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 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
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

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.

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