Without double-checking any of your specific calculations, I have one
(recently-educated-via-automotive-class) comment:

Do not use a deep-cycle battery as your starter battery - use one starting
battery and one deep discharge battery (aka "cycling" battery) and a battery
isolator.

"The brief high-current flow required of a starting battery is produced by
using relatively thin plates, compared to those used in a cycling battery.
The thicker plates of the cycling battery will provide a constant current
drain for several hours.  Using a starting battery in an application calling
for a cycling battery will shorten its life considerably.  The use of a
cycling battery to start and operate a car will cause excessive internal
heat from the brief but high current draw, resulting in a shorter service
life."  [Automotive Electrical & Electronic Systems, Check-Chart 2000]

Plus, you will not get the same amperage output from a deep discharge as a
standard battery, which is important in cold temps and as the battery ages.
(4cyl engines tend to draw between 120A and 175A when starting.)

David Jaffe
Portland, OR

-----Original Message-----
From: Larry Chase [mailto:lchase@attglobal.net]
Sent: Tuesday, November 19, 2002 10:49 AM
To: vanagon@yahoogroups.com; wetwesties@yahoogroups.;
vanagon@gerry.vanagon.com; Syncro@yahoogroups.com;
ev_update@yahoogroups.com
Subject: [WetWesties] Electrical Consumption & Battery Recharge
Calculations

Electrical Consumption &  Battery Recharge Calculations.

Based on all the input I got from List Members and helpful
Product reps at Optima, Crutchfield, Arizona Solar and Uni-Solar ....

This is an overly simplistic, but I hope useful summary.

Please challenge and suggest areas where my calculations may be off.

My Usage Assumption One:

Power Consumption ... (running off batteries only)

Per night =  20 amp hours * 12V = 240 watts per night total

Details,

18 LED Strip Light = .180 amps per hr * 3 hrs = .72 amps
18 LED Reading Light = .180 amps per hr * 3 hrs = .72 amps
LCD TV = 3amps per hr * 4 hrs = 12amps
Sat Receiver = 1amp per hr * 4 hrs = 4 amps
Misc Ghost Usage = .500 amp per hr * 4 hrs = 2 amps

Total per night = 19.44 amps or 233.28 watts

Recharging:

Solar Panels ... Two Uni-Solar 32 Watt  Flexible Panels @
64 watts * 4 hrs per day = 256 watts

http://www.solar-electric.com/usf-32.html

Solar Charge Regulator & Controller: ....to be determined

Battery:

OPTIMA D750 Yellow Top Deep Cycle Battery = 2 (one is the starter
battery)

Reserve Capacity - Minutes: 124
Capacity (C/2 rate) - Amp Hours: 52
Capacity (C20 rate) - Amp Hours: 65

Total Amp Hours with 2 batteries = 104
Needed Amp Hours = 20
Extra Capacity = 84

Battery Charger: (to be used when 110V is available)

Deltran Battery Tender Charger designed for Optima Batteries

110 VAC Optima/Hawker / 12V 6amp

http://www.batterystuff.com/battery/deltran/onboard_charger.htm

Notes:

1. Second Optima is starter Battery ... also backed up by a Jump Starter
PowerPac

http://www.batterytender.com/catalog/product_info.php?products_id=36

3. Largest Uni-Solar Flexible Panels available are 32 watts output.

4. Usage estimates are based on my own needs calculations on actual
products I plan to use.

My Usage Assumption Two:

Running the Vehicle Stereo instead of the LCD TV & Sat Receiver
 (not included in the above assumptions).

Average Power Consumptions for a Vehicle Stereo System (actual system
not purchased yet)

CD/Receiver = 6-10 amps per hr
Satellite Radio Receiver = .500 amp  per hr
Amplifier = 10-20 amps  per hr

The mean average is approx 23 amps per hr.

The nightly usage would be  23amps - 4 amps (LCD TV & Sat Rec)) = 19
amps per hr additional

The extra battery capacity of 84 Amp Hrs would enable the stereo to be
played for approx 3.65 hrs.

But the problem is recharging the batteries.

You would need to recharge 104 amp hrs / 1240 watts instead of 20 amp
hrs / 240 watts

The current Solar assumptions will get you 20 amp hr / 240 watts,
leaving a delta of 84 amps / 1000 watts

If I assume a 75% efficiency on the VW 90 amp alternator then I would
need to run the engine approx 1 1/4 hrs to supplement the Solar.

Disclaimer .... none of this assumes three staging Charge rates/times
required by Deep cell batteries. But have built in a large "Fudge
Factor" in excess of 15% to compensate for this.

In conclusion.

Solar will recharge "Usage Assumption One UNASSISTED.

Solar plus 1 1/4 hrs of the VW Alternator will recharge "Usage
Assumption Two".

The actual system will also be supplemented by a small 1000kw Honda Gas
Generator.

But that's a whole other discussion.

Comments Requested

Hitting the Trail Soon,

Larry Chase

Email: lchase@attglobal.net
Web: www.roadhaus.com - Under Construction
What: The Great North American Road Trip
When:  01.02.03
How: RoadHaus - 1990 2.2 L  VW Westfalia Syncro
Today: Mesa, AZ - 12V Stuff
From: Mesa,  AZ