Importance of Volt meter as an accessory

[sagaboy]

Importance of Volt meter as an accessory

Before getting a car Volt metermeter take note that not all car digital Volt meter are of the same quality or have the same accuracy (avoid analogue ones as they are difficult to read). From my years of using digital Volt meter for my Vw, here are some of the advantages of having it as an accessory for your VW
1. You get immediate status of your car battery condition and electrical St charging system.

2. When you turn on the starter key and before starting the car, look at the displayed battery voltage; if it is less than 12.2v it means that the battery is not holding its charge, leakage in your electrical system or your generator/alternator was not charging the battery when you were driving.

3. After starting the car the Volt meter should display 14/14.2 Volt with a cold engine/alternator and as the engine/alternator warm up the built in electronic sensor will lower the voltage to 13.8v

4. The minimum battery charging voltage is 12.9v if you are using too many accessories and drawing too much current or during night driving the Volt meter will display your battery charging status.

5. If your current usage is heavy the Volt meter may display below12.9v (at this stage your batter is no longer being charged) and if you electricity usage exceed what your alternator/generator can supply the Volt meter may display below 12.6v this means that your are using up your battery stored charge.

6. If the Volt meter consistently display below 12.9v or during minimal usage of electricity like when the turn signal is on or when the head light or wiper is on; this an indication that your battery is not holding its charge perhaps due Sulfidetation, internal short and is drawing excessive current from the alternator/generator.

7 when you turn the starter key andthe Volt meter display a fully charge battery status of 12.6v or higher but when you try to start the car and the starter does not turn it is an indication that the battery plate are sulfide and unable to store any charge.

[Piledriver]

Note it is important to connect the voltmeter ~directly to the battery if at all possible.
There is ~zero current, so wire size/length and power draw is not an issue.

Otherwise (attached at fusebox etc) you are measuring the voltage drop in the wiring/switches etc, and will depend greatly on load and wiring condition. The charging circuit does not go through the fusebox.(unfused, for better or worse)

Analog dash-mounted meters are easier to read at speed (rotated so at "normal" pointer is vertical)
They are also frequently not accurate (even major brands) and non-adjustable.
Test, preferably before purchase.

Note also using the factory headlamp circuits to control a separate pair of relays for the headlights, running on it's own 10-12 ga fused circuit powered direct from battery (run separately) will improve lighting dramatically in my experience.
Even tapping headlamp relay power off pre-fusebox makes a huge difference.

Connecting voltmeter at fusebox is actually highly educational, but will not accurately tell you if the battery charge state.

A shunt type (remote) ammeter (shunt electrically at battery or alternator) will tell you if you are charging or discharging.
it is really just a very sensitive voltmeter, which measures across a very low resistance high current resistor.(really just a calibrated bit of wire)

Use of common direct acting ammeters usually cause more problems than they solve.

[Ol'fogasaurus]

"A shunt type (remote) ammeter (shunt electrically at battery or alternator) will tell you if you are charging or discharging.
it is really just a very sensitive voltmeter, which measures across a very low resistance high current resistor.(really just a calibrated bit of wire)

Use of common direct acting ammeters usually cause more problems than they solve."

The ammeter's main draw back is heavy wire (usually 8 or 10 gauge) running forward to the meter directly from the generator/alternator then back to the starter solenoid before the rest of the wiring in the car is fed power. In the past there has been a tendency not to be protect this long run by a fuse or circuit breaker which can be done quite easily.

As 'Pile said, the ammeter measures things real time (I think that is what he said anyway) and, if you monitor the gauge regularly, it can show problems as they happen or, in some cases, problems that are starting to happen such as a sulphated battery (they still do that don't they?) . The ammeter measure draw vs. charging system input into the battery. Dead shorts vs. intermittent shorts and so on.

When I started up a car (with an ammeter) I always sat and watched the ammeter until the needle came down and then determined just how long it took. A habit most people had that knew much about the ammeter.

Anyway, the volt meter is easier to wire and is usually adequate.

Lee

[Piledriver]

A "remote" shunt ammeter puts the high current shunt electrically at the alternator/generator etc, so it doesn't require miles of high current wiring, so ~zero losses. Eliminates the downside of the typical ammeter setup.

...of course having BOTH a shunt ammeter and an (accurate) voltmeter would be ideal.

Having inaccurate pretty dash filler that pretends to be instrumentation is a complete waste tho.
(I'm looking at you, VDO)

[Marc]

...Having innaccurate dash filler that pretends to be instrumentation is a waste tho.

[Ol'fogasaurus]

"...of course having BOTH a and an (accurate) voltmeter would be ideal."

https://www.bluesea.com/articles/552 I think a very good description of a DC shunt ammeter.

More about them

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

I whole heartedly agree with that, just not always practical is it.

http://en.wikipedia.org/wiki/Shunt_(electrical)

http://www.ehow.com/facts_5019375_ammet ... shunt.html

[Piledriver]

That pretty much beats it to death

There will be a test...

[Ol'fogasaurus]

That's my job sir.

[Fiatdude]

I'm still having the problem of the Idiot light being smarter than me

[Ol'fogasaurus]

Is it a bright or dim idiot light