amp gauge 6 volt positiive ground

[Erwin]

i am trying to hook up a new (used) amp gauge to my 48 ford f2 pickup with a postive ground 6 v system. as the pics show it has two allegator clips. i tried hooking it to the voltage regutor batt connection and the other side to the generator but get big sparks and smoke. anyone know how to properly hoiok up this thing? thanks for your help and interest.

[Bloo]

Someone has put those alligator clips on to use it as test gear.

 

Ammeters are a dead short internally. They measure current flow, in amps. They are not grounded, and don't care about 6 or 12 volts, only amps. They don't care very much about positive or negative ground either, as they are not grounded. They just read backwards if the polarity is wrong. If an ammeter reads backwards, reverse the leads.

 

An ammeter has to be connected in series to work. On a car, that typically means it goes between the charging system and the battery.

 

The charging system output is the "BAT" terminal on the voltage regulator if you have a generator, and the big post on the alternator if you have an alternator.

 

The battery connection is the not-grounded side of the battery.

 

Keep in mind that when you are driving, and the charging system is working and keeping up with demand, the charging system is the source of current, not the battery.

 

A car from 1948 would typically be wired something like this: A wire from the "BAT" terminal runs from the engine compartment under the dash. It then connects to one ammeter terminal. It may first go to a light switch or a key switch, but will get to that one terminal.

 

Another wire runs from the second ammeter terminal to the ungrounded post of the battery. Usually on an actual car, it doesn't run quite all the way. It goes to a post on the starter or starter solenoid where it connects directly to a battery cable. The current then flows through the battery cable to get the rest of the way to the battery.

 

Most electrical loads (lights, ignition, heater, radio, etc.) are connected to the charging system side of the ammeter. This is because you want the ammeter to only read whether the battery is getting charged or discharged. The current source is the charging system. If an accessory like a radio was connected to the battery side, the ammeter would read charge current plus whatever the radio was drawing. You would never know exactly how much charge the battery was getting.

 

You can't just hook up an ammeter to test something with everything still connected normally. As test equipment, you have to break a connection somewhere and connect the ammeter in series, so that the current flows through the ammeter. An ammeter is a dead short internally, and can only measure flow (Amps).

 

This is in contrast to a Voltmeter, which has extremely high resistance internally. A voltmeter can be connected between a current source (like a charging system or a battery) and ground. It just measures "electrical potential" (as a textbook would call it) in Volts. Voltage is something that just sits there and can be measured, like how much gas is in your tank can be measured, or how much pressure is your tires can be measured. It is not flow, and so nothing needs to be disconnected to measure it.

 

 

Edited November 4, 2022 by Bloo (see edit history)