[Rbernst929]

What is the voltameter actually measuring? Is it battery power, or alternator power? If it is battery power, does the lower reading on the dial indicate a battery going bad? Or, if alternator, are the needle fluctuations merely reading varying loads and the battery and alternator is ok? -Bob.

 

[maserati of minneapolis]

I assume it works the same as any other voltmeter - it's monitoring overall system voltage. If the car is off and the key is in the on position, it will be giving you battery voltage. If the car is running it's giving you overall voltage. The only way to get a direct alternator output reading is an ammeter. Normal voltage is usually around 14-15v, and a lower\higher voltage can signal a poorly functioning battery or charging system. The battery and voltage regulator usually buffers the charging system, and a wildly fluctuating readout can signal an issue as well. Its pretty normal for the voltage reading to fluctuate slightly as electrical draws on the system fluctuate - ie, the battery is recharged from starting, or the A/C is cycling on and off, while running the defroster, etc..

 

[Rbernst929]

According to my dealer...

According to my dealer some fluctuation is normal and nothing to worry about. But, my "usual" reading around level 14 sometimes dips to below nearer 12 when running and stays there.. is this a problem or not? Or, WHEN does the dial indicate a problem that should be rectified by the dealer? -Bob.

 

[Skidkid]

I assume it works the same as any other voltmeter - it's monitoring overall system voltage. If the car is off and the key is in the on position, it will be giving you battery voltage. If the car is running it's giving you overall voltage. The only way to get a direct alternator output reading is an ammeter. Normal voltage is usually around 14-15v, and a lower\higher voltage can signal a poorly functioning battery or charging system. The battery and voltage regulator usually buffers the charging system, and a wildly fluctuating readout can signal an issue as well. Its pretty normal for the voltage reading to fluctuate slightly as electrical draws on the system fluctuate - ie, the battery is recharged from starting, or the A/C is cycling on and off, while running the defroster, etc..

This is as good of an answer as can be easily explained in the forum. The subject is pretty complicated.

Voltmeters measure potential, ability to do work. Amps represent that potential doing work. Watts represent the actual work.

You can volts but little or no amps, Amps with low voltage, or any other combination. It basically depends on the load.

The alternator will generate a maximum voltage and it can source a maximum current. The battery is like a giant capacitor, it stores energy. The wires are really resistors.

If you start at one point and measure the voltage drop across each of the sections, working your way back to the start, you will find that it sums up to 0 volts.

Example: assume the alternator is floating at 14 volts and the battery has a shorted cell so it only goes to 12 volts. The other 2 volts are being disipated in the wires. Assuming that the two sides are the same it is 1V each. The wires would probably get noticably warm.

A batteries voltage is determined by the number of active cells. If one shorts, the voltage on a battery will drop. The alternator will try to hold the voltage up to charge the battery. This will cause a high current. The current will be limited by the max output of the alternator OR by the internal resistance of the wireing harness & battery.

It is a system and it all interacts. Make sense?

 

[Rbernst929]

Sure it makes sense, but..

Sure that makes sense, but to a layman under practical working circumstances.. WHEN should I be worried my battery or alternator needs looking at? In other words, do I not care how low the needle on the dial reads, unless the warning light comes on? -Bob.

 

[barbuckle]

For what it is worth - the manual says about the Voltmeter:
"...indicates battery voltage and operation of charging system.
With battery in good condition, with engine off and key at MAR it indicates between 10v and 13v.
With engine running indicator moves to values over 13v.
The low charge warning light indicates possible problems in the recharging system
When starter key is turned on to MAR warning light switches on, but should switch off as soon as engine starts. Any delay in its switching off with the engine idling is not indicative of malfunctioning."

Not sure about that last sentence(typo - or Italian engineering again!)

 

[maserati of minneapolis]

Yeah that last sentence doesn't make much sense.

I'm pretty sure the electrical light comes on if the system voltage drops below 10v, or if the alternator is no longer producing power (thrown belt, or some other failure). If you suspect your charging system has a fault somewhere, your dealer's service department can hook up the SD3 computer, and get live monitoring of a lot more sensors that would indicate different systems turning on and off, exact live voltage readings, as well as any stored codes that could indicate a momentary problem or inconsistent sensor \ module.


Bear in mind there is a twin thread http://www.maseratilife.com/forums/showthread.php?t=2975 to this regarding voltmeter fluctuation and a possible link to an impending F1 pump \ relay issue. It will be interesting to see if anything comes of that, but in the mean time it's one of those things to be aware of, but probably not freak out about too much unless things are really varying from the norm.

 

[M!]

of course a voltameter measures... eh... volta?

 

[Skidkid]

Here is some additional theory. The exact values will depend on the car but this should give you an idea of how it should work.

There is one more component in the system. The alternator contains a regulator so you don't over charge the battery. If a battery over charges it gives off hydrogen and has a dramatically shortened life.

As noted, with the key on but engine not running you should display the battery voltage. I would expect that to be approx 12 volts. This assumes you don't have the lights or other electronic stuff turned on.

When you first start the car it should jump up ot 14 volts or so. This will recharge the battery, replacing the power used to start the car.

After some time, approximately 20 minutes, the voltage should drop back to a lower level. This is the system providing power to the car but not charging the battery. I would expect this to be somewhere between 12 and 14 volts but it is pretty system dependant.

Overall the voltage shouldn't change too much once you get to this point. The regulator should hold the voltage stable and source the amount of current required to stay at that level.

So long as the car starts well I wouldn't worry. If I start to notice a slower crank I would first suspect the battery. Charging systems are very reliable, much more so than batteries. I would replace the battery and check the system again. If that doesn't work, seek professional help.

This all assumes that you have already checked and made sure that all connections are tight and free of corrosion. This includes both ends of the battery cables, not just the battery end.

The F1 pump speculation is possible. There is a thread on this subject on Ferrari Chat and they speculate on relay failures related to F1 failure. In theory -- the pump is electic powered. It raises the pressure then cycles on & off to maintian the pressure required to shift gears. If the pump stays on all the time the pressure would rise to a point that would cause the pump to stall. This would result in a very high current draw and you should be able to see that in the system voltage.

 

[maserati of minneapolis]

of course a voltameter measures... eh... volta?

Makes me think of the Mars Volta every time I see it..

http://en.wikipedia.org/wiki/The_Mars_Volta