I converted my shop to led from fluorescent.These are direct wire no ballast. Ran all new wires in conduit. The compressor is a 5hp single phase on a 60 amp breaker with 125amp main.

I replaced compressor motor in 09. Compressor I installed in 1977 and has never given me a problem with the lights. I can run the TIG on a/c high frequency with no flutter. Lathe, Milling machine, grinders nothing else has a effect on the lights. I went through every connection double checking neutrals and grounds in the whole shop with no faults.

My other led fixtures are pre assembled don’t have a problem and my standard non converted fluorescent fixtures are ok. I have read about harmonic balance in large compressors but have not found a cure. I have spent a couple of days just rechecking everything but I still have the problem. Can you help?

  • 1
    Does your compressor have a starting capacitor with it? Jan 27, 2018 at 17:43
  • Yes it does the motor is a Dayton 5k676, compressor is a speed air 5hp single ph. All purchased from Granger Supply.
    – Chuck
    Jan 27, 2018 at 19:28
  • 3
    I'm far more interested in the make/model of the LED lights. A compressor is just yet another motor load and a fairly typical induction motor. The onus is on the lights to work properly around things like that, and that should be easy work for switching power supplies such as those used in LEDs, as switching supplies can extract usable power from almost any power waveform. Unless there's something seriously wrong with your service. Are these LEDs dimmable? Perhaps they are misconstruing motor noise as a command to dim. Jan 27, 2018 at 20:46
  • No these are not dimmable.They are from www.eledlights.com model4hlbt8x018un60c. 2520 lumin cct6000k . I spent about 1 1/2 hours on the phone with the owner of that co. today. I forwarded them videos in normal and slow motion so they could see it. Not real visible on video from my phone in normal mode. But in slow motion it really magnified the problem. I’m going to have record voltages and amp loads tomorrow for more testing. Thanks
    – Chuck
    Jan 27, 2018 at 23:28
  • These are not dimming as you would perceive, they just have a slight flutter to them and it is quite noticeable just working in the shop
    – Chuck
    Jan 27, 2018 at 23:31

4 Answers 4


I don't believe motor starting flicker is the source of your problem. I have the same issue, and during my time working at a power company, there was actually one client who had this same issue after retrofitting to LED tubes.

The flicker that you notice is well below 60Hz(My assertion, not yours) and is continuous from your descriptions as the compressor runs. The discussion of the starting capacitor or a soft start is actually a totally different problem. What happens when your compressor begins its compression stroke, and proceeds to end it, is that the torque required to turn it increases steadily and then drops off sharply as the compression stroke is finished and the piston passes over top dead center.

This varying motor load results in the line current varying at a lower than 60Hz frequency (typically the compressor turns much slower than 60Hz). As the current varies up and down in phase with the compressor, the voltage drop across your wires also varies, meaning the voltage at the LED bulbs is also going down and then up every time there's a compression stroke.

For reference, my compressor is a behemoth I inherited from my father. It's rated at 5HP and draws 28 amps RMS on a 240V circuit, and still causes this problem. The fact that my pole barn is the furthest thing from the service entrance on the house (and thus the transformer) doesn't help, nor the fact that I have a 10kVA transformer. The compressor operates at about 3-4 Hz (estimated based on my hearing) and the lights flicker about that fast too.

The problem is due to poor light design (assuming your voltage flicker is in spec, and it very well may be, as my former company had done voltage studies on a customer with this problem to see if the flicker was caused due to out-of-spec flicker voltage and found nothing). I haven't torn apart any of the LED tubes I used to retrofit my house, but I suspect they forego active power factor correction circuits in order to make them cheaper, because that type of circuit should be able to compensate for this type of issue(Look up Active PFC).

Whether or not light-strip-in-fixture LED lights have better designed power supplies or not I cannot comment on because they are obnoxiously expensive($80 USD per fixture where I can retrofit a 4ft 4 light LED fixture to LEDs for 10 bucks a bulb at $40 USD!) and that has prevented me from purchasing them.


Are you tombstones in good shape and are all the wire connections tight. How much voltage drop do you experience when the big motor starts. What size wire is feeding the shop and how long is it. How old are the breaker panels and breakers both at the service and the shop panel? Have you tried another new lamp from another mfg? I say these LED tube lamps are a stop gap measure to tide people over until they can afford new genuine LED strip light fixtures. (the driver in the tube LED is just not quality enough to deal the the voltage fluctuations.)

  • Tombstones are good and tight All fixture were removed and rebuilt on the bench so I could be sure everything was just right. Going to try different bulbs from another supplier today and take voltage readings.Breaker panel and breakers were installed around 1981. Supply to breaker is box is 2/0. I have tried other economy light fixtures that are all pre wired as you would hang over a work area and these work fine. I will be testing other bulbs today and do my voltage readings. My existing fluorescent fixtures don’t have any issues. Thanks Chuck
    – Chuck
    Jan 28, 2018 at 11:58
  • The Phillips bulbs from Home Depot do not flicker. The voltage at the tombstones with just the lights on is 126.4The voltage at the tombstones with the compressor running is 124.6-124.9 Still testing Thanks
    – Chuck
    Jan 28, 2018 at 18:14
  • Chuck, I'm glad the Phillips tube worked. FYI The only voltage we are concerned about in this situation is in that 1/2 or 1/4 second that the large motor comes up to speed. P.
    – Paul Logan
    Jan 28, 2018 at 21:38
  • That 1/2-1/4 second is hard for me to capture on my meter. I’ve tried Thanks
    – Chuck
    Jan 28, 2018 at 22:22
  • There is no room in the magnetic starter to put my clamp around amp clamp. I going to try it in the breaker box tomorrow, there should be more room in there Thanks Chuck
    – Chuck
    Jan 28, 2018 at 22:26

This is a huge load for a 120v line , you should consider if the compressor motor can be converted to 240v to change it. The draw would be only 28 amps 240v where the book value for a 5 HP 120v is 56 amps. A possible solution to your problem is that the lights are on the same leg as the compressor move the lighting breaker to the other leg and this may solve the problem. Since it sounds like you changed the motor FWIW most air compressors are rated at the locked rotor value so a aircompressor that states 5 HP is usually truly closer to 3HP of a real HP rated motor. Most of the Dayton motors I have worked with are dual voltage converting to 240 may also help. Motors create a phase imbalance in the voltage/ current where voltage is leading current plus some EMF or inductive kickback, the heavier the load the bigger the imbalance and this may be the root of the problem. So try and move the breaker up 1 position or convert to 240v as possible solutions. (I have never seen that large of a motor on 120v).


This is in response to all the information that has been given by @Chuck.

My best guess is that when your compressor comes on at full load it is causing your voltage to sag due to the huge start-up demand. LED drivers are designed to accept a large number of voltages (something like 90-264VAC). When your compressor starts and a sag takes place your LED driver is sensing the change in voltage and tries to adjust to the new voltage availability, and without going into a lot of boring details, the LEDs begin to dim while the driver tries to stabilize. In the meantime of course, power to the compressor is dropping and your whole system stabilizes.

The reason I asked about your capacitor is that its primary duty is to store and provide extra energy for start, which would prevent just what I described. So if someone is coming out with meters, you might have him check the capacitor and see if it is working or degraded. Many times it doesn't have to degrade too much when you start having problems. In fact sometimes no more than a 5% loss. You will have to check the compressor manufacturer's recommendation for that information.

It is obvious you have a compressor and LED compatibility problem and just maybe it can be fixed with a new capacitor. If the compressor start up is still a problem and if it is the problem. The only other method I would know of to fix it would to be to set up some sort of soft start which would not be inexpensive. Before I would get into that I would check the capacitor.

Good luck.

  • The compressor start up is great just the light compatibility issue Thanks I have testing to do
    – Chuck
    Jan 28, 2018 at 16:24

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