Magnetic base LED machine light - WARNING MAY BE UNSAFE

If you want a low cost solution to lghting for your machine and also to keep SWMBO happy, buy two of these magnetic base 30 LED sewing lights. One for her and one or more for youself. They are less than £5 on Ebay from China

Link

H

As requested

http://www.ebay.co.uk/itm/321974937183?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

<http://www.ebay.co.uk/itm/321974937183?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT>

Malcolm

Thanks you Malcolm.

Geoff - Cannot have enough light.

Mine arrived PDQ and ARE bright.

Geoff - Perfect.

I'd be careful with stuff like this. Shipped direct from Hong Kong ie made just over the border in some unknown Chinese factory. No obvious CE marking (for what that's worth) and the Chinglish is very powerful (magnetic adsorption?? - sounds like woo medicine!).

Make certain you use an RCD with these, particularly if you put them anywhere near swarf and coolant. Personally I'd stick to buying electrical gear from a reputable / recognised UK outlet.

The IKEA type lamps with proper CE-marked low voltage (wall wart) transformer have got to be much less risky.

Murray

It makes sense to keep conductive materials away, but where do you think Ikea electronic products are made ? And they don't use transformers anymore because of the cost of the copper, they use an electronic inverter just like the lamp and they are made in mainland China too The electronic inverter has inheriently better isolation between input and output.

As they are double insulated an RCD will offer little protection in the case of an internal short Protect the wiring by using a 3A fuse, which incidently neither USA or Europe 2 pin plugs are fused. So fit a UK 13A plug and 3A fuse.

You can buy the identical unit from Amazon (UK) supplier for £7.99) or from the sewing machine distributors for £25

So yes, Caveat emptor, but do some research first.

Malcolm

Malcolm

Regarding the Ikea alternative, the Janszo, has anyone else had problems with the swiitches on these? The first one I bought has found its way, attached to a home-made mag base, on to my little CNC mill. The original switch developed an intermittent bad contact that caused the light to randomly dim. I've replaced that with a new in-line light switch, now my second one, clipped on to a tool rack to illuminate the lathe, has started the same trick, and I'm sure I've noticed the third that is used as a desk lamp in my study doing the same.

Grrr.

I have six of those sewing machine lights (20 LED model) on various tools in the shop. Two are over a year old. They are in my opinion the best thing since sharp tools. Small, no heat, little current draw (I never turn them off) and easy to mount! I need more......

Pete

You're missing the point. By law any products sold in the EU must be CE marked and this is a legally binding declaration that all the creepages and clearances have been met, the materials used are approved for use as insulators, the approved temperature range of the safety barrier components is not exceeded and the EMC (emissions and susceptibility) have been tested and meet the statutary requirements - amongst other things.

There are plenty of products that come nowhere near meeting the basic safety requirements. One excellent way to acquire them might be to buy direct from China, without CE mark and knowing nothing about their parentage. On the other hand, if you buy from a reputable company like IKEA, they will have ensured that any products they stock are properly approved and have meaningful CE marking. Whether they are made in China or not is beside the point.

As for switch mode power supplies (they are not called inverters), there is no reason to suppose that they are any more or less safe than a 50/60Hz transformer. It's perfectly simple to construct either sort using minimal creepages and clearances, using unapproved insulation and safety critical components. Believe me, in several decades developing power electronics products, I've seen plenty examples that were potentially lethal.

The benefit of using an RCD is that you would be protected against a breakdown in the isolation barrier - such as you might find if it were designed by a cowboy. If a hazardous voltage appears on a user accessible part and generates a current through the user to ground, that user would be very grateful to have the RCD trip. To qualify as "double insulated", you have to meet certain requirements.

Failure of the primary circuit generally causes a fault current to flow and (again) the regulations require this to happen in a manner that will not result in a hazard (shock, fire etc) - it is a requirement to have a fuse on the AC connection to limit the fault current. The notion that unfused US and EU plugs somehow present a hazard is fatuous.

Murray

Oh dear, sometimes a little knowledge is a dangerous thing. You need to dig out your basic electronic reference books and look up the definition of an inverter.... Converts DC to AC. SWMP are generally DC output. Look up the definition of the word converter also. These LED lights use inverters, the mains is rectified, converted to AC and fed to the LED diodes which conduct on one polarity and an anti-parallel diode conducts in the other.

As toroids are used for the majority of small inverter applications, for reasons you may or not be aware of, will have creapage and clearence distance greater than can be achieved with an iron cored transformer. But you also need good layout practises.

As with all standards, some manufacturers comply, some don't and some are criminal. A major european manufacturer, VW, comes to mind as does the fire death trap Vauxhall Zafera.

To tar all Chinese electronics manufacturers with the same brush is fatuous and scaremongering.

As to being fatuous, take a trip to Savoy Place and search the index in the library journal reference, don't use the online version, it does notgo back far enough. I think the argument about 2 pin non fused plugs was raging in the 1960 and 1970s

Malcolm

Malcolm, not a good idea to use anti-parallel diodes as you suggest as the efficiency is limited to 50% before you even start. I think it much more likely that the mains is rectified, converted to high-frequency AC to enable using a small transformer, rectified back to DC then use very probably a buck converter with a flywheel inductor and diode to drive the LEDs efficiently, with some control to keep a constant current. Actually for an LED light which is entirely self-contained, like a light bulb, you wouldn't need a transformer as isolation is not a requirement - just rectify, add a smoothing cap, then a buck converter to feed constant current to the LED.

John

As the saying goes, there are many ways to skin a cat. I don't think they are designed for efficiency, as overall power consumption is so low, but it does depend on the circuit design, a flyback converter springs to mind, inherently output short circuit proof as you can only get out the power that is put in, and a high efficiency design that uses very few components. I have one of those in front of me, sadly demised when I connected the output to the mains. No fires, just dead as a result.

What is almost certain is the the small to medium power copper wound, laminated iron cored transformer is heading for extinction.

Malcolm

"Regarding the Ikea alternative, the Janszo, has anyone else had problems with the swiitches on these? "

Yes John, I have. I looked into changing the switch but decided to try primitive surgery first. The switch body is welded together, so I drilled a small hole (1 mm from memory) in the middle of the back, and squirted some aerosol switch cleaner in. It's quite possible that WD40 would do the trick if you haven't got switch cleaner. It's still working 2 years later, and if it gets funny again I shall try another squirt. I have a second switch beginning to play up, so that will get the treatment shortly. Safety isn't an issue, since the switch is only operated at 4 volts, and it's mains isolated.

Incidentally, the plug and socket on the wall wart are the standard 2-pin DIN connectors as widely used on 1970s hi-fi. Still available, and very handy to know if for any reason you need to extend the lead.

George

Low voltage switches nee a 'wiping' action to keep them working well, perhaps they have used a switch really intended for a higher voltage.

> What is almost certain is the the small to medium power copper wound, laminated iron cored transformer is heading for extinction.

I remember my dad explaining all the reasons why SMPSUs would never catch on (noise, reliability), back in the 70s. Specifically he told me not to use one for my hi-fi amp, so I bought a wind your own transformer kit.

Neil

Edited By Neil Wyatt on 11/04/2016 08:27:41

Malcolm,

**LINK**

They need to be efficient to keep everything as cool as possible for reliability.

George, thanks for the confirmation that I'm not alone in having problems with the Janszo switch. IIRC, the one I replaced screwed together. When I took it off the mechanism was woeful, just a lug that pushed the contact surfaces together, no wiping or toggle action at all. At least the replacement has a toggle, though not a wiping type. Seems silly to have a long life LED light and supply circuit then fit a switch that fails.

With proper levels of design the type of core used is immaterial. An E-I design is inherently more tolerant of assembly issues than a toroid, there is really nothing to stop the former being assembled with nothing other than wire windings on each half of the bobbin and it fully meeting isolation requirements, whilst the latter must have a multi layer taping separating the windings to achieve any reasonable level of isolation.

For the reasons why a toroid is superior to E-I designs and why you can't design out the disadvantages; see the paper by Texas instruments: **LINK**

The difficulty winding a toroid is the major reason for not using them, but the ingenious Chinese seem to have overcome that one.

Malcolm

That isn't quite true. Any product "placed on the market" and being subject to a Directive that requires CE marking must carry a CE mark. It is an offence to apply the CE mark to other products.

The CE marking is the responsibility of the manufacturer or his agent/importer in the EU. If you buy direct from a Chinese manufacturer that responsibility lies with yourself if you place the item on the market. If it is for your own use it is not being placed on the market. The CE marking doesn't have to be on the product itself but can be on the packing or the instructions.

Having said all that, I see in one of the Ebay photos that it is CE marked!

Russell.

Disclaimer: My knowledge is based on working on a standards committee in Brussells some 15 years ago so things could have changed!

The point I was making is you can very easily achieve isolation using injection moulded plastics with separate primary and secondary sections on an E-I core, whereas with the toroid isolation is only achieved through the use of very specitic deliberate actions and materials during the very complex winding process.

With a toroid the means of isolation are always without exception buried within the construction and are not suitable to later non destructive visual inspection, the exact opposite of a transformer with separated bobbin E-I construction.

The claim that a pair of toroid windings will somehow achieve better isolation than an E-I core is one I cannot agree with.