Loads Yes & No! by Compass Marine How To

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Loads Yes & No!

OK here's the gotcha we talked about. Nearly every instance of trouble shooting battery monitors I've come across can be lead directly to where you've connected your DC negative wires.

A shunt reads the loads on the system as measured as voltage drop, in mV levels, across the shunt. This shunt is a 500 amp 50 millivolt shunt. This means that at 500 amps there will be a 50 mV drop across the shunt. Knowing this the monitor manufacturer can make the display correspond to any load from 0 to 500 amps or 0 to 50 mV.

If any load, such as a bilge pump ground, is wired ahead of the shunt or on the -BATTERY side of it, the load will NEVER be seen, recorded or measured by the monitor. All DC loads on-board should be read by the battery monitor. Inverters, battery chargers, alternators, solar, wind, DC distribution panel, LPG detectors etc., etc., on and on.

Keep in mind that many marine alternators are case grounded and thus the system ground, which on most boats is the engine block, is the ground path for the alternator. While I much prefer an isolated ground for alternators many boats just do not have alternators with this feature and they use the case as the ground. Due to this, the ships main ground connection should be connected to the -LOAD side of the shunt and NOT ahead of it or on the -BATTERY side.

Anywhere you see a green arrow is safe to connect DC negative load wires. The ONLY wire that should connect to the battery is a single negative jumper wire from the -BATTERY side of the shunt. No other wires should be connected on either the neg battery post or the -BATTERY side of the shunt.

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Henry Dennig 03-Mar-2016 23:11
R.C.,
What about the temp sensors that are on the negative battery post for the alternator and inverter temp sensor?

LarryM 22-Jul-2012 19:41
I recently purchased a boat with an Adler Barbour Cold Machine installed. It is wired through an on/off switch directly to the house battery bank, and is not being monitored by the Blue Sea digital battery monitor about 15' away. I found the owner's manual for the Cold Machine where they clearly state that the 12v negative connection was to be made directly to the battery/bank negative terminal, and NOT to the load side of an ammeter shunt. There was some reference made to the voltage drop across the shunt which could cause the system to cycle more frequently or draw more current. Does this sound correct to you? I would really like to monitor the current consumed by the refrigeration.

Henry Dennig		03-Mar-2016 23:11
R.C., What about the temp sensors that are on the negative battery post for the alternator and inverter temp sensor?

LarryM		22-Jul-2012 19:41
I recently purchased a boat with an Adler Barbour Cold Machine installed. It is wired through an on/off switch directly to the house battery bank, and is not being monitored by the Blue Sea digital battery monitor about 15' away. I found the owner's manual for the Cold Machine where they clearly state that the 12v negative connection was to be made directly to the battery/bank negative terminal, and NOT to the load side of an ammeter shunt. There was some reference made to the voltage drop across the shunt which could cause the system to cycle more frequently or draw more current. Does this sound correct to you? I would really like to monitor the current consumed by the refrigeration.