AR Giulia IBS Data Interpretation

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bowdenandymecom
Posts: 17
Joined: 20 May 2017, 20:34

AR Giulia IBS Data Interpretation

Post by bowdenandymecom » 26 Feb 2019, 18:05

I’ve been trying to make sense of MES 4.3 logs of my Giulia Quadrifoglio’s BCM data, particularly ‘Battery Current from IBS’, for some months without success.

MES documentation suggests the logged value is current in Amps. However, the logged value during a recent 12 minute journey ranged from -900 to +1000 with an average around about 200.

Using a clamp ammeter over the battery earth lead, I’ve deduced the true current in Amps may be obtained by dividing the logged value by about 128. Thus the true average current during the recent drive was a charge current of about 1.5A.

Then the variation of the current is confusing me. Applying the 128 conversion factor, during the drive, the battery current was recorded by MES as varying frequently between about 1A and 8A charge with rare excursions to 6A discharge.

The logged current changed from 1A to 8A and back to 1A in as little as one second.

I really can’t believe the battery current would actually vary in that manner.

Further, there seems to be a strange relationship between the logged Battery Current and logged Battery Voltage.

During the drive of about 12 minutes MES logged battery voltage as about 13.4V for about 90% of the time. The battery voltage rose to between 14.6 and 14.8V for short periods.

This has been explained by some Giulia owners as the alternator only charging the battery when the brakes are applied. In effect, this provides a crude form of regenerative braking by means an ‘intelligent’ alternator.

Generally, the average logged current was about 6A charge when the battery voltage was low and 1.5A charge when the battery voltage was high which just can’t be true.

Perhaps, I’m misinterpreting the Battery Current as logged by MES. Perhaps, MES can’t be trusted. Perhaps, the Battery Current reported by the BCM bears no relationship to the actual current.

I've tried, but failed to attach an interesting plot of voltage and current over time.

Anyone able to offer an explanation?

Andy

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