On Feb 9, 8:33 am, Jeff wrote:
Geoff Schultz wrote:
Jeff wrote in
:

Geoff Schultz wrote:
Get a controller that diverts voltage above the maximum charging
voltage of the battery to a resistive load. In my case this is the
water heater with 12V and 120V heater elements. 100% of the power of
the solar panels will go to charging the panels up to that point.
You can't produce more power than the panels are generating.

I personally use a Morning Star TriStar controller to control both my
wind generator and solar panels and it works great.

-- Geoff
So, are you saying that if the panels are putting out 17 volts and the
battery is only taking 14, then 3 volts are applied to the heater? I
don't think that's the way it works.

That's exactly what I'm saying. It's called Diversion Mode and on the
controller you set the maximum voltage which is allowed to be applied to
the batteries. Anything above that is diverted to the load.

The only time that this occurs is when the batteries are fully charged.
The vast majority of the time the charging load of the batteries drops the
output of the solar cells to a voltage less than the maximum allowable
voltage and thus nothing is diverted.

For details please see the manual:
http://www.mrsolar.com/pdf/morningstar/TS_Manual.pdf

Yes, this is how the tristar works. And for some people, it works
fine. However, for those of us whose power usage far exceeds the
charging ability, the diversion mode would rarely be turned on. In my
case, it would only happen if I had just run the engine, and at that
time the water tank is fully heated.

The diversion mode is suited to boats with excess generating
capability, such as trade wind passagemakers with wind or hydro
generation.

For systems where the solar panels will fall behind the load, the new
MPPT (Maximum Power Point Tracking) systems will generate more power
at the battery. Many panels will put out up to 17 Volts, and their
Wattage will be rated at this level. A normal regulator will reduce
this to an appropriate charging Voltage, perhaps 13.5 Volts if the
battery is discharged. However, the current is not increased so the
net Wattage will be reduced.

A MPPT controller is a DC-DC converter that will drop the Voltage down
without reducing the Wattage. An 85 Watt panel that can put out 5
Amps at 17V will put out 6.3 Amps at 13.5 and stay up at 85 Watts. A
normal controller would only allow 67 Watts.

Thus, the controller is not "creating more power than the panel
outputs," its adjusting the Voltage so that 30% of the power isn't
thrown away. As I've said, I've watched the current go from 8 to 10
Amps when the MPPT is turned on.- Hide quoted text -

- Show quoted text -

Yes, i agree. I want to add my support again for this explination and
any negative comments (except maybe those negative comments against
practical sailor's reliability) that followed my post early in this
thread are unjustified. Let's face it, the affordable controllers that
have historically been available are simple an did little more than
keep the voltage at 12.6 volts, and if the voltage of the batteries
exceed the voltage of the panels, the controller will prevent the
batteries from draining. In this arrangement, the panels were setup
with enough cells to insure that 12.6 volts would be reached in
overcast days (or they would be useless), which means on sunny days
you end up with 18 even 19v. New controllers can match the panels to
the batteries better ... and without any snake oil, you get more bang
out of your solar cells.

In regards to practical sailor, they have demonstrated their
independence and willingness to tell it like it is, perhaps that is a
better description than reliable. If they measure a 25% increased
output in AMPS with the new technology controllers, I can take that to
the bank. However I will concede there are problems with some
articles. When it comes to bottom paints, I realize as I read the
articles the limits to their testing. To be really scientific and
valid the tests would be repeated on a second set of samples by a
different organization or employees, but it's amazing what they do for
limited $. The article on winches was just way off the mark. Also
they recently had an article on 2006 editions of two books in regards
to 12V boat systems, that was extremely poor, one of the books in fact
does not have such an edition. I could not get a response back from
them when I pointed it out. Perhaps the loss of their star editor has
a big influence, I don't think he would have let that article on
Winches fly. But .. it is real refreshing to read their articles,
especially boat reviews. I am getting tired of reading boat reviews in
sail magazine that are absolutly meaningless, and really hate to read
words such as "we only had light winds today, but judging from this
boats design it will be a real performer" ... do meaningful
journalism, go out and sail the boat again on a windy day would
you ? In that light, Practical Sailor looks reliable to me, just not
scientifically so.