Date: Sun, 25 Jun 2006 21:13:35 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Making an alternator a smarter charger? [LVC]
In-Reply-To: <449F0D66.1090505@gmail.com>
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At 03:25 PM 6/25/2006 -0700, Mike Elliott wrote:
>Dennis, I hadn't considered the effect of 14 - 14.8 absorption voltage
>on the headlights and other driving devices in the Vanagon. That's a
>darn good point. If a fellow had a second alternator for charging the
>deep-cycle house battery, then a smart regulator like this might make
>more sense. But with a single alternator and knowing that the lifetime
>of an incandescent bulb is proportional to the 12th power of the voltage
>overage or underage, I'll think I'll take a pass on this device.
That's why the device has an input to command it to limit the output
voltage so as to protect lamps etc. You're supposed to use it when
indicated...
>Your point about spending that money on a second battery is a good one,
>but when I'm climbing a 7% grade for several hours in 90F weather in a
>1.9L WBX, every pound I carry adds to the engine load. This may be my
>years of lightweight backpacking talking, but Group 31 and T-105
>batteries weigh 65lbs . . .
Mike, starting batteries are simply not designed to supply deep
discharges ever; they expect to run at some state of high charge for
their entire life. They are designed for supplying huge current very
briefly, and they're good at that. 300 amps for one or two seconds
to crank an engine is a breeze, and a 650 CCA battery is rated to
deliver 650 amps for 30 seconds at zero Fahrenheit without falling
below ?8 volts?. In amp-hour terms that's a whopping 5.4 amp-hours
for the tongue-hanging-out cold-start rating; 300A x 2 seconds is 83
milliamp-hours. You could start your car ten times with a set of
alkaline AA batteries if they could only deliver the current! Ask
starting batteries to function as deep-cycle charge reservoirs and
they will rapidly fail.
You can't have your cake and eat it too. If you want ultimate energy
density, you will hunt far and wide to find denser storage than
diesel oil, and gasoline is not far behind. Over ten kilowatt-hours
per kilogram. If you want quiet, you're still ahead of the curve for
fuel cells so you have to look at batteries which have truly lousy
energy density compared to liquid fuels. The navy once went into the
jewelry business (so to say) because batteries made of silver offered
noticeably higher energy density than ones of lead. They found it
too rich for their blood, I believe. Lithium-sulfur (?) at 400F (?)
is supposed to be very promising, but probably the size you want is
below the knee in the curve. The cellar in the phone company
switching office is filled with ?Edison cells? ?Leclanche? Ai, they
all run together...oh well...anyway, they work extremely well for the
telco but you'd find them heavy and finicky I suspect. So for the
common man we have crummy old lead-acid at 0.025 kwh/kg, and your
Total Cost of Ownership will go way up if you use current-delivery
devices (i.e. starting batteries) in an energy-delivery
application. **TANSTAAFL**. If you've got the bucks, lithium
batteries are an exciting possibility -- I see a number of 0.350
kwh/kg though I'm not sure if that's the room-temperature
variety. But remember they explode if you charge them improperly so
don't mess about. There Is No Such Thing As A Free Lunch -- you
can't win, you can't break even, and you can't get out of the
game. And there will Never Be a good five-cent cigar no matter how
much this country needs one...
Rgds,
d
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage," '85 GL "Poor Relation"
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