me too, whatever he said.  yeah, I would have said that too but he lives in
the east and got up earlier.  whatever it was he said.

m

> From: David Beierl <dbeierl@ATTGLOBAL.NET>
> Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
> Date: Fri, 14 Dec 2001 03:32:06 -0500
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: 2nd battery relays & the Hella in particular
>
> At 01:27 AM 12/14/2001, Frank Grunthaner wrote:
>> In a message dated 12/13/01 12:47:48 PM, dbeierl@ATTGLOBAL.NET writes:
>>
>> << but your finding that #10 wire requires a 20-amp
>> fuse is consistent with the theory.
>>>>
>>
>> David,
>>
>> I most strenuously object to your misuse of the word "theory" here. The
>> restivity variation of wire by diameter was well established experimentally
>> long before the birth of the parents of the listees. The theory of the
>> variation of restivity with cross-section of the metal was postulated,
>> promulgated and verified so long ago that the original archival journal paper
>> is probably in need of chemical restoration (certainly well known in
>> Maxwell's time).
>
> <snerk>  I agree "theory" is a bad choice.  I was talking about the
> allegation by the mysterious expert B. C. (who as we know works in a highly
> technical position for Exide and is in a position to know this sort of
> thing) that a 12-ga connection between the two batteries would result in a
> worst-case charging current of 15 amps to the second battery, and usually
> much less.  This would be under the assumed condition of a stock Bosch
> internal regulator, i.e.  max 14.1 volts at the B+ terminal.
>
> Now four feet of 12-ga wire (his assumption for gauge and mine for length;
> I don't know what's in the Hella kit) at 20C should have a resistance of
> 6.35 milliohms, or 6.35 millivolts per amp.  That means at fifteen amps we
> get a drop of just under a tenth of a volt across said wire.  Allowing an
> equal amount (wild guess) for incidental resistances gives two tenths volt
> difference between the starting and house batteries at a charging rate of
> 15 amps on the house battery.
>
> So the question devolves to: Given an empty house battery and a full
> starting battery, will the charging voltage of the house battery always be
> within 200 millivolts of the starting battery?  If not, then we're going to
> exceed that fifteen-amp charge rate.  Unfortunately for us all, our
> regulation point is at the wrong end of twelve or fifteen feet of
> various-gauge wire depending on model year (for the '84 that's a doubled
> 12-ga from alternator to the junction box, then 8-ga to the starter, then
> 2-ga to the battery), so how the (*#$#@(*^ is anyone supposed to know what
> the battery terminal voltage is going to be under different charging regimes?
>
> My conclusion:  The Vanagon charging system is a fex [sing. feces],
> cynically designed to minimum standards and based on the assumption that it
> doesn't actually matter how the bloody battery charges since it is always
> at "full" charge and never needs charging anyway; likewise it doesn't
> matter that "full" charge is nowhere near full and any battery installed in
> this miserable excuse for a system will permanently lose capacity, but
> nobody will notice since we're only ever drawing a couple of amp-hours out
> of it to start the beast and the rest of the time its major function is a
> filter capacitor.   All right, I'm exaggerating all over the place.  Rant
> off.  Fact is, it's good enough -- barely -- for starting, but utterly
> inadequate for charging a house battery that actually gets used; and a
> regulator sense lead to the battery B+ terminal would be a big improvement
> (short of putting in a smart regulator).  Running humongous copper from
> alternator to battery is a more expensive and less satisfactory way of
> approximating the same result, i.e. having the battery charge voltage be
> what the alternator thinks it is (but it has the desirable side effect of
> maximizing available starter current).
>
> So getting back to the question at hand... <g> -- under this Pleistocene
> (Plasticine?) system, full of first- and second-order side effects, what is
> the actual worst-case charge rate through a battery-coupling relay and
> attached wiring as supplied in the Hella kit?  And what is the "normal"
> rate?  Beats the heck out of me...I have a gut feeling that Mr. Cantrell is
> off by a factor of two or so, but a gut feeling is all it is.  Is it
> possible, for example, that a fifteen-amp *fuse* has more resistance than
> the whole rest of the circuit?  Ok, I checked -- automotive fuses run in
> the range of 50 - 125 millivolts at rated current, so it's a first-order
> effect.  I'd sure like to see some experimental data...
>
> cheers
> david
>
> David Beierl - Providence, RI
> http://pws.prserv.net/synergy/Vanagon/
> '84 Westy "Dutiful Passage"
> '85 GL "Poor Relation"
>