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-----
+AD4- From: pic microcontroller discussion list
+AD4- +AFs-mailto:PICLIST+AEA-MITVMA.MIT.EDU+AF0-On Behalf Of Lawrence =
Lile
+AD4- Sent: Wednesday, January 23, 2002 4:04 PM
+AD4- To: PICLIST+AEA-MITVMA.MIT.EDU
+AD4- Subject: Re: +AFs-ee+AF0-: solar site charging system
+AD4-=20
+AD4-=20
+AD4- I built a charge controller for a friend's solar system some time =
ago.
+AD4-=20
+AD4- I've built a linear charge controller out of a 2N3055 and=20
+AD4- some other stuff
+AD4- for this very application.  After having lived with it, i'd=20
+AD4- stay away from
+AD4- any linear regulation of any kind.  The LM317 or the 2n3055=20
+AD4- are power hogs,
+AD4- won't work with low dropout voltages, and also have all the=20
+AD4- same probs you
+AD4- mentioned.
+AD4-=20
+AD4- Ditto for the zener regulators.  Dump them with Nixon, 8 tracks, =
the
+AD4- bicentennial and all that other 70's stuff.
+AD4-=20
+AD4- Take your PIC and drive a P-channel mosfet as a pass=20
+AD4- transistor, filter the
+AD4- output a little and run it into your A/D port.  If the=20
+AD4- voltage is too high,
+AD4- turn off the mosfet, if it is too low, turn it on.  You'll be=20
+AD4- surprised how
+AD4- easy this is.   +ACQ-5 should build it, and a mosfet can handle a=20
+AD4- lot more than
+AD4- 1.5 amps no sweat.
+AD4-=20
+AD4- Check your output voltage - I think lead acid batteries are=20
+AD4- fully charged at
+AD4- around 14.7 volts but my memory leaks so look it up.  I'd regulate =
the
+AD4- output at the fully-charged voltage of the battery, and shut the =
solar
+AD4- charging down when the battery gets full.
+AD4-=20
+AD4-=20
+AD4- --Lawrence
+AD4-=20
+AD4- ----- Original Message -----
+AD4- From: +ACI-JB+ACI- +ADw-alphaone+AEA-ROF.NET+AD4-
+AD4- To: +ADw-PICLIST+AEA-MITVMA.MIT.EDU+AD4-
+AD4- Sent: Wednesday, January 23, 2002 12:37 PM
+AD4- Subject: +AFs-ee+AF0-: solar site charging system
+AD4-=20
+AD4-=20
+AD4- +AD4- I have a panel that delivers up to 21.5V in full sun with =
3.5A
+AD4- short-circuit
+AD4- +AD4- current. This panel is used to charge a 17Ah 12V sealed=20
+AD4- lead-acid battery
+AD4- that
+AD4- +AD4- can be floated at 15V for cyclic usage patterns, with a=20
+AD4- maximum charge
+AD4- rate of
+AD4- +AD4- around 1.5A. Using a LM317-T set at 15V with no ballast=20
+AD4- resistor (using
+AD4- +AD4- internal battery resistance) this works fine in full sun,=20
+AD4- but anything
+AD4- short of
+AD4- +AD4- about 17V at the panel results in zero charging. I would=20
+AD4- like to utilize
+AD4- the
+AD4- +AD4- power available when the panel is at any point above the=20
+AD4- battery voltage
+AD4- so
+AD4- +AD4- that I am not wasting that energy.
+AD4- +AD4-
+AD4- +AD4- A switching regulator with a wide input range, say 12-30V=20
+AD4- to 15V out would
+AD4- be
+AD4- +AD4- perfect, but I have yet to find one.
+AD4- +AD4-
+AD4- +AD4- Should I drop the 317 and simply shunt the panel output at=20
+AD4- 15V with a
+AD4- Zener? I
+AD4- +AD4- don't care about anything over the 15V point, as I don't =
want to
+AD4- over-charge
+AD4- +AD4- the battery. This of course assumes I can find a 15V/50W=20
+AD4- zener to mount on
+AD4- the
+AD4- +AD4- panel.
+AD4- +AD4-
+AD4- +AD4- Are there better alternatives? There is a 16F873 in the =
project with
+AD4- available
+AD4- +AD4- A/D and TTL ports, so that may be an option with the right=20
+AD4- components, but
+AD4- I'm
+AD4- +AD4- running out of experimentation time, so I'd rather not =
venture into
+AD4- something
+AD4- +AD4- that +ACI-might+ACI- work.
+AD4- +AD4-
+AD4- +AD4- I can justify up to about +ACQ-50 for the components.
+AD4- +AD4-
+AD4- +AD4- --
+AD4- +AD4- http://www.piclist.com hint: The list server can filter out=20
+AD4- subtopics
+AD4- +AD4- (like ads or off topics) for you. See =
http://www.piclist.com/+ACM-topics
+AD4- +AD4-
+AD4- +AD4-
+AD4-=20
+AD4- --
+AD4- http://www.piclist.com hint: The list server can filter out =
subtopics
+AD4- (like ads or off topics) for you. See =
http://www.piclist.com/+ACM-topics
+AD4-=20
+AD4-=20
+AD4-=20

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