How Do I Charge My Solar Battery With A Generator?

Having a solar energy system for your household is a great thing for various reasons. You get to save a lot of money and it is also great for the environment. But sometimes the sun or the wind isn’t enough when it comes to charging the solar battery that enables you all the power for your household. Are there other ways to charge the solar battery and how to do it?

You can charge the solar battery on your solar energy system using a generator. For example, you can do it by using a high-quality 230-volt battery charger run from the generator’s 230-volt output. This option helps you to fully charge your solar battery as fast as possible.

It is important to mention that a typical mobile generator with nominal 12-volt output while charging a battery is about 13.6 volts. That means that the voltage may bring a flat 100 amp-hour battery to about half charge within 5 hours. That voltage is very low for fully charging your solar battery which means you’ll be needing a stronger generator.

Can You Charge Solar Batteries With A Generator?

Having an extra generator to charge the solar battery of your solar energy system is a great idea because there are going to be many times when the sun isn’t shining or the wind isn’t blowing which is why your batteries are going to be low. This is an extra option to charge your solar battery using fossil fueled generator.

One must mention that battery charging with a generator can often be a slow and shallow process, or it may barely work at all. For example, mobile generators run all day in vain attempts to fully charge the RV battery from the 12-volt output of their 230-volt generator. Even if it says ”battery charged”, that output is suitable for running small 12-volt lights and appliances without a battery. However, there are some options that can speed it up.

Benefits Of Portable Generators

The great thing is that there are portable generators that maintain their rated output for only a few minutes. That means that their continuous output limit is usually around 80% of the actual power. So in reality you are getting an 800-watt of power from a 1000-watt generator. However, this is more than enough to power a quality 30-40 amp charger.

It is important to mention that you don’t even think about buying a cheap generator, just avoid it. It is suggestable to not go under 99$ chain-store special because such generators are noisy and polluting. Another thing to mention is that their electricity output is ”dirty”. This means that they can sometimes do damage to so-called switch-mode battery chargers, or may not even run them at all.

High Quality RV Battery Chargers

Unfortunately, high-quality RV battery chargers are not cheap. The prices go around 350$ or more. But what is important is that you do not skimp on this because any savings on a cheap battery charger is going to be wiped out by its inefficiency and you do not want that. This means running the generator for longer and using more fuel as well.

One must say that some cheap solar battery generators and chargers can destroy batteries. There are some that can withstand over-voltage charging. That is why it is important to buy high-quality chargers that work quickly and reliably. Some popular brands are better than 90% efficient which is what you’re looking for.

Switch-mode Battery Charging Via Generator

As I mentioned earlier, there could be some issues with generator and switch-mode inverter chargers, which are smaller and lighter than transformer-based chargers. There are some switch-mode chargers that are reasonably efficient, on the other side, there are some that work well but need ”clean” electricity.

What is important to mention is that some cheap generator’s output is usually ”dirty”, particularly so if the generator runs out of fuel and sputters to a halt. In case this happens, it usually causes the switch-mode charger’s protection circuits to cut off the supply which can wreck the charger, and you don’t want that.

This is the worst that can happen to you because resolving this problem is almost impossible. Generator vendors usually deny responsibility because their products drive most electrical loads without problems. Not to mention that the battery vendors may also deny responsibility because, as they say, their products work fine on clean electricity. It is recommendable to buy the quiet inverter type units because these usually work very well with switch-mode chargers.

How Do You Charge A Solar Battery With A Generator?

The great thing about those of you who are thinking about getting a generator to charge your solar battery is that there are a few ways on how to do it. To be precise, there are 3 ways to charge your battery bank. You can read about these methods from best to worse (most efficient to least efficient). Most efficient means getting more kWhs per dollar spent.

The ideal situation to charge the solar battery of your solar energy system would be to have enough solar, wind, or micro-hydropower. The sad thing is that this can be almost impossible in some climates which is why some need to buy a generator. However, the best solution, when it comes to generators, would be a DC generator made from a fossil-fueled engine and 3 phase alternator that is rectified to DC.

Charging Your Solar Battery With Gas Powered Generator

Charging your solar battery with a gas, propane, or diesel generator can cost anywhere from 2.50$ to 5.00$ per kilowatt-hour compared to the .05$ to .60$ per kilowatt-hour most utilities charge. This option is very expensive as well as an environmental disaster. Most fuel-powered generators have very little emissions controls and are made to wear out in a matter of months when being used to charge solar batteries in an off-grid power system. 

The following steps will show you how to charge the solar battery with a generator using as little fuel as possible. The recommended maximum charging voltages for most AGM or gel batteries are around 14.6 volts. However, it is very important to check the manufacturer’s recommendation in order to do it right.

Bulk Charge At 10% Of The Battery Bank’s C20 Rate

This method requires you to set up your system to charge the solar battery efficiently which is why you must program your inverter or battery charger to charge at 10% of the battery bank’s C20 AH rating. It is advisable to consult your battery manufacturer’s literature for the C20 amp hour rating.

To get the most out of the generator you bought to charge your solar battery, try your best to achieve the 10% of the bank’s AH rating. However, there will be times when this is not possible such as having too small of a generator or too small of a charger. You could charge at a lower current, but it wouldn’t be as efficient.

On the other hand, if you charge with more than 10% of C20, you risk damaging the batteries due to overheating and over gassing. Even if you have a much larger battery generator, 45 amps are the target charge rate for this battery bank. Any less will result in excess generator run time and fuel consumption, any more can result in damage to your solar battery.

Program Correct Bulk Voltage Into Charger

Bulk charging is a method when you apply a predetermined amount of current (10% of C20) to your batteries until a specific voltage is reached. This specific voltage is known as the bulk voltage. If your solar battery bank is low all of the charging capability will go into the batteries. 

It is advisable to consult your solar battery manufacturer for the correct bulk voltage setting. The next step would be to examine your charger’s manual to learn how to program the bulk voltage. Some manufacturers list that you need to be careful in these situations:

  • the bulk voltage per cell
  • the bulk voltage per battery
  • the absorption voltage
  • the bulk/absorption voltage
  • the bulk voltage as a range
  • the daily charge voltage

Determining Bulk Voltage With Multiple Cells

If your bulk voltage is listed per cell, think of each cell as being two volts:

  • a 6-volt battery of battery bank has three cells
  • an 8-volt battery or battery bank has four cells
  • a 12-volt battery or battery bank has six cells
  • a 24-volt battery or battery bank has twelve cells
  • a 48-volt battery or battery bank has twenty-four cells

Once you know how many cells you have, you need to multiply the volts per cell by the number of cells you have. If your battery bank is 48 volts you know it will be made up of 24 cells.

Design A System That Will Shut Down Once Bulk Voltage Is Reached

One must mention that the bulk charge, when done correctly, will bring your solar battery bank to an 80% state of charge. Using your generator for anything but a bulk charge is very inefficient. It would be better to use your generator as a bulk charger and your solar, wind, or micro-hydro to bring the batteries to 100% state of charge.

How Fast Will A Generator Charge A Battery?

If you asking yourself how fast will a generator charge a solar battery, it is important to mention that a generator’s typically unregulated 13.6-volts is far too low for full and fast battery charging. However, it may half-charge a flat 100 amp-hour lead-acid battery within six hours or so. One must mention that from there on, charging progressively reduces. And it may take a further 24 hours to charge it over 70%. And a week or more to fully charge it which is quite a slow process.

However, there is a simple and effective solution to this. You should charge the battery with a 240-volt (or120-volt) battery charger powered by the generator’s 240-volt outlet. The size charger required varies with battery capacity and types as well which is particularly so for LiFePO4 batteries.

There is a general guide. For example, most lead type batteries below 180-200 amp-hour typically have a recommended maximum charging current of fewer than 40 amps. For these batteries a 25-amp charger is adequate.

Reasons Why Generator Isn’t Charing Your Solar Battery

It is important to mention that there could be some reasons or malfunctions as to why the generator you bought isn’t charging your solar battery. If the solar battery hooked to the solar system isn’t charging properly, the failure can be caused by a variety of issues. It could be a battery problem, wrong system wiring, or a problem with the solar charge controller settings.

Diagnosing Problems With Your Solar Generator

There are a few steps on how to diagnose the problem:

  1. You can use a multimeter to measure the entire system. It will measure electricity from the solar battery and solar charge controller to the solar panel. You should first disconnect the solar panel and measure the voltage.
    • As long as there is sunlight, there will be solar output. If however, the voltage cannot be measured, it may be a problem with the solar panel or rectifier diode. It is also important to mention that is necessary to measure the voltage of the battery.
    • The actual battery may be less than 20% of the nominal voltage. This is when an extra charger is needed to charge the solar battery.
  2. Another step would be to measure the terminal output voltage of the solar charge controller. You should examine whether the output voltage is within the proper range.
    • If the output does not reach the defined value, it is probable that the solar controller has problems. Then you should replace the charge regulator to try to fix it and make it work again.
  3. The last method would be to test the solar batteries. You should measure the battery voltage and make sure that the battery voltage is not too high nor too low.
    • Both too high or too low affects the charging which is what you should take into consideration.

Solar Charge Controller Isn’t Charging Battery

If the solar charge controller isn’t charging the battery correctly, there are 4 factors your need to consider. They are the solar charge controller factors, solar panel factors, solar battery factors, and environmental factors like weather. This is a common problem that many people will encounter and it is easy to solve. 

Follow the instructions step by step to troubleshoot and replace the solar charge controller. This will restore the connectivity of the solar system. However, one must mention that a solar panel won’t charge a dead battery. This is why you should take good care of it. The solar charge controller will automatically detect the battery voltage.. And if the battery is dead, the charging process won’t work. 

It is recommended to use an individual battery charge to fix and restore the dead battery. Do this before reconnecting it to your solar system again. It is very important to read all the manufacturer’s instructions to do all these tasks and take good care of both your solar system and the generator. If you have any questions, we advise you to reach out to your generator’s manufacturer and ask for advice.

Further Reading On Solar Generators

For more information on solar generators, try reading through some of our detailed articles below:


I'm trying to make the world a bit greener every day, whether that's through my day job or helping others make green choices for their homes.

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