I have idea for my first project It will earn me enormous browny points with my wife I would like to use the MCU to control charging of 12 v lead acid battery from cheap solar panel and use this to power led lighting at a certain low light threshold that would then remain on for a certain time. Obviously this may be considered akin to using a sledge hammer to break something fragile. I think I might see how to sort the light activation and consequent timing. However I have no idea about the charge controlling issues of lead acid batteries and would appreciate any advice. Looking forward to fresh winter eggs Simon

One tidbit for you is that deep-cycle marine type batteries can handle the constant charge and discharge much better than regular lead-acid batteries. This is the reason they are used for boats and RVs.

As far as charging, I'm tossing a guess out there for the more experienced nerdkitters: Would a simple voltage divider and the adc perform the task? Also, I'm thinking you would need to disconnect ssaid voltage divider when not in use so that the battery is not continuously being used when in the "storage" state.

Thanks treymd

I am not sure what functions the charge controller performs

I presume it (1) monitors the charging current limiting it if it is excessive and (2) from monitoring the battery voltage determines when the battery is being overcharged subsequently turning the charging circuit off

(3) during the periods the light comes on i.e. when it gets dark the controller would need to disconnect the charging circuit

I have a vague idea about 3 and no idea about 1 & 2 except that I will need to use relays to switch "Hi current "circuits on and off

can I use ADC to monitor voltage and ADC to monitor current by measuring voltage drop across known resistance

Not sure how to limit current other than switching in resistances.

or Am I barking up the wrong tree

Simon

Hey swragg.

This is another project of mine which i have not done much work on. I purchased a couple of solar panels off ebay to play around with and some AGM sealed lead acid batteries. Ive done a bit of research into charging them depending on your type of battery depends on the charging cycle.

My plan is to just monitor the voltage and control the charging current via a large mosfet switching it on and off maybe using PWM to maintain voltage depending on the cycle. e.g. If voltage has hit peak 14.4v which means its almost charged throttle back the current until voltage starts dropping and increase if it drops too far back. I was also going to use high wattage diode so the battery charge wont leak back into the panel during the night.

I am not worrying about switching the charger off when something is switched on. Whatever I run off the battery will have a voltage regulator so sending 18v (from the panel) to a device should not matter.

Another thing to think about is stopping the battery from being discharged too much. From memory your doing your battery damage if it drops below 11.8v (under load) at this point you would want to stop anything discharging it any further. With lead acids it may only takes one full discharge to seriously decrease its capacity in the future.

I will probably get back to this project after christmas. Let me know if I can help you with anything.