Amp meter wiring diagram?

Question

I would like a wiring diagram to install an AMP meter in my boat, my boat has a small Mazda diesel engine with an alternator to supply charge back to the battery.

Answer 1

To work properly, an amp-meter must be in series with the entire positive cable feeding the boat's electrical systems EXCEPT the large cable going directly to the starter.  In "series" means the entire +12V battery cable (except starter cable) is broken with the line from the battery being connected to the "+" terminal on the meter and the line feeding power to everything else connected to the meter's "-" terminal.

If your battery's positive terminal has only one large cable hooked to it, you'll have to trace the cable to the terminal strip or buss panel where you find the large cable that goes directly to the starter motor and the second main positive cable that feeds all the boat's other electrical systems. If such doesn't exist, then you will have to be creative in splitting the boat's main power line from the starter's large cable because the amp-meter will be hooked only in series (inline) with the cable feeding the boat's main power buss (excluding the starter cable).  This allows the meter to indicate a discharge when the engine isn't running, and show the total alternator charge current (minus system discharge current) to the battery when the engine is running.

Once you've got a place to break the main positive cable feeding only the boat's electrical systems, it's probably going to be back near the battery and your amp-meter is probably going to be installed up on the boat's dash or control panel.  This means you'll have to cut the main electrical cable back near the battery and splice in (or use a heavy terminal strip) to connect a long piece of cable from the battery side of the cut up to the meter's "+" terminal; then run another large cable from the meter's "-" terminal back to connect with the cable feeding the electrical system on the other side of the cut.

If you use a standard "inline" or series amp-meter, the cables running to and from the meter (back to where you cut the main power cable) will be fairly long; so, to prevent loss of voltage (voltage drop) with higher current demands through a very long battery cable, you should use cable that's at least the next wire gauge larger than the existing battery cable.

A much easier way of doing this is to shop around for a "remote sensing" amp-meter instead of a conventional "inline" or series meter.  The remote-sensing meter has a shunt pickup device that's quickly connected up between the heavy battery cable ends back at the point where you cut the main cable; then, only two small meter feeding wires are ran forward to the meter itself.  It's much less hassle to install, and there's no worry about running expensive heavy cable a long distance that could possibly rub and short out at some later time.

Unless you're really concerned about monitoring the amount of discharge or charge (in amps), you can do very well with only a voltmeter that's installed in the control panel and quickly hooked up with small wires between the ground buss and any 12V fuse terminal that's "hot" all the time.  Simply watching the battery's voltage level will let you know if it's getting low or being charged.  Hope this helps.

Answer 2

Amp meters need to be in series with the circuit