brian
Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA
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 Posted: Wed Feb 22, 2006 6:58 am Post subject: Voltmeter location (was: Question for Bob or ?) |
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Robert L. Nuckolls, III wrote:
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At 08:10 PM 2/21/2006 -0800, you wrote:
>
>
> I've wired up my RV-6 per figure Z-11 (mostly) and when I turn on the
> master switch, I'm seeing 11.5 volts on my voltage gauge.
Okay, that's about right for an e-bus driven voltmeter seeing hte main
bus through the normal voltage drop in the bus isolation diode.
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The reason to have a voltmeter as opposed to a lo-volt/hi-volt indicator
is to show the actual voltage on the battery. You need to know the exact
voltage on the battery to ensure it is being fully charged without being
overcharged. It is also the indicator for remaining capacity in the
battery, i.e. when the battery is delivering system power and its
voltage drops to 10.5V (12V battery), the battery has delivered all its
energy and is now "dead".
I hold therefore that the proper place for a voltmeter is to read
battery voltage. You can measure battery voltage on the main bus when
the battery contactor is closed or you can measure battery voltage on
the e-bus when it is connected directly to the battery. Other than that,
the only place where you can always measure the battery voltage is right
at the battery.
If it were up to me, I would pick a digital voltmeter that had a sense
lead separate from the power lead (a three- or four-lead device -- does
anyone make one that is not part of an energy monitor?) to read battery
voltage. The drain for a device like this is so low as to allow it to
remain connected to the battery even when all other loads have been
removed. A drain of a couple of microamps through the sense lead is not
going to drain a battery faster than its self-discharge rate.
--
Brian Lloyd 361 Catterline Way
brian-yak at lloyd dot com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery
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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery |
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