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Replacing a 24V AC machine lamp

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Calum Galleitch18/06/2022 18:32:35
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194 forum posts
65 photos

My lathe has a lamp:

screenshot from 2022-06-18 18-05-53.jpg

The lamp used to work, then it made a fizzing noise and stopped working. I took the lid off, removed the bulb (a G6.35 halogen), and ascertained that it appeared to be intact. Noticing the legs were covered in what can only be described as grime, I wondered if some sort of deposit was blocking the healthy flow of electrons. A rinse in vinegar and an overnight dry, I popped it back in, and, success! A working light.

For a few days. Then once again a fizzing sound followed almost immediately by darkness.

This time I thought I had better take it to bits and check it properly, which I did, and found some very old and tired looking wiring. And I found a lampholder, looking like one of these:

screenshot from 2022-06-18 18-04-46.jpg

The one I have is somewhat elderly, and along with the wiring I think it should be pensioned off. Which leads me to the problem: what to replace it with? I am stuck (well, do not want to replace) with 24V AC. As far as I can see that pretty much rules out LED solutions as there doesn't seem to be anything commercially available that would be a drop-in replacement. The lampholder itself doesn't seem to be available any more (at least in quantities less than 100), and the reflector is 65mm, not the 50mm standard used in household bulbs.

The ideal would be I guess a GU4 type bulb and holder, or something like it. I can reuse the reflector of course, but I'm not sure if there's anything it would attach to out there. I could make a holder out of Delrin but I'm not sure Delrin and a 150W halogen bulb are a great mix.

Clive Brown 118/06/2022 18:46:38
869 forum posts
47 photos

Not helping a great deal, but Iunderstand that halogen bulbs are, or will shortly be, banned for sale for domestic use. When I recently looked to replace one, I found none in the normal retail outlets. It's LED or nothing it seems

 

Edited By Clive Brown 1 on 18/06/2022 18:48:26

Frances IoM18/06/2022 19:04:15
1283 forum posts
28 photos
lorries have I think 24V batteries - are there any LED lamps suitable for mounting within your light fitting
Robert Atkinson 218/06/2022 19:44:30
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1246 forum posts
20 photos

No problem getting G6.35 24V AC LED lamps

Random amazon example

https://www.amazon.co.uk/GY6-35-Dimmable-Equivalent-Halogen-Flicker/dp/B0B2LPN7DB/ref=sr_1_5?keywords=g6.35+24v&qid=1655577664&s=lighting&sr=1-5

No idea if it is a good seller just an example of a lamp.

Robert G8RPI.

Calum Galleitch18/06/2022 19:48:00
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194 forum posts
65 photos

Yes, the lamps themselves are easy - it's the holder I'm looking for, or if the holder can't be found a replacement for the whole assembly.

Lorries/campervan electrics are DC and seem to have all gone over to LED already - I did think that was the obvious place to look but I couldn't see anything obviously useful.

Richard Millington18/06/2022 19:48:45
71 forum posts
4 photos

If you are coming off a multi tapped transformer see if you can swap the supply to 12v. I have replaced mine with MR16 lamps, you can get new lamp holders from Toolstation.

https://www.toolstation.com/search?q=mr16%20lamp%20holder

Jon Lawes18/06/2022 20:35:10
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995 forum posts

Just speculating, is there going to be a problem going from 24v AC to DC? I wonder if thats an RMS value.

peak418/06/2022 20:47:55
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1787 forum posts
193 photos
Posted by Calum Galleitch on 18/06/2022 19:48:00:

Yes, the lamps themselves are easy - it's the holder I'm looking for, or if the holder can't be found a replacement for the whole assembly.

Lorries/campervan electrics are DC and seem to have all gone over to LED already - I did think that was the obvious place to look but I couldn't see anything obviously useful.

These don't look a mile out
https://www.amazon.co.uk/GY6-35-Holders-Ceramic-Halogen-Connection/dp/B00CERLCJA

Bill

Bill Davies 218/06/2022 21:09:39
287 forum posts
11 photos

Would a diode cut 24 VAC to something suitable for a 12V bulb? RMS gives the equivalent DC power level, (filament) bulbs aren't too fussy regarding voltage, a continuous higher voltage giving reduced life.But this varying from 0v to about 17V rapidly, and filaments have a degree of thermal inertia.

Bill

noel shelley18/06/2022 21:36:04
1445 forum posts
23 photos

A small block bridge rectifier and a capacitor would give you DC, there's almost no heat so provided you can insulate the leads just solder the wires to the bulb, auto motive systems are 28V so youhave many options ! Good luck. Noel

Howard Lewis18/06/2022 21:37:36
6314 forum posts
15 photos

At the risk of being corrected, a diode to rectify 24V AC to DC would only cut about 1.4 V from the supply voltage.

A single diode in one lead will result in half wave rectification, giving a large ripple effect.

Inserting a bridge rectifier across the supply will provide full wave rectification, but still with a distinct ripple.

Seems a bit OTT to put in a proper smoothing circuit for a lamp.

Possibly a LED lamp, designed for 24V could cope with .a rough 22V supply?

Howard

David Millar 318/06/2022 22:30:40
24 forum posts

I recently replaced the lamp holder in my bathroom fan with integrated light. The lamp holder looked identical to the pic the OP posted.

I sourced a replacement from a local electrical trade wholesale outlet.

I had presumed it was 12V but didn't look closely at it. It may be 24V.

David

Maurice Taylor18/06/2022 22:53:45
219 forum posts
36 photos

Hi ,this lamp holder is for sale on ebay , 24 volt ac bulbs for sale on Amazon . Nice easy job.

Maurice

Michael Gilligan19/06/2022 06:40:34
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20289 forum posts
1064 photos

Gallum

I think the underlying problem that you have is the inadequate quality of contact in that type of holder.

The lamp pins oxidise because of the heat generated by contact resistance

A much better arrangement [commonly used in microscope illuminators] is to clamp the pins down on a vee groove; but, of course, you may not have space to do this.

MichaelG.

.

P.S. __ digressing somewhat: This article may be of general interest

https://zeiss-campus.magnet.fsu.edu/articles/lightsources/tungstenhalogen.html

Edited By Michael Gilligan on 19/06/2022 06:57:11

Michael Gilligan19/06/2022 08:25:44
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20289 forum posts
1064 photos

Too late to edit, but this is the style of pin clamping/connecting used on my big LOMO microscope:

.

035fbddf-eb04-4a4c-b7d1-f593d6f1baf0.jpeg

.

MichaelG.

Calum Galleitch19/06/2022 09:15:39
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194 forum posts
65 photos

> I think the underlying problem that you have is the inadequate quality of contact in that type of holder

Yes, I think you're right - both the lamp itself and also the wires connecting to the switch are both in pretty dubious state. Nowadays when you buy these lampholders they tend to come with wire pre-attached, but mine just had a push-fit, one of which has failed entirely.

Peak4's link above looks spot-on, so I have ordered one and hopefully that will last another twenty years!

peak419/06/2022 11:42:00
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1787 forum posts
193 photos
Posted by Calum Galleitch on 19/06/2022 09:15:39:

.........................

Peak4's link above looks spot-on, so I have ordered one and hopefully that will last another twenty years!

If you ordered directly from that link, they should certainly last for 20 years, as I think it was for a pack of 10 .
wink

Bill

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