Solar Powered Lead Acid Battery Charger

[amindzo]

I want to make a solar powered battery charger for lead acid battery with PIC16F877A. I found this application note in microchip website that is very useful but i want to change this to use solar cell and PIC16F877A.
**broken link removed**

In that charger they charge the battery with high current (1.0 A) but by using solar cell for my application i don't have this current, i should charge the battery with 270 or 300mA. i want to charge a 12v, 7.2AH lead acid battery and i have a 18v, 5W, 300mA solar cell so how can i change that charger to make my own one?

 

[amindzo]

i don't want you to write a code for me. that code is C but i want to write my code in picbasic pro, i want you help me with changes in electronic devices and changes in the algorithm for my application.

 

[MikeMl]

Read and follow the instruction in this post:

Before you can build a charger, you have to know something about charging batteries.

 

[amindzo]

thank you very much, that was very useful but i don't know yet can i charge lead acid batteries with low current because in every charger i saw,the battery is charged with at least 1.0A current.

 

[MikeMl]

I use a 1/4 A solar panel to maintain two 12V lead-acid batteries (one starting battery, the other is a deep-cycle storage battery). The solar panel is multiplexed to the two batteries as needed by the controller. Now this is a "maintainer", not a "charger", used to keep the batteries from self-discharging when the boat is not in use. These batteries are charged by the engine-mounted alternator (at a rate of ~40A) when the engine is running.

Charging a lead-acid battery can be done with much lower currents than 1A; it will just take much longer. For example, if you have a discharged 50Ah battery, it would take ~70h to charge it at 1A, 700h at 0.1A. You have to put in 70Ah to get 50Ah out, because of the Columetric Efficiency cited in the reference. At very small charging currents (~20mA), all of the charging current is going to overcome the battery's self discharge leakage, so it will never charge. This is the basis of the small unregulated dashboard-mounted solar panel automotive battery "maintainers" as sold by Harbor Freight.

 

[amindzo]

my solar cell can charge the batteries with 200mA current so i can charge the batteries with this current.

 

[blueroomelectronics]

Have you calculated how many sunny days it would take to charge even a small Lead Acid battery at 200mA?

 

[MikeMl]

I think the OP lives in a very SUNNY area, which makes me wonder why they need nuclear power so bad

 

[amindzo]

it takes three days to charge 12v,7,2AH lead acid battery with 200mA but consumption is not too high to discharge the battery in one night. after complete charging i disconneted the solar cell and connected my circiut to the battery and my circiut worked 33 hours. but in my application, the circiut should only works in the nights (7,8, or 10 hours atlast) so the battery don't discharge fully so it the day not sunny and the battery doesn't charge fully in a day we have some storage in the battery for two days or more.

 

[MikeMl]

In the event that the battery doesn't recharge, it is very important that your charge controller include an algorithm to disconnect the load from the battery if the state-of-charge of the battery drops below ~10%, assuming that this is a "deep-cycle" battery. Automotive starting batteries shouldn't be used for cyclic use, or discharged below 90% of their full capacity.

 

[amindzo]

i can't understand what exactly you said. you mean that i shouldn't charge the battery until it's empty? should i wait that the battery is getting empty and then start to charge it? in my last post i said that when my battery is full it takes about 33 hours to empty ( with load that consume 300ma) but my circuit works only on the nights (maximum 9 or 10 hours) so the battery doesn't get empty it it start to charge next day. i use this battery (12v 7.2AH) to be sure that if the battery doesn't charge fully in a day it has storage to work for another day.

 

[MikeMl]

No, I said that in the event that the sun doesn't shine for a few days, and the battery is running down, you should arrange your controller to disconnect the load rather than to deplete the battery beyond 10% remaining capacity. As soon as some sun power is available, then recharge as much as possible, as fast as possible, but terminate the charge when full charge is reached.

 

[amindzo]

ok, i'll do this but my first question and my first ask is about making a controller that do these things and i attached a useful file for this application but i want to do this project with PIC16F877, picbasic pro and solar cell but the application note that i found is made by PIC14C000 and C but i want to change it. which parts in the software and hardware should i change? i don't want you to write me a code just suggest me (with hardware and algorithm of the software) how can i change this?

 

[MikeMl]

Pull the algorithm(s) out of the AP note, and re-implement those algorithms in you choosen processor using a language of your preference.
Go to the PowerStream website (I posted the link before) and read about charging batteries. You have to understand what you are trying to do,.,,,