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Old 05-11-2016, 08:58 PM   #1
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Light flashes when freezer compressor cycles off


Hi folks,

New here, looking for a bit of advice about the following behavior:

I have an upright lamp and a chest freezer plugged into the same wall socket. Not always, but sometimes when the freezer compressor turns off, and the lamp is OFF, the lamp will flash.

This makes no sense to me because the lamp's own dimmer is in the OFF position, so even if there was a current spike in the building's wiring, it would have to jump the switch to even get to the light bulb. The bulb is a small halogen.

The building is a 2011 construction quadraplex, so new.

The flashing is annoying, but I can deal with it. What's more important is to know if this is a symptom of a bigger problem. Should I just avoid plugging anything into the same outlet as a freezer?

Thanks!

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Old 05-11-2016, 09:05 PM   #2
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Re: Light flashes when freezer compressor cycles off


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Originally Posted by Lokiv2 View Post
Hi folks,

New here, looking for a bit of advice about the following behavior:

I have an upright lamp and a chest freezer plugged into the same wall socket. Not always, but sometimes when the freezer compressor turns off, and the lamp is OFF, the lamp will flash.

This makes no sense to me because the lamp's own dimmer is in the OFF position, so even if there was a current spike in the building's wiring, it would have to jump the switch to even get to the light bulb. The bulb is a small halogen.

The building is a 2011 construction quadraplex, so new.

The flashing is annoying, but I can deal with it. What's more important is to know if this is a symptom of a bigger problem. Should I just avoid plugging anything into the same outlet as a freezer?

Thanks!

Switch off spikes. You know how capacitance is the tendency of a component to store electric charge? Well, you can think of inductance as the tendency of a component to maintain an electric current.
Suppose you have an inductor with one end connected to ground and the other connected to a power supply which is putting 1A through it. What happens when you cut off the supply is that the inductor still "wants" to have 1A running through it. The voltage at the top end of the inductor will go negative as it tries to draw current out of whatever it is connected to. For a perfect inductor with its terminals open-circuit, the voltage it will generate is theoretically infinite. In practice of course inductors are never perfect, but you can still get many thousands of volts out of an inductor just by putting a current through it then shutting off the current.

Voltage shutoff spike is probably high enough voltage to jump the switch gap. If it bothers you put it on another circuit.

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Old 05-12-2016, 08:11 AM   #3
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Re: Light flashes when freezer compressor cycles off


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Originally Posted by Cement_Frank View Post
Switch off spikes. You know how capacitance is the tendency of a component to store electric charge? Well, you can think of inductance as the tendency of a component to maintain an electric current.
Suppose you have an inductor with one end connected to ground and the other connected to a power supply which is putting 1A through it. What happens when you cut off the supply is that the inductor still "wants" to have 1A running through it. The voltage at the top end of the inductor will go negative as it tries to draw current out of whatever it is connected to. For a perfect inductor with its terminals open-circuit, the voltage it will generate is theoretically infinite. In practice of course inductors are never perfect, but you can still get many thousands of volts out of an inductor just by putting a current through it then shutting off the current.

Voltage shutoff spike is probably high enough voltage to jump the switch gap. If it bothers you put it on another circuit.
What type of lamp is now plugged into your "upright lamp"?
If it is a CFL or LED, while Cement_Frank wrote "Voltage shutoff spike is probably high enough voltage to jump the switch gap ", it is more likely that there is a capacitor across the switch contacts concerned.
I do note that the "Switch" is part of and associated with a "Lamp Dimmer", which is why the presence of such a capacitor is likely.

If the lamp concerned is an "incandescent", the problem you described would be most surprising.

Please advise.
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Old 05-12-2016, 10:05 AM   #4
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Re: Light flashes when freezer compressor cycles off


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Originally Posted by FrodoOne View Post
What type of lamp is now plugged into your "upright lamp"?
If it is a CFL or LED, while Cement_Frank wrote "Voltage shutoff spike is probably high enough voltage to jump the switch gap ", it is more likely that there is a capacitor across the switch contacts concerned.
I do note that the "Switch" is part of and associated with a "Lamp Dimmer", which is why the presence of such a capacitor is likely.

If the lamp concerned is an "incandescent", the problem you described would be most surprising.

Please advise.

Thanks for the responses, I learnt something already

So the lamp has 2 parts: big top light, and a smaller 'reading light'. The top light has a CFL and an incandescent who refuses to die, the smaller bottom light is a small (G8?) halogen. The smaller, halogen light is the one that flashes. Not the top.

I will post a link to a similar one after this post, since I need at least one post to be able to post a link

The lamp has 2 dimmer switches: one for the top, one for the smaller light.
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Old 05-12-2016, 10:06 AM   #5
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Re: Light flashes when freezer compressor cycles off


This is the format of the lamp in question. Not this exact one, but has all the same parts.

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Old 05-12-2016, 09:20 PM   #6
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Re: Light flashes when freezer compressor cycles off


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Originally Posted by Lokiv2 View Post

So the lamp has 2 parts: big top light, and a smaller 'reading light'. The top light has a CFL and an incandescent who refuses to die, the smaller bottom light is a small (G8?) halogen. The smaller, halogen light is the one that flashes. Not the top.

The lamp has 2 dimmer switches: one for the top, one for the smaller light.
We have two such lamps of similar design - but somewhat different in appearance.
These lamps came with R7 100 W halogen (tube) lights in the top but we wished to substitute LED replacements. When this was done, the replacement LEDs "flashed" at intervals of a few seconds when switched off at the "dimmer" switch. This was due to a capacitor across the contacts of the dimmer switch and taking this "out of circuit" cured this problem.

Of course, none of this helps your problem.

Since the small halogen light is the one that is flashing I suspect it is the circuit controlling this lamp is what is being affected by the switch spikes from the freezer. (The reason that it is random is that the switch off could occur at any point in the AC cycle and, if this occurs at or near the Zero point, flashing would be unlikely.)

My suggestion to prevent these "spikes" from affecting the dimmer control is to suppress them by using one or more "Clip On Cable Ferrite Core Noise Suppressor Filters". You can find them under this heading on ebay.
These come in various sizes to clip together over the "power" cable to suppress the pulse before it reaches the dimmer circuitry - so be sure to buy a size appropriate for the power cable diameter.

You may also put such suppressors on the power cable for the freezer, to stop the pulses from getting into the "house wiring".

(You will find them "built in" to many cables used for computers etc.)

Last edited by FrodoOne; 05-12-2016 at 09:40 PM.
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Old 05-14-2016, 09:33 AM   #7
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Re: Light flashes when freezer compressor cycles off


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Originally Posted by FrodoOne View Post
We have two such lamps of similar design - but somewhat different in appearance.
These lamps came with R7 100 W halogen (tube) lights in the top but we wished to substitute LED replacements. When this was done, the replacement LEDs "flashed" at intervals of a few seconds when switched off at the "dimmer" switch. This was due to a capacitor across the contacts of the dimmer switch and taking this "out of circuit" cured this problem.

Of course, none of this helps your problem.

Since the small halogen light is the one that is flashing I suspect it is the circuit controlling this lamp is what is being affected by the switch spikes from the freezer. (The reason that it is random is that the switch off could occur at any point in the AC cycle and, if this occurs at or near the Zero point, flashing would be unlikely.)

My suggestion to prevent these "spikes" from affecting the dimmer control is to suppress them by using one or more "Clip On Cable Ferrite Core Noise Suppressor Filters". You can find them under this heading on ebay.
These come in various sizes to clip together over the "power" cable to suppress the pulse before it reaches the dimmer circuitry - so be sure to buy a size appropriate for the power cable diameter.

You may also put such suppressors on the power cable for the freezer, to stop the pulses from getting into the "house wiring".

(You will find them "built in" to many cables used for computers etc.)
Great info, thanks a lot! I'll look for those noise suppressors.

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