volt meter vs. amp meter

[bkreigsr]

For an electrical moron, which would be a better indicator of how the charging system is performing? Volt meter or amp meter?

I just don't want to be dead in the water again this year at the track if, and when, my alternator takes a dump on the trip there.

thanks

Bill K

[the]

I don't fully understand volt v. amp, but one of my cars has both.

For an indication of how the charging system is working, I think volt is better. I think that's exactly what the voltmeter is measuring - the charge.

My ammeter rarely moves. Once when an electrical item malfunctioned (an electric motor seized up), the ammeter told me something was wrong - it showed a heavy draw of current on the system when the electric motor was activated. The motor wouldn't spin, but the gauge showed heavy draw.

[bkreigsr]

thanks the
that's the direction I was headed towards. I just needed some justification for going to one vs the other.
Bill k

[rick-l]

It has bee along time since I've seen an ammeter in a car. The last one I drove was a 65 Mercury.

How is an ammeter implemented in a new car? Since it measures current in to and out of the battery there has to be some kind of resistor (shunt) in the lead to the battery.

With either meter you still need to know how to interpret the results

[munsonbw]

Maybe I am mistaken, but I was under the impression that an ammeter was a better indicator of alternator performance. Reason being, that the ammeter reads current and the voltmeter is obviously voltage. A weak battery could show 12.x Volts, but still be weak. I am not sure if an alternator could ever put out the proper voltage, but insufficient current to properly support the electrical functions of the car. If this is possible (when failing), the ammeter would tell you something is wrong. To me, a volt meter is not much better than an idiot light, which makes sure that the alternator is putting out 12+ V.

[Early_S_Man]

You can, indeed, lose 1/3 or 2/3 of your alternator's rated current output when one or two rectifier diodes blow ... regulator will maintain proper Voltage output right up to 1/3 of max-rated load.

The Voltmeter is a much more useful tool ... simply because people generally don't know what Amperage the various loads draw! It is bad enough knowing system Voltage is supposed to be between 13.2 Volts and 14.5 Volts ... when you throw in the concept of variable loads, the brain [most, anyway] overloads!

Because of the dependence on embedded microprocessors and digital logic, later model cars are much more likely to sustain damage when system Voltages rise above 15 Volts. Consequently, it is important to monitor the system Voltage to monitor the health and performance of the Voltage regulator! Whether the degraded performance is detected when just having ocassional spikes above 15 Volts, or when system Voltage is steady 15 Volts, or higher ... it is important to catch the faulty Voltage regulator before an expensive battery or control module is cooked!

[porsche930dude]

i was under the impression that an ameter was better because it measures draw and a voltmeter measures how much is being put out. I think thats right? But i usually just run a voltmeter because an ameter is much more involved to install properly

[GrantG]

If convenient, I think having both would be useful...

[RoninLB]

imo a 911 volt meter is a must have. An amp meter if you so desire after the volt meter install.

[LakeCleElum]

An amp meter reminds me of the "Lucas" days......So yesterday....Go with a digital volt meter...

[RoninLB]

if I wanted an amp ga I'd have aircraft ga mfg Westach Instruments make up a dual 2.25" consisting of volts and amps and install it on the console. Probably same prices as their routine dual ga's. A nice install would be trick.

[RoninLB]

Bingo

[bkreigsr]

what makes the ammeter more complicated to install?

My Fluke hand-held just bridges the ends of a continuous wire, right?

Ronin, I like that unit

thanks
Bill K

[slodave]

Originally posted by RoninLB
Bingo

That looks a lot like a gauge you would find in an aircraft. It would be very accurate!

Dave

[RoninLB]

Originally posted by bkreigsr


what makes the ammeter more complicated to install?

not to be silly but on some circuits an amp meter can be installed on the ground circuit.


your options may want to start with a shunt amp meter coming off the alternator. I don't know all the options as I've never explored an install. An amp meter install can be a party waiting to happen?

A red LED w/a momentary push button sw could read exactly 1 or 2amps in either direction which the meter, that's now reading 0, isn't designed to do. You could be draining 2 amps and not know it from only a meter. Then again you could install 2 amp meters. One for alternator and another in-line with the starter solenoid to see if it's drawing current or the problem is a connector. I believe you could eliminate the expensive shunt with a mv meter instead of an amp meter and tapping into the alt hot line at 2 distant points. The mv meter will read a proportional amp flow.


research this one out as this could be more fun than just doing a volt meter.

[RoninLB]

Originally posted by bkreigsr

Ronin, I like that unit

I don't consider a v or amp meter something that you have to constantly monitor like the idiot light. If you blow a fan belt seconds count before you cook the engine.

Dual cht gages in below pic same deal. Above the dual cht on the console is a single volt meter. The console works.

[psalt]

Hello Bill,

Both gauges will tell you about a failed alternator, but so will the idiot light. Overall the voltmeter is a better gauge. One problem with ammeters is that all circuits must flow through the gauge for it to be accurate. This means that the wiring to the gauge must be able to handle the max output of the charging system. This is especially important if you jump a dead battery. The gauge shows the net overall current flow and if any circuits are wired directly to the battery it will be incorrect. Once alternators became standard on cars in the sixties and outputs rose, the voltmeter won out because of the wiring cost issue.

Paul

[RoninLB]

[munsonbw]

I am not sure how accurate they are, but my '68 Bronco had a ammeter that just clamped to the main charging wire from the alt. I did not have a shunt, and all of the current did not go through the meter. I guess it is the same principal that your higher functioning multimeters have, just a clamp around the wire.

[RoninLB]

the tool box amp meter that lays on top of the wire works on the wire's magnetic field.

The shunt creates a voltage drop that is measured at a voltmeter disguised as an amp meter.