Difference between UPS & Inverter

@thebigk • Oct 26, 2024

Oct 26, 2024

1.4K

It looks like there's a lot of confusion about the difference between UPS & Inverter. This seems to be one of the common question asked in electrical / electronics exam viva and also something everyone (irrespective of your engineering discipline) should know - because if you are in the area that gets frequent load shedding, you ought to buy one at your home or home office. Let's have a quick look at the difference between UPS & Inverter.

UPS Explained (In Layman's terms)

UPS is an abbreviation of of Uninterruptible Power Supply or Source. There is a good chance that your desktop or laptop or printer is connected to the main supply via UPS in between. Why is it required? Well - the function of the UPS is to provide instantaneous or near-instantaneous make up for the sudden power loss which may damage the sensitive electronic gadgets like computers, printers, servers etc. The UPS box would contain a battery and some circuitry (will explain below) that makes this happen. Most UPS are designed to protect gadgets from voltage spikes, voltage drops, instability of the main frequency and harmonic distortions as well.

Following UPS diagram will make the things clearer (what's inside the box) -

Image Credit: Wikipedia

As you can see - there's a batter that kicks in when something abnormal happens to the power source. Under normal circumstances, the charger will keep charging the battery so that it's ready for the power issues. Remember that the battery provides DC supply which must be converted to AC before it can be fed to your electronic gadgets. That's where the inverter comes into picture.

Inverter Explained (In Layman's terms)

An inverter inverts - from DC to AC and the output AC can be upped to any level required with the use of transformers. That's all about it, you should know. There are several types of inverters, but that's beyond the scope of this discussions (if someone's interested, discussions are welcome).

So, the battery inside your UPS feeds the inverter with DC power and the inverter 'inverts' it into AC supply.

The thing to remember: A UPS has inverter 'inside' it. Most of the people will tell you that they've bought an 'inverter' at their house to address the load shedding. Understand that what they're referring to is an 'inverter' with a 'battery'. Because only 'inverter' won't solve your power problems on its own.

So it's the battery that solves your power backup problems.

What I find astonishing is that most of the people have differentiated UPS & Inverter on the basis of 'switch-over' time, which is beyond me. Would love to hear your thoughts on the topic.

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Ramani Aswath

@ramani-VR4O43 • Apr 25, 2013

K: What I find astonishing is that most of the people have differentiated UPS & Inverter on the basis of 'switch-over' time, which is beyond me. Would love to hear your thoughts on the topic.
Generally UPS refers to a situation where the power is always through an inverter. On the input side of the UPS one has a AC to DC step down rectifier that is permanently connected to the battery. (I have to qualify this with the proviso that there can be circuitry that protects the battery form overcharging)
The battery is connected to an inverter and pulse smoothing circuitry that provides acceptable sine wave out put. Circuitry can be added to ensure that the out put voltage is within specifications and spikes are snubbed.

What this implies is that whether the mains supply is present or not the output is always from the inverter through the battery on the input of the UPS. This means that there is no switching required at all since it is always the battery that is the prime source of supply to the inverter.

We had to use such UPS in certain defence projects, where reliability has to be guaranteed. Sometimes even redundant UPS are used.
For less critical applications what you have said applies.
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Kaustubh Katdare

@thebigk • Apr 25, 2013

I referred to a few of the UPS circuit diagrams and found the simplest one on Wikipedia which shows that batter is in parallel with the supply and kicks in only when there is distortion in the supply. I get the point that the output is always through the inverter - and is provided by the battery.

I'm wondering whether the switch has been completely eliminated from the modern designs? Also what are the advantages and disadvantages of such system?

One immediate disadvantage I think is that the battery will always be in the power consumption mode -which may result into higher electricity bills.
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Ramani Aswath

@ramani-VR4O43 • Apr 25, 2013

One immediate disadvantage I think is that the battery will always be in the power consumption mode -which may result into higher electricity bills.
UPS is wasteful. Expensive, long life batteries and elaborate protection circuitry is built into sophisticated UPS systems.
A truly uninterrupted supply splurges power. Cost is given the go by.
I am wondering if we can think of a bridge ultra capacitor between the parallel supplies you describe, which can bridge the time of changeover. In that scenario ordinary solid state switches can do the job. Costs can be contained.
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Ankita Katdare

@abrakadabra • Oct 6, 2016

Someone asked me to answer this question on Facebook DM. Just shared this link. CE is such a rich resource for answers to innumerable questions.
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