oohh.. and i thought that 350mA is coming from the solar panel..
i need converter to buck or boost the voltage to have the optimum point to charge the battery..

this is where my problem is for now.. i need to get bigger current for the whole system..
which can charge the battery and as well as use to buck or boost the output of solar panel for the maximum power point to charge battery..

there are so many elements i need to consider for now..

numbers of solar panels, output of the solar panels, micro-controller to control DC-DC converter to maintain at MPPT level, how the micro-controller to control DC-DC controller, how the DC-DC converter output can be change according to the battery voltage level, and charger controller (to cut-off the charging process)..

 

You do not need to boost the voltage and you cannot boost the current. All you need is a battery charger circuit that stops the charging when the battery is fully charged.

A dead 12V/7Ah battery needs 350mA for 20 hours to be fully charged. The charging current might be only 50mA on a cloudy day and might be only 100mA in the morning of a sunny day. Each hour produces a different charging current especially since the solar panel does not track the sun across the sky.
Simply calculate how much current you need for how long.

 

My method of implementing MPPT is by Perturbation and Observe method (P&O)..

"In order to draw maximum power from the PV array, usually a DC/DC converter is inserted between the PV array and the battery. An MPPT controller is also connected to the DC/DC converter to ensure the operation of the PV array at its MPP by means of implementing an MPPT algorithm. In MMPT algorithm, when the solar radiation and temperature are varied, each of the MPP corresponds to only one value of the input resistance of the converter. Thus, as the solar radiation or temperature changes, the value of input resistance seen by the PV modules will also change so as to locate the new MPP."

That why i need converter.. to relocate new MPP when elements varied.
For my case, temperature wont be considered for now..
I think my project is:

let say the battery is around 10V.. So my solar panel can produce 0.3A to charge my battery at float voltage- 14.4V(maximum battery can accept right?).. when the battery is reaching the 14.4V, my system need to decrease my voltage and maintain at 13.8V until the battery is fully charged.. my system need to optimize that charging part..

 

@Ionic, thank you for ur detailed response. what i mean is if 12V battery is hard to implement because of needed more solar panel, my project allow me to CHANGE my battery from 12V to 9V(project requirement are flexible because the main reason for my project it to create a maximum power point tracking solar charge controller)

a)As AG has already explained to you, Lead Acid batteries do not come in 9V.

b)The main reason for your query here really is not so that you can buy or build a MPPT. It's a part of the whole system that get you to your main reason, capturing "free" energy, that is, once the system pays itself back. If the end game is to use a 12V 7HA battery to operate electrical equipment such as lights, radio's...etc. then you need understand how fast your 7AH battery will discharge and then need to be recharged again. The 7AH battery, when fully charged can produce 7A of current for 1 hour and then you will need to recharge it. If you follow the math through:

3.5A for 2 Hrs.
1.25A for 4 Hrs.
1.0A for 7 hrs.
500mA for 14hrs.

convert these numbers to Watts and you can figure out how long you can opperate a 60W incandescent bulb for (better, of course a florescent equivalent consuming only 15W) This will help you determine the size of battery(s) you need and the ideal solar cells to sustain this system.

because i am making a MPPT solar charge controller system, i need to maintain my solar panel output at around 13.8V for uninterrupt charging of my 12V or 9V battery.

Yes, for the most part you will want to have a minimum output viltage of ~13.8V

let say my solar panel rating is 18V 5W.. so the current I will be getting is 0.28A right? however, if i limit my voltage at around 14.4V, can i enlarge my current while maintain power at 5W? if can, please tell me how to do so?

This, essentially, is the purpose of the MPPT system. It will regulate the voltage to optimize the maximum charging current for your battery.

Some theory here:
http://www.solar-electric.com/charge_controls/mppt.htm
http://en.wikipedia.org/wiki/Maximum_power_point_tracker

if cant, is there any other way to enlarge my current while limit my voltage at 14.4V and power at 5W?

[/QUOTE]

Again, the MPPT system really is the way to go. In doing this the MPPT will give you more charge current by limiting the difference between the solar voltage and battery voltage. It may reduce the charging voltage to 12V if the battery voltage is only 10.5V and thus provide more charging current. The only other way to maximize the system is to track the sun with the solar panels.

Solar panel -> convert to AC -> transformer(to boost the voltage and current) -> regulate them for higher V and I -> convert back to DCl -> DC-DC converter for optimizing charging of battery..

I don't understand the logic here. The more you convert and manioulate, the more you end up loosing and not gaining. Converting to AC and back to DC prior to charging is only wasteful. You CANOT take 15W and make it 20W, you can only hope to only hope to attain as close to the rated Wattage as possible...the reasin for the MPPT.

is the above got the rational to get it work? about using the transformer, i get the infomation from MPPT description which they mention they use transformer to boost up V and I, regulate them and convert back to DC and using DC-DC converter for MPPT optimizing

Don't know where you saw this. You'll end up spending twice the money on conversion equipment than you do on the solar panels themselves.

oohh.. and i thought that 350mA is coming from the solar panel..
i need converter to buck or boost the voltage to have the optimum point to charge the battery..

Nope. If you boost the voltage to have enough to charge, then you just reduced the current to charge and lengthened the time to charge. If you boost the current, then you run the risk of not having enought voltage to charge the battery. Either way the power stays the same or even drops some.

this is where my problem is for now.. i need to get bigger current for the whole system.. which can charge the battery and as well as use to buck or boost the output of solar panel for the maximum power point to charge battery..

Nope. You caan't boost power. You solar panel says 15W, you'll be lucky to get that. Boosting power requires adding enery(power) to the system and the only way to do this is to add more solar panels that provide more power.

there are so many elements i need to consider for now..
numbers of solar panels, output of the solar panels, micro-controller to control DC-DC converter to maintain at MPPT level, how the micro-controller to control DC-DC controller, how the DC-DC converter output can be change according to the battery voltage level, and charger controller (to cut-off the charging process)..

You need to start with your goal, what amount of power do I want, and what you are going to use it for. If you want to power a reading light that consumes 15W of power at 120V it will draw 125mA. 7A/.125A = 56Hrs. Thus to read for three hours a night your 7AH battery can operate your reading light for ~18 nights before you need to recharge it. With fairly slow charge rate, say 24Hr at 280mA you could keep it topped off by placng it out on your charge system for for a couple of days within the 18 day period.

**Someone check my math here, this seems like a lot of days!!!

iONic

 

The 7AH battery, when fully charged can produce 7A of current for 1 hour and then you will need to recharge it.

No.
It provides only 350mA for 20 hours as is printed on it.
It probably provides 700mA for 8 hours (not 10 hours).
It probably provides 1.4A for 3 hours.
It probably provides 2.8A for 1 hour or less.
It might not provide 5.6A even for a few seconds.

convert these numbers to Watts and you can figure out how long you can opperate a 60W incandescent bulb for

60W from 12V is a current of 5A that the little battery might not be able to provide.

If you want to power a reading light that consumes 15W of power at 120V it will draw 125mA. 7A/.125A = 56Hrs. Thus to read for three hours a night your 7AH battery can operate your reading light for ~18 nights before you need to recharge it. With fairly slow charge rate, say 24Hr at 280mA you could keep it topped off by placng it out on your charge system for for a couple of days within the 18 day period.

No.
15W from 12V is a current of 1.25A. The little battery will be dead in about 2.5 hours, not 54 or 56 hours.

 

AG, Your right on all accounts. I knew that puney battery couldn't do that much work. I think I fed it some steroids...som really fuzzy math!

Thanks for embarrasing me!! At least he's got the feel of that battery now, one single 2.5hr reading session before needing to recharge.

I guess he'll have to do all his reading from a 1W 350mA Luxeon LED, which isn't too bad if the light is within 3ft. of the book. Then he can read for up to 20Hrs.

i