circuit..
Hope this comes across ok..

+ solar ---|-----|  |-----|---inductor---|----resistor---|
          cap    FET    diode           cap            load
           |              |              |              |
- Solar ---|--------------|--------------|--------------|


Mosfet has a resistor from gate to source, then a transistor
is used to switch it off/on.

Resistor is 10R just for the testing purposes, but even with
0.1R the same thing happens.

Inductor.. made a mistake here.. it is actually 47uh
it has 0.39Ohms and Imax 0.9A and is open would ferrite bobbin..
(info from Farnell catalog)
I tried it again with 4 of these in series to give me more
inductance but same results..

Battery is 3V6 600mAH.

I intend to have my micro determine battery full charge and
switch the voltage out of the FET to something to cover a
trickle charge + circuit usage.

Cheers
Peter Mcalpine


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Richard Prosser
> Sent: Thursday, 20 March 2003 11:07 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Solar charging of batteries
>
>
> Can you draw or post a circuit diagram?
> R P
>
>
>
>
>                     Peter Mcalpine
>                     <petemca@BIGPO        To:     PICLIST@MITVMA.MIT.EDU
>                     ND.NET.AU>            cc:
>                     Sent by: pic          Subject:     Re: [EE]:
> Solar charging of batteries
>                     microcontrolle
>                     r discussion
>                     list
>                     <PICLIST@MITVM
>                     A.MIT.EDU>
>
>
>                     20/03/03 12:57
>                     Please respond
>                     to pic
>                     microcontrolle
>                     r discussion
>                     list
>
>
>
>
>
>
> Hi All,
> well got sun this morning but that is being slowly diminished by
> a dust storm.. some days...
>
> OK, I think I have a problem but not sure where it lies.
> Basic setup..
> 12V 1W cell
> 470uf cap
> IRL9014 P MOSFET
> Schotky diode to gnd (not sure why I need this)
> 470uH inductor
> 470uF cap
> 10R (current measure shunt)
> 3.6V NiMH battery
>
> PWM @ 30Khz
>
> Now, what i am seeing is the solar voltage collapses very
> quickly with low duty cycle.. roughly.
> 1% Vsolar = 19V 0ma
> 5% Vsolar = 15V 10ma
> 10% Vsolar = 10V 25ma
> 12% Vsolar = 4.5V 50ma
> from there it sits at about that level, and I get same
> current level (which is almost the SC current of the cell).
>
> I guess that my problem is either...
> 1. solar cell can't cope
> 2. bad choice of components in switcher ie Inductor
>
> I think it is 2..
> the 470uH value is just something I have to hand, but I
> should really calculate it out but am unsure of how to do
> this.
>
> Much thanks to everyone who has got me this far :)
> Cheers
> Peter Mcalpine
>
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Peter Mcalpine
> > Sent: Wednesday, 19 March 2003 6:10 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: [EE]: Solar charging of batteries
> >
> >
> > Hi All,
> > well finally getting some time to myself (as no one is
> > paying there bills to me at present, so there work
> > goes on hold...)
> >
> > So far I have built some hardware and implement a PWM
> > output to control it, and just manually control the
> > duty cycle and see what happens.
> > Solar cell -> cap -> fet switch -> (schotky to gnd) Coil
> >  -> cap -> 180R load resistor.
> >
> > Just finally got some sun to test but it is late in the
> > day and the sun is low on the horizon..
> >
> > With solar panel connected direct to the load 9.4mA
> > With the PWM set to optimum output to load 10.5mA
> > increase of 4mW :)
> > Not much but considering I have almost no sun energy its
> > still tells me gains are being made :)
> > Sun dependant will move my test gear outside and try it
> > properly tomorrow. Should have some test software to automate
> > the control running by then also :)
> >
> > Cheers
> > Peter Mcalpine
> >
> > --
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