solar phone charger with buck converter

[Arcamax]

Those 2596 modules are quite handy though I would be leary of drawing much more than a half amp from them.  Pun #5 is the one on the far right and it goes to common neg. That pin is lifted and a circuit is added as in the TI/National May 2002 data sheet figure 22 Undervoltage Lockout.  Change the base resistor to a pot so it is adjustable.  A typical 12V solar panel has an open circuit voltage of 21V and a power point of 17-18V.  The ideal zener should be about 2V below the power point,  The power point is usually around 80% of open circuit voltage.  It is not too critical, a 12V would work fine.

It is harder for me to come up with a zener than a TL431, an opamp with a 2.5V reference.  These are found in about any PC power supply near the opto and in many older wall warts.  Use that in place of the transistor.  They switch at 2.4V so a 10K and 100K pot divider circuit would be adjustable to 25V.  The 431 can only clamp down to 2.5V so a 15K to 4.7V divider is needed to feed pin #5 to get the ON voltage below .6V.  In order to insure it turns off the 47K collector pullup has to be changed to 10K to get a high enough OFF voltage.

The input power (solar panel) to the module has to have at least 1000uf added to it to store the panels current for short periods during the off periods.   Set the voltage pot to 5V or whatever charge voltage is needed.  That insures the maximum voltage.   Place a resistor on the output so the converter is slightly overloaded, output voltage under set point.   Then adjust input voltage for maximum output.  Pane power point voltage does not vary with light intensity.  Only panel temperature changes that voltage, it increases with colder temps.  Even then a summer setting would work fine in cold temperatures.

if i use this buck convertor should i still mod it with either zener or lm431  http://www.ebay.ca/itm/DC-DC-Buck-Step-Down-Converter-Module-LM2596-Voltage-Regulator-Led-Voltmeter-/160995621268?pt=LH_DefaultDomain_0&hash=item257c163994

Also does it matter what the input current of the solar panel to this converters output

[Seekonk]

I suggest you re-read everything again.  Without a circuit to control the input voltage at the panels power point voltage, a buck converter will overload the panels in low light levels.  This may be beyond your capabilities.  Your constant PMing is inappropriate.

[Arcamax]

so its a charge controller i need right.

[suicidaleggroll]

Yes

Please read this thread, it might give you some information about efficiently pulling power from a solar panel:
https://www.eevblog.com/forum/beginners/dcdc-converter-that's-efficient/

That's talking about a big multi-kW array for a boat, but the same principles apply to a small phone charger.

[Seekonk]

The basic 2596 is sufficient, adding a display will just suck up power that should go to the phone.  If you don't control the power point it will be less efficient.  Solar panels are constant current sources.  Draw too much current and the voltage drops like a rock.

[Arcamax]

ok now i know i need a charge controller and that buck converter http://www.ebay.ca/itm/1-Pcs-DC-DC-Buck-Converter-Step-Down-Module-LM2596-Power-Output-1-23V-30V-EK-/201126191001?pt=LH_DefaultDomain_0&hash=item2ed40e1f99

and you guys say more voltage of solar is better, so should this 18v be good enough http://www.ebay.ca/itm/1PC-3-4W-18V-188mA-Mini-Solar-Panel-Module-System-Epoxy-Cell-Charger-DIY-B045-/311007312320?pt=LH_DefaultDomain_0&hash=item48697af9c0  or do i go less current

[Seekonk]

I wrote a long reply, but site timed out and I lost it.  I think I'll just wait till you stop spinning.

[Arcamax]

hmmm what

[Arcamax]

ok then i think ill get these items then
  1-step-down dc regulator, looks OK/genuine. http://www.ebay.ca/itm/DC-DC-LM2596-Step-Down-Adjustable-Buck-Converter-Power-Supply-Module1-5V-35V-/360672163864?pt=LH_DefaultDomain_2&hash=item53f9bc7818
  2-probably my own diy charge controller
  3-this solar panel, http://www.ebay.ca/itm/18V-2-5W-Solar-Panel-Module-Solar-System-Solar-Cells-Charger-DIY-120x194mm-Mini-/361099099137?pt=LH_DefaultDomain_0&hash=item54132efc01 (try the ones i have again first). it doesn't matter what buck converters input current from solar and controller does it, the panels i have now are low? mine supposed to be 80mA(max i think)   
  4-zener in case of failure.