Lastmanagenemt: unnötig erhöhte LL-Drehzahl? | Posts 16+

Hi,

"Immediately after a cold start, the display shows 14.6 volts (with the headlights and afterglow on), which then drops to 13.6 volts when I turn on the two seat heaters. However, this is because the meter is still drawing power from the same supply as the seat heaters, which is connected to the thin cable of the cigarette lighter socket (rated for 10 amps, the seat heaters draw 7.5 amps), which explains the voltage drop through the cable."

I'll definitely install a separate measurement line for that.

Best regards,

Jan.

Julian wrote:

During a proper cold start, the generator's load was never above 45%, which would be approximately 63A. And I have more consumers "in the system" than you do... fascinating!

It's important to remember that the maximum power output of a lithium-ion battery (e.g., 90 A x 14 V = 1.26 kW) is only achieved at high rotational speeds.

At idle speed, each alternator only produces a fraction of its maximum output (approximately 1/3, according to an old book on automotive electrical systems) and therefore needs to be operated with a significantly higher duty cycle of the regulator to achieve the same current output as at rated speed.

Therefore, with a 45% load at idle, a 140 A LiMa battery likely doesn't output 63 A, but perhaps around 20 A.

My 90A LiMa would then provide even less power, or conversely, would already be running at full capacity controlled by the regulator.

In addition, the alternator's power output drops off very sharply at lower engine speeds. That is, a 7% reduction in idle speed (like the 840 rpm I'm experiencing instead of 903 rpm) could potentially result in a 25% loss of power (this is just an estimate).

Quote:

What is the capacity of your battery?

70 Ah.

(approximately 1/3, according to an old book about automotive electrical systems) and therefore, to provide the same amount of current, it must be powered with a significantly higher regulator duty cycle than at its rated speed.

Therefore, with a 45% load at idle, a 140 A LiMa battery likely doesn't output 63 A, but perhaps around 20 A.


Maybe? Your book must be old, or written by ADAC.

To verify the utilization rate (I had previously discussed this with Gremlin without success), I installed an ammeter on the generator at the company yesterday. At 35% utilization (in the MSG), I measured 50A, while the theoretical value would be 49A.
Then I connected some consumers and increased the load on the LL to 50%, measuring 71A at 50% load.

To be honest, I don't know how the percentages are calculated, but I believe I have verified the MWB with this method.

Hi Ulf,

Did you already read the following? https://community.dieselschrauber.org/en/viewtopic.php?t=6826

The number of consumers is likely to be quite low for your Polo, but perhaps the issue of short trips is relevant.

Marco wrote:

The number of consumers is likely to be quite low for your Polo, but perhaps the issue of short trips applies.

Yes, short-distance travel could be included.

As a counterbalance to the few consumers, I probably only received a 90A alternator, while our ALH Ibiza has the 120A one (like my ex-Basis-G3 did).
Or, one might believe that one can save money on the LiMa (lithium-ion battery management system) because the load manager is monitoring it .
Well, my personal consolation is: Weaker LIMAs are slightly lighter than powerhouses (and also cheaper to replace later).

@Julian:
Your measurements and calculations naturally confirm your assumption.

This morning, I experienced the same familiar issue: a very slow increase in the onboard voltage after startup, during the afterglow phase.
I slightly adjusted the accelerator pedal, and sure enough: I could increase the voltage by pressing the accelerator, which was noticeable on the display and in the brightness of the headlight.

-> Another "proof" that my engine was running at full throttle, i.e., (still) unregulated, and also that the "problems" would be significantly less severe at the factory-specified idle speed (903 rpm according to VAGCOM).

I'll connect the laptop in the next few days and log the alternator load.

ulf wrote:

Well, my personal consolation is: Weaker LIMAs are slightly lighter than powerhouses (and also cheaper to replace later).

You have to give it to Ulf, he always finds a solution!

'Our Passat also has a higher idle speed when cold (after adaptation, approximately 950-970 RPM). However, this is constant. Once the temperature reaches around 70° Celsius, the idle speed drops to 880 RPM.'

However, he already exhibited this behavior before the adaptation (although within the range of 800-880 revolutions).

The old 1Z model didn't have that feature; it always ran within the same range (although, if it was really cold, it might sometimes run a little higher, but I didn't notice it).

Best regards, WarLord.

WarLord wrote:

Our Passat also has a higher idle speed when cold (after adaptation, approximately 950-970 RPM cold). However, this is constant. But when the temperature reaches about 70° Celsius on the display, it drops to 880 RPM. He had exhibited this behavior even before adapting (only within the range of 800-880 revolutions).

What engine does the Passat have?

Is this a 115 HP PD engine with the KB ATJ transmission?

This morning, it even reached over 1,000 revolutions per minute (but it was also very cold, and the car hadn't been running for quite a while, about a week).

Best regards, WarLord.

Okay, here's another update:

At approximately 840 rpm and with a warm engine, running the low beam headlights, rear window defroster, heater on full blast, and the radiator fan on setting 1 (next to the engine and the priming pump) is enough to overload the alternator: the onboard voltage drops to approximately 13 volts.

Okay, the radiator fan (which I can manually control) rarely runs, but its power consumption could probably be replaced by using the high beams and brake lights.

This means that at this load level, there is no remaining capacity for afterglow or for a higher charging current for the battery after a cold start.

Since it seemed a bit weak for a diesel engine, I checked the charging pulses of the alternator using an oscilloscope (voltage drop on the thick cable from the alternator to the battery). If there are faulty diodes (and consequently reduced alternator output), there should be gaps in the pulse sequence.
However, it wasn't the case that it was broken; rather, my "small" 90A LiMA (alternator) seems to be okay and is just a bit overwhelmed by the reduced low-speed RPM.

Well, the battery management system will take care of things, and I also have the voltage indicator...

Okay, so yesterday I was tinkering with my friend's Golf 4 (1J, ALH engine, 44,000 km, manufactured in 5/00), as he also has a 90A Valeo alternator and a 70Ah battery. (But it also has manual air conditioning, seat heaters, 4FH [likely referring to a specific feature or system], central locking with remote control).

The vehicle is driven exclusively in a very short, 3km round trip, and when it starts, the interior lights noticeably dim, which suggests that the battery is not charging properly.

The LL (likely referring to a motor or fan) was factory-set to 903 RPM, I reduced it to 840 RPM and then tested it. The supply voltage was 14.36V at the LL speed.

When the rear window/mirror heaters, all lights, seat heaters, etc. were turned on, the voltage would briefly drop (to around 13.1V) and then rise again to 14.36V.

I then adjusted the LL (likely referring to a motor or fan speed) to a maximum of 945 RPM. With the same test image, the increase to 14.36V took approximately twice as long as it did at 903 RPM (around 2-3 seconds).

@Ulf:
Are you sure everything is okay with the power supply of your 9Ns? I don't think 13V is high for such low-power devices, perhaps your voltage regulator is faulty.

Julian wrote:

The LL was factory-set to 903 RPM, I lowered it to 840 RPM and then tested it. The supply voltage was 14.36V at the LL setting. When the rear window/mirror heaters, all lights, seat heaters, etc. are turned on, the voltage drops briefly (~13.1V), but then rises again to 14.36V.

In my opinion, that was the sum of all power consumers plus the decreasing charging current from the battery (still from the starting process).
Or did the engine's idle speed automatically increase without any throttle input?

Quote:

Then I adjusted the LL to a maximum of 945 RPM.

Here, the same test image was used, but the increase to 14.36V took approximately twice as long as at 903 RPM (around 2-3 seconds).

Quote:

If that happened without restarting the device, I would suspect a regulator bug. Below the maximum load of the line management system (where the excitation current is still pulsed, i.e., < 100%), voltage dips need to be corrected much faster than what can be detected with VAGCOM...

Are you sure that everything is okay with the power supply of your 9Ns? I don't think 13V is high for such low-power devices; perhaps your line regulator is faulty?
Perhaps my battery actually has a noticeably higher power consumption for short trips, which isn't always compensated for immediately after a cold start?
Our ALH}(!) Ibi immediately revs up to approximately 1100 rpm after every cold start (although there is no voltmeter on board); my Polo apparently only revs above 840 if 13 V are not reached within approximately 5 seconds.

As I mentioned, the oscilloscope showed a completely normal regulator function: below approximately 14.5 volts, a continuous sequence of charging pulses, while above that, a pulsed sequence of charging bursts (I hope that's the correct term).
According to that, the regulator is behaving completely normally.

If the LIMA (likely referring to a specific device or component) had increased internal resistance, it should manifest as increased heating... I'll be doing some temperature tests soon.

Perhaps my transmission is translated to a slower gear ratio than the one on the Golf...

Or did the engine's idle speed automatically increase without any acceleration?


No, the motor speed remained at 903 RPM.


Perhaps my transmission is translated to a slower gear ratio than the one on the Golf...


Well, generally speaking, it usually spins twice as fast as the KW.

P.S.: I was able to verify the Vagcom voltage using a voltmeter at the battery terminals.

Hi,

"However, the behavior with the ALH IBI is strange. My very similar ASV IBI doesn't do that, even when I turn on both seat heaters, the lights, and the rear window heater shortly after starting the engine. The RPM remains at around 920 (which I haven't lowered yet)."

Best regards,

Jan.

Jan6K wrote:

The thing with the ALH-Ibi is also strange - my ASV-Ibi, which is quite similar, doesn't do that. The RPM stays at around 920

.
Hi Jan,

Perhaps it's because you don't have glow plugs?
(-> Charge the battery quickly to its maximum voltage so that the heating system doesn't have to be turned off again immediately due to the charging demand?)

I remember that my AFN (also with glow plug heating) ran a bit higher than usual for a while after a cold start in very cold weather.

Hi Ulf,

That could be it... the heat pump is quite a power-hungry appliance compared to other consumers (if you have one).

Best regards,

Jan.