Battery Drain: Normal Amperage Explained

Hello everyone,

I'm having an electrical problem with my Audi 80 1.9 TDI (03/94, 90 hp, B4). The battery is completely drained after the car has been parked for a while – sometimes it takes a week, other times two. It seems like there's some kind of parasitic drain.

I'm now going to connect an ammeter to the battery and check which fuse needs to be pulled to identify the source of the problem.

Questions:

- Should I connect the ammeter between the cable and the positive or negative terminal of the battery? Or does it not matter (I would generally assume it doesn't, but you never know)?

- How many Amperes flow when all switchable consumers (radio, lights, alarm system, etc.) are turned off? The control unit, the clock, and the radio (even when switched off) certainly draw some power continuously, but approximately how much is that? I would guess well below one Ampere , but there's a difference between 0.05 and 0.5.

"Thank you!"

Computational reflection: With a 64Ah battery and a "base current" of 0.1A, the battery would last for a parking duration of 640 hours, which is approximately one month... correct?

It doesn't matter where you connect your ammeter. The important thing is to unscrew the terminal and then reconnect it using the ammeter. (Only measure in the voltage range between the positive and negative terminals.)

The current should not exceed 50 mA by a significant amount.

You correctly calculated the theoretical discharge time. Unfortunately, most batteries no longer have their nominal value.

Best regards from Mulag.

Quote:

Unfortunately, most batteries no longer have their nominal value.

... and most of the time, they are not full either.
And a little bit of remaining capacity for starting up also doesn't hurt .

Hello,

"Newer cars often have a higher idle current of 50-200mA for the first half hour due to features like hands-free systems. After that, it should drop below 50mA. In an older Beetle without a radio, the idle current is zero. This means you can often start the car directly after a year in the garage. However, with cars from the 1990s onwards, depending on the condition of the battery, things can get tight after about 6 weeks."

Best regards,
Christian.

chris11 wrote:

Hello, Newer cars often have a higher idle current in the range of 50-200mA for the first half hour, especially when equipped with hands-free systems, etc.

After that, it should drop below 50mA.

I finally took some measurements.

- Standby current with the hands-free system disconnected: 0.06 A (60 mA).
- If I connect the hands-free device but don't insert a phone, it draws 0.16 A (which is equal to 160 mA).
- When I turn on the alarm system (with ultrasonic interior monitoring), the current jumps to a hefty 1.48 A - which is quite a lot, isn't it? That's a good 1.3 A for a simple alarm system }.

If it's actually the case that the idle current of 160mA continues to decrease towards 60mA after half an hour, then that's fine. But why does the hands-free system consume so much power when it's supposedly doing nothing?

By the way, I also found the error: It's the CD changer (from Sony) – it was drawing power even when the radio was turned off, and the current draw fluctuated up to 1.2 amps.

Based on this, one can calculate that the battery, with the alarm system activated (1.3A) and the vacuum cleaner running (averaging around 0.7A – for easier calculation), will not last a full 32 hours before being completely drained.

HI,

Are you sure that the alarm system still needs more than 1 ampere of power even after hours with closed doors and flaps? I would assume that it drops significantly.

I would equip the cigarette lighter socket with a microswitch that only allows power to flow when a phone is inserted. Alternatively, you could simply connect it to the ignition positive terminal, or use a relay connected to the "S" contact so that you can make calls even when the engine is off.

Best regards,

January.

When I turn on the alarm system (with ultrasonic interior monitoring), the current jumps to a hefty 1.48 A - which is quite a lot, isn't it? That's a good 1.3 A for a simple alarm system .
Something is wrong! The alarm system should not require more than approximately 10mA after being in operation for about 30 seconds. If you have opened the windows, or if there is movement inside, the power consumption may increase, but it should not exceed approximately 100mA (unless it is beeping and flashing ).

Regards,
Stefan.

Of course, I hadn't had the ammeter connected for that long – I will observe it for a longer period next time I have the opportunity.
Connecting the car phone system to the ignition-powered circuit is a very good idea – I have no idea why I connected it to the constant power supply instead, but perhaps that's why the radio signal isn't being properly transmitted. I'll try switching it to the ignition-powered circuit as well.