Floor lamp is pulsing on/off once per second - any idea why?

Thread Starter

RogueRose

Joined Oct 10, 2014
375
I have a floor standing lamp, those ~6ft tall lamps that are often like $20 at big box stores. It has a switch on the side that IIRC would work with a 3 way light to select 3 different levels. Well one day the bulb burnt out and I replaced it with a standard bulb. Now when I turn on the bulb it turns the light on & off about once a second so the light pulses. Turn the knob one more click and the light stays on permanently, once more = off, once more back to flashing & once more back on - repeat.

I live in the states & I have ~121vac @ 60hz.

I've tried about 20 different bulbs and they all do this, though I don't have any 3 ways ATM. It does this with LED, incandescent & CFL's so it doesn't seem to be bulb related.

I was wondering if maybe there is a rectifier in the circuit that has 1/2 shorted but I would think I'd get a much faster pulse than 1 per second, I'd get 30 per second. All the bulbs work fine in other lights so I have no idea what is going on with this.

Any idea what is going on?
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Thanks for the link but what I don't understand is why there are 3 positions available with a single wattage bulb:

Off
Flash 1 per second
On

If I put a 3 way bulb in then there would have to be 4 positions available:

Off
50w
100w
150w

If the lamp was off I would turn it 3 clicks to get full power while with a normal bulb, starting with light off, 3 clicks turns the light back to off.

How can the switch have 3 positions on one bulb and 4 on another. That is the real question about what is going on.
 
Usually a standard lamp will get two off positions when used in a 3-way socket. There is an extra ring, so you get the middle, the outer ring and both along with the socket side.

It's very possible that something is amis with the base of the bulb or the socket. e.g. it makes contact, gets warm and moves away or something like that. Adding a solder blob on the base might raise the bulb so it wont happen and you;ll get two offs.

In your example you have a 50 W element and a 100 W element.
probably 50 W to the center, 100 W to the ring.

So, Off (ring and center open)
50 W, just the center connected to L
100 W just the ring connected to L
150 W, the ring and the center connected to L or 100 W in parallel with 50 W

The screw thingy is connected to N,
 

Tonyr1084

Joined Sep 24, 2015
4,046
Your account of how the switch is behaving - I'm going to challenge you on that. A 3 way lamp has four positions, as you've stated. Yet, and this is why I challenge your description:

Click #1 turns the lamp on and it flashes.
Click #2 turns the lamp on steady.
Click #3 turns everything off.
The next click goes back to click #1.

There's no way that configuration can be a 3 way system. 2 way makes no sense as it's just too easy to turn it into 3 way. The only way I can conceive this being a problem is if the switch is some kind of electronic switch, one that has multiple light levels.

I've torn apart several microwave ovens. Speaking of the light under the kind of microwave that goes over the stove, the most common light source is low and high. The way they achieve low is by sending current through a rectifier. This blocks half the current and you get half the light. But the light is on continuously because incandescent filaments heat up and radiate light. So you don't perceive their flashing. When you switch to high, a relay bypasses the rectifier and the light gets full current. Thus, two light levels.

So on this premises, if your light is a CFL or an LED and it's flashing it may be due to the power supply inside the lamp not getting proper voltage. Look down into the socket. There should be a center tang that makes contact with the base of the lamp. Then there's the screw base, that makes contact with the ring of the lamp. IF there's another contact in there, between the screw base and the center tang then you need a bonafide three way light bulb. If there is no extra tang between center and screw base then a standard incandescent bulb should give you TWO light levels, not three.

This is the only thing I can come up with as to why your bulbs flash on and off every second (approximately). However, electronics are evolving fast, and I'm certain I don't know everything about lamps, fans, electronics, cars, flying saucers - - - . So someone may disagree with my assessment. But the best any of us can do here is go on the picture you paint. In other words, we can only see what you describe. If your description is inaccurate then our help can only be inaccurate. Unless someone challenges you on your description. One way to put this to bed is to take a picture of the socket and upload the file so we can all see what you have. Then someone will chime in with the exact answer you need. All I've done is to make assumptions based on your descriptions. And to be honest, my assumption is that you're starting off on the wrong premises.
 

Thread Starter

RogueRose

Joined Oct 10, 2014
375
Your account of how the switch is behaving - I'm going to challenge you on that. A 3 way lamp has four positions, as you've stated. Yet, and this is why I challenge your description:

Click #1 turns the lamp on and it flashes.
Click #2 turns the lamp on steady.
Click #3 turns everything off.
The next click goes back to click #1.

There's no way that configuration can be a 3 way system. 2 way makes no sense as it's just too easy to turn it into 3 way. The only way I can conceive this being a problem is if the switch is some kind of electronic switch, one that has multiple light levels.

I've torn apart several microwave ovens. Speaking of the light under the kind of microwave that goes over the stove, the most common light source is low and high. The way they achieve low is by sending current through a rectifier. This blocks half the current and you get half the light. But the light is on continuously because incandescent filaments heat up and radiate light. So you don't perceive their flashing. When you switch to high, a relay bypasses the rectifier and the light gets full current. Thus, two light levels.

So on this premises, if your light is a CFL or an LED and it's flashing it may be due to the power supply inside the lamp not getting proper voltage. Look down into the socket. There should be a center tang that makes contact with the base of the lamp. Then there's the screw base, that makes contact with the ring of the lamp. IF there's another contact in there, between the screw base and the center tang then you need a bonafide three way light bulb. If there is no extra tang between center and screw base then a standard incandescent bulb should give you TWO light levels, not three.

This is the only thing I can come up with as to why your bulbs flash on and off every second (approximately). However, electronics are evolving fast, and I'm certain I don't know everything about lamps, fans, electronics, cars, flying saucers - - - . So someone may disagree with my assessment. But the best any of us can do here is go on the picture you paint. In other words, we can only see what you describe. If your description is inaccurate then our help can only be inaccurate. Unless someone challenges you on your description. One way to put this to bed is to take a picture of the socket and upload the file so we can all see what you have. Then someone will chime in with the exact answer you need. All I've done is to make assumptions based on your descriptions. And to be honest, my assumption is that you're starting off on the wrong premises.

Thanks for the reply. I checked out the switch before I posted and tested it about 5 times and it is as you describe above - the positions:
Off -> 1 click = Flashing
Flashing -> 1 click = on constantly
On constantly -> 1 clock = off
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I thought of the rectifier but that doesn't seem to explain it. Also the light is probably at least 15 years old, probably 15-25/30 years old. I'd take it apart but it isn't really made to take apart and go back together w/o something breaking it seems. I'll have to take a closer look and see if I can get the switch loose. I'll also take a look at the socket and I'll try to get a 3 way.
 
Post a pic of the socket. If it's a standard socket, they may have used a rectifier to get lower wattages, so measure the voltages.

EDIT: The voltages may need to be measured with a small load to "see" the diode if there is one.
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
4,046
That is not the switch sequence for a three way. Can you take a photo showing the inside of the empty socket.

Bob
That's what I proposed. He apparently misspoke when he first called it a three way switch.

I'm thinking the problem might not be in the switch, it might be the kind of lamp being used. Try a regular incandescent bulb (with filaments). If it still flashes then the problem is likely in the switch.
 

BobTPH

Joined Jun 5, 2013
2,207
He claims he has tried LED incandescent and fluorescent, all with the same result.

The switch is probably the type that uses a diode for half brightness.

Possibly a poor connection heats up then breaks when the diode is in.

Bob
 

Tonyr1084

Joined Sep 24, 2015
4,046
@BobTPH Yeah, I agree, it's likely a bad connection heating and breaking, cooling and making. However, I don't recall the TS saying -- tried other incandescents. I could be wrong. Nevertheless, my thought is that an LED or CFL on half wave rectification might not like that, and cause the flashing the TS describes.
 

Lo_volt

Joined Apr 3, 2014
92
Wikipedia has a great explanation of the inner workings of a 3-way light bulb and fixture.

Below is a picture of the third contact in the socket and another showing the ring on the bulb that makes touches that contact.
3Way_Socket_Contacts.jpg 800px-3Way_Bulb_Contacts.jpg
Source: Wikipedia

I tend to agree with the bad switch contact. Weird that it's pulsing at about 1 Hz.

RogueRose can you find another lamp fixture like it to see if it has the same issue with standard bulbs?
 

MisterBill2

Joined Jan 23, 2018
4,903
@BobTPH Yeah, I agree, it's likely a bad connection heating and breaking, cooling and making. However, I don't recall the TS saying -- tried other incandescents. I could be wrong. Nevertheless, my thought is that an LED or CFL on half wave rectification might not like that, and cause the flashing the TS describes.
I can promise you that some CFLs do not like half wave power, or SCR controlled power. They become very angry, spit out nasty smoke, and leave you in the dark.
 

BobTPH

Joined Jun 5, 2013
2,207
I can promise you that some CFLs do not like half wave power, or SCR controlled power. They become very angry, spit out nasty smoke, and leave you in the dark.
Nobdy us disputing that, but if you would simply read the first post you would know that it does the same with an incandescent bulb.

Bob
 
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