T&T: DC Voltage Measuring

[Richard Cook]

Hi Don,

I'm no expert, but here are a few thoughts from my experience:

I'd think measuring voltage at a cabin light fixture might give you a 
lower reading than measuring it at the battery post, because of the 
resistance of wiring and connections in between.  You might want to try 
at the battery to compare.

I have a Link meter that monitors both starting and house banks, and 
over the years I've come to believe that monitoring amp-hours remaining 
in the starting bank is of little use.  If I were doing it over, I'd 
install a one-bank monitor.   OTOH, having readily available a precise 
indication of the voltage in the starting bank is sometimes handy.

The shunt that goes with the Link meter allows it to monitor amp-hour 
usage over time, something a multimeter cannot do.  The meter not only 
gives me a very accurate indication of the remaining capacity of the 
house bank, but also of the exact rate (amps) of usage and/or charging 
at any given time.

I can see exactly how much current any device uses.  Being able to 
accurately monitor charging rates keeps me on top of developing issues 
with my charging system, which does require occasional maintenance - 
alternator brushes, corroding or deteriorating connections, etc.

To me, as a cruiser with a fairly limited size house bank, it's more 
than well worth it.

Richard Cook
New Moon (Bounty 257)



captiva at att.net wrote:

> I've found different places that tell me what voltages of the house bank
> represent a fully charged battery or one that is 50% charged, etc.  Since I
> don't yet have a panel mounted dc voltage device, I've been using my multi
> meter that is connected temporarily to a cabin lighting source to measure the
> house bank voltage.  First, is what I'm reading a good indicator of battery
> charge if nothing has been turned on for six hours or more?  After a night at
> anchor with an anchor light on, is that voltage a good indication of battery
> charge in the morning?  I'm trying to determine why (other than ease of use)
> one would spend $150-$250 to see exactly what I'm seeing on my  multi meter.
> Since I always turn off the starting batteries except when actually
> starting/running, I don't see a reason to see their voltages on regular basis.
> Am I missing something?  I've also seen a lot of references to shunts.  Does
> my multi meter have one that takes the place of permanent shunts for an
> installed dc voltage monitoring system?