(ET) Solar power for an Elec-Trak.

["Christopher Zach" <czach computer org>]

Lee writes:

> BTW, charge current from the charger peaks well beyond the 7 A you are
quoting.  The batteries are 205 to 225
> Amp Hours, so even if you only use 25% of the capacity, you are going to
be charging long hours.

Oh yeah, absolutely. If the charger can do the whole tractor in 5 hours,
that's 200a/h divided by 5=40a/h. 40*36=1,440 watts/hr which sounds in the
ballpark for the quoted charge times.

(Note: For the rest, I am assuming my panels will put out an average of
7amp/hrs. Technically they are rated to put out 10 in full sun; 7 is what I
will get in this miserable winter weather, so we'll say 7 and be happily
surprised...)

So I charge with the sun, and the sun is there for 4 hours a day so...

7*4=28amp/hrs per day.

So to charge the whole tractor from flat dead batteries (200amps, let's
leave *something* in there), it would take

200/28=7.1 days

Or a week. Maybe 8 days since the sun god sometimes hides behind a
raincloud. Now if I mow my one acre a week and use 1/2 the batteries (say I
burn 100amps to do the job) we have:

100/28=3.5 days

Or on the average 4-5 days. Since I mow my lawn once a week at most, the
solar panels have enough juice to charge the battery core with power to
spare.

That's the neat part about solar panels: They are always producing power
when they get sunlight. It's a simple matter of pressure vs. time. You can
do a lot with solar if you're willing to wait the time. I've been draining
the shed batteries with everything from the lights, to the floodlights, to
the big power drills and saws. As long as I don't run everything for a 
hours
on end, the solar panels can restore the batteries while I am at work over
the week. Same for the tractor.

The only thing you have to watch for is to make sure you can charge your
core battery pile above say 50% in about a week. If you can't, you run the
risk of sulfating your batteries, or of having discharged batteries freeze.
Thus you wouldn't want to flat charge a Elec-Trak with three 20 watt panels
(which can put out about an amp total, meaning it will take 200hrs or 50
days to recharge. By then the plates will be toast). But three 120 watt
panels can do the job (and get the tractor above 20% in a day, thus keeping
the batteries from freezing down to 10 degrees). In the winter, I will
probably set a min limit of 25% on the batteries; any lower and I will
manually charge them via 110 volts.

And to be quite honest, if this works I will probably go out and get 
another
3 panels. But only if I need it. Because I have found that most of the 
time,
the two panels I have up there now don't do anything (the shed batteries 
are
fully charged) And they are only a total of 80amp/hrs at 24 volts. So I 
have
room to spare for the moment. Thus the tractor (in the grand scheme of
things, it's really going to be a diversion load) Besides, at that point I
will (of course) have to build another shed to hold the extra panels....

And hold the tractor...

Chris