the legend on the strap DOES NOT inform you of the type of battery, it is a warning that a Li-ION battery may be fitted; utter madness.

Lithium batteries use a different technology to Lead Acid batteries.  The nominal, open circuit, voltage of a single LiPO4 cell is 3.6V whilst a Lead Acid Cell is 2.1V.  Different numbers of cells are connected in series to create the desired battery voltage (4 x LiPO4 cells  or 6 x Lead Acid cells).  So,  a fully charged Lithium battery will have a different "open circuit" voltage to a Lead Acid battery.  Both are referred to as 12V batteries as the car electrics are 12V though a fully charged Lithium battery might read 14.4V (4 cells x 3.6V) across the terminals where a Lead Acid battery might read 12.6V (6 cells x 2.1V). Importantly, the initial charging voltage and subsequent "float" voltage used to maintain the battery in a fully charged state will differ with Lithium batteries requiring both higher initial charge voltage and higher float voltages.   That's why you should use the right kind of charger.
 
post edited by mikegibson - 2021/01/29 21:51:05


2019 992 C2S Cabrio, Midnight Blue
2009 997 Gen II C4S Cabrio, Meteor Grey
1999 996 Gen 1 C2, Zenith Blue

4 Replies

Lancerlot
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Re: Charging a 992 via Footwell Socket 2021/01/29 21:10:38 (permalink)
Good post, thank you very much for the useful info. 
 
Strangely, following this routine in my Macan GTS doesn't always work. With everything plugged in as you describe and with a nice array of yellow LED's showing the path of charging progress, off I go to let the process take care of itself. However, on returning the next day, lo and behold I find the dreaded flashing green LED indicating the charging circuit has become disconnected. I'm using the centre console socket though, so it might be different with the 992 footwell socket.
 
Having had this happen several times now, I have found it more reliable to leave the car for 30 minutes after switching off the ignition, then connect up the charger. This seems to work consistently in my particular case as the electronics recognise electrical input as opposed to output. 
 
BTW: AGM = Absorbent Glass Mat. Apologies if I'm being pedantic, just in the interests of accuracy. 
 
Regards,
 
Clive

The older I get - the faster I was!
Past - 924T, '911 SC, 911 C, 911 C2, 964, 996, 996TT, 997TT, 997GT2, 430 Scuderia, 997TT, 997TTS, 991.2TTS. Macan SD. Macan.2 GTS
Schuey
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Schuey PCGB Member
Re: Charging a 992 via Footwell Socket 2021/01/29 21:17:16 (permalink)
Thanks Mike, I will refer to this when my car lands and if I have such issues. 

2021 Porsche 911 (992) Carrera S on order
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2020 BMW S1000RR Sport with Performance Pack
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2020 Triumph Bonneville T100
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mikegibson
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mikegibson PCGB Member
Re: Charging a 992 via Footwell Socket 2021/01/29 21:59:54 (permalink)
Lancerlot
Good post, thank you very much for the useful info. 
 
Strangely, following this routine in my Macan GTS doesn't always work. With everything plugged in as you describe and with a nice array of yellow LED's showing the path of charging progress, off I go to let the process take care of itself. However, on returning the next day, lo and behold I find the dreaded flashing green LED indicating the charging circuit has become disconnected. I'm using the centre console socket though, so it might be different with the 992 footwell socket.
 
Having had this happen several times now, I have found it more reliable to leave the car for 30 minutes after switching off the ignition, then connect up the charger. This seems to work consistently in my particular case as the electronics recognise electrical input as opposed to output. 
 
BTW: AGM = Absorbent Glass Mat. Apologies if I'm being pedantic, just in the interests of accuracy. 
 
Regards,
 
Clive


Thanks Lancerlot.  No idea why I typed "Advanced".  Sadly I don't have a Macan GTS to play with!  The Charge-o-mat manual is written in a way that I do wonder whether Porsche acknowledge that this process is not 100% reliable; they basically state "If charging stops after 30 minutes try again"!  I tend to check that the charger is still active 30 minutes after plugging it in albeit, I have never had an occasion where it has stopped.


2019 992 C2S Cabrio, Midnight Blue
2009 997 Gen II C4S Cabrio, Meteor Grey
1999 996 Gen 1 C2, Zenith Blue

N4THO1979
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N4THO1979 PCGB Member
Re: Charging a 992 via Footwell Socket 2021/02/23 20:25:20 (permalink)
Thanks for sharing this info. Followed these instructions to the letter (992 March 2020 build, with CTEK MXS 5.0) - been charging nicely all day. 
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