electrical question - 2nd ammeter

[Chargermal]

Basically - my current factory ampmeter works, but I have a second aftermarket ampmeter as part of a gauge cluster i would ike to hook up.

To be clear - I am talking ampmeters (amp gauge) here, NOT volt meters.

I dont want to put it in series with the factory one, so here's my idea -

I want to run a second wire from the p+ terminal of the alternator, to the + side of the a/market ampmeter, and then another wire from the _ side of the ampmeter, to the "live" (constant power) side of the fuse box?

1- The issues are: Will the alternator "support" me running a second ampmeter from the alternator p+ terminal?

2 - Is connecting the - side of the ampmeter to the live side of the fuse box appropriate?

3- If connected this way, will both ampmeters read the correct current if running off the same altenator p+ terminal?

[Chargermal]

Heres a pic showing what I mean-

[Dragsinger]

To me, you have potential trouble by using the diagram you posted. At the very least, it will not show accurate amp flow. However, I need more info to make a solid judgment.

What car is this? What is the alternator amp rating? What is the total expected amp draw with all systems operating?

And remember this, when using an in-line amp meter, all current flows through the meter. That is to say, if the total system load can be 50 amps, all 50 amps passes through the meter.

Again, to me, if you must have an amp meter, a style that shows current flow without being in-line with the load is a much better choice. [example, an inductive meter]

As a side story, I am old and worked on old cars. Many cars up to the mid 1960's had in-line amp meters and those meters were a source of trouble. It can be noted, I am not aware of American car built after about mid 1960's that uses an amp meter. There may be a good reason for that! In fact, there is a good reason. As more and more electrical load has been added to modern car systems, in-line amp meters were not practical. It would take a high quality, expensive meter to be in service for years under a 100 plus amp load.

[Masher Manufacturing]

Drag, there were a few cars into the 70's that used amp meters ( Chrysler products ) but these burnt out due to increasing loads.

In the 80's some cars ( Dodge Omni and Ford Ranger mini trucks ) used amp meters but these were remote shunt meters. This is where a very low known resistance ( just a length of wire ) has a volt meter ( with a amp meter scale ) across this resistance. With this system the higher the amp flow the larger the voltage drop across the resistance.

This system is widely used in industrial equipment but since cars don't use the carefully calibrated resistance, automotive use is pretty much ineffective.

As for the drawing, your diagram will show about 1/2 of the _Charging/ Running _ amps per meter that the alternator puts out. It _will not_ show a battery discharge.

Why don't you want to run the amp meters in series? Why do you want two amp meters? Why don't you want a volt meter?

In the old days of generators load needed to be managed to prevent battery discharge. A amp meter was well suited to this. A zero reading shows energy is neither leaving or entering the battery. It does not show the running amps of the car.

Modern cars with alternators do much better than generators so a idle / low speed discharge is pretty much a thing of the past. Also modern cars require more amps to run systems. With more amps to contend with, the wire size required is much larger and the extra runs into the dash make for more wiring mess. A volt meter with it's smaller wires gives a much better window into charging system health as it is a instant indicator of overvoltage that will cook a battery.

Also, being a fully charged battery shows 12.66 V and a running charging system shows ~ 14.7 , loss of charging shows up instantly.

[Chargermal]

Sorry for the delay - and thanks for the replies-

As for the drawing, your diagram will show about 1/2 of the _Charging/ Running _ amps per meter that the alternator puts out. It _will not_ show a battery discharge.

That pretty much answers the question - I suspected it might not accurately read with two running off the one terminal.

Drag, there were a few cars into the 70's that used amp meters ( Chrysler products ) but these burnt out due to increasing loads.

71 A Body Chrysler - factory ampmeter in the instrument cluster

Why don't you want to run the amp meters in series? Why do you want two amp meters? Why don't you want a volt meter?

I have the ampmeter as part of an old school 3 gauge cluster.

Series means I have to pull the instrument panel -

Id run a voltmeter if it had come with then three gauges, but it doesnt.

[vinmann]

Chargermal,

I'm a little confused by what you are trying to do.

If you are running alot of accessories and are afraid of burning out your factory ampgauge then by paralleling two gauges would work.

Typically an ampmeter goes between the battery and the rest of the car. The rest of the car includes the alternator, the lighting circuit, the B+ (live) side of the fuse box and the ignition switch which includes the ignition and accessory side of the fuse box. The ampmeter would read only the load going in or out of the battery. It does not read how much the alternator is puttig out or how much the rest of the car is using.

In your installation you do not show if the original method of supplying the live side of the fuse block is used or if you spliced your ampmeter into it.

If the original supply of the live side is still in place then your ampmeter will do nothing. If you splice the ampmeter in then it will read the load of the live side and possibly the rest of the car depending which side of ampmeter the lighting circuit and ignition circuit are connected. In this scenario both ampmeters would read the same whenever the alternator has no output.

I would connect the second ampmeter to the alternator to measure its output.

[Chargermal]

I would connect the second ampmeter to the alternator to measure its output.

So if we put aside the wiring of the original amp meter (it works fine and I dont want to mess with it....)

How can I wire in the aftermarket amp meter without putting it "in series" with the factory gauge?

[af2]

I would connect the second ampmeter to the alternator to measure its output.

So if we put aside the wiring of the original amp meter (it works fine and I dont want to mess with it....)

How can I wire in the aftermarket amp meter without putting it "in series" with the factory gauge?

+ = +/ - = -
= Parallel

[_Scott_]

If you put two "identical" ammeters in parallel, they will each read half of the total current.

The way they are drawn above, the two ammeters measure different things, so there is no reason to think they will read the same. That's not necessarily bad, just understand what each one is measuring.

If you want them to read the same, wire them in series.

[vinmann]

Your battery will connect to two things. One is the starter motor. The other is the rest of the car. Find the wire (or wires) that connect the rest of to car to the battery. Disconnect it (them) from the battery and connect it (them) to the ampmeter - . Then connect the ampmeter + to the battery. Now all current flowing in or out of the battery goes through the ampmeter except the starter motor. I'm not sure how to bypass your original ampmeter.

[Engguy]

Scott is correct.

They have to be in series, to read the real current value.

[Chargermal]

OK, thanks guys - series it is then.