From: John De Armond
Subject: Re: Solar Kit
Date: Mon, 29 May 2000 22:27:45 EDT
Newsgroups: rec.outdoors.rv-travel

Bob Beckwith wrote:
> 
> Thanks for all the advice.  I have a TT and plan to use two GC 6 volt
> batteries for my power source.  If all the 45W solar unit will do for
> me is trickle charge these two batteries then maybe I would be better
> off not spending the 500.00.  Thanks again all.  As previously stated
> our camping lifestyle is to probably only dry camp for max 5 days and
> then be on the road.  If I drove for 5 or 6 hours would this in itself
> charge my batteries back up or would I have to plug in to a power
> source?  Maybe my best investment might be a small Honda or Coleman
> generator???

Bob,

You've received a bunch of (mostly BS) answers from the various
fanatics.  Now let me suggest how you can figure out what YOUR needs
are.  There is no substitute for accurate use data.  Once you figure
out how much power you use, then you can figure out what resources
you need.

One of the easiest and most accurate ways to determine your power
usage is to install a battery gauge of the sort that measures
current draw from the battery(s), runs the Perkut equation (to
account for the apparent loss of capacity in a battery due to
discharge rate.) and displays how many amp-hours you've used and how
much battery capacity remains.  I have a Cruising Equipment Co
E-meter but there are other brands.  Don't make the mistake of
getting one of several "gas gauges" that are nothing more than
voltmeters calibrated to read "capacity".  They don'.

The E-meter displays amps consumed or charged, amp-hours, percentage
of charge remaining and several other parameters.  Once you KNOW how
much power you use per day or trip or whatnot, THEN and only then
can you decide what sources of power you need.

Unless you travel in the desert, can take the heat and read by
candle light, solar isn't going to do much for you.  Example:  My
Maxxair turbo fan draws 10 amps at full power.  That's 120 watts at
12 volts.  A 45 watt solar panel would supply only about a third of
the power just that one appliance uses.  Another example:  My
vision's not so hot in low light isn't so hot so I use a 55 watt
light to read by in bed.  Again, this load swamps the solar cells. 
(yeah, I only read at night but the solar cell only generates in the
sunlight so it evens out.)

Just driving around will likely do all the charging you need if you
do it every so often and you have heavy wire running to the trailer
battery.  That is one way of charging from the alternator.  Another
way is to put an el-cheapo square wave inverter in the truck,
running 120 volt AC to the trailer through a light gauge wire and
feeding a battery charger in the trailer with it.  Yes, it's less
efficient than running a welding cable back to your trailer but it's
sure easier to manage.  We've done it that way for years with our
catering trailers.

If you don't drive enough to charge your batteries, then the
generator becomes the next option.  There are a couple of brands of
engine-driven battery chargers available that directly generate 12
volts to charge your batteries.  Probably the niftiest is the Subaru
minimite that I wrote about last week.  If you choose to go the
route of a 120 volt generator and battery charger, make sure the
battery charger and generator are compatible.  Some aren't because
of the high peak current drawn by battery chargers.  Only way to
know is to test.

The other option is to use a combo converter/charger.  The better
ones have input power factor correction to make them generator
friendly.  The good part of this setup is that you can fast-charge
the batteries either from the generator or shore power.

John