Battery Voltage

[ziopinulo]

Hi all, ive a 3b to prj mod with tfsi cop, under fool boost and High RPM my UBATT drops to 12,5. Other than that the car runs well. Have you also noticed this? I tried new regulator, battery is fine and charged, in cruising UBATT from 13,2 to 13,7

[johne]

This suggests to me an issue with where and how UBATT is measured. The only way to be certain of your real battery voltage is to put a quality voltmeter connected directly to the battery terminals.

I don't believe you have a problem; this is the consequence of measuring voltage on wires connected to the battery carrying varying currents that change with load and RPM.

[ziopinulo]

Thanks for reply Johne,
UBATT is measured by the ECU so dont think a bad reading.
Then i ll put a friend with multimeter over battery terminals

[johne]

It's not a bad reading, it's the reading in the ECU at the place it's being measured but it doesn't mean it's the accurate reading of the voltage at the battery.

[tekstil]

Same here, logged my car today, under WOT UBATT drops to 12.4v @ 5600rpm. It starts dropping as soon as boost comes in. Normal cruise same 13.2-13.5v.

[Laaf]

This is the reason why installing a relay for the fuel pump is recommended if not mandatory on these cars when tuned.