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Date: Thu, 24 Oct 2013 12:46:21 -0400
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Subject: Re: [LML] Re: Odyssey PC680 Batteries on Firewall -- Cool Enough?
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From: Todd Long <toddlong1@gmail.com>
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Under what load do you see the 1.2v drop?=20


Typing and grammar errors courtesy of Siri and the iPhone.

> On Oct 24, 2013, at 8:08, jeffrey liegner <liegner@ptd.net> wrote:
>=20
> Chris,
>=20
> The back battery (behind the aft bulkhead) does have a trickle drain via t=
he panel's clock.  This is why the voltage trickles down over time (days, we=
eks) relative to the isolated battery on the firewall.  My observation is in=
dependent of this variable.
>=20
> But when both batteries are fully charged, either with dual alternator out=
puts or plug-in charger, the delta is 1.2V to 1.3V as seen at nearly the sam=
e point behind the panel.
>=20
> I had originally planned for copper cables, and measured the drop based on=
 6ft, but found the weight to high.  Aluminum is used, and the drop is signi=
ficantly greater than copper (as we know), and the result of roughly 6ft of 2=
 gauge is 1.2-1.3V demonstrated.
>=20
> If this were the cranking battery, it has an impact on amps available tot h=
e starter, which is another 3-4 ft further forward.  When I have experimente=
d with cranking off the aft battery, it definitely is weaker, a problem if c=
old start.
>=20
> Jeff
>=20
>=20
>=20
>=20
>=20
> On Oct 24, 2013, at 6:00 AM, Lancair Mailing List wrote:
>=20
> From: Chris Zavatson <chris_zavatson@yahoo.com>
> Subject: Re: [LML] Re: Odyssey PC680 Batteries on Firewall -- Cool Enough?=

> Date: October 23, 2013 7:45:51 AM EDT
> To: lml@lancaironline.net
>=20
>=20
> Jeff,
> Something sounds amiss with your batteries.  Longer cables will indeed inc=
ur a voltage drop under load, but I assume the voltages you listed were open=
 circuit or lightly loaded.  You mentioned the difference is larger after si=
tting longer.  Is there perhaps a low current drain on one battery?
> A 6 ft section of 4 gauge wire will see a voltage drop of 1.3 V when carry=
ing about 900 A.
> Any open circuit voltage south of 12.5 V is worth investigating.
>=20
> Chris Zavatson
> N91CZ
> 360std
> http://www.n91cz.net/
>=20
> --
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