Can an Inverter Overcharge Batteries?

This question is often asked by new solar power users. And the concern is understandable since their appliances are connected to the system. If the inverter overcharges the battery, is it dangerous? We have the answers right here.

An inverter draws power from batteries, it does not charge them. An inverter charger however, charges batteries and can overload them..

Inverter vs. Inverter Charger

To understand the difference between an inverter and an inverter charger, let us look at how they operate, The following explanation will highlight their similarities and differences. It will also make clear why inverters cannot overcharge batteries but an inverter charger might. These are applicable to most solar inverters, including small 400 watt systems and large units with thousands of watt capacities.

How Regular Inverters Work

A regular inverter does one thing: convert DC to AC power. It is often used in solar power systems because solar panels generate DC power. To run most home appliances, you need an inverter to convert the current. A great example is the Giandel 5000W Modified Sine Wave Inverter.

Inverter sizes vary, from portable 100W types to 5000 watts. No matter the size, their function is the same, turn DC into AC.

In a grid tied solar system, the inverter does not require batteries. The grid supplies the power. In an off grid system, the inverter uses a battery bank to run whatever you load onto it.

The inverter does not charge the battery. The inverter takes power from the battery to run appliances.

Batteries in off grid systems can be charged by solar panels, a generator or another power source. Batteries can even be charged by electricity.

Whether your inverter is on or off the grid, there is no way it can power a battery. But it is a different matter if it is an inverter charger.

How an Inverter Charger Works

An inverter charger has all the features of a regular inverter, but it also has a transfer relay and battery charging function. The Renogy 2000W Inverter is a good example of this, capable of converting 12V to 120V and charge batteries too.

Designed for RVs and boats, inverter chargers have an integrated transfer switch. With this feature the inverter charger can sense if there is another power source available.

If there is a power source like AC for instance, the inverter charger automatically moves the load to this source. The system also uses that to recharge the battery.

As you can see, the only major difference between the two is the charging property. If you have a typical inverter and the battery gets overcharged, it is due to the solar panels or whatever power source you are using.

But what are the odds an inverter charger actually causes overcharging? If you have a well designed inverter charger by a reputable manufacturer, it is very slim. These systems have numerous safeguards designed to prevent this.

How an Inverter Charger Might Overcharge Batteries

So if you have power shore access and connect it to the inverter charger, the system will use that to recharge the battery.

Charging is similar to other batteries, and there is also the potential to overcharge. Ideally the system should have overload protection built in. Once the battery is full, the charging should stop.

A poorly designed inverter might overcharge the battery however. So the best way to avoid this is to use a charge controller. A charge controller has built in protection against overcharging and overloading, protecting both the battery and inverter.

Modern inverter chargers have protection against overcharging. But it does not hurt to be extra careful. Make sure to use the charging function only as directed.

What to Do When the Inverter Battery is Fully Charged

If your inverter has charging properties and the battery is full, you should turn it off. Most systems have a safety feature that stops the charge from accessing the battery when it is full.

The safest way to handle this is to unplug the charger. Inverter chargers usually have a control panel where you can see the battery charge level, usage, capacity etc. From here you can customize various settings and even shut it off.

Lithium batteries are particularly sensitive to overcharging. They have many benefits over lead acid batteries, but you have to be careful about overcharging them.

This is another case where a charge controller is important. Actually you should always have a controller when using solar batteries. But it is especially important if you use lithium batteries with inverters.

Does an Inverter Consume Electricity After Fully Charging a Battery?

Yes. An inverter always consumes power when it is turned on. Even if the system does not carry a load, it will use a bit of power when in standby mode.

If your inverter charger has fully charged the battery, the system should automatically stop charging. In some cases you may have to manually turn it off.

Whatever the case, an inverter or inverter charger will draw power when it is on. The only way to stop it is by pulling the plug.

Doing that prevents the system from using power. However the benefit of keeping the inverter in standby mode is it turns on quickly. And you don’t have to reconfigure your settings.

Think of the standby mode as your computer sleep mode. It is faster to open a computer from sleep mode compared to coming from a full shutdown.

Basically it comes down to a question of saving energy versus convenience. Some prefer one over the other so it is up to you.

it also depends on how much you rely on the inverter. If you are running an off grid system from the inverter, you definitely have to keep the system on. Otherwise your appliances will cease to run.

Why is My Inverter Battery Always in Charging Mode?

Solar inverters are always in charge mode to do trickle charging. This is how the battery remains charged.

If the inverter runs fine there is nothing to worry about. You should only be concerned if the inverter suddenly stops working.

Again, a charge mode is only available with an inverter charger. If you have a standard inverter, it will not charge the battery. The system will pull amps / current from the battery to run its load.

The above information assumes the inverter charger is not damaged of course. It is possible the always charging mode is due to a faulty connection somewhere. If you are not sure, inspect the wirings for the inverter and batteries. Loose wiring may produce all kinds of error messages on the system.

There is another possible reason why it is always charging. If you are using the inverter and power is being depleted, the system will keep charging so the load can keep running. In this instance it is appropriate.

How to Maintain Inverter Batteries

• Follow the instructions. This one is simple enough, but it offers the best protection against battery overcharging. Use the inverter or inverter charger only as directed.
• Use only compatible batteries. Most inverters work with FLA and lithium batteries, but check the manual first. And you should only use one type. Do not mix lithium, AGM and gel .This will not necessarily cause overcharging, but it could damage the inverter.
• Do not load at the inverter maximum capacity. If the inverter capacity is 3000 watts, the maximum load should be 2800 watts.
• Do not fully discharge the batteries. Doing so will have long term detrimental effects on the battery. Recharge at 50% for FLAs, and for high end AGM you can push it to 70%. For lithium you can discharge up to 90%.
• Maintenance. Lithium batteries do not need maintenance, but lead acid batteries do. Some need water refilling every two weeks for instance. Follow the maintenance schedule and it will go a long way to prolong the life of the battery.

If you are experiencing all kinds of problems with the battery charging, it could be a sign of wear and tear. Batteries that are several years old usually take longer to charge, but some display erroneous messages that it is overcharged when in fact it is not storing power.

Conclusion

One of the keys to ensuring solar power safety is understanding how each part works. If you have a regular inverter, you don’t have to worry about overcharging batteries from it. And if you have an inverter charger, take all safety precautions advised by the manufacturer.