Battery or Regulator?

[Tom]

I have a 6 month old OEM battery which was flat this morning. I called the NRMA and he checked the battery and alternator.

The alternator is putting out 15 volts and the battery is putting out 14.95 volts. Is this normal He thinks this is too much and is cooking the battery

But he doesn't know if this reading is normal for an MX-5 so I am checking with you gurus.

If the voltage is too much then my regulator is stuffed. If it is not too much then my battery is stuffed.

Any suggestions

Tom

[NMX516]

AFAIK the alternator on any 12V car should be pumping out around 13.5 to 14V. Over 14V would have me concerned. I think it is your regulator.

[Inf3ct0R]

NMX516, have you checked yours lately?

I think all NB's have a high voltage output...

[CT]

13.9 volts is about the average for an NB AFAIK. There is no regulator as such in the old school way, it is regulated from the ECU.

[NMX516]

Admittedly, haven't checked mine on the 5. But I wouldn't have thought there would be any differences between makes/models etc with a 12V system, is there??

[Inf3ct0R]

13.9 volts is about the average for an NB AFAIK. There is no regulator as such in the old school way, it is regulated from the ECU.

really?
mine spikes like hell to about 16 volts, and im wondering why im always blowing globes..

[CT]

It certainly will spike up and down but if the field control is doing it's job it should average around that mark. My cars ECU compensates for big spikes like the fans turning on by upping the field control by 10-15% above the average target. 16v for a prolonged period will certainly start to kill things.

[Tom]

Thanks for all the replies!

I think the NRMA got sick of sending their road service to get me started so they sent their battery bloke around who gave the battery a check and found that the battery had a dead cell.

Thanks again,
Tom