Battery energy balance in short-distance TDI operation in cold temperatures

Hello everyone,

With the freezing temperatures we've been having, our engines have to preheat for a long time. After a night on the road and a temperature of -12 degrees Celsius, mine had to preheat for about 15 seconds before it finally started on the first compression.

And then there's the afterglow, the glow plug heating, the lights, the rear window heater, etc... that's a huge amount of electricity being consumed.

What do you think the balance sheet looks like for a 10 km city ride, like the one I currently do (max 60 km/h, maximum 1500 RPM, with a water temperature of around 70 degrees at the end)?

Does the alternator's output at the low engine speed (usually 1200 RPM) provide enough power to compensate for the high energy consumption at the beginning?

What do you think? Currently, there are no problems... so it's more of a theoretical question.

Best regards,

Jan.

Hi!

The LM already provides enough power at idle speed, that's for sure!!! Just trust!

Best regards,
Uwe

Uwe wrote:

The LM already has enough power at idle speed, which is definitely sufficient!!! Just have trust!!!

...and if "blind" trust isn't enough: install a voltage monitoring system.
As long as there are 14 volts present, the battery will be charged at its maximum rate, and higher engine speeds would be completely unnecessary.

During the pre-glow phase, the battery is loaded with 40 amps for 15 seconds, and during the starting process, it's loaded again with 400 amps for 3 seconds. This results in a total of approximately 2000 amp-seconds, which is roughly 1% of the battery capacity that needs to be recharged.

Even with a ridiculously low 10 amps (compared to the alternator's 120 amps), it's finished in just 200 seconds, or 3.3 minutes.

I know that in reality, charging current curves at constant voltage tend to be asymptotic (???), and that the battery's efficiency being less than 1 further extends the charging time, but overall, it probably gives a reasonable estimate of the correct order of magnitude.

Hi everyone.

You are probably right... because I hadn't calculated yet.

But with mathematics, you can (almost) solve any problem.

Best regards,

Jan.