I have a customer who bought an existing building and remodeled it. The entire electrical, HVAC systems, etc were replaced. We installed a new 400 Amp Single-Phase Service(120/240 Volt), and the local utility company connected the new service to their old bank of transformers. When the ACs turn on, the lights dim. We have checked connections, wire sizes, etc, and everything is fine. The engineer for the utility company suggested there was a problem with "Scroll Compressors". They are going to change out the transformers, and increase the size of their secondary wiring feeding this service. Does anyone know anything about, or experienced this problem with these type compressors?
Scroll AC Compressors
- Thread starter bozone
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- Status
barbeer
Senior Member
- Location
- Pinellas County, FL
This is a relatively common thing....... I did not know that a scroll compressor would cause it any more than a regular compressor, maybe there is greater in-rush?
barbeer
Senior Member
- Location
- Pinellas County, FL
Rheem used to say "scroll inside" on the units, I still do not exactly know what it was, maybe a gimmick!
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I looked at the Carlyle website and depending on the size of the unit, a single phase unit without 2-speed motor or VFD could have an inrush as high as 150A.
Certainly this could pose a problem for the transformers ahead of the service entrance, depending on how the service was sized.
Certainly this could pose a problem for the transformers ahead of the service entrance, depending on how the service was sized.
Disclaimer: I'm not real familiar with 1ph motor starting issues.bozone said:
Mike H told a pretty good story in one of his classes about the AC dimming his house lights. The POCO put in a pretty good size xfm and he still got some dimming.
A power monitor here would be really good. See exactly what is causing the dimming and if the fixes are infact doing anything.
The utility is doing their part and that's good. But it still may not be enough (see MH story).
Look at the compressor motor inrush - possibly a really high inrush for motor size, and a really low pf. If that is it, here are a couple of suggestions:
1. I never hear about anyone using pf correction capacitors on 1ph motor loads. I don't know why not. Call the AC mfg and see it they have any suggestions for sizing. Consider sizing for minimum dip at inrush. Even if you let then stay on-line during running (after inrush is over), the only downside is a slightly leading pf
2. Ask the mfg for data on the inrush current. Also ask if they have data on what voltage sag does to their inrush current. What you are looking for here is a high inrush that may require larger than normal conductors to reduce the inrush voltage drop. i'm working on one of those right now.
carl
dbuckley
Senior Member
- Location
- Canterbury, New Zealand
stickboy1375
Senior Member
- Location
- Litchfield, CT
Try installing a hard start kit.
weressl
Esteemed Member
bozone said:
The transformer should be sized for the starting load of the largest motor. In the case of compressors this could be considerably worse than an ordinary motor. (Of course this seldom happens with the utility company.)
The rule-of-thumb is that you take your steady load kVA from all other sources, take your largest motor and multiply its HP with 3 to arrive at the transformer size.
Of course the utility would also need to make sure that the inrush does not cause significant voltage drop on the primary side of the transformer, eg. the incoming feeders are large enough. (Another thing that may not happen.) Things can still be aggravated if you have multiple motors starting at the same time.
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