Inverter Backup Calculator Widget

Add an inverter and UPS backup calculator to your website. Buyers enter the number of batteries, their Ah and voltage, the load and the inverter efficiency to see how long the backup lasts - or enter the hours they need to see the battery size to buy.

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<iframe src="https://a2z.tools/embed/w/inverter-backup-calculator" title="Inverter Backup Calculator by A2Z Tools" width="100%" height="830" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

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How it works

The widget uses the A2Z battery engine. A bank's stored energy is batteries x Ah x volts whatever the wiring, but the wiring decides the bank voltage and current: series strings add voltage, parallel banks add amp-hours. Backup time is the usable energy (after the depth of discharge you allow and the inverter efficiency) divided by the load. In reverse, it finds the Ah each battery needs for a target backup time. A rough inverter VA rating is shown too; it divides the load by an assumed power factor of 0.8, a sizing convention rather than a measured value, and the widget labels it that way.

Calculation method

  • Bank energy (Wh) = number of batteries x Ah x V
  • Backup (h) = bank energy x usable % x inverter efficiency / load W
  • Ah needed (bank) = load W x hours / (bank V x usable % x efficiency); series: each battery = bank Ah, parallel: bank Ah / count
  • Inverter VA (assumption) = load W / 0.8, rounded up to a whole VA

Worked examples

Two 150 Ah batteries on a 24 V inverter

Inputs: Backup time, 500 W, 2 x 150 Ah 12 V in series, 85% efficiency, 80% usable

Result: 4 h 54 min; bank 24 V 150 Ah; 3.6 kWh stored, 2.45 kWh usable; inverter at least 625 VA

3,600 x 0.8 x 0.85 = 2,448 Wh; 2,448 / 500 = 4.9 h.

Battery size for four hours

Inputs: Ah mode, 500 W for 4 h, 2 batteries in series, 12 V each, 85%, 80%

Result: 122.5 Ah per battery

2,000 Wh / (24 x 0.8 x 0.85) = 122.5 Ah.

An estimate for planning. Battery capacity falls with age, temperature and high discharge rates; ask the battery and inverter maker or a qualified installer to confirm the system size.

Limitations

  • No Peukert or temperature correction; lead-acid banks at high current deliver less than this estimate.
  • The 0.8 power factor behind the VA figure is an assumption, not a property of your load.
  • Does not account for the inverter's idle consumption, charging time or battery ageing.

Where publishers use it

  • Inverter and battery dealers' product pages
  • Home-backup buying guides for regions with regular power cuts
  • Electricians quoting UPS systems for shops and offices
  • Rural and off-grid energy blogs

Questions

Do series or parallel batteries give more backup?

Neither - the stored energy is the same. Series wiring raises the voltage (for a 24 V or 48 V inverter), parallel wiring raises the amp-hours at the same voltage.

What efficiency should I use?

The figure in the inverter's datasheet at a load close to yours. Efficiency usually drops at very light loads, where the inverter's own consumption is a larger share.

Why use only 80% of the capacity?

Discharging a battery completely shortens its life, and many inverters cut off before the battery is empty. Set the usable percentage to what your battery maker recommends.

How is the inverter VA figure worked out?

As the load in watts divided by 0.8, an assumed power factor for mixed household loads. Motors and compressors need extra headroom for starting surges, so check the maker's sizing advice.

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Inverter Backup Calculator
https://a2z.tools/battery-backup-runtime-calculator

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