308 voltmeter? Anybody ever installed one?

Mike from what i understood the light would go out when the engine was reved. It would glow when you turned on the directionals (usually at idle or slightly above) and whith the brakes on at a stop light. I find this normal and if you plug in a digital volt meter you can see the span of voltage from start to idle to cruise and so on. I believe that the light glows at about 11.5 - 12 volts. I'll check but this seems to be the case.

 

Steve,

Yes, the generator light will begin to glow below some alternator-ouput threshold voltage (not sure what it is - your numbers seem in the right area).

Yes, the light stays on solid until the alternator kicks in (this good--if your alternator fails and you're ever "running off the battery", you want to know about it).

However, that the light would glow with your turn signals and brakes is NOT normal behavior. Something is wrong if putting on your brakes is causing the battery recharge voltage thrown out by the alternator to drop to the 12V range (from say 13V). Although this may be the behavior you observe in your car, and that Greg328 is having, it is not normal and indicates a problem. It's one thing if (a) you have a weak, stock 55A alternator, and (b) are driving with your high beams, wipers, and a 50w x 4 channel amplifier driving your stereo... Then your alternator might not be able to keep up, your headlights may dim, the G light might glow, and even more so with the added load of the current drawn from the brake lights.

But from an upgraded alternator, with no other accessories running, again, this is not normal.

It is also possible that the "Electric Board" that a lead from the alternator connects to before eventually connecting to one side of the "G" light has a problem (my 328 wiring diagram shows this wiring setup).

--Mike






--Mike

 

Here's my voltmeter installed. The tough part was finding one with a "bottom sweep". I opened it up and tried to paint the needle similar to all the stock gauges. I also green marker to give the illumination the same look (I didn't go so far to make it dim like all the OEM ones).
Image Unavailable, Please Login

 

Wait a second....WHY do you want a volt meter anyway? An AMMMETER is the way to go. The volt meter just tells you when you're already f'ed. The ammeter will give you a constant read on your power drain and charging. If your alternator is going bad you'll get plenty of warning with an ammeter.

The drawback is you have the + battery in your dash so using the correct gauge wire and care in hooking it up is essential. I'm not familliar with Ferrari wiring but basically one side hooks up to the same lead as the + side of the battery that connects to the alternator. The other side connects to the ignition switch's first click position (at least on my car). Of course these leads go elsewhere as well...I'd consult someone before hooking one up.

Ken

 

I disagree. Most of the automotive world says that if you can only have one gauge, get a voltmeter. Less electrical risk, easier wiring. That's why you don't see ammeters in cars anymore, and haven't for a long time (except some VWs, I guess), but many cars include a voltmeter.

A voltmeter will show an overcharging or undercharging condition that could be caused by a failing alternator (voltage regulator). It also shows the overall health of the charging system--i.e. is the alternator working (14V) or am I running off of the battery (12V)?

I do agree that the info that an Ammeter shows would be useful, yes, but I've tried for about two years design the hookup for it in my 308 and 328, and haven't been able to make it happen. Running the wires to/from the alternator is part of the problem. Cost/benefit just isn't there--so my VDO ammeter is in a box.

--Mike

 

Correct me if I'm wrong, but doesn't an ammeter measure the current and wouldn't it have to be in series of the circuit. What current would you want to measure? Are you talking about total current? What values would indicate normal or abnormal readings?

I personally did this to replace the clock, since it would run about 5 minutes fast every week. I had originally installed a vacuum gauge and decided that gave me useless info. I also don't really trust the "generator light" on the dash. The volt meter was a good choice for me.

Henry

 

An ammeter does indeed have it's current sensing element in series with the current being measured. There are a couple places where it could be interesting:

Between the battery & everything else (ie: measure current into & out of the battery).

Between the alternatory & everything else: Measure what the alternator's putting out.

However, that doesn't necessairily mean that the current being measured has to be brought to the dash.

You can install a high current, very low value resistor called a shunt in series with he current you want to measure, then use a voltmeter to measure the voltage across the shunt. For example, a 0.001 Ohm shunt would have 0.001 Volt across it for every Amp. A 100A load would show 0.1 volt.

However, finding an appropriate low voltage meter to mount in the dash might be a tad challenging.