Voltage Meters and Amp Meters: Summary

September 26 , 2006
By Sunny Sutton

Often, especially on bigger boats, you'll see both a voltage meter and an amp meter. To understand if its worth having both, we must first understand the difference between amps and volts.

A volt meter measures the constant power the battery is supplying. This reports to you the general condition of the battery. If your volt meter tells you anything less than 11v you probably want to have this looked into (i.e. the battery).

An amp meter, on the other hand, measures the varaiblue output. An amp meter is going to tell you how much electricity a circuit or device needs. The more accessories, appliances, etc. that you have in use, the more current that is going to be needed to run these.

To us an old analogy, amps are like the size of the water pipe and volts are the water pressure.

An amp meter can be useful in determining if if the devices you are running require as much current (or more) than your alternator can produce. If you're close to the maximum output, this may not leave much current left over to charge the battery. This can be useful on boats with outboard motors with low-current alternators. An amp meter can also be a useful diagnostic tool. If your amp meter is showing a high reading with all appliances and devices turned off, there may be a short or a fault somewhere.

In summary of both of these tools:

A Volt meter tells us about the charging system:

• low voltage means its not functioning
  (or we have high system load current)
• high voltage means the regulator is bad (or unregulated)

An Amp meter tells us more about battery condition:

• high current means the battery is low in charge
  (or the charging voltage is too high)
• low current means the battery is up in charge
  (or the charging voltage is too low)
  *the ammeter also tells us the current draw of the accessories when the engine is not running.