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To power a 5000W inverter, you have to consider more than just the number of batteries. The battery capacity, the inverter voltage input and how long you need to use the inverter are important. Large inverters are used as emergency power backup, so determine how many hours the system will run. The formula is hours needed x watts = total watts / volts = battery amps.
A 5000W inverter requires at least one 450-500ah 12V battery or two 210ah 12V batteries to run for 30-45 minutes. A 750ah 12V battery is needed to run the inverter for 1 hour. A 2500ah battery is required for a 4 hour discharge time. You have to double the capacity for each if you don’t want to discharge the battery at 100%.
Batteries for Inverter Calculation Examples
To illustrate further, suppose you bought a 5000W inverter with a 12V input like the WZRELB Pure Sine Wave. If you use the inverter’s full capacity, that is 416 amps an hour. (5000W / 12V = 416). Theoretically a 450-500ah battery can run the system for an hour. But inverters are not perfect and some energy is lost, so more likely it is 30-45 minutes. Of course the figure will be different if you have a 24V, 36V or 48V battery.
However that figure supposes you will run the battery down to zero, or a 100% discharge. We have stated in other posts on this site that lead acid batteries should be recharged at 50%. So you need at least a 750ah-800A battery to run the inverter for 30-45 minutes without totally depleting the battery.
No matter what the voltage is, the ah rating in series configured batteries will always be that of the smallest battery in the setup. Multiple batteries increases voltage so the power supplied (in watts) increases.
With four 210ah 48V batteries, the inverter receives 104ah hourly. With a full discharge the inverter can run at maximum load for two hours or 10kwh (10,000W). Bottom line: no matter what the battery bank voltage, it must provide 5000W for every hour you want the inverter to operate.
Battery Size for Inverter Chart
This chart shows how much power is required for different types of inverters. This table assumes you’ll be using the battery to full capacity. Double the capacity for each column if you’re going to recharge the battery at 50%. The optimum capacity is for a four hour discharge, and the minimum is for one hour.
|Inverter Output in Watts||Optimum Capacity||Minimum Capacity|
Again, the DOD (depth of discharge) here is close to 100%. You can do that with lithium batteries but for lead acid the DOD is at 50%. These inverter and battery sizes are common for solar powered homes. They are less frequent in RVs except for the really large ones. Make sure the capacity is suitable for your camper before buying.
How to Find the Right Battery Inverter Size
The calculations above are useful if you want a general idea of how much power you need. But if you want to be more specific, follow these steps.
1. Add your Total Load Requirements
5000W is a lot of power but do you really need that inverter size? The best way to find out is to add up the total watt usage of all your loads. Include every appliance and device you plan to run on the inverter. Do note that refrigerators and air conditioners have surge requirements so a large system is definitely required.
2. Check the Inverter Input Voltage
A lot of inverters have 12V or 24V input, but 36V, 48V and even 96V and others are not uncommon. Make sure your battery matches the input. The battery doesn’t have to be a specific match as long as the total is the same. Example, a 48V inverter will work with a 12V battery if you have four hooked up (12 x 4 = 48).
3. Determine How Many Hours You Need to Run the Inverter
This is crucial. How long do you plan to run the inverter? Is it for a couple of hours? 5 hours? 12 hours or more? This tells you how many watt hours you need and how much the battery capacity has to be.
Suppose your 5000W, 48V inverter needs to run for 6 hours. If the power load factor is 0.8 then the volt amperes (VA) is 130 amperes. Your battery must be able to provide minimum 130 amperes. 48V 130 ampere batteries are uncommon so you may opt for a 200 amperes instead.
4. Calculate Battery Storage Capacity
Battery capacity is measured in amp hours (ah). With our example here you need four 200ah-220ah batteries. We like the PowerStar 200ah batteries because they are leak free and have a low pressure vent design. That should be sufficient to run a 5000W inverter for 8 hours more or less.
These steps are best suited for homes that need a large power backup. For RVs, the needs are usually smaller and the calculations more straightforward.
Calculate Battery Size for Inverter For RVs
For RVs it is much simpler. Add the total watt consumption of every device you will run and divide it by 12. 12 is for the voltage which most RVs use. If the total is near 5000W then a you need a 460ah-500ah battery. If not, a smaller inverter will do.
Most RVers have a solar generator to power their devices. If you have a solar panel installed you probably don’t need such a large inverter. While a solar generator can power a refrigerator, most RVers use a mini fridge to save power.
You will need more than 5000W if you decide to run an AC though. Powering an air conditioner for 10 hours is about 7000W. You need a 640ah battery minimum. At a 50% depth of discharge that is almost 1300ah or thirteen 100ah batteries This is why you rarely see RVers use solar power for refrigerators or AC units unless it is a compact version. They just consume too much power that could otherwise be used for other appliances.
Battery Overhead and Discharge Rate
Technically , 416 amps is sufficient for 5000W, but add another 50W for overhead so it’s 460. So 460ah or better yet 500ah will operate an inverter without any problems. A faster discharge rate erodes the battery bank’s life cycle. A slower discharge rate does the opposite.
A 460ah battery bank keeps the inverter running for 30 minutes at a full 5000W. Lowering the inverter load prolongs the battery life. Reduce the load from 5000W to 3000W and the battery will last an hour or so. You can do this with any inverter, but do so only if it’s practical. If you calculated your total load requirement and realized you don’t need to use that many, load reduction will help the battery.
Should Inverter Batteries be in a Series or Parallel Connection?
It depends on the inverter. Check your inverter installation guide and it will tell you whether to configure the batteries in series or parallel. Both connections have the same purpose, increase power that goes in the inverter. Whether it is series or parallel, the input power will be similar. Current x voltage = input power. A series or parallel configuration will not change that.
However, connecting batteries in a series has some advantages. You can use smaller wires, reducing energy loss. A parallel connection means each battery has a unique internal resistance. The long and short of it is this leads to unequal power distribution in the system.
However there are cases where a parallel setup may be better. You can find more information in your inverter’s installation manual. You may also find relevant information in your battery’s product guide.
Other Points to Consider
These are large numbers so you need to plan ahead before committing to buy. To recap here are the biggest points you should bear in mind.
- The inverter capacity
- The inverter DC input voltage
- The load you will supply to the inverter
- Most 5000W inverters have a 24V or 48V input. You can buy 48V batteries or any battery volt as long as the total is 48.
- Do not let lead acid battery discharges drop below 50%. When calculating battery sizes for inverters, assume that you will use only 50% of the battery capacity.
- The battery capacity determines how long the inverter can run. This is important if you will use the inverter as a backup power system.
- A tubular battery is better suited for an inverter than flat plate batteries.
The inverter is one of the most important parts of a solar system. If it is too small the system will not run. If it is too big the batteries will not be optimized. By knowing how many batteries are needed, and the right specs, you’ll have no issues running solar power to the maximum potential.