Charging voltage too high?

[cbez]

I put in a regulator from Dean and I see it climbing after start and running all the way up at 15 volts (measured at battery).

Seems high to me? It was a freebie so I'm not bent out of shape if it's not useable.

[Nissanman]

Depends on the condition of the battery: if it was low to begin with then the regulator will try to charge it once the engine starts.
A fully charged battery will see 13.8V approx at the terminals if the VR is functioning correctly.

[Bwk2000]

Even with a poor condition or undercharged battery, a properly functioning voltage regulator shouldn’t let the battery charge above about 14.2V. If you’re running in the 15V range with a good battery, your freebie is a paper-weight.

[david premo]

I would say that if you fully charge the battery and then test it, you would get a more accurate idea of what is going on. The factory manual for the roadster lists voltage regulator should be between 13.5 to 14.5 volts. Also a battery will not charge if the voltage is not greater than demand. A 12 volt battery produces about 2.2 volts per cell, making a property charged battery around 13 volts. The 14 volts you are seeing might be alright if the battery is not fully charged.
Dave

[cbez]

I'm sitting at 12.8 on a new agm battery so I don't think it's an undercharged battery situation

[david premo]

12.8 volts is about 13 only .2 volts off from target voltage. Good enough is just fine here, I would say you are fully charged.
Dave

[garth]

15.0 Volts is a bit too high but not a big concern and as others have suggested it is an indication of a fully battery.

Original Nissan voltage regulators were adjustable. I think there are adjustment instructions on this site or if not, generic instructions can be found online. Note be sure to adjust the voltage sensing relay (fine wire wound coil) and not the current sensing coil (heavier coil wire). I've adjusted mine to a 14.40 Volts limit @ 2000 rpm for rapid charging and extended battery life. Battery is 10 years old and still cranks hard.

Running with the parking lights on should keep the voltage below 14.50 Volts too.