Now that I have a cockpit voltmeter, what readings should I have?

H.G.P. · 05-30-2003, 09:56 PM

What readings on my voltmeter should I have with:

1. Idle?

2. Acceleration?

3. With the headlights/high beams on ?

Thanks

Joeaksa · 10:04 PM

I have on my 85 model:

Ignition on only: 12.3-12.6

Idle: 13.4-13.7

Running: 14.4-14.7

With a load: 14.5-14.2

With a load means lights, fan and such. With everything on it might get to 14.0 but rarely. Since your car is a bit older and the alternator possibly not as stong, it may dip a bit but should not get too far down, even under a load. Would like to see 13+ at all times no matter what the load.

The car operates using the battery, period! The alternator only replenishes the battery. I had the regulator go out years ago (before I had the voltmeter) and the readings off of the VOM I used went to 16.0 volts.

Been driving with a cockpit voltmeter for years now and would not be without it!

Joe

H.G.P. · 05-30-2003, 10:05 PM

Thanks...all those coorespond closely to my readings, except the last time I had the headlights on it dropped some. But I've only needed the headlights once since meter installation.

H.G.P. · 05-30-2003, 10:08 PM

...and I assume "load" includes acceleration?

Joeaksa · 05-31-2003, 05:42 AM

Acceleration has nothing at all to do with it. Once the motor speed is above 2000 rpm's or so you can be full throttle or coasting down a mountain, but the alternator should hold everything you throw at it without losing its capacity to recharge the battery.

Joe

H.G.P. · 05-31-2003, 09:15 AM

Quote:

Originally posted by Joeaksa
Acceleration has nothing at all to do with it. Once the motor speed is above 2000 rpm's or so you can be full throttle or coasting down a mountain, but the alternator should hold everything you throw at it without losing its capacity to recharge the battery.

Joe

The needle goes somewhat up when I rev.

masraum · 05-31-2003, 09:22 AM

when you turn on headlights, a/c fan, heater/defroster fans, or wipers the voltage will drop, as long as it doesn't go below 12.5-13 with everything in the car running you should be ok, but normal numbers will be 13.5-14.5.

H.G.P. · 05-31-2003, 09:54 AM

Quote:

Originally posted by masraum
when you turn on headlights, a/c fan, heater/defroster fans, or wipers the voltage will drop, as long as it doesn't go below 12.5-13 with everything in the car running you should be ok, but normal numbers will be 13.5-14.5.

OK. That sounds like me. I haven't looked at it yet with the wipers on yet though. I like this voltmeter. Thank you.

Joeaksa · 05-31-2003, 03:37 PM

Big things are the fan, A/C, rear window defroster and headlights. Wipers should drop it a tenth or so but not much more.

Its a good tool to have... Remember that the "idiot" light can stay off and the alternator still not be working. There is a diode that triggers the "alt" light to come on and if that diode is still working and the rest in the alternator are blown, the alternator will not keep up with the demands of the car.

The "idiot" light is still doing its most important job though! Anytime the light comes on, stop immediately! It could be that your alternator is working fine but the fanbelt has come off, stopping any and all cooling air to your "aircooled" 911 motor.

Both of the above scenerio's will be shown by the voltmeter showing "battery" voltage, which should be 1-1.5 volts or so lower than normal for that situation. Either way, stop and check the fan belt immediately. If its only your alternator or a diode blown you can still drive home, otherwise its get the spare out of the trunk.

Joe

RoninLB · 05-31-2003, 04:49 PM

Quote:

Originally posted by Joeaksa

... Remember that the "idiot" light can stay off and the alternator still not be working.
Joe

or it can be over-charging...........Ron

pwd72s · 05-31-2003, 04:58 PM

Ron's point is a great one. Too much voltage can do more damage than not enough. Since I don't want to add any brackets, consoles, or gauges, I bought a unit that plugs into the cigarette lighter, gives a digital voltage reading. The only downside so far is that I have to remove the unit if I want to open the glovebox. The plus side is it can be used full time as opposed to getting a multitestor read out from the battery posts.

H.G.P. · 05-31-2003, 06:04 PM

I really like my voltmeter installation, for me, very clean, and functions as a unit along with my other gauges. As for the fan belt. I carry an extra belt, but I still am not sure where the pulley tool (I purchased from Pelican, with the "prongs" on it), goes onto the pulley??? Is the nut holding the pulley belt ever difficult to remove, even with the pulley tool?

carreradpt · carreradpt's Garage

HGP, Joeaksa, really stupid question here. Where does the voltmeter wire up to? Do any of you guys have a diagram? And where did you install it in the car?

Joeaksa · 05-31-2003, 09:42 PM

Dan,

Any + (positive) lead in the interior will suffice. You just want to monitor the voltage in the system. I stuck it to the tach in my car and it is right in front of my face all the time. Ran the wires under one of the instruments and took the power off of an instrument.

H (what is your name BTW??),

The two pronged wrench goes in the pulley face and holds the shaft while you loosen the nut. Not difficult but putting all the bits together with the shims sometimes takes some patience!

Ron is correct, especially in the newer cars. I have a DME fuel injected car and the surges in voltage when my alternator went tits up can do some real damage to any electrical circuit. I saw my headlights pulsing and then put a VOM into the system and found the problem. Thats why I have one built in today!

Joe