About 2 years ago I converted an automotive shop from florescent to LED T8(120 volt). They worked great until we changed the compressor today to a new more efficient and more powerful one (both 240 volt. the old was 20 amp, new 32 amp). 200 amp service.

The lights flicker like crazy while the compressor is running. An unacceptable amount. This is probably from the large inductive startup load? I have checked many things. Loose connections, voltage drop. everything seems to be wired correctly. I have even discussed with knowledgeable electricians.

It seems this is a not so common problem surfacing with the new LED technology. The solutions I have come up with are, 1. have power company supply dedicated service just for compressor. 2. change the size of pulley to reduce the demand of the motor(may or may not fix the problem).

Can anyone provide any input? Thanks Kenny

  • 1
    There was a great part of "Hunt for Red October" where an Alfa sub was sprinting, running the reactor's turbines and cooling pumps so hard the whole reactor was shaking. The operator noticed the pressure gauge jiggling and figured it was shaking just like the rest of the ship. In fact it was not shaking, it was accurately indicating pressure variations. I wonder if this larger compressor is exposing real problems in your electrical panel or service lateral which are causing your line voltage to actually vary, and the LEDs are faithfully reflecting that. Jan 23, 2018 at 3:08
  • The best way to see what is going on, is to do measurements. If you don't have the equipment to do that, hire a professional. Is that 240V split phase? What kind of LED lamp do you have? Most good LED lamps are fed by SMPS which do not really care about voltage variations unless its really really bad.
    – PlasmaHH
    Jan 23, 2018 at 13:48
  • Is this shop on a separate sub panel? You said automotive shop so that makes me think commercial with its own service. 32 amps should not be a problem unless the main panel is very small like a 60 amp panel then I could see possible issues with loading and emf noise generated by the compressor, if the voltage is good I would verify the grounding especially if the ballast are still in use modern ballast start having problems if the neutral to ground voltage goes over .5v and some will not work at all at 2v or this is what I have found and sometimes requires an additional ground rod.
    – Ed Beal
    Jan 25, 2018 at 15:05
  • I think you answered your own question OP, You said "more powerful one" and I'm guessing it wasn't previously like that with the old compressor, have you checked the amp draw of the compressor while the light and everything on the circuit are on.
    – user70085
    Oct 21, 2018 at 19:57

3 Answers 3


I believe I may be experiencing the inverse of your situation

My ceiling fan power is separate from the LED lights in the fan. If the fan isn't powered up to 100%, the lights flicker like crazy. Once it's turned up all the way... they're fine.

... so my theory is... you don't have enough juice any more. Assuming these are bulbs, if you unscrew a few, and run the compressor, do the remaining still flicker?

I think the dedicated service for the compressor is a good train of thought. I only question sustainability over the long term and future growth. You may want to look into your current wiring set up for a possible more permanent fix.


When you changed the compressor did you verify the wire is heavy enough for the larger load? Pulling half again more current on the same size wire would cause more voltage drop. A common voltmeter may not respond fast enough to show the pulsating voltage. At the very least, put the lights on a separate circuit from the compressor.

I like your idea of changing to a smaller pulley to reduce the torque load on the motor (hence, the motor current) but that'll reduce your compressor output volume, and it's probably easiest to change the light wiring if needed.


It could be an enormous variety of factors that are all compounding into what you're seeing or just one or two major issues, the only thing you can do is call in an electrician to actually determine the causative factors here. Not discussions, physically in the building and checking and measuring things.

If the supply from the service provider is rapidly dropping when the inrush of the compressor starts then you need to deal with the utility or upgrade the wiring to the compressor. You didn't indicate you did this during the updates so I'm suspicious of the branch circuit supplying the power to the new higher load compressor.

If the supply from the service provider isn't fluctuating severely then you have cheap lights that can't compensate for minor voltage fluctuation and your only recourse is to either scrap them for better units or find someone to upgrade the power supplies inside them with better capacitors.

Cheap chineseium electronics have a bad tendency to be poorly engineered and the power supplies are terrible, the only way to fix that is to buy better equipment or have someone that knows about electrical engineering reverse engineer the design to determine the faults. Then they can advise you to either purchase better power supplies or modify the existing components with better materials.

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