I'm just trying to figure out the normal operating range of an alternator.

The best I've found is:


15.3 is not a high voltage condition for the alternator.

The range on the cluster is :

6.2-9.1 volts, low voltage mark and below. 16.9-19.1 volts, high voltage mark and above

However, there is no source for these values. Does anyone if the above is correct?
9.2V seems too low and 16.8V seems very high to be considered normal.

Note: I intend to use the electrical system to power a 15V rated device.

  • Does the device need 15V, or is that the top of the range? The important thing to keep in mind is that automotive voltage isn't exactly stable. It's not as bad as household AC, but if you need constant voltage you'll want to use a regulator and an appropriate capacitor bank, and if you need 15V you'll have to come up with some kind of a voltage multiplier as well. Commented Jul 11, 2015 at 6:30
  • @Lathejockey81 The device is specified to work from about 9V to 15V, however I could re-rate it to work higher at a lower current. If as Paulster2 says >15V is bad then we can limit the maximum voltage it to 15V and state that the alternator must be healthy. I really need to find a maximum healthy alternator voltage.
    – SeanJ
    Commented Jul 14, 2015 at 10:11
  • A healthy alternator is typically in the low to mid 14s as Paulster2 stated. The last one I checked was holding steady at 14.4. The only way you would see sustained voltage above 15 is with a bad regulator. You should be just fine. The post you referenced looks like someone is reading the volt meter explanation as expected charging voltage range. Someone else called him out on it and he responded sarcastically... Not a good sign. Commented Jul 16, 2015 at 2:20
  • @Lathejockey81 Thanks for getting back. "You should be just fine." I appreciate what you are saying but ideally I'd like a specification that I could reference, e.g. EU directive says alternative must operate within X & Y. Maybe such a standard does not exist?
    – SeanJ
    Commented Jul 16, 2015 at 12:41
  • It looks like there may be SAE standards, but I'm not about to spend $70 to get a look at them. It does sound like a failing battery can cause voltage to run above 15 (and fry alternators - but that's another story). You can be confident that a healthy system will be above 11v, and if you're concerned about over-voltage conditions from unhealthy vehicles, then put a regulator in your input circuit. Commented Jul 16, 2015 at 14:47

1 Answer 1


The normal range for most alternators to run is ~14.1vdc. When the system is run higher than that (in the range you are talking about ... 15vdc plus), it will boil (and ultimately ruin) the battery. Depending on the load, the regulator may put out more than 15vdc, but this will be on a very short term basis.

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