Part of what I was trying to do is figure out the best location for reading the voltage for the gauge on a Mini. I think there was another thread that asked about this awhile back.

On the MPi car, it appears to come off the ignition switched circuit before that circuit feeds the fuse box. So if the diagram is correct, the gauge is unfused. On the other car with the gauge, I have a diagram of how Nick routed the gauge feed I believe. I just need to find it.

I have one more car to wire up. I don't think there are any issues, I was just surprised at the range of output readings.

Terry

Terry:

On cars that come from the factory with a volt meter, it is hard to know where the volt meter is connected in the electrical system.

The built in gauge is hardly any better than an idiot light.

Where do you intend to connect the real meter? You can get different readings at different places at different times. You can get different readings at different places at the same time.

The voltage across the battery will be different if the engine was just started than if the engine has been running for some time.

If you think you have electrical problems with either of your cars, take them to a good repair shop and have a load check done.

The technician will use a meter that has a big resister in it that can show the voltage under load. That is the best way to check.

Your car dealer service dept, an auto electrical shop or a Sears Auto Service will probably do it for free.

Russ

So the one car without a gauge, I used a real meter. I plan to check them all with that meter. I just realized that there a diffeence in the cars with gauges. My car is the one in 13 volt range and my wife's is in the 14 volt range. I was a lttle concerned that hers was over charging.

Terry

Terry:

Did you take all of your readings with the same meter?

An automobile instrument panel meter will not be as accurate as an electronics lab type meter.

A panel meter is just an indicator. All you need to know is the alternator charging the battery and keeping up with the power demands of the car or is the alternator overcharging the battery when the engine is running, or is the battery holding a charge when the engine is off.

The Mini does have a long run: the battery cable.

There will be different readings depending on the state of charge of the batteries. Two 'identical' factory new batteries can have different voltages.

Another variable is where the volt meter is connected such as the output terminal of the alternator, the 12 volt side off the coil, the battery terminals, etc.

Basically, there is no 'usual' or 'standard' place to check the voltage, only the place you want to know what the voltage is.

Russ

A typical "12 volt" car battery suposedly produces 2.2V in each of 6 cells or 13.2V. To charge it, one theoretically needs an opposing voltage higher the battery in order to 'push' through it in reverse. So your 13.2-13.7 alternator might just barely recharge the battery, whereas the other one would do much better. The lesser one might have weakness in its diodes or voltage regulation. On the other hand, too much charging voltage will cause the battery to off-gas. I'm not sure how that plays out on unvented batteries, but the older ones with vented caps will produce a distinktive odor.

I noiw have volt meters in two of our cars and have read the output voltage on the third car.

One car reads 13.2 -13.7 depending on speed, another 14.2- 14.9.

The third is only at idle with no load and it is 14.7.

This is with all aux accessories off. I know the reading will vary with how you take the reading and I have learned that GM managed output in some cases by having long "sense" wires and planned for the voltage drop. But in a Mini there are really no long runs.

I have been told that all my readings are in the normal range. It just seems odd that they vary that much with basically the same alternator.

Terry