T&T: DC Voltage Measuring

[John Tones]

Don - you should be OK with the battery voltage reading PROVIDED that 
there is no draw on the circuit that you are taking the measurement 
from. If there are lights that are "on" in the circuit that you are 
using you take the chance that there may well be a voltage drop through 
poor connections. Much better to run a pair of fused leads from the 
batteries to somewhere convenient for the multi-meter if you are going 
to continue monitoring this way.
A shunt is a device that creates a very small voltage drop across it 
that can be measured on a matching meter to display current flow - _not 
voltage_. Generally marine shunts that we would be using are rated for a 
maximum of 500 amperes draw and give the meter 50 MV for that draw with 
the meter calibrated accordingly.
The big advantage that a battery monitor device gives is that you can 
see at a glance how much you are drawing from the batteries in amperes 
and quickly switch to monitor the voltage (at the batteries) under that 
current draw as well as monitoring the charge rate in amperes. Generally 
everything BUT the starter is run through the shunt so that you have a 
complete over view of what is happening to the batteries.
We have an "E - Meter" on Penta and I have found it to be great as it 
has allowed me to monitor what current draw various loads are demanding 
and adjust our use of the loads accordingly. For instance I found by 
experimenting with the Never-Cold fridge that it drew less when powered 
by the inverter than it did running on a 12 volt input. I have changed 
some lights to LED's for general lighting in the main cabin and again 
decreased the load significantly.
Just one guys way of approaching things.
Good Luck
John Tones  MV Penta
Sidney, BC