Using an old fluorescent momentary on/momentary off switch in lamp rewire

Thread Starter

taylorroesch

Joined Apr 28, 2020
5
Hey,
I am trying to update my grandfather's old desk lamp with LED but using as many original parts as possible. This is the switch at the top of the lamp that controlled the fluorescent ballast in the base. I would like to use this switch to control an LED tube.

The red button of the switch is "momentary on" while the black is "momentary off".

It is my understanding that I could control a relay with these two buttons. First, is that true? Second, what relay would I need? I'm having trouble figuring out the wiring and terminology of what I might use.

I am flexible about whether the LED tube is 120v AC or 12/24VDC. Would one or the other make my life easier trying to fit it into a lamp base?

Thank you for any advice.Gaynor-Knudsen switch.jpg
 

Dodgydave

Joined Jun 22, 2012
9,938
I assume the Red button is a Normally Open switch,( like a door bell push) and the Black is a Normally Closed type, the voltage would depend on the relay coil , which can be wired as a latch that is operated with the buttons.
 

ebeowulf17

Joined Aug 12, 2014
3,275
Hey,
I am trying to update my grandfather's old desk lamp with LED but using as many original parts as possible. This is the switch at the top of the lamp that controlled the fluorescent ballast in the base. I would like to use this switch to control an LED tube.

The red button of the switch is "momentary on" while the black is "momentary off".

It is my understanding that I could control a relay with these two buttons. First, is that true? Second, what relay would I need? I'm having trouble figuring out the wiring and terminology of what I might use.

I am flexible about whether the LED tube is 120v AC or 12/24VDC. Would one or the other make my life easier trying to fit it into a lamp base?

Thank you for any advice.View attachment 205601
Are you sure that it's a pair of momentary switches? It reminds me of old pushbutton light switches that got installed in walls.

https://restoringross.com/what-the-heck-does-an-1890s-light-switch-look-like/

Screen-Shot-2017-01-06-at-5.25.21-PM.png
 

Dodgydave

Joined Jun 22, 2012
9,938
Yes that's one of several ways to to make a Latching switch, the relay coil voltage depends on your light voltage, so if you want to use mains voltage then a mains relay coil will do.
 

MisterBill2

Joined Jan 23, 2018
8,455
YES, that button switch can probably control a small relay to switch on and off the power. First, you need to determine which of those four terminals connect to which switch, And hope the switches are not internally connected to each other. The circuit shown would work.
 

shortbus

Joined Sep 30, 2009
8,470

Tonyr1084

Joined Sep 24, 2015
5,862
Two switch fluorescent lamps I've used have one button for power and the other button (momentary) for starting the lamp. The main button determines whether the lamp is ON or OFF. The momentary (start) button applies full voltage to the filaments to heat up the mercury inside the tube. When you release the start button the lamp goes full on. To turn the lamp off you click the power button. However, if the power button is OFF then you can't start the lamp with the start button.

More wiring info on the switch is needed. If both lines are connected to mains (hot and neutral) or if (for instance) the two on the left are the ON / OFF wires and the two on the right are for START. Or however it's originally wired.
 

ebeowulf17

Joined Aug 12, 2014
3,275
That's how a similar lamp I once had worked, push one for on and then the other for off. Can't imagine that they used a relay or logic needed for momentary buttons back in the day.
That was my first guess - then later I doubted myself because the pictured switch has four wires, and I can't figure out any reason for it to have four wires if it were the simple on/off switch we're thinking of. They all seem to have either two or three (depending on whether there's a ground wire or not.)
 

ebeowulf17

Joined Aug 12, 2014
3,275
Two switch fluorescent lamps I've used have one button for power and the other button (momentary) for starting the lamp. The main button determines whether the lamp is ON or OFF. The momentary (start) button applies full voltage to the filaments to heat up the mercury inside the tube. When you release the start button the lamp goes full on. To turn the lamp off you click the power button. However, if the power button is OFF then you can't start the lamp with the start button.

More wiring info on the switch is needed. If both lines are connected to mains (hot and neutral) or if (for instance) the two on the left are the ON / OFF wires and the two on the right are for START. Or however it's originally wired.
That's very interesting. I've never heard of that arrangement before, but it sounds like a very likely candidate! I agree with @shortbus that it seems unlikely the original lamp required latching relays, but the switch doesn't look quite like I'd expect if it were a simple pushbutton on/off. Your description seems the most likely so far.

I think I shared those latching relay schematics prematurely. I agree with you that more details on the original lamp wiring and/or thorough testing of the switch behavior is needed. Can't design a lamp around a switch until we know the nature of the switch!
 

MisterBill2

Joined Jan 23, 2018
8,455
That's how a similar lamp I once had worked, push one for on and then the other for off. Can't imagine that they used a relay or logic needed for momentary buttons back in the day.
Those desk lamps used a single series ballast and the red button took the place of the starter. Pressing the red button put the ballast and the two filaments in series across the line, as soon as the filaments glowed the red button was released and the inductive kick started the tube glowing. Pressing the black button opened the circuit and the light switched off.
So there was no need for any latching relay since the latching function was provided by the tube becoming conductive. LEDs do not work that way. I have fixed several units like that and so I know how they worked.
 

MaxHeadRoom

Joined Jul 18, 2013
22,855
That is also what was used in fittings with starters the starter contact is initially made for the heaters, then opens due to bi-metal strip,
The first fittings to come out all had the thermal starters,
I recall in one factory with poor heating first thing in the AM, the maintenance guy used walk along under each fitting waving a parafin torch to get them started!
Max.
 

MisterBill2

Joined Jan 23, 2018
8,455
I think that the red button also closes the switch that the black button opens, but I am not sure about that, The same arrangement was also used f9or kitchen under-cabinet countertop lights in the late 60's and into the eighties. It solved the problem of no place to put the starter.
 

Thread Starter

taylorroesch

Joined Apr 28, 2020
5
Those desk lamps used a single series ballast and the red button took the place of the starter. Pressing the red button put the ballast and the two filaments in series across the line, as soon as the filaments glowed the red button was released and the inductive kick started the tube glowing. Pressing the black button opened the circuit and the light switched off.
So there was no need for any latching relay since the latching function was provided by the tube becoming conductive. LEDs do not work that way. I have fixed several units like that and so I know how they worked.
MisterBill2 I think you are right.

Thank you all for helping me out! I've had real trouble trying to figure this out.

I looked up the patent application (no. 2355303) and found this:

"For purposes of illustration, let it be assumed that the push button switch construction is to be employed in connection with a so-called fluorescent lighting system in which the lamp, usually employing mercury vapor, is provided with a heater or filament element which, to start the lamp, is energized, usually momentarily, and in 55 which, to stop the operation of the lamp, the main lamp circuit is interrupted, usually only momentarily; in such systems or such an arrangement it is desirable to relate to the lamp circuits an impedance usually and preferably in the form of a condenser, in order to counteract or eliminate such reactions of the operation of the lamp upon the power or supply circuit as would, for example, cause interference with radio or like reception by instruments powered from the same supply circuit or by instruments located within the influence of the lamp or its associated circuit or circuits. Where the switch is intended for such an installation it is provided with a normally open switch connected to the heater or filament circuit so that the latter may be energized for a suitable period of time to start the lamp, and with a normally closed switch in the main lamp circuit and the actuation of which open-circuits the lamp for a sufficient interval of time to halt the light-emitting discharge in the lamp; where an electrical device such as a condenser is needed, as in the above-stated i1- lustration, I preferably incorporate the device mechanically and electrically into the switch assembly to form therewith a single compact unit."



So if I had a constant current 12v power supply to supply power to the LEDs (LED = <10A@12v) and the relay, how do I go about selecting which relay is correct for this application? The amount of options on pages like Mouser, Newark or Digikey are nearly impenetrable for a novice like myself.



Many thanks again!
 

Thread Starter

taylorroesch

Joined Apr 28, 2020
5
Two switch fluorescent lamps I've used have one button for power and the other button (momentary) for starting the lamp. The main button determines whether the lamp is ON or OFF. The momentary (start) button applies full voltage to the filaments to heat up the mercury inside the tube. When you release the start button the lamp goes full on. To turn the lamp off you click the power button. However, if the power button is OFF then you can't start the lamp with the start button.

More wiring info on the switch is needed. If both lines are connected to mains (hot and neutral) or if (for instance) the two on the left are the ON / OFF wires and the two on the right are for START. Or however it's originally wired.
Here is a drawing submitted with the patent application. After reading the replies the language in the text started to make sense. Thanks again!
 

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Thread Starter

taylorroesch

Joined Apr 28, 2020
5
I am also open to using a 120v direct wire LED tube if you all think a 120v coil relay would fit in the base. The base is cast iron and has a cavity that is 7" long by 4.5" wide and 1.5" deep. Optimally everything (DC power supply & DC relay or 120v relay) would fit into this base.
 

Tonyr1084

Joined Sep 24, 2015
5,862
Unfortunately I'm not able to open the drawing. All I can see is tiny thumbnails of the switch.

Using the two switches wired correctly, you can use the normally open (red) button to energize a relay that connects the LED's to the power and the normally closed (black) button to interrupt power to the relay to shut the lamp off. I can bang out a drawing of how to - but at present I still don't know how the switch is wired.

How's your testing skills? What I would suggest is use an ohm meter to find which two of the wires are connected through the black button. Check it to all the other wires. Then it's likely the other two wires are the red button. That's all you need to know. From there it's a simple matter to wire in a relay.
 

Thread Starter

taylorroesch

Joined Apr 28, 2020
5
Unfortunately I'm not able to open the drawing. All I can see is tiny thumbnails of the switch.

Using the two switches wired correctly, you can use the normally open (red) button to energize a relay that connects the LED's to the power and the normally closed (black) button to interrupt power to the relay to shut the lamp off. I can bang out a drawing of how to - but at present I still don't know how the switch is wired.

How's your testing skills? What I would suggest is use an ohm meter to find which two of the wires are connected through the black button. Check it to all the other wires. Then it's likely the other two wires are the red button. That's all you need to know. From there it's a simple matter to wire in a relay.
Thank you Tonyr! Testing I can definitely do. I work as a set lighting technician on movies and TV shows (which means I know very little but enough not to hurt anyone).
:)
I also don't mind desoldering the connections and attaching the correct wiring if that's what is required.
 

Tonyr1084

Joined Sep 24, 2015
5,862
Here's a drawing of how you'd go about hooking it up: You'll need a DPDT relay so that when you push the red button the LED's come on. For a moment you complete the ground leg, energizing the relay. The first set of contacts hold ground on the relay keeping it on. The second set of contacts provides power to your LED's.

When you push the black button you remove power from the relay and the LED's. The relay falls out and stays out until you push the red button again. You'll need a relay rated for the proper voltage for the coil and the proper amperage for the contacts. In this drawing I assume no voltages - you're the engineer on that part.

1588281662830.png
 
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