Ahem..
To keep things as simple as possible, let's make some assumptions:
1. We need zero volts to run the starter. This means we can use all the
voltage available for heating up the battery.
2. It takes 120 amps to crank the starter. This is a figure I picked for
convenience.
So, if we pull 120 amps out of the battery, and that results in zero volts
at the terminals, then all the voltage is being dropped through the internal
resistance of the battery. This means that under these conditions the
internal resistance is 0.1 ohms, since 120 amps x 0.1 ohms = 12 volts, by
Ohm's law.
Then we're going to run the lights for a few (?) minutes. Figure on 120
watts total for 10 amps. So now the heat dissipated in the battery is 10 x
10 x 0.1 = 10 watts. The equivalent of three instrument panel lights.
Better get a battery blanket.
Theo
> -----Original Message-----
> From: Chris Thompson [SMTP:cthompson@rrinc.com]
> Sent: Monday, January 17, 2000 1:27 PM
> To: 'Steve Laifman'; BRENNAN,STUART (A-Andover,ex1)
> Cc: Tigers (E-mail)
> Subject: RE: Cold Start Myths
>
> Robert Palmer must be off today. I fully expect we'll get a dissertation
> on this, but I recall doing the calculations in Physics 101 twenty some
> years ago showing that the heat generated by turning on the lights prior
> to starting (and then turning them off when starting) had net positive
> effect.
>
> Since this was Physics 101, I'm sure there were numerous simplifying
> assumptions. But the Professor swore that it worked.....
>
> Chris Thompson
> Executive Vice President
> Recognition Research, Inc.
> 1750 Kraft Dr. Suite 2000
> Blacksburg, VA 24060
> 540.961.6500
> 540.961.3568/fax
> cthompson@rrinc.com
> www.rrinc.com
> B382000331
>
> -----Original Message-----
> From: Steve Laifman [SMTP:Laifman@Flash.Net]
> Sent: Monday, January 17, 2000 7:16 AM
> To: BRENNAN,STUART (A-Andover,ex1)
> Cc: Tigers (E-mail)
> Subject: Re: Cold Start Myths
>
> Stu,
>
> With all due regard to the knowledgeability of Theo Smit and Steve Murphy,
> for
> whom I have the utmost respect. And, since I'm freezing here at 75 F
> today, let
> me share some of my experience.
>
> I did live in Illinois for 6 miserable years. Just across the Lake/Cook
> county
> line on the Lake, where 2 weeks of below 0 weather (F, not C), and
> mosquito/muggy
> summers left me 1 month of nice weather, I scurried back to California,
> where I
> was born. Now don't get me wrong, Illinois, other than the weather, was a
> marvelous place to live. The people were just great, the schools good,
> the
> Italian food fantastic (bought forget Mexican food).
>
> So, back to the cold - really cold. Luckily my car was in a semi-heated
> garage.
> But, I've had to park at the airport with below 0 for days. Getting
> started was
> no joke in the middle of a parking lot. They did have a truck that came
> by with
> jumpers, though.
>
> Many people owned a 'battery heater' from Warshawsky's (J.C. Whitney, to
> the white
> bread people), as well as a 'block , or sump heater', which could plug in
> if you
> were at home. So the battery, and engine were relatively warm.
>
> The concept that cold electrolyte decreases power is accurate. So the
> question
> is, "does a 20 amp drain heat the battery electrolyte sufficiently to make
> up for
> the power it has drawn". Of course, you wouldn't start the car with the
> lights
> on, but 20 amps times 12 volts is 240 watts into the lights. I've got to
> believe
> that figuring the resistance of the battery into that equation would show
> a heat
> dissipation in the battery. The only issue would be 'is it sufficient to
> overcome
> the drain and make a difference?'.
>
> I'll leave the calculations to the electronickers and thermo-dynamicists,
> but it's
> in the correct direction, and not totally ridiculous, like those Passive
> Radar
> Jammers.
>
> Steve
>
> --
> Steve Laifman < Find out what is most >
> B9472289 < important in your life >
> < and don't let it get away!>
>
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