solar batteries

Can Solar Batteries Be Recharged with a Charger?

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If there isn’t any sunlight for a few days or some of your solar modules are broken, can you charge a solar battery without there? What kind of charger is needed to charge these types of batteries? Let’s dive in and address the answers to these questions.

First of all, yes, you can charge solar batteries without the use of solar modules or sunlight by using an external charger. In fact, any battery or cell can be charged with the right type of charger. Solar batteries are simply rechargeable cells. The only important part of finding a backup charger for your solar batteries is identifying the type of cell you’re using and choosing an appropriate charger for that particular kind.

Each type of battery type has its own parameters for both charging and using it as a power source. If the voltage and current of a charger is not compatible with the parameters of a cell, it will not only permanently damage the cell but also become a serious fire hazard. Read on to learn how to identify the cell type of a battery and choose the proper charger for the battery you have.

Why would you charge solar light batteries in a battery charger?

The lifespan of batteries is defined on the basis of how often they are charged and discharged. This is referred to as a “cycle.” So, when batteries are charged and drained frequently, they will last for fewer days compared to the batteries you use less frequently.

Partial Discharging of Batteries

If you do not fully discharge and use up the power stored in your solar batteries, this does not allow them to fully complete their “cycle,” thereby extending the lifespan of the batteries. However, after longer periods of time, this partial discharging creates a layer of deposits on the electrodes of those batteries, and this reduces their capacity.

Therefore, sometimes, it is necessary to fully discharge before recharging your batteries to use again. By doing so, this helps them retain their capacity and function with proper life cycles to avoid damage.

If a battery is not discharged and drained for too long, it is recommended that you try to discharge it completely and then charge it using an external charger.

Not Discharging Battery for Too Long

Ideally, a battery (voltage source) should have zero internal resistance. But, practically, there is always a little bit of internal resistance in the form of a few ohms. If a battery is not discharged or charged for a very long period of time, it may die due to a buildup of internal resistance. If it’s left for an even longer period, it will be damaged permanently.

These batteries can be charged using external chargers to revive them from ‘death’ and prevent permanent damage. External chargers provide relatively higher currents and charge batteries at higher charging rates. They also have the capacity to charge in multiple steps, providing a different current rate at each step, to avoid damage to the batteries.

Batteries and Charger Types

Before charging your batteries in a charger, as well as before choosing an appropriate charger for your batteries, one must have basic knowledge of the types of batteries, the types of chargers, and current ratings. This will help you choose the appropriate charger for specific battery types. The following subsections summarize these concept.

Solar Battery Types

Can Solar Batteries Be Recharged with a Charger

There are multiple types of batteries, and these vary in their construction and the materials used for the electrodes (anode and cathode). The most common types of batteries used with solar lights are either Li-ion or Ni-Cd since both are compact and have high current densities. Also, both of these have a greater number of life cycles than other types of batteries, too. Nickle metal hydride (NiMh) and Lithium Polymer (LiPo) batteries are also common.

Voltage Level

Each type of cell has its own voltage range for both charging and discharging. Therefore, each type of battery needs to be charged accordingly. The charging cut-off voltage level is defined for each type of cell. For example, a 12 V battery made of Li-ion cells will have 3 cells in a series, and each cell provides around 4.2 V when fully charged. These need no more than 4.5 V per cell while charging. Similarly, a Ni-Cd cell provides an output of only 1.2 V, and for 12-volt batteries, 10 series of cells will be needed.

Due to these specific requirements, knowledge of battery types and the total voltage needed to charge your batteries is important. If these factors are not considered, serious damage to the cell may occur and can result in a fire. (As an example, a series of 3 cells of Li-ion batteries must only be charged with a charger that gives maximum of 14.6 V at output. Additionally, a single cell of Ni-Cd be charge by charger that is at 1.5 V maximum.)

Current Capacity

Charging and discharging current capacity is also very important to know for both your batteries and your charger. Some batteries can withstand higher charging current rates, but there is a limit to the charging currents for each battery.

Normally, standard batteries are rated in Ampere-hours (Ah), and small batteries are rated in the smaller unit, mAh. This is what’s referred to as the “capacity” or “C rating” of a battery. Batteries can be charged and discharged safely within their own specified C ratings. Most solar chargers used for charging batteries charges at slow rate: C/10 or 0.1C.

For Li-ion batteries, the safe limit is up to C/2. This means that if a battery has a capacity of 10 Amps and its charging limit is C/2, you can charge the battery at a constant current of 5 Amps.

So, before choosing a charger, make sure that the current it provides is less than the safe limit of the current capacity of your batteries. For that, check the capacity of the battery or cell, then choose your charger once you have the necessary information.

Caution: Keep in mind that multiple cells/batteries in parallel will increase the current capacity, and cells in a series will have the same capacity as a single cell. Multiple cells in a series will increase the voltage only.

Charger Types

From above subsection, you should now know that you will have to choose a charger according to your battery type. It should be able to charge your battery or cell to the maximum voltage according to demand. For example, if a solar battery has a Ni-Cd cell in it, it should be charged at a maximum of 1.5 V, and the voltage will be 4.2 and 3.8 volts in the cases of Li-ion and LiFePo cells respectively.

Similarly, the current rate of a charger must also be within range of 0.1C to 0.5C of the charged cell. If the cells are of smaller capacities and the charger has a higher current rate, it will heat up the cell and destroy it. You can find a universal charger that can charge any type of cell, though, allowing used to adjust the parameters themselves.

Having a Cut-off System

One of the most important aspects of a charger is the cut-off system. A charger must cut off charging the cells and batteries once they are fully charged no matter what. Overcharging cells will result in permanent damage of those cells. for example, if a Li-ion cell is charged beyond 4.2 volts, it will break the membrane inside the cell and both of the electrodes will be combined, making the battery nonfunctional.

A charger without protection from overcharging will continuously provide a current to a cell, and the heat that will produce will result in a fire or bursting of the cell. So, it’s incredibly important that you choose a charger that has a built-in cut-off system in it.

The voltage level, current limit, and cut-off system are available in single kit, commonly known as battery management system (BMS), and these are readily available on the market. This BMS is available primarily for Li-ion cells.

How to Use a Battery Charger to Charge Solar-Powered Lighting Batteries

For charging solar-powered batteries by means of an external charger, you can stick to the following steps:

  1. Find the type of the battery/cell. You can find this information usually on the cell or battery itself.
    1. If the type of battery is not written anywhere on the battery itself, check the terminal voltages of individual cells to get an idea of the type of cell you likely have. For example, the terminal voltage of a Li-ion cell is around 3.4 volts, and a Ni-Cd cell has a voltage of 1.2 volts.
  2. Check the current capacity of your battery/cell. This should be written on the battery. If the capacity is not marked down, simply find code of the battery or cell. Search the code on the internet to get an idea of what you may have.
    1. Find the maximum C rating according to the type of battery.
  3. Choose an appropriate charger based on the maximum voltage and charging current of the specific battery or cell that you have. For example, if you have a Ni-Cd cell, the charger will need to cut off charging at 1.5 V and provide a 0.1C charging current.
  4. Keep checking the temperature of your battery/cell when charging. If the temperature is continuously increasing, stop charging immediately. Lower the rate of charging as this temperature increase is due to a high current flow (higher than maximum capacity).

Frequently Asked Questions

How long does it take to charge a solar battery on a charger?

The time required for charging depends on rate of charging current of the charger.

For instance, if a 10Ah battery is charged through a charger that provides 1 Ampere of current, this will fully charge the battery after 10ah/1A= 10 hours

How can I charge a cell with a charger that gives higher voltages?

Voltages add up when cells are connected in series, so if you have a charger that provides higher voltages, you can attach multiple cells in a series to match the voltage of the charger. If you do not have multiple cells to connect in a series, you cannot charge your battery/cell with the charger that contains higher voltages at its output.

Final Words

Any solar battery cells can be charged by using an external charger if you consider the cell in the same way as a common rechargeable cell. When choosing to do this, you should familiarize yourself and gain knowledge of battery and cell types, their terminal voltages, and their current capacities.

You should also seek out detailed information of any of the available chargers. The charger you choose should have a compatible voltage level with your cell or battery for safe and effective charging. It should only provide a current that is within the safe limits of the cell, and it should also have a proper cut-off system for when the battery is fully charged, so you can avoid any fire hazards.

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