Ask PYS: Power

Rick, on Oct 04, 2013 asked:

I noted in the October PY that your Tech Talk section has a question which may answer a minor issue I have always had with my battery monitor. The current readings whether charge or discharge, have always had a bit of fluctuation. The cable from the shunt to the monitor, approximately 50’ long, is a twisted pair but is not shielded. I’ve often wondered if using a shielded cable would rectify this. Also the cable routes through some very heavily cabled areas of the boat.

Twisted and shielded pair cable makes a significant difference; you'll recall that a shunt measures slight variation in voltages, about to 50 millivolt to be exact. Which such low numbers it is possible for a long cable run to have voltages induced by running along a non-shielded or twisted cable.

Best way to troubleshoot is to route a new cable temporarily on the cabin floor and see how the ratings fluctuate. If the readings improve significantly we can run a new appropriate cable instead.