Magnetic base LED machine light - WARNING MAY BE UNSAFE

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Yes

More common than not these days for consumer goods. Double insulation is considered 'inherently safe', the problem with this design is that it appears it may not be double insulated.

Neil

Sounds unusual... against my learning anyway. I recently bought a product from Taiwan, it came with a tiny moulded 3 pin plug, no approval marks on the casing, i thought to myself "theres no way a fuse is in there" so i cut it off and bought a BS/CE approved plug from wilkos and sorted it. I wasn't going to risk using an electrical appliance without a fuse.

I've been known to experiment at times but never on safety.

Shoutout to Neil, I was listening to planet rock earlier and the host mentioned your name for a phone in request? any truth to that?

Michael W

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It would certainly be interesting to see how they handle the insulation [if any] inside, and adjacent to, the [presumably metallic] gooseneck.

MichaelG.

Edited By Michael Gilligan on 29/06/2016 23:28:21

OK despite my initial respones (top of page 2)  I'm convinced. Fortunately I have 40v on the milling machine for driving stepper motor, so I'm dumping the circular box of electronics and driving the LEDs direct from 40v with suitable dropping resistors. I'll report back when I've done it as to how well it works. Currently I've worked out that there are 2 parallel arms, each with 15 LEDs in series, but no way of ensuring each arm takes the same current, so I'm going to cut the appropriate track and put a small dropper resistance in each arm. Watch this space

Edited By duncan webster on 29/06/2016 23:30:13

Wise man, Duncan

You may deserve a pay-rise [ref. Your earlier post]

MichaelG.

An old joke in Information Technology is that "Fail Safe Systems fail by failing to fail safely" and earth systems are a case in point. They also have the potential to become dangerous.

A domestic single phase mains supply is actually part of a three phase distribution system. The earth / neutral / live arrangement reduces the risk of electrocution in the event that a fault causes a metal case to become live. But the arrangement we consider "safe" itself becomes dangerous if an earth or neutral fault occurs on the supply side. For example a neutral fault can cause the domestic live wire in an entire street to rise to 440V. This destroys equipment, blows fuses, and could cause fires.

The good news is that electricity providers take care to reduce the risk of earth/neutral faults. It does happen though: errors bonding transformers; an inadequate earth at the sub-station (perhaps caused by corrosion); sabotage; theft; and accidental physical damage to the network are all possibilities.

Risk is something to be managed. Ideally all electrical equipment should be double insulated and designed so that people and water can't get at the innards. As that's impracticable we just have to take care, bearing in mind that not everything on sale is automatically suitable for workshop use.

Cheers,

Dave

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Wise words, Dave

MichaelG.

Well, i guess i learn something new quite often..if not everyday.

Michael W

OK, some more pics (sorry about the quality - I didn't have much time). these show how the thing is assembled.

Couple of points:

- The round magnetic base containing the pcb is crowded - the switch has to sit well down between the higher components. And it's assembled pretty much blind (!)

- There appears to be no additional insulation inside the metal conduit (gooseneck). I don't think two insulated wires running inside could be considered double-insulated (could it?).

- The ends of the conduit sit in counterbored holes in the housings at each end which prevent it from protruding into the respective enclosures (pcb and led head). Nonetheless the bare metal is pretty close to the 40V terminations at the pcb and it's my opinion that it could still short if, say, the wires were stripped back a little more than necessary. It might also be possible for the wires to fray at the cut ends of the conduit.

Thanks, Bandersnatch

The Gooseneck is more tidily installed than I feared it might be ... But the whole thing is too risky for my taste.

MichaelG.

Could the box not be filled with a sealant? this would prevent any short.

Clive

I've modded mine to work off 40V DC. When I prised the back off the lamp unit I found tat red wire went to -ve and blac wire to +ve, which wasn't a good start. Doesn't actually matter as long as it's wrong both ends, which is was, but I've made it right. Then cut track and soldered on an extra lead. The existing circuit board is in the bin, replaced with dropper resistances to ensure current sharing. I used 2 off 100 ohm in parallel in each leg as I didn't have any 50 ohm. Now works off the stepper motor power supply, all it needs is an in line fuse, it wouldn't fit in the little box.

I'll just keep an eye out for another 40v transformer for the other one, not worth buying one, although with a lot more surgery I could make the LED board be 6 lots of 4 in series and run it off 12v. Life's too short!

Edited By duncan webster on 01/07/2016 12:48:58

Edited By duncan webster on 01/07/2016 12:50:37

Edited By duncan webster on 01/07/2016 12:51:36

Hi Duncan,

Your pictures are causing another mystery. I can't see them in your original post but as you see they appear when I quote it!

Anyway, looking at Bandersnatch's post and Mike P account of his blue flash moment, Sherlock Duffer concludes that MikeP's lamp must have had a bare wire inside the metal goose-neck. As the lamp circuit floats, it could have been either the plus or minus wire that shorted.

I wonder if you might need in-line fuses on both plus and minus? Depends on your stepper motor supply, which could be floating, or negative ground, or positive ground.

The extra fuse isn't a safety feature - it further guards against the possibility of a short damaging your stepper motor supply. (Perhaps!)

Dave

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I hope you're right, Dave ... But the other [much more severe] possibility is that the upstanding end of R2 somehow made contact with the metalwork [see earlier picture from Bandersnatch, above] ... I still can't tell how plausible this is; but I definitely don't like the layout.

MichaelG.

Edited By Michael Gilligan on 01/07/2016 13:42:04

I'm late to the party on this thread as I bought an LED light from a reputable company and won't buy any more as I simply don't like the quality of light it gives off. I'll use the one I've got but won't buy any more for the time being. I very much prefer the halogen work light on my mill to any LED's I've seen so far.

There have been several reports of dangerous LED lights without proper earthing so to suggest that having a CE mark makes the item safe is simply incorrect. And thats without China's fake "China Export" mark on many items that end up here.

If it's very cheap there's probably a very good reason. Keep safe out there!

The reason you couldn't see the pictures was that I wrote the post, then couldn't seem to get the pictures in, so posted it so I wouldn't lose it, then found out how to do it and edited the psot.

Anyway, I don't know whether my power supply is earthed on the LT, but I know it's isolated (I made it). I can easily earth one side of the LT winding on the transformer. Is this the right thing to do? Seems to me that if it's floating I can't get any leakage to earth. There is already a big fuse to limit current from the power supply, I was just going to put the fuse in to protect the LED wiring, not me, I think I'm reasonably safe at 40v

Edited By duncan webster on 01/07/2016 13:51:10

Just noticed this, It's possible Michael - I'm a regular listener (and emailer) to Planet Rock and Radio 4. Apparently I was on Feedback last week...

Neil

Good on you, it's a great station. You kinda get a rough spectrum of all rock and few gems in between. Alice and the hairy bikers can be funny to listen to. Always depends on the tastes of the hosts alot of the time.

I actually listen to smooth extra also (because the signals bad on the main station) but i dont like to admit to it :P

Apologies for the mini sidetracking. Conversation always leads elsewhere!

Michael W

Edited By Michael Walters on 01/07/2016 14:02:36