manual solar tracker
how do i make a 48v charge controller?
i would like to make my own solar charge controller to cut off charging when my 8x8volts lead acid batteries, so that they will not over charge.
Complicated, I’d buy a commercial version. The rules are quite complicated. Scale them up to 48v as needed. Below is from one reference. Note that a temperature value is required. There are dozens of other references.
But even if you buy one, it’s good to know the rules, as not all controllers follow them.
TM 9-6140-200-14, a battery maintenance manual created by the Army, recommends a maximum charge rate of 5A for high capacity 12v batteries, such as the 6TMF 12v 120AH battery.
Charging the battery at a higher rate will cause the internal temperature to rise, which decreases the lifespan of the battery. Batteries last much longer at 60°F than they do at 100°F. It takes them a considerable amount of time to cool down once they are heated up.
If a 12v battery discharges to 12.5v @ 77°F, plate sulphation will begin. This is the #1 cause of early battery failure. For 48v batteries, this is 50v @ 77°F, but it needs to be adjusted according to the battery internal temperature. You can check the internal temperature by measuring the positive terminal’s temperature.
There are three basic phases to charging a lead-acid battery:
1) Bulk charge – the battery is charged at a constant current until it’s 80%-90% charged.
2) Absorption charge – the battery is charged at a constant voltage (roughly 2.33v per cell, or in your case about 56V) until it is nearly 100% charged.
3) Float charge – the battery is charged at 2.26v per cell at 77°F (in your case, 54.2v) indefinitely.
For maximum battery life, the voltages need to be adjusted according to the internal temperature of the battery. It is a negative temperature coefficient; –0.003v per cell per °C below 25°C, –0.003v per cell per °C above 25°C. Since your battery has 24 cells, that’s –0.072v per °C.
Charge controllers are sold to consumers as separate devices, often in conjunction with solar or wind power generators, for uses such as RV, boat, and off-the-grid home battery storage systems. In solar applications, charge controllers may also be called solar regulators.
A series charge controller or series regulator disables further current flow into batteries when they are full. A shunt charge controller or shunt regulator diverts excess electricity to an auxiliary or “shunt” load, such as an electric water heater, when batteries are full.
Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. Pulse width modulation (PWM) and maximum power point tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery’s level, to allow charging closer to its maximum capacity. Charge controllers may also monitor battery temperature to prevent overheating. Some charge controller systems also display data, transmit data to remote displays, and data logging to track electric flow over time.
A majority of modern charge controllers utilize two or three stage charging to help further maximize battery life. The three stages used are constant current, constant voltage, and float.