Flickering issue has me a bit stumped

[md21722]

I have (2) 5 HP single phase, dual stage air compressors. When they are both running I notice slight flickering in smaller wattage (60W) incandescent and fluorescent light bulbs. If only one is running the flickering is almost unnoticeable. Using a Fluke 325, I measured motor current and they read 23A before they stop which is nameplate. Voltage at the main panel drops about 2V for each running compressor. Starts at 246V, drops to 244V with one compressor running, and drops to 242V with both running. At the magnetic starter, I am reading 239V. Wire is 50 foot of #10 all the way to the motor. Lights do not dim excessively when they start, not really any more than when the air conditioner starts. While running, voltage at the panel between hot and neutral is about 121-122 and does not bounce around. Panel is 100A. Neighbors say they don't see any flicker. Any ideas as to why the lights have the slight flicker and if there's anything I can do about it?

 

[cybrdyke]

Everyone's different and everyone's eyes are different. There are people that can see 60 cycle fluctuation and there are those that cant. And from your description, that's what you are seeing.
If you want to get rid of it, then switch them to LED. LED lights have an electronic driver that pulses the diodes at a very high frequency that is impossible to see.
Good luck,
CD

 

[md21722]

Yeah, I will admit my eyes are sensitive to it. Back when computers had CRT monitors I couldn't use anything less than about 72 Hz refresh otherwise I'd get a headache. Others never noticed at 60-66 Hz. It's not a big deal to me, as long as the neighbors don't care, and they've already said they can't see anything. I just thought something like this would show up on a good meter as voltage fluctuation, etc. but I'm not. Out of curiosity, would something like a VFD make it better or worse?

 

[larry_g]

Is there any possibility that the lights are physically bouncing or moving with the vibrations from the compressor? Is it all lights or only a select couple?

lg
no neat sig line

 

[md21722]

Is there any possibility that the lights are physically bouncing or moving with the vibrations from the compressor? Is it all lights or only a select couple?

lg
no neat sig line

Good thought, but it's not physical movement. I did get that once before out of another compressor that would make a 200W ceiling light vibrate, even though it was on rubber pads and the quietest of the bunch. That compressor is gone now. The lights I'm talking about are in the kitchen and bathroom. In the shop I have big old school incandescents, a couple of 300W and a 200W and I can't see any flicker out of them. It's almost like the bigger current draws are not susceptible to it.

 

[sberry]

This is normal. I am on a rural line and can see it, not so much with 3 hp and less with a heavy service upgrade and new ******. Takes a lot of power on compression stroke.

 

[Mr. T]

I know this a long shot but you could be bumping up against the limit of your transformer. If the transformer is starting to saturate that might cause harmonic distortion? That could cause your lights to flicker.

Although I'd assume some other weird stuff beyond flickering lights might be going if that were the case.

 

[md21722]

I know this a long shot but you could be bumping up against the limit of your transformer. If the transformer is starting to saturate that might cause harmonic distortion? That could cause your lights to flicker.

Although I'd assume some other weird stuff beyond flickering lights might be going if that were the case.

You may be right. I have no idea what the transformer is and I'm a bit leery of calling and asking. In this area the biggest current draw is air conditioning. Stoves, heat, and even the clothes driers are usually natural gas. Though I would've thought if the transformer was the weak point, I would suffer a voltage drop problem when they start up. The Fluke registers around 213V for a split second before it goes back up, which is even within the 10% guideline if you believe in that.

 

[79firebird]

I know this is a long shot but try putting the amp probe on the main line coming in on each side and check the draw. My old work had lights that would dim a bit with both compressors on. On a 200 amp panel it was drawing 190 on one side 80 on the other. Swapped some breakers around and it was fine.

 

[LS6 Tommy]

Everyone's different and everyone's eyes are different. There are people that can see 60 cycle fluctuation and there are those that cant. And from your description, that's what you are seeing.
If you want to get rid of it, then switch them to LED. LED lights have an electronic driver that pulses the diodes at a very high frequency that is impossible to see.
Good luck,
CD

I see LEDs flicker all the time, especially on automotive applications...

Tommy

 

[cybrdyke]

I see LEDs flicker all the time, especially on automotive applications...

Tommy

I suppose there are a lot of definitions of "flicker". It could be a short voltage drop, a power quality issue, a lot of different things. From the OP's description, I took it to mean a constant 60 cycle flicker.

 

[jlmotox]

Loose wire?
I had my house lights flickering and doing weird stuff. When I would turn on my compressor it would barely start and lights would dim. Had my electrician buddy come and look at everything and he found the main ground broke off where it mounts in the panel. Lucky my house didn't burn down! You can see where it was arching against the main line. Just a thought for you...

 

[LS6 Tommy]

I suppose there are a lot of definitions of "flicker". It could be a short voltage drop, a power quality issue, a lot of different things. From the OP's description, I took it to mean a constant 60 cycle flicker.

Which is exactly what I see. Espeicially cheapo LEDs or unrectified ones like Christmas light LEDs...

Tommy

 

[Mr_fixit]

I have a 5 hp motor on a compressor that does that. I haven't solved the problem yet, but I think one leg of the motor is pulling way more amps than it's supposed to. .This has been doing this since new. It's in a detached garage, fed from a sub panel and it causes the lights in the house to flicker every second that it runs. Power company says its not their problem. They claim that they put a meter that logs the voltage drop on the line and did recrimp the transformer connections 400' away from the house.

I haven't figured out what to do next.

 

[md21722]

Hmmm... I have a main lug panel with the 100A service panel breaker at the meter. All the wires at the main lug panel are tight as I've already gone through them twice. This has happened since I put them in. they are WEG 5 HP single phase running brand new champion R15 pumps.... air output measures fine.. the problem could upstream of the panel but wouldn't i expect to see some weird voltage issues on the 120V legs to ground? I haven't been able to measure that, they are all rock solid? I'm inclined to think it is an upstream transformer or service issue, for some reason it just can't handle 46A 230V of load, but can handle the start current just fine??? I dunno... that's why I'm asking.

 

[CGT80]

I have had a similar issue lately, but it doesn't seem related to an ac or compressor starting up. The refrigerator fan slows and my bathroom and closet lights dim. Finally, I read the voltage and it was dropping to 108 volts for a second or two and then back up to 122-123. I checked the sub panel for my suite (mother in law suite in a house) and my electrician buddy checked the main panel but never saw it act up. I suspected it was either a lose connection or it is due to Edison's transformer. They replaced the connections at the weather head, due to weather exposure, but I wonder if their transformer isn't compromised or if the neighbors are using more power than in the past and it is under size. We have 60 solar panels and feed back into the grid, even while the voltage drops.

My buddy said the way to check is to install meter that can monitor the voltage over time, but I would just expect a run around from edison.

 

[md21722]

I have a 5 hp motor on a compressor that does that. I haven't solved the problem yet, but I think one leg of the motor is pulling way more amps than it's supposed to. .This has been doing this since new. It's in a detached garage, fed from a sub panel and it causes the lights in the house to flicker every second that it runs. Power company says its not their problem. They claim that they put a meter that logs the voltage drop on the line and did recrimp the transformer connections 400' away from the house.

I haven't figured out what to do next.

You could put a clamp meter on each of the motor leads and see.

In my case the motors are running fine, both are drawing equal current. The A and B phases in my panel are relatively balanced, there is a 4.5 or 7 A difference because of lighting. I just don't use a lot of power. I have hooked up the clamp meter to each to verify.

 

[md21722]

This is normal. I am on a rural line and can see it, not so much with 3 hp and less with a heavy service upgrade and new ******. Takes a lot of power on compression stroke.

So you got a bigger service and they put in a bigger transformer and you still see it? So basically every time there's a compression stroke it has the effect of drawing enough power to make the lights do their thing?

 

[wyliesdiesels]

You may be right. I have no idea what the transformer is and I'm a bit leery of calling and asking. In this area the biggest current draw is air conditioning. Stoves, heat, and even the clothes driers are usually natural gas. Though I would've thought if the transformer was the weak point, I would suffer a voltage drop problem when they start up. The Fluke registers around 213V for a split second before it goes back up, which is even within the 10% guideline if you believe in that.

213v is actually quite low- 106v per leg.

And the PoCos around here have a 5% tolerance.

I would check all your connections in the panels. Have u measured voltage at the main service panel?

I had an issue a few years ago with too much voltage drop on one leg. I left my fluke 87V on peak low mode and left it for a few days. Voltage was dropping to about 103v.

Called the PoCo and the troubleshooter found a bad splice on the pole...

 

[md21722]

The Fluke 325 reads 213V only during inrush/startup. While running I'm getting 242V at the panel and 239V at the motor.

I had read that transformers are commonly sized to allow 10% drop during motor startup, maybe I misapplied that. I was thinking 230 - 10%.

 

[cybrdyke]

Which is exactly what I see. Espeicially cheapo LEDs or unrectified ones like Christmas light LEDs...

Tommy

Yeah, if they are real low end units, like some of the flexible tape varieties, then they dont have a driver.
CD

 

[md21722]

Out of curiosity, is there a meter that can display or graph the voltage bouncing just enough to make the lights flicker? In another thread folks are mentioning the 87V, etc. I'm not saying I want to buy a meter to see what I already know is happening, I'm just curious if/what meter can do it?

 

[wyliesdiesels]

Out of curiosity, is there a meter that can display or graph the voltage bouncing just enough to make the lights flicker? In another thread folks are mentioning the 87V, etc. I'm not saying I want to buy a meter to see what I already know is happening, I'm just curious if/what meter can do it?

I have an 87V. It doesnt do graphing. It only has a digit display.

But i can use the low high avg function, leave it hooked up and come back later and see what the low, high, and avg voltage it measured was. Ive used it on several voltage drop service calls and it worked fine.

If u want a graphing meter u would have to get a fluke power quality meter and unless u have a huge chunk of change sitting around, u wont be able to afford one($$$$s). Also, for someone like u, it would be a waste of money unless u use it constantly. Your situation is a need it once, fix it and be done with it.

If youre only seeing the VD during startup, thats normal.

Motors have huge in-rush currents usually 4x-8x FLA.

If the voltage dropped and stayed low then u have a bigger issue.

 

[md21722]

I have an 87V. It doesnt do graphing. It only has a digit display.

But i can use the low high avg function, leave it hooked up and come back later and see what the low, high, and avg voltage it measured was. Ive used it on several voltage drop service calls and it worked fine.

If u want a graphing meter u would have to get a fluke power quality meter and unless u have a huge chunk of change sitting around, u wont be able to afford one($$$$s). Also, for someone like u, it would be a waste of money unless u use it constantly. Your situation is a need it once, fix it and be done with it.

If youre only seeing the VD during startup, thats normal.

Motors have huge in-rush currents usually 4x-8x FLA.

If the voltage dropped and stayed low then u have a bigger issue.

The volts drop to 213V for the split second that the motor starts. After that the panel mains read 242V. Hot to natural shows no irregularities. But the small watt incandescent lights still flicker slightly, presumably on each the compression stroke where the motor presumably draws more power. I was just wondering what meter could "see" that. Thanks for the insight. I agree, not worth the coin. But since I was looking at meters, I was just wondering what model would do that job.

 

[wyliesdiesels]

What meter do u currently have?

 

[md21722]

What meter do u currently have?

I have an old Craftsman DMM. Obviously not up to the task. It bounces around a few volts with just the lights on. I was using a borrowed Fluke 325 to measure the volts & amps of the compressors.

 

[sberry]

242 to 213 is quite a drop. Our poco field eng was here for something the other day and he said we can now start 25 hp with soft start. It doesn't do me much good though, I wpuld like to run 75 or 100 but the nearest 3 ph being 2 miles its a problem.

 

[pinkerton]

I feel like you need to "see" this on an oscilloscope - you can get a cheap one

 

[Clevername]

This sounds like noise generated by the motors on your compressors. Maybe you could put ferrite beads around your motor leads. Check the ground wire on your compressor motors and make sure you have a good earth ground. I am an ME not an EE so...

 

[pinkerton]

Plug a lamp into a UPS powered from a bulb socket that flickers - then you'll know if it's noise.