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You are here: Home / Tech Questions & Answers / Q&A: Will a ‘Modified Sine Wave’ UPS damage a computer?

Q&A: Will a ‘Modified Sine Wave’ UPS damage a computer?

Posted on July 2, 2025

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Question from Celina:  I have a question about battery backup devices, Rick.

I went to our local office supply store to buy a battery backup for my iMac and the man I talked to said I needed to pay extra for one that provides “pure sine wave” AC current. The one he tried to sell me costs over $100 more than the one I had planned to buy.

He said the cheaper “modified sine wave” models can damage my iMac because it was designed to only accept only a pure sine wave signal. Is that true? 

I’m a very frugal person and I hate wasting money by buying something that’s more expensive than it really needs to be. But then I don’t want to damage my computer either.

What’s your opinion on this? And if you don’t mind, can you recommend a battery backup/UPS that would be a good fit for my iMac?

Rick’s answer: You’re right to be concerned about the safety of your iMac, Celina.

They are great machines, and as you know aren’t exactly cheap. But that being said, I don’t believe you need to purchase a pure sine wave UPS for your machine.

The power supplies in virtually all well-built modern computers can tolerate a modified sine wave AC power source just fine. In fact, there are millions of them being used every day around the world.

You do need to pay attention to the size of the unit (in VAs) however. Make sure you get one that has enough battery capacity to provide steady current to your computer and other devices without having to work at its full load potential.

You didn’t specify the actual model of your iMac, but any quality battery backup unit that’s rated at 600VA or higher should work just fine for you and give you a decent cushion in terms of reserve capacity.

Since you asked for a specific recommendation, I believe this one from APC would be a great choice. I own three of them and they’ve been workhorses in my home and office for going on three years.

Bottom line: You don’t need to pay extra for a Pure Sine Wave UPS. Just choose a good brand that can comfortably power your computer without having to “strain”.

Bonus tip: This post explains why your surge protectors could be giving you a false sense of security.

 







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