Solar panel

[Sandun]

Hi my dear friends - i have a small solar panel 5w 18/20 v 27/33mA - i want to know what size battery may i can charge from it is it 12v 4.5Ap battery ?the battery that i going to use - And want to know , what size solar battery charging controler , may i use ? Is it ? 10W one - this work not for my car , it is for home emagancy lights - thank u

[Ufudu]

Sandun, I am not an expert, but a 33mA panel will not do much to charge anything really; it may be good enough to maintain charge on a battery (trickle charge) but not much more.

The calculations are simple: The panel maximum current will be the charger (regulator/controller) maximum current too; add a bit for safety (say 25%) and that will spec that.

Most small gel 12 lead acid batteries are 7 Ah or so; the 10W controller will be fine.

You can estimate the time it will take to charge a 7Ah battery at 33mA; this will be 7/0.033hours = 212 hours (of sunshine)..... and that does not take into account any leakage or losses....

[Sandun]

Thank u -I am sorry - yesterday i found how to calculate Ap - my soler Ap not 27mA it was .27A - So 18v 5w .27A soler panel 5W/18v =.277 = 277mA - I going to use 12v 4.5A Battery - Then using ur calculation method , now i can calculate it like this
if 1000mA = 1A
4.5Ax1000=4500
4500mA/277mA = 16 hours
if i use 2 solar Like this = i will can charge 4.5A 12v battery with in 8 hours
is it Ok ?
so must i buy Charging controller = is it 10A

[Ufudu]

Yes, that is more or less correct, I presume you mean 4.5Ah not 4.5A battery.

The actual charging time will vary depending on the state of the battery and other factors.

You don't need a controller as big as 10A, a 2A controller will be fine for 2 panels.

[Sandun]

Oh... problem is i can not buy 2A controller in Sri Lanka - only 10A and more

[Ufudu]

10A should work too.

[Sandun]

Thank u - the solar Amp will low when come out from the controller ?

[Ufudu]

The controller will regulate the voltage and therefore limit the current as the battery becomes fully charged.

[bmcecosse]

You really won't need a 'controller' - use an old car battery and it will absorb the power you mention without any problem. Just use the lights for an hour os so every week to check all is well - and make sure the battery is topped up with distilled water from time to time.