How Many Batteries for a 3000 watt Inverter?

You are here because you want to run a 3000-watt inverter from one or more batteries.

No problem.

Let me tell you how you should do it. Read the whole article because most blog articles which are answering this question get it wrong.

We need to satisfy two criteria before we can tell you what battery you need. These are:

  • C-rate (in this case, discharge)
  • Current

C-rate

The C-rate of a battery is the rate at which the battery can deliver the promised capacity of a battery. For example, the C-rate of a 100Ah lead-acid battery is 0.2C. That means that we can discharge the battery with a 20 Amp load (100Ah x 0.2= 20A). You can discharge the battery with a higher load, let’s say 40Amps, but then the capacity of the battery will be reduced because of internal heat generation.

The C-rate of lithium batteries (LiFePO4) is 1. That means that a 100Ah battery can be discharged with a 100 Amp load and it will deliver 100Ah.

We want to respect the C-rate of the battery because that will give us the longest battery life. If we abuse the battery by discharging at a higher current than it’s made for, then the battery will get damaged and its lifespan will decrease.

Current

The second point is the current draw from the battery to the inverter. We do not want to draw lots of current from the battery to the inverter. If we do, we need big and heavy cables. Big and heavy copper cable means a lot of money.

Another point here is that if you crimp the wires yourself, you want to limit the current. Your crimping tools might not be suited for a high current application. Therefore we need to be safe and reduce the current. I recommend not going over 100Amps if you create the system yourself.

Now how do we reduce the current in the wires?

Easy!

Increase the voltage.

These are my recommendations for system voltages respectively to their inverters:

  • 12V battery system -> inverter below 1000W
  • 24V battery system -> inverter from 1000-2000W
  • 48V battery system -> inverter from 2000W to 4000W
  • More inverter power -> have multiple inverters in parallel

If you want to run a 3,000W inverter, you should have a 48Volt system. This will reduce the current to a safe level in a DIY system. If we calculate the current, it will be: 3000W/48V=62.5A, now imagine having a 3,000W inverter on 12V: 3000W/12V= 250A!

Putting it all together

We know that we need to have a battery that has enough capacity to satisfy the c-rate and we need to have a high voltage battery.

Lead-acid

If we build this system with 12V 100Ah lead-acid batteries we can calculate the following:

We know that we need a 48V system. That’s 4 batteries in series.

If we put 4 batteries in series we have one 48V 100Ah battery.

The c-rate of lead-acid is 0.2C. We can draw 100Ah x 0.2C = 20Amps. That’s not enough to power the 3,000W inverter.

We saw previously that we need 62,5A if we have a 48V system. That means we need three parallel strings of 4 batteries in series for a total 12 batteries.

12 lead-acid batteries in hybrid connection 4 batteries in series and then 3 in parallel for a total of 12 batteries
12 lead-acid batteries in hybrid connection

That is how you efficiently run a 3,000 inverter on lead-acid batteries.

Lithium

If we do the same calculations for a 12V 100Ah lithium battery, we become the following:

We still need a 48V system. So the 4 batteries in series stay the same.

We now have a 48V 100Ah lithium battery.

The c-rate of lithium is 1. We can draw 100Ah x 1C = 100Amps. That is enough to power a 3,000 watt inverter without damaging the battery.

You need to have 4 lithium batteries in series to power a 3,000 watt inverter.

4 lithium batteries in series
4 lithium batteries in series

Read my article about the best 12V lithium batteries.

Conclusion

Figuring out what kind of battery you need to run a 3000-watt inverter is not as straightforward as you think. Hopefully, you know now how to put your system together. Remember that lithium is cheaper in the long term.

If you want to know more about connecting batteries in series or parallel, visit my guide with diagrams here.

Get my book on Off-Grid Solar Power

19 thoughts on “How Many Batteries for a 3000 watt Inverter?”

    • Hi Nick,
      I agree with SEJANAMANE, this is great info and I love the way you present and organize the details. I also picked up the book!

      Reply
    • Good day SEJANAMANE

      I am about to go off grid.

      I have a 200/250w solar panel
      a 30a control charger
      A db box with 4-6 breakers at 32a fuses one is 10a for the lights… And a 200ah lead solar battery.

      I had a 1500w inverter it burnt out.

      But i now want to get a 3000watt inverter

      How do i go about my system now what will i need?

      Another battery?
      Another control charger
      Bigger fuses
      Bigger solar panel

      Please help!

      Kind regards.
      Kaylin Lance Dawson.

      Reply
      • The maximum current you should draw is 40A (200Ah*0.2C-rate). A 12V, 3000W inverter will draw 250A max. You need to increase your battery capacity to 400Ah and get a 1000W inverter instead. That will give you a max current draw of 83A. That is a properly sized system.

        Reply
        • Super. Thank you so much.. I did forget to mention that the load i want to put on the inverter is over 1500watts daily use(appliances) {no heated appliances}.

          How many batteries should i have for a 3000watt inverter and should my charge controller (30a) be bigger as well as the fuses in the db box (32a)

          Reply
          • For the current: 3000W/48V=62A or 3000W/24V=125A. Up to you to choose 24 or 48V. I recommend using server rack lithium batteries.
            Lithium: 125Ah*0.5C=50A => 48V,125Ah (6kw) or 24V,250Ah

        • Ok so i figured that
          1000w-2000w inverter will be safe on 2x 12v batteries of 200ah correct?

          So if my load is say 1400w (all appliances)
          Is it safe to say i can run a 1500w inverter on 1x 12v 200ah battery as not all the appliances that = 1400w will be operating at the same time and those that will be will = to 780w(appliances) used throughout the day, on and off (on from 8am-12pm and off from 12pm-4pm and on again from 4pm-10pm.

          Reply
  1. quick question I have eight 12v 20Ah how many to power my home? I have 12 100 watt panels could you please give me some info on what I should do please and thank you, I too am getting your book..

    Reply
    • Hello Roy, first, you need to find out how many kWh you need in a day. The worst-case scenario would be winter. From there you can fill in my off-grid load calculator. This is located in the top menu. From there you can go and put your system together.

      Reply
  2. if I want to start with about 1000W need but plan to grow, which is best, to purchase the larger inverter & 12V battery up front and grow battery capacity as needed or purchase a smaller inverter and battery and upgrade batteries and inverter as needed.

    Reply
    • If you know your loads will increase, you should get the bigger inverter. However, you need to size the wires and fuses based on the bigger inverter. That’s going to cost you more. Alternatively, you can add more inverters in parallel to increase the output later. Then you need a more expensive inverter that can do this. Keep in mind the idle current of a bigger inverter is bigger.

      Reply

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