Magnetic base LED machine light – WARNING MAY BE UNSAFE

[duncan webster 1Participant @duncanwebster1]

I ordered 2 but only got one adapter. Being a cheapskate I thought I'd cut off the 2 pin and fit a UK 3 pin plug. Note the adapter doesn't seem to have a fuse, so this might be a good idea anyway. The actual copper is very small indeed. I twisted it together with a short length of thicker flex to give the screws something to bite on. No doubt someone will have a better way, I rejected solder as that relaxes under screw connections. I've no doubt the copper is sufficient, must be very low current.

[TendorParticipant @tendor]

No one seems to have mentioned that the ebay unit has a mains lead running right up to the magnetic base which is therefore exposed to the machinist's environment of hot swarf, cutting tools and sharp-edged lumps of metal. The cable's sheathing is very 'minimal' whereas most machine tool mains leads have, or should have, substantial sheathing.

On the other hand, the Jansjo is powered by the SMPS located at the wall socket with the lamp supply lead at about (IIRC) 4V. Putting aside the possible failures within the SMPS, it seems to me that the Jansjo-style with 'remote' SMPS is the safer option for the machinist's environment.

[Enough!Participant @enough]

Thanks for the info about the plug. I pointed out to the seller that it didn't properly fit a 115V NA Outlet and his response was:

" thanks for your message and you can change the plug leg angle, then it will be tight. "

In other words "bend the prongs a bit" !

Fitting a new plug is a bit problematic here (Canada) since our devices always come with a moulded plug. You can get manually-wired plugs but they are relatively uncommon and designed for much heavier wiring. I don't think the strain-relief would work well (if at all) on a wire of this size. And the tininess of the conductors would be an issue too.

It's probably better to home-brew a splice to an existing moulded cord. I've done that before using a small Hammond plastic component box which can then be filled with RTV or epoxy.

[Enough!Participant @enough]

Thought I'd just write a postscript to this.

Since I wasn't really happy that the mains plug didn't really fit the local system and didn't want to use the vendor's recommendation of "bending the pins" to compensate, I decided to take mine apart to see if I could perhaps modify it to run from a lower voltage wall-wart or USB.

The picture shows the pcb after I removed the leads going to the LED. There is (apparently) no isolation from the mains supply. I had hoped that the orange-brown component that looks like an old-fashioned capacitor (or even older-fashioned condenser) was a miniature encapsulated transformer. However it only has two leads and appears to be …. a capacitor (it's marking is blurred beyond legibility).

With the lack of mains isolation, I don't think I'd want to run this device in a workshop environment.

Before I removed the LED leads I measured the DC voltage across them at 40V. Not a particularly convenient voltage for a wall-wart and I could see no easy way to cut/jumper the PCB in the LED head for a lower voltage.

[ Incidentally the two leads going from the mains PCB to the LED head were Red and Black respectively with Black going to the pad marked " + " and Red to the pad marked " – ". The connections were similarly reversed at the LED board so it did actually work. ]

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Clive India on 12/04/2016 10:33:03:

Come on guys – it's a light innit – not as complicated as a hypervapotron.

Plug it in, if it works it lights up. If it don't – throw it away.

Is there anything more to be said?

.

I think Bandersnatch has now said it, quite eloquently.

MichaelG.

[Bruce EdneyParticipant @bruceedney59949]

That circuit is a pretty standard low current step down circuit. I have got two of these lamps. One on my mill and one on my wife's overlocker. As an electrician I have no problem using them in the workshop or anywhere else for that matter.

Bruce

[CirclipParticipant @circlip]

Seem to recognise the components and basic layout in the photo as the standard years ago (30) inside the PIR sensors fitted to external Halogen Light units?

Regards Ian.

[MuzzerParticipant @muzzer]

Posted by Bruce Edney on 24/06/2016 05:55:30:

That circuit is a pretty standard low current step down circuit. I have got two of these lamps. One on my mill and one on my wife's overlocker. As an electrician I have no problem using them in the workshop or anywhere else for that matter.

Bruce

In that case you should know that lighting and other mains equipment is not permitted within any area that could be recognised as "Zone 0" (ie a "wet" area frequented by users) unless it is IP67 rated or better. Where you have metal dust, swarf and coolant present and the lamp is accessible to the user, basic intelligence (or training, failing that?) would suggest you should know to treat that as Zone 0 – particularly if you claim to be a "competent person". You appear to be recommending others to follow your own practices. Really?

Hence the previous suggestions that at the very least, RCDs / MCBOs would be a minimum sensible precaution when installing questionable mains equipment like this in a workshop. You will notice that there is no protective ground connection.

The IKEA lamps are an even better solution, as the entire lamp unit is SELV (inherently safe, if you like). The power unit itself needs to be mounted away from splash and swarf – but as it plugs into a 13A socket, you should have that covered already – outside of any Part P notifiable areas.

Murray

[Bruce EdneyParticipant @bruceedney59949]

Murray

They are marketed as Sewing machine lights –

I was commenting on the circuit which is quite safe and used in many devices.

In NZ our regs require new circuits and in the case of my home all outlet circuits to be RCD protected. I do not use coolant on my mill (yet) and if I did I would be changing my lighting source. The base of the light in question is quite well sealed (unless someone has pulled it apart).

There is no protective ground because it is double insulated.

Bruce

[Enough!Participant @enough]

Posted by Bruce Edney on 24/06/2016 20:06:08:

The base of the light in question is quite well sealed (unless someone has pulled it apart).

Not that well sealed around the strain relief. It's basically ' bunged up ' and wouldn't allow gobs of metal to get in but I'm quite sure liquid could enter.

I don't quite get the "double insulated". The only thing isolating the input AC from the lamp head itself is the circuit board between traces and/or the components. Isn't that single insulated? With a non-polarised plug to boot.

As a non-electrician I'll pass in my shop.

[Bruce EdneyParticipant @bruceedney59949]

Double insulated means that metal parts have layers of separation between them and live components

From wikipedia (so it must be right )

"The basic requirement is that no single failure can result in dangerous voltage becoming exposed so that it might cause an electric shock and that this is achieved without relying on an earthed metal casing. This is usually achieved at least in part by having two layers of insulating material surrounding live parts or by using reinforced insulation."

Bruce

[Martin 100Participant @martin100]

Posted by Bandersnatch on 23/06/2016 22:08:24:

The picture shows the pcb after I removed the leads going to the LED. There is (apparently) no isolation from the mains supply. I had hoped that the orange-brown component that looks like an old-fashioned capacitor (or even older-fashioned condenser) was a miniature encapsulated transformer. However it only has two leads and appears to be …. a capacitor (it's marking is blurred beyond legibility).

With the lack of mains isolation, I don't think I'd want to run this device in a workshop environment.

I'd be interested to see the reverse of the PCB and what track separation they used. Also the markings and hopefully manufacturersname on the brown capacitor.

[Mike pParticipant @mikep]

i would like to add to this thread as i bought one of these lights in the original thread and was using it on my mill. Within less than 5 minutes of use the flexible neck touched the quill and with a blue flash I received a mains current shock before the RCD cut in, Without even looking inside I threw the thing in the scrap. I reported the fault to the supplier and received a reply saying this has never happened before, but the fact is it did and anyone wearing a pacemaker could have been in serious trouble so I say to those praising this lamp BEWARE

[Neil WyattModerator @neilwyatt]

Mike,

Can you dig it out of the bin and check what the fault was , if possible – was it mis-wired or a short to earth?

I'm changing the title of the thread.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for posting, Mike

Glad to know you lived to tell the tale.

MichaelG.

[Malcolm Parker-LisbergParticipant @malcolmparker-lisberg38138]

Mike P

Something does not add up in your description of the course of events: A blue flash would trip the breaker, indicating a short to the earthed quill, at this point of contact, in the miliseconds before the breaker opened, no voltage would be available to give you an electric shock. as all the metalwork would be at earth potential !

Malcolm

[Michael GilliganParticipant @michaelgilligan61133]

Some interesting comments about RCDs **LINK**

MichaelG.

[Enough!Participant @enough]

Posted by Martin 100 on 28/06/2016 16:48:52:

 

I'd be interested to see the reverse of the PCB and what track separation they used. Also the markings and hopefully manufacturersname on the brown capacitor.

 

OK, here are pics of both the component side and trace side of the (single-sided) PCB. For orientation, the PCB is flipped laterally (left to right) between these shots. Also I'm adding the schematic that I traced out from the PCB. If the diode across the output (zener?) is the wrong way round, blame me. I was never good at diode polarities/marking (so I became a Mechanical Engineer).

The PCB measures 0.95" across its flat sides.

As I mentioned earlier, all the markings on the brown capacitor are smeared and illegible.

 

 

Edited By Bandersnatch on 28/06/2016 22:46:34

[Malcolm Parker-LisbergParticipant @malcolmparker-lisberg38138]

Michael

 

There is an old saying… "It's the volts what jolts, but the mils that kills"

But the voltage is required to drive the current. A blue flash as the short occurs won't give enough voltage to jolt as a weld is most likely to occur between the components.

No blue flash: touch a live wire, circuit to earth through the body will give a jolt and trip the breaker.

The "let Go" phenomenom determines whether you live or die. Less than 6mA and you can let go, more than 22mA, with AC, results in Tetanic Contraction, which means the muscles permantly contract and you can't let go.

 

30K resistor looks like 3K with the photo colours.

Malcolm

Edited By Malcolm Parker-Lisberg on 28/06/2016 22:59:00

[Enough!Participant @enough]

Posted by Mike p on 28/06/2016 17:34:08:

i would like to add to this thread as i bought one of these lights in the original thread and was using it on my mill. Within less than 5 minutes of use the flexible neck touched the quill and with a blue flash I received a mains current shock before the RCD cut in, Without even looking inside I threw the thing in the scrap. I reported the fault to the supplier and received a reply saying this has never happened before, but the fact is it did and anyone wearing a pacemaker could have been in serious trouble so I say to those praising this lamp BEWARE

Is it possible that the short was from the 40V LED output to ground? I would think that would give a fair spark if it wasn't current-limited. It just seems from the construction of this thing that the most likely short to the metal conduit would be either damaged insulation on the LED wires or a short from the conduit to the wire connections on the LED PCB – particularly if the conduit on your particular sample protruded more than anticipated into the LED housing (see pic).

(Incidentally, I do have a pacemaker ….. or actually an ICD which is arguably worse)

[Enough!Participant @enough]

Posted by Malcolm Parker-Lisberg on 28/06/2016 22:50:31:

30K resistor looks like 3K with the photo colours.

Just to confirm, it is actually orange-black-orange.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Malcolm Parker-Lisberg on 28/06/2016 22:50:31:

There is an old saying… "It's the volts what jolts, but the mils that kills"

.

Indeed there is.

However; a 'jolt' whilst working on a machine tool is something I prefer to mitigate against.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Capacitive divider circuits as drawn by Bandersnatch are a respectable design. The safety critical component is the brown capacitor he marked with a question mark.

Whether or not the lamp is suitable for a workshop surely depends on the workshop. I'd be happy to use one in an indoor hobby room, less so in my garage workshop, and definitely not in a bathroom.

It's a pity Mike P hasn't been able to provide more information about his faulty unit. In the absence of evidence we can only guess what was wrong with it. I suspect an insulation fault put the metal sleeve at 40V DC. You would get quite a bang from a 100uF capacitor charged to 40V. And 40V is sufficient to give you a jolt if you have damp hands. Try licking the terminals of a PP3 9V battery!

You do have to be careful with this stuff. Many years ago I read of an unusual fatal accident resulting from a 30V DC shock. A colliery worker running to get out of the rain fell against a sheet of corrugated iron that in turn contacted an uninsulated low-voltage main. The poor chap was very unlucky: he was wet, sweaty and then the iron sheet maximised the flow of current due to the size of the surface area connection it provided.

Knowing that 30V can be fatal didn't stop me building a small Tesla Coil to make 1m sparks, but I only operated it after writing a risk assessment. 600W at 6000V; about 1MV out; x-rays; ozone; arcs; potential to interfere with a pacemaker etc. The high-voltage output isn't particularly dangerous because it's low current, but if the spark jumps to a mains connection like a lighting circuit, mains current can flow down the ionised path. That's very dangerous.

The fun part is the effect a Tesla Coil can have on a computer. From the patio, it turned on my daughter's Apple which was indoors 5 metres away and unplugged from the mains. I found the computer stalled on a blank white screen with the cooling fans full on. I had a bad few minutes waiting to see if would reboot successfully. Please don't tell her – it's a Secrecy in the Workshop issue.

Cheers,

Dave

[duncan webster 1Participant @duncanwebster1]

I ask merely for interest, as mains electrical safety is out of my pay grade. As the supplied 2 pin plug isn't handed, you can get live on the side with the 100 ohm resistor in series, so the + output to the LEDs can be at mains potential? Or have I got it wrong?

If I'm right would we be better chopping off the supplied plug and connecting to a 3 pin, which is handed? Always supposing you can work out which is which.

[Martin ConnellyParticipant @martinconnelly55370]

Quite right Duncan. Imagine a poorly wired socket with live and neutral crossed. With this circuit plugged in but the socket switch off the positive terminal will rise to mains voltage.

Martin

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