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Reply-To: "David Carter" <dcarter@datarecall.net>
From: "David Carter" <dcarter@datarecall.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-741737@logan.com>
Subject: Re: [FlyRotary] Re: Battery voltage (was: Racetech RV6A Forced  Landing)
Date: Wed, 16 Feb 2005 13:29:44 -0600
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I just installed an SVR-20 (18ah) AGM motorcycle battery in my 1993 Ford
Escort, with brass posts (provided free by mail by manufacturer, Westco
Battery, www.svrbatteries.com, 1-800-372-9253).  This is the "next bigger"
brother of a tiny but robust battery, SVR-14, pointed out by the electric
drag racer Bill Dube <bdube@boulder.nist.gov .  I found a local motorcycle
shop, chocked at his $92 retail price, asked him, "Is that the best you can
do?  Other small batteries cost about $60."  He looked up "his cost" of
$54.50, added 10% and applicable taxes and fees and sold it to me for $67.
I went in intending to buy the smaller SVR-14 14ah battery but ABSOLUTELY
"CHOKED" AT THE SMALL SIZE AND BOUGHT THE NEXT SIZE LARGER.)  In hind sight,
I'd have probably done as well with the smaller battery.  I get about 3
minutes more capacity out of the slightly larger battery.

Anyway, before pulling my standard flooded cell battery, I disconnected
ignition and fuel injection pump and had the wife crank the engine on her
'95 Escort while I observed battery voltage - dropped from 12.6v to 11.0
(stabilized).  We did same thing on my '93 Escort (which had my VW Bus's
larger battery installed) & it dropped from 12.9v down to 11.5v - not as low
probably because of being a bigger capacity battery.

Then installed the tiny 18ah battery and cranked with ign & fuel pump
killed:  Went from 12.5v (been sitting a month since I bought it) down to
11.0, same as the '95 Escort with std sized battery.

So, that's my contribution to "battery voltage when cranking" issue.

David


----- Original Message ----- 
From: "Wendell Voto" <jwvoto@itlnet.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Wednesday, February 16, 2005 12:36 PM
Subject: [FlyRotary] Re: Battery voltage (was: Racetech RV6A Forced Landing)


> At 05:11 PM 2/16/2005 +1000, you wrote:
> >Bill,
> >What would you expect the battery to show under starting load.
> >George ( down under)
>
>          The Hawker Odyssey PC 680 that most folks use has an internal
> resistance of 0.007 Ohms. A typical starter draws perhaps 200 amps in cold
> weather. This means that the battery voltage will drop 200 x 0.007 = 1.4
> volt initially. If the battery is fully charged,the voltage will be
> about  12.8 - 1.4 =  11.4 volts for the first few of blades. As you
> continue to crank, the voltage will continue to decline. If you continue
to
> draw 200 amps for 60 seconds (at 77 degrees F) the battery voltage will
sag
> down to 7.2 volts.
>
>          If you do crank for this long, it might take as long as ten
> minutes for the battery to charge back up to 13 volts. (Of course this
> depends on the size of your alternator and the draw from other loads on
the
> system.)
>
>          There are nifty charts and graphs at:
>
> http://www.batterymart.com/pdf_files/odyssey_guide.pdf
>
> Went to this site and is good, however no weights are given. One curious
thing, the 625 seems to outperform the 680 in CCA, CA, HCA, and reserve but
not in PHCA. Looks to me if you don't need to few extra cranking amps, the
625 would be the battery of choice (it should be lighter?)
Wendell
>
>
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