ATG (JulAug10) - Connecting Battery Gauges

By Editor,


How do I connect a battery gauge?

Wayne From Villages, Florida


First let’s talk about what those things are. Some call them charge indicators and some call them discharge meters. So which is it? The market offers two styles of meters to monitor battery voltage. One meter is digital and one is analog. The difference between the two is the analog is basically a voltmeter. The digital meter is more of a battery discharge indicator (BDI). However, during non-use (no load) the meter can tell battery pack charge. But its real value is reading discharge voltage to prevent over discharging the batteries. The value to this is we do not want the cell voltage during discharge to go beyond 1.70 volts per cell. That will be close to 80% discharge of the battery pack. Without monitoring the amount of discharge, damage to the batteries can occur. So, how do we connect the meters?

Analog or Digital will connect the same way. It has always been an industry standard to connect directly to hard positive and hard negative. What this means is connecting as close to the main battery car connections as possible. There are several good reasons for this. One reason is the activation wiring is usually too small and does not truly represent the power side of the system. So connecting to the small activation wiring is not as accurate as connecting directly to the battery pack. Another area of concern is connecting to the key switch. I do not recommend this at all! The reason being is the key switch has resistance. This resistance will give you a false reading. The other reason for not using the key switch is not all key switch circuits are positive voltage. If a key switch activation is desired I suggest utilizing a relay in that circuit. This will allow on/off of the meter if you want to do that. However, it is not necessary to turn the meter off. The draw on the batteries is so low it will not cause battery discharge.


Note: some digital meters do utilize a third connection for key switch activation. You can use this if it is indeed a positive circuit. Still connect the other two wires to hard positive and negative.


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