When do I need a charge controller to charge a battery with a solar panel?
This is a very common question and one that is crucial.
In most cases, you will need a charge controller to safely charge a battery pack. This prevents overcharging and reduction in the battery life of the system.
Battery technologies such as Lithium Ion, Lithium Iron Phosphate, Nickel Metal Hydride, or Nickel Cadmium require a charge controller to safely recharge the battery pack. Lead acid batteries are the exception to the rule. If you are trying to charge a lead acid battery quickly or using a large solar panel, you will want a charge controller to keep the battery from overcharging and drying the electrolyte.
Using a solar module for low current maintenance charging can be done safely without a charge controller as long as the solar panel output is <1% of the battery capacity. For example, if you have a 12V, 100Ah battery, this could be safely trickle-charged with a panel capable of supplying up to 1A at 13.4V.
By the nature of how solar will cycle on and off each day as the sun rises and falls, not all charge controllers will be safe for lead acid or AGM batteries if solar is used.
Most notably, chargers using a three-stage charging algorithm will slowly dry out the battery once it has reached a full charge. This is because when the solar starts producing power each morning, the charger will start at stage 1. It will quickly switch to stage 2 since the high battery voltage indicates a close to full charge. During stage 2, the charger will top off the battery and balance the cells by taking the battery voltage up to 14.3-14.6V, which will take a few hours. After that, the charger will move to stage 3, a float voltage maintenance charge at 13.4V with a trickle of current.
The high voltage cell balancing that occurs in stage two causes the battery to dry out and reduces its lifetime. Three-stage chargers work very well when connected to the grid and only take the battery through stage 2 once and then hold it in stage 3. The repeated cell balancing in stage two occurs due to the daily on-off cycling of the solar that destroys the battery.
Charge controllers aren’t just nice to know about. They could very easily be a part of your system and one that you must utilize to avoid damaging your battery.
Do you need a custom solar solution for your application? We would love to be a part of your next project.
We will discuss your design and setup and ensure that you get the best possible performance from your solar, battery and charge controller, helping you create a fantastic system.
We look forward to learning about your project and partnering with you to meet your unique needs.