Heat Pump Startup Makes The Lights Flicker,,, Is That OK??

[CADplans]

Well, we have a new heat pump, I watched the tech monitor the running amps,, only about 17 amps.
The compressor is a "screw type" rather than a piston of the old days,,
The screw type should have lower startup amp demand.. no pistons to get moving,, ?

What surprises us, is that the lights will "dim" momentarily as the compressor starts.

I am wondering if I now notice this because of the new LED bulb technology, or is it an issue with my power coming from the utility?
(NOTE: We have not noticed anything else to be capable of making the lights dim)

The reason I want to blame the LED bulbs rather than the incoming power is the extreme speed that LED bulbs can respond with turn off/on.
I notice this on the taillights of cars, if the pickup has an LED third brake light, and filament regular taillights, you see the LED come on and off quickly.
The filament bulbs in the other taillights slowly come on,, then slowly turn off.

So, filament bulbs would tend to "look" like they stay on, even if the power fluctuates for a very short time.

I have checked the wire sizes, the connections, there is a new breaker installed.
I have a strange electrical service that was typical in the 1970's,,
The heat pump breakers are in their own panel, with its own main feed coming from the meter base.

The lighting that dims momentarily is connected to a separate main 200 amp panel, that is connected to the same meter base.

There is no "main" breaker in the heat pump panel, only the small 60, 30, 25 amp breakers.

If this is an issue, it seems like it must be due to the transformer servicing my house.
(I am the only one served by that transformer.)

Even if that compressor required 4X amps,, that should only be about ~70 amps,,
I would not imagine that small of a load to be able to make the lights dim??

So, if my bulbs dim on compressor startup, should that be something I investigate further,,?
or do I just learn to live with another "QUIRK" of LED lighting??

 

[Will S]

LED bulbs are very sensitive to even slight voltage (instant) fluctuations. Nothing to be concerned about.

 

[ultrarunner]

Yes but the LED kept working when utility power was 56 volts for several days due to a blown pole transformer...

The T-8 ballasts in the neighborhood kitchens were all toast.

Is the heat pump adequately wired?

Code here often requires heavier gauge such as all 30 amp dryer circuits must be 8 Guage... and similar.

 

[2manyrocks]

Are all the connections tight? (obviously checked with the power shut off)

Do you have copper or aluminum service entrance wiring?

 

[CADplans]

Is the heat pump adequately wired?

Code here often requires heavier gauge such as all 30 amp dryer circuits must be 8 Guage... and simil

That would be easy to rewire,, from the panel to the disconnect outside is only 4 feet,,
Then the outdoor disconnect to the outside compressor is way less than 6 feet.

Presently, it is wired with 10 gauge.

The outdoor unit specifies that the maximum circuit protection shall be 25 amps,,
Should I use 8 gauge, or 6 gauge??

I doubt that 6 gauge will fit in a 25 amp breaker,,,,,,,,,,,,

If nothing else, a larger wire may make it easier for the compressor to start,,
the compressor may last longer,,,,,,,,,

 

[CADplans]

The service entrance to the panels is aluminum, everything else is copper.

I would have to get the electric company out to tighten the aluminum..
they would readily do that,, they are SUPER accommodating to things like that.

 

[2manyrocks]

I suggest that you get them to check the tightness of your service entrance connections and see if that helps. While they have the power off, that would be a good time to check other major connections.

 

[RustyA]

200 amp service here house built in 2000. Our 5 year old screw type 18 seer heat pump slightly dims our led bulbs on startup. I would not worry about it.

 

[ponytug]

Have you checked to see if you can see the voltage drop with a meter?

If you install a larger gauge wire, there will be a higher voltage at the heat pump, which will lower the current draw. Whether it lowers the draw to the point of the LED dimming not being noticeable is a different question. A larger wire will slightly reduce the wasted energy due to the higher resistance of the existing wire. I believe 6ga wire is as large as you can go into a 35Amp breaker. If it were me, I would replace the breaker while you are at it on general principles.

There is also the possibility that the electrical service itself has a higher resistance point in it, but if that were the case, I would have expected your old heat pump to dim your lights even more.

I think if it were me, I would be inclined to wait and see if it bugged me enough to go through the hassle of upgrading the wiring. It is going to cost more than a candy bar, and might make no observable difference.

All the best,

Peter

 

[2manyrocks]

Aluminum expands and contracts over the years sometimes loosening the connections. This is a common problem with 1970 era houses built with aluminum service wiring. Sometimes water gets in the service entrance causing enough corrosion to increase resistance. If the local utility will check it for free, I would ask them to check it, especially if it is an older home.