AMP METER/VOLTMETER

Neal

Lifetime Supporter
An ammeter measure current flow from the alternator and is an indication that your alternator is charging the battery. A voltmeter only measures batter voltage so you can't necessarily tell if you are charging.
 
That can be fixed....

An ammeter is always in line. If you connect a high resistance line in parallel somewhere in the circuit, and then measure current across that, then by varying the resistance, you can 'tune' the ammeter down to a sensible level. This means that the scale on the ammeter may be wrong, but it still shows relative changes.

Regards

Neil
 
should also add that this parallel circuit MUST be added across a section that is disconnected when the ignition is off.... otherwise you'll keep finding that your battery is going flat!

Neil
 
Thanks Neil. Thats what I thought. My MK-IV
simply has a light that glows when discharging. My Lola had an amp meter but when I switched to a high power alternator it was always pegged. I changed to a volt meter and it seems to work.
Best
Jim
 
G

Guest

Guest
Also keep in mind that although your alternator is capable of putting out 180 Amps (I have a powermaster that is 180 amps for the EFI and lots of lights up front) it won't necessarily be doing it all the time because of the, in most cases today, built in regulator that will only provide the amps the system needs. So if the battery is dead and you have all of your lights on and the A/C blower is on high and you have a compressor plugged into the 12V socket, then yes the ammeter will be pegged. Otherwise, no, it will only show what the system is demanding. Volt meters have become the norm because of this: the system should be at around 13.5-14v all of the time. Also, an ammeter is OK as long as it is OK, but if it should short out or be damaged, you can have real problems.
 
An further point on Amp meter VS Volt meter.

If you have an Amp meter only, you will know that the alternator is attempting to recharge the battery, but you won't be able to tell if the battery is accepting the charge until it's too late.

If you have a Volt meter only, you will know that the battery is currently charged, but you won't be able to tell if the alternator is recharging until it's too late.

Having both is best.

Just a footnote... if you are buying an Amp meter, make sure that it is of reasonable quality. A poor Amp meter can "steal" power and get very hot.
 
I don't really see the utility in an ammeter. If the alternator is charging, then the voltage across the battery will be on the order of 14-15 volts, a little higher than the 13.2 nominal voltage of a "12-volt" lead-acid battery. If the alternator is not charging, then the volt meter will show less than 13.2 volts.

Regards,
Mark
 
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