I’m installing a 75W solar panel. It will charge a 100Ah car battery which will drive LED lighting around the house, maybe more. Rather than buy a charge controller, I have decided to build one. It’s function is fairly straight forward. Their will be two relays. One connecting the panel to the battery, the other connecting the battery to the load.
The panel relay will be on while the battery voltage is below 14v, then turn off to avoid overcharging, then turn on again when the battery voltage falls to 13.8.
The load relay will turn off if the battery voltage drops below 10v to avoid over discharging, then turn on again when the battery voltage reaches 11v.
These figures are estimates based upon various things I have read on the net and will probably need some tweaking, but you get the idea.
There is a more efficient charge control system called Maximum Power Point Tracking (MPPT) which is beyond my design capabilities at ATM, but I may have a go at some stage. A good MPPT can apparently add as much as 30% power under certain circumstances by ‘matching’ the source voltage/current with the battery charging voltage/current using high frequency switching techniques, allowing the panel to always be operating at it’s highest efficiency. (Perhaps someone knows where I can get a kit?)
The simple solar controller I’m designing will of course use a PICAXE to manage the monitoring and switching. To improve accuracy, I’m thinking of using a zener to drop the battery voltage into the <5v range, rather than using a simple divider. I’m also thinking of having the relays wired so that they conduct when no power is applied and turn off when powered. It seems to me that this could save a little power.
I foresee no problems at this time and have begun to order parts, but I would like the benefit of any advice/experience here at the forum. TIA.
The panel relay will be on while the battery voltage is below 14v, then turn off to avoid overcharging, then turn on again when the battery voltage falls to 13.8.
The load relay will turn off if the battery voltage drops below 10v to avoid over discharging, then turn on again when the battery voltage reaches 11v.
These figures are estimates based upon various things I have read on the net and will probably need some tweaking, but you get the idea.
There is a more efficient charge control system called Maximum Power Point Tracking (MPPT) which is beyond my design capabilities at ATM, but I may have a go at some stage. A good MPPT can apparently add as much as 30% power under certain circumstances by ‘matching’ the source voltage/current with the battery charging voltage/current using high frequency switching techniques, allowing the panel to always be operating at it’s highest efficiency. (Perhaps someone knows where I can get a kit?)
The simple solar controller I’m designing will of course use a PICAXE to manage the monitoring and switching. To improve accuracy, I’m thinking of using a zener to drop the battery voltage into the <5v range, rather than using a simple divider. I’m also thinking of having the relays wired so that they conduct when no power is applied and turn off when powered. It seems to me that this could save a little power.
I foresee no problems at this time and have begun to order parts, but I would like the benefit of any advice/experience here at the forum. TIA.