High Current: >200mA Quiescent Current

Hello,

I'm having trouble with my father's car. The battery keeps draining, and a measurement of the quiescent current showed almost 300mA, which I believe is significantly too high. However, the Audi workshop claims that this is normal for these types of vehicles and that there's nothing they can do about it. It's an A8, manufactured in 2000, with a 3.3 TDI engine.

I was able to identify the following 'energy-guzzlers' by systematically switching off the circuit breakers.
- Combination instrument: approximately 20mA.
- Alarm system/central locking with deactivated interior monitoring: approximately 100mA
- some low-power consumers in the single-digit mA range.

But now, here's my actual problem:
Although I had pulled all the fuses in the passenger footwell and trunk and, for safety, I had also removed the thick power cable of the relay distributor in the passenger footwell, approximately 85mA continued to flow.

Therefore, my main question is: Which device(s) are not covered by these fuses and can still draw this amount of current? I really don't want to disassemble the entire vehicle (which is significantly more difficult with this model than with my Golf) and trace every cable.

Second question: Is it normal for the alarm system and central locking system to draw 100mA together?


Audi only gave my father the tip to disconnect the battery at the airport when traveling. They said that most drivers of larger vehicles would do that... That can't be true, that's something...

Regards,
Private.

Hi!
I'm afraid your workshop is right! Vehicles of the class you mentioned do indeed have a massive amount of quiescent current draw. Even S-Class models with good equipment often won't start after just 1.5 to 2 weeks of inactivity. That's why the SL model switched to a dual-battery system. This ensures 100% starting capability even after 4 weeks or more...
And it's also true that many vehicles of this class have had a battery disconnect switch retrofitted. Sad but true!

Best regards,
pretzel

P.S.: I suspect that the "missing" milliamperes are being consumed somewhere within the vehicle's onboard network control unit or battery management system (I'm not sure what Audi calls it...).

That's why, in the SL series, they switched to a 24-volt battery system. This ensures 100% starting capability even after 4 weeks or more...


Why do you think they did that on the Maybach as well?

However, I have to disagree; that's not common practice (at least for MB). The S-Class is only allowed to draw a maximum of 40mA. Initially, the problem was that some vehicles had a programming error where the standby mode was missing in the software for several control units, causing the car to be dead after a week of inactivity. An update reliably fixed this.
With the current E-Class, the navigation system and the TMC receiver were often problematic... what do you think, why are they using the old navigation system again in the SLK?

For this Audi, the only solution I can think of is to try replacing the comfort control module.

"Well, that's a great thing. I'm buying the most luxurious car on wheels, driving to the airport for one of my many appointments, and now I'm taking out the emergency key for the keyless go system and disconnecting the battery... or turning off the main switch. Now I finally understand what that emergency key for the keyless go system is for... (!)."

Okay, seriously. My Golf can't even compare, but in my car, the idle current draw goes way above 30mA when you press the TIM button on the navigation system (probably also affecting gamma, delta, and whatever else is there). But you can probably rule that out since you've already removed all the fuses.

It's a really dumb idea, but could it be that a car that's so vulnerable to theft might have one of those interesting GPS tracking devices installed later? Surely that would consume a lot of power, or am I wrong?

Okay, so my Garmin GPS device is drawing power at 3V and 75mA from the batteries.


I'm going to measure my Octavia later, just for fun.

CU Gremlin.

...in my case, the quiescent current increases far above 30mA when you press the TIM button on the navigation system (probably also affecting gamma, delta, and whatever else is there). But you can probably rule that out if you've already removed all the fuses.
That should be safely prevented by simply pulling the fuses, considering it's the original Audi radio.

It's a very stupid idea. Could it be that a car that is so susceptible to theft might be retrofitted with one of those interesting GPS tracking devices? Surely that would consume a lot of power, or am I wrong?
Nothing is impossible... On the other hand, my dad has been driving the car for almost two years and doesn't know anything about it. If the previous owner (a car dealership) had installed something like that, they would have definitely bragged about it during the sale. I would certainly assume that. (On the other hand, I also thought that pulling those fuses would have cut off all power...)

Thank you for your kind words so far...

Regards,
Private.

Okay, I'm currently standing next to the car (Wi-Fi is pretty cool).

The quiescent current draw is 50mA, of which 3mA is for the standby heater.

While the TIM (Time Interrogation Multiplex) function is active, the radio consumes approximately 300mA of current every 3 seconds for about 200 milliseconds. During a broadcast, it draws 300mA.

CU Gremlin.

Gremlin wrote:

so, I'm currently at the car (Wi-Fi is pretty cool). The quiescent current draw is 50mA, of which 3mA is for the standby heater. While the TIM (Time Interrogation Multiplex) function is active, the radio consumes approximately 300mA of current every 3 seconds for about 200 milliseconds. During a broadcast, it draws 300mA. CU Gremlin

"My Octavia seems to be satisfied with about 23mA. I haven't yet figured out exactly where that current is being used. I initially thought it was quite a lot, because that adds up to a good half ampere-hour per day. That's almost 16.5Ah per month. But looking at your figures, I seem to be doing pretty well. Do you have an alarm system? The 3mA from the auxiliary heater probably ends up in the TP5 receiver. I think that's quite low."

But what the private area is measuring is clearly too much. Even 300mA means 7.2Ah per day and 50.4Ah per week.

@Private Area: Have you ever measured the current draw of the starter motor? It seems to be connected directly to the battery in the A8.

Regards,
mcgregg

@Private Area: Have you ever measured how much current the starter motor draws? It's probably connected directly to the battery on the A8.

No, I haven't disconnected the cable from the starter motor yet. While the constant 85mA reading for the starter motor seems strange, if no one has any other ideas, I will test that again.

Does anyone happen to have a diagram or overview of the voltage distribution for the car's electrical system? I suspect there might be some hidden fuses and distribution points.

Has anyone ever measured the alarm system/central locking system of an A8? 100mA seems excessively high to me, even for that.
'Similarly, I think the 20mA current draw for the control unit is a bit high. On the other hand, that also includes the radio clock, the timer for the auxiliary heater/fan, etc. Besides, I'm not going to worry about such minor issues for now.'

@brezelmann01:
What does such a car have that consumes electricity without being turned on, something a basic Golf doesn't have? Of course, the A8 has significantly more electrical components, but most of them should be de-energized without the ignition being on, or at the very least, they should be de-energized after a timer expires.

Regards,
Private.

Hi!
Okay, starting with the already mentioned Keyless Go system, phone charging/car phone functionality, on-board network control, potential comfort features like seat memory (which partially moves the steering wheel up and the seat back when entering), and even the instrument cluster – all of these consume a significant amount of power, even in the deepest standby mode. It all adds up. However, my descriptions above actually referred to pre-production vehicles from DC. But even with today's production models, 40mA is not enough. Otherwise, why would you use an autonomous starter battery?

Best regards,
Dirk.

Considering that modern microcontrollers consume only microamps in power-down mode, it's a valid question to ask where all that current is flowing.

'I still owe something to the receiver for the ZV (Zero Voltage) functionality, but it's not 20mA. And everything else consumes nothing in power-down mode. After all, there's wake-on-pin-change for bus communication, etc...'

Well...

CU Gremlin.

Considering that modern microcontrollers consume only µA in power-down mode, the question arises: where are all those currents flowing to...?

'That seems to be our problem, Gremlin. We come from an electronics development background, and we know what's possible. The problem is that the people at VAG are less interested in how little power is possible, and more interested in what's cheap and reasonably acceptable.'

'However, anything that disables the car within a month or less is, in my opinion, unacceptable. And with 300mA, even a 100Ah battery will be completely drained after 14 days. Considering that it also needs a few amp-hours for preheating and even more to start the engine, you quickly realize that even a week is pushing it, assuming the battery was fully charged beforehand... And that can't be normal, even for VAG.'

I will first try to locate and identify the unknown, unmetered 85mA that are being drained, and then, if possible, I will further divide the current exceeding 100mA that is going through the main fuse/alarm fuse. Disassembling something on this car is a completely different undertaking compared to disassembling a Golf 3 like the one I drive. Therefore, I remain open to any further suggestions regarding the cause of the problem, so I can search more effectively.

Regards,
Private.

It's possible that the (faulty) alternator is drawing some current – we've seen cases like that before.
Of course, pulling the fuses didn't help.

The 100mA of the central locking system also seems too high to me.
Close all the doors, windows, trunk, and hood of the car completely, and then measure the power consumption after 5 minutes. It might decrease slightly.

Based on my experience with Audi, the onboard electronics consume a significant amount of power for about 90 minutes after the key is removed, even without using features like GPS or the phone.
However, this value rapidly decreases after the timer expires, as the microcontroller then clears its memory and enters save mode.

If you want to measure quiescent current, you must wait or disconnect the battery for more than 5 seconds.

Did you have all the flaps closed during the quiescent current measurement (I assume you did).

Then it can take up to 4 hours for things like the navigation system and everything else to switch to the sleep position. Only then can you make a statement about the quiescent current, and check what hasn't been turned off.
It's possible that you're already aware of this, but I'm writing it again to minimize errors.

So, of course, I had closed all the doors and flaps, and I waited, but only for about 15-30 minutes (I was drinking coffee at the time, and I didn't pay close attention). In any case, it wasn't 90 minutes or even 4 hours.

So, I'll probably repeat the whole process again in the morning and make sure everything is prepared by the evening.

Awkward, awkward. I would have estimated the times to be much shorter (around 5-10 minutes).

Thank you for the tip. I will check the voltage again after waiting for more than 4 hours and, if necessary, have the alternator checked.

Regards,
Private.