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'[ee]: solar site charging system'
2002\01\23@133703 by JB

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face
I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit
current. This panel is used to charge a 17Ah 12V sealed lead-acid battery that
can be floated at 15V for cyclic usage patterns, with a maximum charge rate of
around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using
internal battery resistance) this works fine in full sun, but anything short of
about 17V at the panel results in zero charging. I would like to utilize the
power available when the panel is at any point above the battery voltage so
that I am not wasting that energy.

A switching regulator with a wide input range, say 12-30V to 15V out would be
perfect, but I have yet to find one.

Should I drop the 317 and simply shunt the panel output at 15V with a Zener? I
don't care about anything over the 15V point, as I don't want to over-charge
the battery. This of course assumes I can find a 15V/50W zener to mount on the
panel.

Are there better alternatives? There is a 16F873 in the project with available
A/D and TTL ports, so that may be an option with the right components, but I'm
running out of experimentation time, so I'd rather not venture into something
that "might" work.

I can justify up to about $50 for the components.

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2002\01\23@142343 by Thomas C. Sefranek

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I often use a shunt regulator so as to extract the maximum charge
possible from the panel.
I run 450 watts of PV panels for Ham radio at home.
Use a PNP POWER transistor with a low power zener in the base as your
shunt..
BYPASS THE ZENER as it is a great RF source.

JB wrote:

{Quote hidden}

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2002\01\23@144357 by Harold M Hallikainen

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Try doing a search on "maximum power point" converters. These are pretty
common in the solar power industry. I did a PIC based one for a solar
powered electric car. There each solar panel had a switching boost
converter. The current out of each converter into the battery was
monitored. The duty cycle driving the FET in the up converter was varied
to maintain the highest output current into the battery. Use of separate
converter on each panel allowed for varying illumination of the different
panels (since the whole car was covered with them).

Harold


On Mon, 23 Jan 0102 18:34:33 +0000 JB <.....alphaoneKILLspamspam@spam@ROF.NET> writes:
{Quote hidden}

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2002\01\23@204928 by jb

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My MOSFET knowledge is pretty limited, not sure how to drive that with a PIC running at 5V. Wouldn't a PNP power transistor do essentially the same thing since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222 to drive the base on the PNP hard with the PIC output, and use the A/D input as you said to detect hi/low thresholds?

Perhaps the MOSFET idea is better, but absent much experience with them, I'm trying to stick with what I know.

Also, you could be right on that 14.7V, but the data sheet on this battery claimed that in an application like mine where the battery will be drawn down frequently, it's okay to set the constant voltage charger to 15V. Of course, now that you've challenged that figure, I can't seem to locate that data sheet, but I'm pretty sure that's what it said.

JB

+AD4- {Original Message removed}

2002\01\23@213618 by David VanHorn

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At 06:38 PM 1/23/02 -0700, jb wrote:
>My MOSFET knowledge is pretty limited, not sure how to drive that with a
>PIC running at 5V. Wouldn't a PNP power transistor do essentially the same
>thing since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222
>to drive the base on the PNP hard with the PIC output, and use the A/D
>input as you said to detect hi/low thresholds?

That's why the P-Mos. Ground is on.
So you put a 2N3904 or similar on the PIC output to slam the gate to
ground, and a pullup resistor on the gate to the drain to turn the FET off,
when the '04 is off.

Don't forget a base pulldown resistor on the '04 so it's off when the PIC
is in reset or crashed!


>Perhaps the MOSFET idea is better, but absent much experience with them,
>I'm trying to stick with what I know.

Learning is good. :) If it makes your head hurt, that's good.
Learn till your head explodes, then back off a notch.

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2002\01\23@223143 by Tom Messenger

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At 06:38 PM 1/23/02 -0700, you wrote:
>
>Also, you could be right on that 14.7V, but the data sheet on this battery
claimed that in an application like mine where the battery will be drawn
down frequently, it's okay to set the constant voltage charger to 15V. Of
course, now that you've challenged that figure, I can't seem to locate that
data sheet, but I'm pretty sure that's what it said.


The number I have stuck in my cranium came out of a Gates Battery Company
manual some 20 years ago. It suggested the following for charging lead acid
batteries.

Charge: 2.467 volts per cell; thus 14.8 volts for a 12 volt battery. Charge
until the cell voltage is at least this high to be 100% charged.

Float: 2.300 volts per cell; thus 13.8 volts for a 12 volt battery. Float
voltage is where you would leave a lead acid battery to keep it charged
(after having gone up to 14.8 volts).

These numbers have worked for me quite nice.  Lead acid cells are not all
that picky though; going to 15 won't kill them. Don't leave them there
though; above the recommended 14.8 volts, they begin to consume water
giving off hydrogen and oxygen. If your car battery gives off a bit, add it
back. If your sealed lead acid battery (gel cell) gives off a bit of out
gassing, it also gives off a bit of it's life.

Tom M.

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2002\01\24@110127 by Lawrence Lile

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My first analog battery charger was not very accurate, it probably floated
at 14.7 or 14.9 volkts dependiong on the temperature and the price of beans
in Bolivia.  My friend killed off a lot of batteries with it, maybe a set
every two years.  So if your charger is intelligent enough to charge up to
14.8, then float at 13.8 until the battery is drawn down to, say, 12.5 or so
then start the cycle again, you'll treat your batteries nicer.

-- Lawrence


{Original Message removed}

2002\01\24@124851 by Dal Wheeler

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face
You also might look at the charge curves shown in the UC3906 lead acid smart
charger chip datasheet...  The device itself probably won't get you where
you want to be with a solar panel, but it might give you ideas for the pic
algorithm...

http://www-s.ti.com/sc/ds/uc3906.pdf

There's also a switchmode schematic on the TI/Unitrode site using this chip
that might work in you're app --it looks to be much more complicated than
the pic approach Lawrence suggests however.

----- Original Message -----
From: jb +ADw-alphaone+AEA-ROF.NET+AD4-



My MOSFET knowledge is pretty limited, not sure how to drive that with a PIC
running at 5V. Wouldn't a PNP power transistor do essentially the same thing
since the CE drop in saturation is what, maybe .2-.4V? Use a 2n2222 to drive
the base on the PNP hard with the PIC output, and use the A/D input as you
said to detect hi/low thresholds?

Perhaps the MOSFET idea is better, but absent much experience with them, I'm
trying to stick with what I know.

Also, you could be right on that 14.7V, but the data sheet on this battery
claimed that in an application like mine where the battery will be drawn
down frequently, it's okay to set the constant voltage charger to 15V. Of
course, now that you've challenged that figure, I can't seem to locate that
data sheet, but I'm pretty sure that's what it said.

JB

+AD4- {Original Message removed}

2002\01\24@143047 by Alan Shinn

picon face
JB,
Find yourself a low dropout regulator. Or make your own with a large PNP
or p-channel FET.  I am presently working on a project with a Micrel
(MIC3902) part with about 375mV drop at 3 amps and even less at 1.5
Amps. It also has a shutdown pin and claims to be well protected from
all sorts of screwups like reverse voltage etc. Get it from Arrow for
about $5.00.

--
Looking forward:
Alan Shinn

Date:    Mon, 23 Jan 0102 18:34:33 +0000
From:    JB <alphaonespamKILLspamROF.NET>
Subject: [ee]: solar site charging system

I have a panel that delivers up to 21.5V in full sun with 3.5A short-circuit
current. This panel is used to charge a 17Ah 12V sealed lead-acid
battery that
can be floated at 15V for cyclic usage patterns, with a maximum charge
rate of
around 1.5A. Using a LM317-T set at 15V with no ballast resistor (using
internal battery resistance) this works fine in full sun, but anything
short of
about 17V at the panel results in zero charging. I would like to utilize the
power available when the panel is at any point above the battery voltage so
that I am not wasting that energy.

A switching regulator with a wide input range, say 12-30V to 15V out
would be
perfect, but I have yet to find one.

Should I drop the 317 and simply shunt the panel output at 15V with a
Zener? I
don't care about anything over the 15V point, as I don't want to over-charge
the battery. This of course assumes I can find a 15V/50W zener to mount
on the
panel.

Are there better alternatives? There is a 16F873 in the project with available
A/D and TTL ports, so that may be an option with the right components,
but I'm
running out of experimentation time, so I'd rather not venture into something
that "might" work.

I can justify up to about $50 for the components.



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beginnings of microscopy.
Make your own replica
of one of Antony van Leeuwenhoek's microscopes.
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2002\01\24@172121 by Peter L. Peres

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Two ways:

1. Use the 317 as before for >17V and a DC/DC boost converter that you get
to build for $10 or so below. The dc/dc would cut out when the 317 begins
to deliver current (which you sense).

2. Lose the 317 and implement a dc/dc with transformer (to avoid
buck-boost) with a standard dc/dc chip or another topology (the one with
the series LC) and use the PIC to implement an optimal power transfer
operation. This would probably be $30-ish (wild guess).

Peter

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