"Larry" wrote in message
...
Ian Malcolm wrote in
:

Assuming the panels can be modelled as an ideal voltage source

Geez. If boat technology gets any better, we'll be able to run a light
bulb off the panel, shining on the panel, and the panel will have so much
power boost there'll be a surplus to charge the batteries!



Larry

Here is something I posted to the "Cruiser's Forum", about MPPT charge
controllers. They are real, and in many cases will increase the charging
current into your batteries. No black magic is needed, but I suppose that
some designs will be better than others. What follows is mostly
theoretical:
-------------
MPPT stands for "Maximum Power-Point Transfer", and it is equivalent to two
switching regulators in series. It operates the solar panel at the load
where the panel delivers it's maximum output power, then converts whatever
Voltage this may be to a Voltage appropriate for the battery (depending on
the battery's charge-state).

This is in contrast to the series-pass, Pulse-Width-Modulation (PWM), or
shunt regulators. In these, the panel output is essentially connected
directly to the battery during the charge-acceptance portion of the charge
cycle, and the panel output is reduced once the battery approaches
full-charge.

An example from my boat: I have three BP 110W panels, wired in parallel.
Each panel has an open-circuit (no-load) output Voltage of 21.7V (ratings at
full noonday sun conditions, with a cell temperature of 25deg C). Each panel
has a short-circuit current of 6.9A. The panel has a maximum output power of
110W, at 17.5V and 6.3A. At any other output Voltage the panel will deliver
less than max power. When I am charging a low battery at (say) 12V, using a
non-MPPT controller (or directly hooking the panel to the battery), the
panel is not operating at maximum power. Looking at the output curve for the
panel, at 12V the panel will be delivering about 6.8A, which is 81.6 W. (I
am reading these Volt/Amp numbers from a chart in the panel specifications.)

With a MPPT controller, the panel would be operated at 17.5V, and be putting
out 110W. Switching the 17.5V down to 12V (assuming 95% efficiency, a number
I pulled out of the air) would give me 8.7 A into my 12V battery. This is a
28% increase in charging current.

Of course, the battery won't stay at 12V for long. As the battery Voltage
rises, the current-boost will be less. At 13.5V, a directly-connected panel
would deliver 6.75A (91W). With an MPPT controller the charge current (at
95% efficiency) would be 7.74A -- still one amp better.

Once the battery reaches full charge and the controller goes into
trickle-mode, an MPPT controller will have no advantage.

These numbers will be different in practice, as the panels won't see
constant full sun, and the panel temperature will usually be hotter. Still,
the MPPT controller ought to give some charging improvement. MPPT
controllers don't use fixed settings, but are constantly dithering the panel
load, monitoring the panel Voltage, and looking for the point of maximum
power.

These days, many panels are wired for 24V (instead of 12V) output, and the
MPPT controller can efficiently convert the output of these panels for use
in charging a 12V battery.

I still have the old-style controller for my panels, but I will probably be
installing MPPT before too long. I may end up putting a seperate controller
on each panel (instead of one controller driven by the three panels in
parallel), because my panels are often partially shaded, and I think I will
get more output if each panel can be independently optimized. I need to do
some testing or modelling to be sure of this. I can't easily add more
panels, so I need to make maximum use of the ones I have.
-------------
Hope this helps.
-Paul

After reading what I wrote below, I decided that it needed a small
correction/comment. It's down at the bottom. -Paul

"Paul" wrote in message
...

"Larry" wrote in message
...
Ian Malcolm wrote in
:

Assuming the panels can be modelled as an ideal voltage source

Geez. If boat technology gets any better, we'll be able to run a light
bulb off the panel, shining on the panel, and the panel will have so much
power boost there'll be a surplus to charge the batteries!



Larry

Here is something I posted to the "Cruiser's Forum", about MPPT charge
controllers. They are real, and in many cases will increase the charging
current into your batteries. No black magic is needed, but I suppose that
some designs will be better than others. What follows is mostly
theoretical:
-------------
MPPT stands for "Maximum Power-Point Transfer", and it is equivalent to
two switching regulators in series. It operates the solar panel at the
load where the panel delivers it's maximum output power, then converts
whatever Voltage this may be to a Voltage appropriate for the battery
(depending on the battery's charge-state).

This is in contrast to the series-pass, Pulse-Width-Modulation (PWM), or
shunt regulators. In these, the panel output is essentially connected
directly to the battery during the charge-acceptance portion of the charge
cycle, and the panel output is reduced once the battery approaches
full-charge.

An example from my boat: I have three BP 110W panels, wired in parallel.
Each panel has an open-circuit (no-load) output Voltage of 21.7V (ratings
at full noonday sun conditions, with a cell temperature of 25deg C). Each
panel has a short-circuit current of 6.9A. The panel has a maximum output
power of 110W, at 17.5V and 6.3A. At any other output Voltage the panel
will deliver less than max power. When I am charging a low battery at
(say) 12V, using a non-MPPT controller (or directly hooking the panel to
the battery), the panel is not operating at maximum power. Looking at the
output curve for the panel, at 12V the panel will be delivering about
6.8A, which is 81.6 W. (I am reading these Volt/Amp numbers from a chart
in the panel specifications.)

With a MPPT controller, the panel would be operated at 17.5V, and be
putting out 110W. Switching the 17.5V down to 12V (assuming 95%
efficiency, a number I pulled out of the air) would give me 8.7 A into my
12V battery. This is a 28% increase in charging current.

Of course, the battery won't stay at 12V for long. As the battery Voltage
rises, the current-boost will be less. At 13.5V, a directly-connected
panel would deliver 6.75A (91W). With an MPPT controller the charge
current (at 95% efficiency) would be 7.74A -- still one amp better.

Once the battery reaches full charge and the controller goes into
trickle-mode, an MPPT controller will have no advantage.

These numbers will be different in practice, as the panels won't see
constant full sun, and the panel temperature will usually be hotter.
Still, the MPPT controller ought to give some charging improvement. MPPT
controllers don't use fixed settings, but are constantly dithering the
panel load, monitoring the panel Voltage, and looking for the point of
maximum power.

These days, many panels are wired for 24V (instead of 12V) output, and the
MPPT controller can efficiently convert the output of these panels for use
in charging a 12V battery.

I still have the old-style controller for my panels, but I will probably
be installing MPPT before too long. I may end up putting a seperate
controller on each panel (instead of one controller driven by the three
panels in parallel), because my panels are often partially shaded, and I
think I will get more output if each panel can be independently optimized.
I need to do some testing or modelling to be sure of this. I can't easily
add more panels, so I need to make maximum use of the ones I have.
-------------
Hope this helps.
-Paul


Comment: I wrote "equivalent to two switching regulators in series", but
this isn't really true, or even helpful. The MPPT controller is essentially
a single switcher, with a power-sensing control loop. The rest of what I
wrote should be OK. -Paul

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.

Larry wrote in
:

Geoff Schultz wrote in
:

You can't produce more power
than the panels are generating.


Ok, here's a little electricity for everyone....

Thank you Professor Larry for the edification. I always enjoy it when
this forum is used to exchange information instead of throwing barbs at
one another.

I am of the personal opinion that boats should have a combination of
solar and wind. I believe that a wind generator gives you a much bigger
bang for the buck, but there are days when the wind doesn't blow and
likewise when it isn't sunny.

You need to regulate both sources. I spend about 6-7 months a year
cruising (at anchor) and rarely have seen the regulator regulate as my
power demands almost always exceed my wind/solar generation capacity.
Any time that I do see the batteries getting topped off, I can always
make more water. If you spend lots of time at a dock connected to a
power cord and your batteries fully charged, then yes, you do need
regulation. (I actually pull the fuse for the solar panels and feather
the generator at dock.)

Solar panels don't care if there's no load attached to them, but wind
generators need a load to keep them from free-wheeling. As a result you
need a controller which can be used in diversion mode with a resistive
load. Due to space and $ constraints, I don't want to have multiple
controllers. I would rather put the cost of another controller towards
more generation capacity.


-- Geoff

On Fri, 09 Feb 2007 07:58:23 -0600, Geoff Schultz
wrote:

Larry wrote in
:

Geoff Schultz wrote in
:

You can't produce more power
than the panels are generating.


Ok, here's a little electricity for everyone....

Thank you Professor Larry for the edification. I always enjoy it when
this forum is used to exchange information instead of throwing barbs at
one another.

Unfortunately the information is wrong.

On Fri, 09 Feb 2007 07:58:23 -0600, Geoff Schultz
wrote:

I am of the personal opinion that boats should have a combination of
solar and wind.

==================

So I guess you would disapprove of my 15 and 20kw generators?

:-)

We have to keep those computers and WiFi bridges going somehow, not to
mention the ice maker, freezer full of Hagen Daz ice cream and steak,
4 zones of A/C, etc.

Geoff Schultz wrote:
You can't produce more power
than the panels are generating.

Larry wrote:
Ok, here's a little electricity for everyone....

Geoff Schultz wrote:
Thank you Professor Larry for the edification. I always enjoy it when
this forum is used to exchange information instead of throwing barbs at
one another.

Goofball_star_dot_etal wrote:
Unfortunately the information is wrong.

Well without any references or explanation and as an anonymous poster,
your word isnt worth anything near as much as if it was printed out on
used toilet paper . .

If I didnt have concerns about RFI, I am capable of designing and
building my own MPPT solar panel controller. It isn't rocket science,
any competent EE tech or HAM operator (e.g. Larry) could knock one up in
a weekend or two, its just that it would take too much time so unless I
cant find something to do that brings in more beer tokens, its easier to
just buy one. Also it gives you someone *else* to yell at if it b***ers
up your reception on VHF channel 16.


For anyone else considering designing a MPPT controller (or just curious),
http://www.intusoft.com/nlhtm/nl78.htm
is good reading and even has Spice models for various types of solar
panel.

To summerise, they conclude that peak power is delivered at 83% of the
open circuit voltage (rather different from my estimate of 50% as I
initially was using an model that was an extremely bad approximation to
a solar cell. I should have googled :-( ), which varies with temperature
and illumination, and that a 10% gain in efficiency is achievable.

This means, if the controller is under 10% of the panel cost, buy it,
its a no-brainer, otherwise get a bigger panel (gross
over-simplification ignoring cost of a liniar regulator, assuming you
CAN fit a bigger panel (or more), you need more power and assuming
price/performance for the panel is a streight line.)

--
Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
[at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL:
'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed,
All varnished hot moulded wooden racing dinghy.

On Fri, 09 Feb 2007 17:45:41 +0000, Ian Malcolm
wrote:

Geoff Schultz wrote:
You can't produce more power
than the panels are generating.

Larry wrote:
Ok, here's a little electricity for everyone....

Geoff Schultz wrote:
Thank you Professor Larry for the edification. I always enjoy it when
this forum is used to exchange information instead of throwing barbs at
one another.

Goofball_star_dot_etal wrote:
Unfortunately the information is wrong.

Well without any references or explanation and as an anonymous poster,
your word isnt worth anything near as much as if it was printed out on
used toilet paper . .


You mean you would like me to post references to the equivalent
circuit AGAIN?

http://groups.google.co.uk/group/rec...13bf8612?hl=en

If people did some homework instead of making wrong assumptions before
posting them as fact, there would be less BS.


Here is a new link for you:
http://patft.uspto.gov/netacgi/nph-P...391&RS=6111391
or http://tinyurl.com/yobfz3


If I didnt have concerns about RFI, I am capable of designing and
building my own MPPT solar panel controller. It isn't rocket science,
any competent EE tech or HAM operator (e.g. Larry) could knock one up in
a weekend or two, its just that it would take too much time so unless I
cant find something to do that brings in more beer tokens, its easier to
just buy one. Also it gives you someone *else* to yell at if it b***ers
up your reception on VHF channel 16.


For anyone else considering designing a MPPT controller (or just curious),
http://www.intusoft.com/nlhtm/nl78.htm
is good reading and even has Spice models for various types of solar
panel.

To summerise, they conclude that peak power is delivered at 83% of the
open circuit voltage (rather different from my estimate of 50% as I
initially was using an model that was an extremely bad approximation to
a solar cell. I should have googled :-( ), which varies with temperature
and illumination, and that a 10% gain in efficiency is achievable.

This means, if the controller is under 10% of the panel cost, buy it,
its a no-brainer, otherwise get a bigger panel (gross
over-simplification ignoring cost of a liniar regulator, assuming you
CAN fit a bigger panel (or more), you need more power and assuming
price/performance for the panel is a streight line.)

Me too! No wimpy wind generator for me. The big screen TV with surround
sound needs more than that can put out...g, not to mention the AC and
other neat stuff that needs MORE POWER!!

"Wayne.B" wrote in message
...
On Fri, 09 Feb 2007 07:58:23 -0600, Geoff Schultz
wrote:

I am of the personal opinion that boats should have a combination of
solar and wind.

==================

So I guess you would disapprove of my 15 and 20kw generators?

:-)

We have to keep those computers and WiFi bridges going somehow, not to
mention the ice maker, freezer full of Hagen Daz ice cream and steak,
4 zones of A/C, etc.

On Fri, 09 Feb 2007 00:19:38 -0500, Larry wrote:

By the way, this is the exact same reason we strive to make a radio with
an output impedance of 52 ohms connected to coaxial cable with an
impedance of 52 ohms

We do for transmission lines, antennas etc., we don't for TX output
tank circuits, I think..
http://www.jaycar.com.au/images_uploaded/impmatch.pdf


connected at the top of the mast to a 52 ohm
antenna....because it creates maximum power transfer from the transmitter
to the antenna. (The radio is actually designed to match certain types
of antenna's natural impedances, not the other way around.) It even
works the other way on receive....so we use a 52 ohm input receiver, too.