well a smps does that takes in a range of voltages and outputs a voltage we want in this case13.5-14.5 I beleive the difference between Vin and Vout should be converted into extra amperage (minus losses due to no device being 100 % efficient) so whats all the fuss about ? another mystical "black box" which nothing more than something we already know about.

the only difference my be that the output should vary with the battery charge so as to be more efficient at lower battery voltage but also rise to keep charging when the battery voltage rises

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Is there anybody help me find a concept of MPPT with ATmega Cointroller?

Thanks for the suggestion

 

It depends on what your battery usage is. From a practical standpoint I've been using on my camper in the mountains a 30 watt panel powering two 6V golf cart batteries in series = 12V with no controller. My typical daily loads (all 12V) are two lights for about 3 hours in the evening, a water pump for about 30 minutes total, an inverter to run a computer and charge various cell/drill/etc. batteries (1 hour) and when it gets cold it powers the blower on the propane heater for about and hour. The battery doesn't boil out and at noon the voltage is usually back to about 13.5V. Once or twice a month we leave for about a week and always come back to a fully charged battery = no issues. I think if you are just charging with no load that eventually you will overcharge and boil out your batteries but what is the purpose in that?

 

you do all that on a 30 w panel ?

__________________
I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately)

www.simonsphotography.org.uk/ - My other hobby
www.rushdenrotaract.org.uk/ - make a difference and have fun !


Never buy "Trust" products, all mine broke !!!

 

I'm a little suprised myself, but yes, 2 x 15 watt panels and my batts are always topped off. In May and late Sept if night time temps are low (< 30*F/0*C) I run a generator in the eves for about 45 minutes to warm up the bed and camper-- of course it tops off the batts I expect.

 

A solar cell is an illumination dependent current source with a parallel inherent shunt diode. see Solar cells

Unloaded, all the generated current goes down the inherent diode. If the panels are 20 watts it means that at 25 deg C they will produce about 1.2 amps at about 16.5 vdc when exposed to one sun (1000 watts/meter^2)

Your panel has 36 cells in series. The parallel diode conduction point is dependent on temperature with lower voltage when hot (0.4v) and higher voltage when cold (0.7 vdc). Since there are 36 cells in series this diode voltage is times 36. To get maximum power out of the panel you run it so the illumination based current source dumps about 0.3% of its current down the diode. This gives the maximum power yield out of the panel.

A Maximum Power Point controller is a switching power supply with a switch pumped coil for power conversion that hunts for a panel loading to produce the maximum V x I yield. The cost does not justify their use unless you are talking about >1000 watt panels.

As a current source you can put the panel directly across the 12v battery and it will pump in 1.2 amps at full sun. Problem is once the battery is charged it will still keep pumping in the 1.2 amps.

A PWM controller is just a series switch that as the battery voltage reaches its charge state the controller starts opening and closing a series connected MOSFET switch to the panel to keep the voltage on the battery in proper range. There is also a disconnect when panel drops below useable level of output.