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Hopefully this is on-topic here. I'm open if I should as on another SE site.

We have an air conditioner heat pump outside, typical to most homes with one. When it kicks on, many of the lights dim for a split second.

Assuming it is not an old unit and it has a problem (maybe it is?) - I am wondering if I can put a UPS (battery-backed power supply) between it and its breaker on the panel. I admittedly don't know if this meets local code.

I would like to first understand if it's a viable solution to home line levels. I'd also like to understand how I should think about its impacts on the lifetime / 'MTFB' of the UPS I'd use.

I understand there will be lots that is specific to the sizing of the heat pump (its load), and maybe other factors. I'm happy to update this question with other needed details.

New Alexandria
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  • You need to call an electrician because this absolutely should not be happening. Fix the house wiring. And yes, Home Improvement Stack and Electrical Engineering Stack would probably be more focused. As written, the question isn't specific enough to be a good fit here. – Phil Sweet Aug 09 '23 at 20:50
  • You can try, but that is not what a UPS is for, and is unlikely to have the desired effect. You might instead connect it to the lights that dim to power them through a momentary loss of power. Whatever you try, make sure your UPS is rated for the amperage needed by what you plug into it and then some. From the other end, you are better off figuring out why your system needs more power than it's getting during that startup. – Abel Aug 10 '23 at 03:09

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The motor on the heat pump has so much inrush current that your line voltage is dipping. This is not a fault, but it's not going to be exactly the same for every other system.

In industry, a common solution is to buy an inrush current limiter. People use these to avoid blowing fuses and circuit breakers, or destroying their UPS with too much current demand.

Another possibility would be to upgrade and modify your house wiring, so that the heat pump is not on the same circuit as anything else, and so that your utility supply can handle the demand.

Another possibility would be to put ~everything else~ on a UPS, so that when your supply voltage dipped, your lights didn't see it.

Another possibility would be to buy a type of light that doesn't dip when there are short voltage dips -- tube florescents are often less sensitive to this kind of dip.

Trying different bulbs, and checking that the lights are on a different circuit are easy places to start.

david
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