At 2:05 PM -0700 7/12/05, Doug in Calif wrote: >I realize that the batteries would have to be replenished after some use >How long would you have to run the alternator to replenish two deep cycles >in the battery compartments? >Say if you ran the engine for 15 minutes how many amp hours to you actually >get back?

That depends on the alternator, batteries and the state of charge.

As long as the battery is under 85% full, you can charge it very fast, especially if it's a AGM like the Optimas are.

Let's say you ran one of these Engel 45s as a fridge at 1 amp average draw for 24 hours. So you would be down 24 amp hours. Now you run your engine with a 95 Amp alternator on it. (What do the Vanagons have stock? My ABA has a 50/90 Amp unit, whatever that means, and the Tdi has a 120 Amp unit) So anyway: Say you run a 95A alternator, it takes about 5A to run the car, so you can get 90 Amps to the battery. You'll charge about 22.5 Amp hours in 15 minutes which almost makes up for a day of refrigeration.

On the other hand, if you have two dead 100 amp hour batteries (70 lbs each) then you can expect to sit there and charge for over two hours to replenish those 200 amp hours of charge.

Also be aware that the alternator does not give out full power at idle. I find I have to rev the engine to about 1500 RPM in order to get full output.

On my Van I run 150 Watts of solar panels on a roof rack. In the desert some months ago it was maybe in the 80's during the day and the panels just kept up with the freezer draw for a week with the panels flat on the roof. I probably had about 200 lbs of batteries on tap. (battery capacity can easily be estimated by the weight of the lead acid battery) If I had run low I could have tilted them towards the sun for more power.

-- -Otmar- http://www.CafeElectric.com Mailto:otlists@evcl.com