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Lathe work light broken how to fix

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petro1head17/05/2014 17:13:10
770 forum posts
152 photos

I have one of those magnetic work lights from rdg. However it's stopped working. Turns out the transformer in the base is caput.

so do I try to find another transformer or convert to 240v and see if I can find a 240v bulb

Ed Duffner17/05/2014 17:30:05
841 forum posts
94 photos

My humble opinion; As long as the lamp is connected via wires and not through the body or stem of the lamp (as some low-voltage light fittings are) ...and as long as the lamp holder assembly can handle 240v, i.e. properly insulated, then I think it would be ok to convert to 240 if you can source a lamp.

I suppose I should add a disclaimer that if you do convert then it would be at your own risk etc.

Ed (qualified electrician for 10 years, 15th edition reg's).

Les Jones 117/05/2014 17:39:42
2261 forum posts
156 photos

Hi petro1head,
I would not advise changing to a 240 volt bulb for safety reasons. Suggestions on replacing the transformer depend on its output voltage and power rating. I would guess it is 12 volt, 24 volt or 50 volts output supplying a 20W or 50 W bulb. What is the voltage power rating and type of bulb (eg bayonet, Edison screw, G4 etc.) ?  Also is it a normal transformer or an electronic transformer ?


Edited By Les Jones 1 on 17/05/2014 17:44:45

Fatgadgi17/05/2014 18:05:58
181 forum posts
26 photos

Hi Petro

I personally wouldn't use 240v either.

Dunno about you, but I have more old transformers from dead chinese gizmos than I can shake a screwdriver at. You know the ones that plug into the mains socket and have the low volt lead from it.

Perhaps one of those could be of use if you changed the voltage of the bulb to suit ??

Cheers - Will

petro1head17/05/2014 18:22:25
770 forum posts
152 photos

I have no problem either converting to 240, remember not long ago all lathe lamps were 240v.

It looks like the usual cheap Chinese type transformer with some electronics thrown in for good measure.

I'll take a couple of photos

petro1head17/05/2014 18:29:42
770 forum posts
152 photos

This is the light -



Edited By petro1head on 17/05/2014 18:31:29

Edited By petro1head on 17/05/2014 18:32:08

petro1head17/05/2014 19:03:06
770 forum posts
152 photos


I think this is a G4 bulb?



I was thinking that I may buy a 12V 35W G4 bulb which will draw 3A, and use a transformer like this - **LINK**

Edited By petro1head on 17/05/2014 19:03:46

Phil Whitley17/05/2014 19:20:45
1449 forum posts
147 photos

The wiring in the stem will only be 12v insulation rated, and the 240V halogen GU10 type get incredibly hot. This is not a safe conversion at all. BIN IT!

Les Jones 117/05/2014 19:42:05
2261 forum posts
156 photos

Hi petro1head,
I suspect this light uses G4 halogen bulbs. I would consider changing from a 24 volt bulb to a 12 volt bulb. One option is to find a cheap desk light similar to this one and use the transformer from that. I seem to remember seeing these sold for about £5.00 in the past. Another option would be to use a 12 volt lighting transformer.


Edited By Les Jones 1 on 17/05/2014 19:45:10

petro1head17/05/2014 19:44:30
770 forum posts
152 photos

I think my solution above is probable the best, most cost effective, solution

John Stevenson17/05/2014 20:12:43
5068 forum posts
3 photos

Hold fast.


Just bought some of these **LINK**


to replace the G 4 bulbs in some of my machine lights. Not sure if they are G4's but identical to the one shown above.


Problem I have is some of my low volt lights are 12v and some 24v.

I know this won't directly help petro1head as his transformer is shot but a simple wall wart type one will run these with no problems.


These will run off AC or DC and 12 to 24 volts, changes 4 so far and all but one have been OK, that one is flickering bad and as I wanted to use the machine I just plugged the halogen bulb back in and will look at it later, judging by the brightness I'm guessing it banging out far more than 24v.


It's probably a 220v input transformer and on 240 it's running high.

They put a nice light out, fit in as a direct replacement and best of all you don't burn yourself on them.


[EDIT] been out to the shop to get some pics for the old tools thread and took a pic of the TOS lathe with just this LED light on, nothing else.






I had to fit the piece of perforated sheet as the original glass cover got broken and plastic won't stand up to a halogen bulb but now I have this LED fitted I can now cut a perspex cover with the laser or even print a new end with the 3D printer.


Surprising how bodging shops have come on in the last few years. wink

Edited By John Stevenson on 17/05/2014 21:21:36

petro1head18/05/2014 05:48:11
770 forum posts
152 photos

Interesting a good option re bulb, also means the current draw is only 0.25A

Thanks for that

FMES18/05/2014 08:57:05
608 forum posts
2 photos

Why not just replace the power supply?

Normally these are variable input 120 - 240 volt ac to dc supplies and are generally available.

They are only variable input due mainly to global power supply differences, so you could even use a standard 240 volt transformer to required lamp voltage, suitably rectified (to prevent strobe effects).

As an aside all of the lathe lamps on our old colchesters (circa 1970s) were stepped down to 50 volts but looked like ordinary incandescent lamps, never mains voltage.

Les Jones 118/05/2014 10:15:31
2261 forum posts
156 photos

Hi petro1head,
From the picture of the old "transformer" it is an electronic one. This is basically a switched mode power supply with no rectifier on the output. The output will be a high frequency square wave. It is not normally cost effective to repair these. I agree with John's comment about burning yourself if you fit 35 watt halogen bulbs in this type of light. (I fitted a 35 watt in place of a 20 watt and found this.)  I changed over to using LED type MR16 bulbs some time ago and would recommend it. The pins on MR16 and G4 bulbs are the same so there is no need to change the holder. One thing I have found is that some (Not all) LED lamps designed for 12 volts do not give the full output when fed from 12 volts DC. I think this is probably the case with the ones in the link John has given. (If you want a detailed explanation of why this is then can explain it.) If you go down this route then I suggest using about a 15 volt power supply.

John, I think the fault with your flickering lamp is one of the LEDs is failing. The three LEDs are probably connected in series and one is intermittently going open circuit. I bought some GU10 bulbs on ebay and all of them failed within a few months. They first started to flicker then failed totally. On taking them apart they had all failed with one LED from a string of 48 going open circuit.


Edited By Les Jones 1 on 18/05/2014 10:18:14

John Olsen18/05/2014 12:19:11
1256 forum posts
94 photos
1 articles

I've got an old desk halogen lamp down on my mill. The transformer in the base failed a while back and I couldn't find one to fit, so I am using an external transformer meant for halogen lamps, hidden in the base of the machine. That one still has the halogen bulb, but I would second the idea of using the modern LED replacements, as they give an excellent light with less heat and are less likely to give you trouble with the sockets, which are often inadequate for the current. Since the LED will draw about a quarter or less current for the same light, it is much less likely that the socket will burn out. (I have had to replace several in track lighting systems.)


Martin W18/05/2014 13:05:52
921 forum posts
30 photos


I agree with Les this looks like a switched mode power supply. However if you look at the trackside picture of the printed wiring board there is a light coloured castellated pattern half way up and on the left hand side. I believe that this is a printed fuse, or perhaps I should say 'was' a printed fuse. If this is on the output side then I suspect that the bulb failed and shorted the output which blew this fuse. If on the input side then most probably it is a component failure. Looking at the general arrangement I suspect this fuse is on the input side of the board but it is not clear.

Assuming that the problem was a failing bulb, and no other damaged occurred, then the board can be easily repaired by soldering in a wire ended fuse of appropriate value across the gap left by the blown track. There even appear to be component solder pads conveniently available. Needless to say that you will need to ensure that any replacement can't short out on to the case or any other metal bits.

Below the fuse is another track that is exposed whether this was caused by the fault or is a production artefact is unclear but may be worth looking at.

While the above doesn't solve your immediate problem it may prove to be a cheaper way to repair the unit.

Good luck and have fun


John Stevenson18/05/2014 13:14:16
5068 forum posts
3 photos

Les don't think it's a led failing, these are brand new and tried two, both do the same and one of these two is now in another machine.

I don't think it's a DC problem either as in many years of working on all types of machine tools the lo-volt system has just been a simple transformer spitting our AC

Like an idiot I should have put a meter across the incoming before I put the light back together which on this design needs 12 hands and a deep socket with the 13mm bit half way up inside the 12" extension.

When I get a minute I'll investigate the transformer on this machine but being hard on to a wall it's not an easy matter to deal with.

V8Eng18/05/2014 14:15:52
1730 forum posts
6 photos

12 hands and a deep socket with the 13mm bit half way up inside the 12" extension.

Very similar to what I needed working on a garden tractor yesterday.

petro1head18/05/2014 15:24:15
770 forum posts
152 photos

Interesting the bulb is fine but I take on board what Les said and will go 20W instead of 35W

Tim Stevens18/05/2014 17:40:11
1622 forum posts

With LEDs you may get more of a strobe effect*, but you will certainly get much less heat.

* ie because the lamp flickers (faster than you can see) you may see rotating parts as stationary or slow moving - just like the wheels on John Wayne's wagon. Dangerous if you do not realise. Filaments heat up slowly so the light is much less variable.

Cheers, Tim

Edited By Tim Stevens on 18/05/2014 17:41:30

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