Installing Ammeter in 911

[7783911]

J Bell aslo does gauge conversions to add a voltmeter to your oil pressure gauge..beautiful work!

[911pcars]

I replaced the factory cig. lighter with this combo digital voltmeter and USB source:



There are also versions that just replace the cig. lighter insert.

S

[Kraftwerk]

Interesting discussion. Lot's of various knowledge. My '86 VW came w/vdo volt-gauge, wish I kept it.

engineerdave I see you joined in 2018 belated "Welcome Aboard" is this really just your second post (?!) :
Way more informative than my first 200 posts...

[AndrewCologne]

I am totally with targa80 here. The big plus of Ampere-Meters compared to Voltmeters is, that you can see the "real current" +/- consumption. So ... best device for letting you know if the battery gets charged properly or if odd "idle current" exists when key is turned off and vehicle is parked.

[911pcars]

Originally Posted by AndrewCologne

I am totally with targa80 here. The big plus of Ampere-Meters compared to Voltmeters is, that you can see the "real current" +/- consumption. So ... best device for letting you know if the battery gets charged properly or if odd "idle current" exists when key is turned off and vehicle is parked.

You're half right.

Current consumption doesn't address current or voltage source (battery and alternator) nor does it indicate if the battery is charging. If the charging or source voltage isn't a minimum of 12 volts, minimal working current flows. In this regard, you need both meters. Current flow in the many branch circuits is variable and current specs for individual (e.g. dome light, IP lights, radio lights, glove box light loads aren't published to reference. IOW, monitoring current flow, while helpful, isn't as important as source voltage.

When ign and Eng is OFF, an ammeter can display active (parasitic) current in the system. Will your ammeter always be active in this mode? I wonder how much current an ammeter needs?

S

[AndrewCologne]

.. nor does it indicate if the battery is charging

If you put the ampere meter in series with the battery then you actually can read if the battery gets charged.

[911pcars]

Originally Posted by AndrewCologne

If you put the ampere meter in series with the battery then you actually can read if the battery gets charged.

How much charging current is typical? I guess if you have a baseline on that vehicle, you would know, but if an ammeter reads 1A during normal operating conditions, is that a normal charge rate? How about with the headlights ON? It might be if the voltage is also creating +12V. However, without knowing the charging voltage, it's a guess if the battery is being charged sufficiently.

The charging system is a simple circuit; basically a single wire from alternator to battery with a mid-connection to the starter along with ancillary control wires for the regulator and IP light and ignition switch. It depends on what section of the electrical system the ammeter is monitoring in these and numerous branch circuits.

It gets more complicated to measure what current levels are "normal" in those numerous branch circuits because current is variable depending on the loads in those circuits as well as which ones are operating, either automatically or manually switched.

Thus, observing the current draw or charging rate to/from the battery is one thing. Observing current draw for the remaining loads in the system is less helpful, but it does help if one has a baseline knowledge of your particular vehicle's electrical circuits. In that aspect, a cheat sheet would be helpful.

Sherwood

[AndrewCologne]

Hi Sherwood,
I know the circuit of the alternator through the regulator to the battery etc. I also built true electronic regulators for my classic cars.

Independent how much current remains for charging the battery, but by this at least you can read that there is one which charges the battery as the amperemeter reads positive.
Im not saying that it makes a voltmeter obsolete, but in case of watching the systems current consumption and charging flow its a better indicator.

[gomezoneill]

I had a 1963 TR3 that had a Ammeter BUT it had a generator and it was 6 volts.