> > A simplistic but usually [tm] effective LiIon charger can be made by
> > ensuring max current is below allowed max. (often 1C) and clamping the
> > pack to not more than say 4.1V x N for N cells. Providing a clamp per
> > cell is better still. While Perry said 4.2V +/- 0.05V, you MUST NOT
> > err on the high side but may safely use a lower voltage per cell.
> > At 4.1V or lower you do not need to ever cut off charging - the cell
> > will trickle out to about 90% of max capacity and happily sit there.
>
> Tell me about, say, charging a 4.2V Li-ion battery from a 4V silicon sola=
r
> panel (8 cells, or maybe 9 cells plus a diode.)  Do you think this would
> work with no additional circuitry at all?

Assume crystalline silicon. Mono best. Poly OK. Price difference now
minimal. Mono better in low light.

Will definitely work BUT MUST clamp output to <=3D 4.2V.
8 cells =3D 4.5V on a good day./ Schottly is 0.3V at 0 current.
Too low really.

9 cells better.
10 cells MUCH better.

Voc ~~~~=3D 0.55V x cells. Depends on quality.High efficiency give
similar Voc but higher Vmpp (V max power point loaded).

10 Cells is day 5.5V x 0.8 =3D 4.4V Vmpp loaded for medium efficiency PV ce=
lls.

For low power clamp with TL431 and 2 resistors up to pkg dissipation
in your context.

For power up to any level clamp with TL431 and 4 or 5 resistors and
MOSFET or transistor shunt of your choice.
2 R to set TL431 level.
2R to drive MOSFET etc.
1 R optional in series with eg FET DS to dissipate some power.

CAN use series reg and turn off load but Vbat then drops slightly and
you have oscillation to fix.

If I_PV_Impp  > Ibatterysafemax need current limit.

For small LiIon at say 500 mAh I max usually 1C =3D 500 mA so Wpv ~=3D 4.5
x 500 mA =3D 2+ Watts.
That's larger than small hobbyist panels so for small panels no Ireg needed=
..

A very small wattage panel COULD be used to just drive battery
directly relying on it not having much steam to do damage > 4.2V but
battery  life will be shortened at best and you may achieve "vent with
flame" on a good day.

TL431 is very cheap. TO92 pkg is limited by current rating (100 mA?)
and a series R will limit dissipation (as R is used to dissipate as
much of Vpanel as possible).
In volume ex China TL431 is about 2 cents!).



          Russell McMahon

            Applied Technology ltd
           +6498372999
            apptechnz@gmail.com
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