What does [battery] voltage mean?

[MrElussive]

Hey,

Today, I was just browsing through my radar detector's instruction manual for some tips on laser detection when I discovered a few features my radar detector can do for me. It can monitor battery voltage and/or outside temperature (via the front sensor). Anyways, since my car already has a thermometer, I decided to employ the battery voltage feature. The manual says that this meter is useful to know if your alternator or battery is low or going to fail soon. When I turn the key one click to the right, just to turn on the radar detector (and enables me to unlock steering wheel and turn on radio/navigation/etc.), the voltage meter reads 12.8 V. When the car is on and I am driving around, the meter reads between 14.6 V - 14.8 V. I guess this is the normal operating voltage, but exactly what is this voltage telling me? What is considered "low" voltage and what does that mean when voltage is significantly lower than normal? Somebody explain this voltage crap to me please.

Thanks,
MrElussive

 

[jrt67ss350]

It is measuring the voltage coming available at the cigarette lighter. Pretty neat that your radar detector can do this for you.

Since the early/mid 50s, cars and trucks have had 12 volt electrical systems (prior to this, they had 6 volt electrical systems). That means that the battery produces 12 volts across the positive and negative terminals when the car is off. When the car is running, the alternator is producing the energy to run everything electrical in the car. Alternators typically have an energy output of about 14.5 or 14.6 volts. So, when the engine is running, the electrical system is really a 14 volt electrical system, even though the battery is only 12 volts. Everything electrical on the car is designed to utilize this 12-14 volt system. It's not really more complicated than that. The battery is really only used to start the car, then once the car is running, the alternator is producing the juice to run everything electrical in the car and to recharge the battery.

So, 14.6-14.8 volts is normal when the engine is running, 12.8 is normal when the engine is off. If you were driving down the road, and all of a sudden, the system voltage dropped to 12 volts, that would be indicative of an alternator or belt failure, and the battery is now supplying the electrical energy for the car. In today's modern, electronics-laden cars, the battery will not last long in this situation, and the car will quit in just a few short minutes.

By the way, due to the steadily increasing amount of electronics in cars, there is a big push by manufacturers to up the voltage of the electrical systems to 24 or 40 some volts.

 

[MrElussive]

Interesting, thanks for the explanation and what to look out for while driving. Being a new car and only having it for 3 years, I'm sure I won't have any issues with the battery and/or alternator, but I will certainly let the detector continue to monitor the voltage.
One thing I did not mention is that my radar detector is a remote install detector (one sensor mounted in the front, small laser detector mounted on the windshield, small control/display unit mounted under dash on left side of steering wheel) so everything is hard-wired to the car, which I'm guessing plays a roll in the voltage meter feature.

 

[Kirby]

Nice description Justin. Regarding the new systems coming in 4 or 5 years, they will be referred to as a 42 volt system and use a 36 volt battery. Think of it as multiplying everything by 3:

today 12v battery x 3 = 36v battery voltage
today 14v charge x 3 = 42v charge voltage

Why? The quick answer is to reduce the diameter of the wiring. The new electronics in the cars need more power. At 12 volts, the wire size must get bigger to handle the current as power load increases. By tripling the voltage, the wire size can be smaller for a given power load.

During the conversion phase they will split systems, with sources for both 12v and 36v.

But you can bet that some people will get confused or not pay attention, and hook up a 12 volt device to the 36 volt bus and P O O F!

 

[MrElussive]

Hahaha, interesting info Kirby. One thing I definitely need is an oil temperature gauge...I would really like to know when the engine is truly warm so I can punch it.