24V rectifier for lighting.

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Says it all really ^^^

MichaelG.

Pedantic I know, but I read somewhere low voltage thick filaments also reduce 50Hz flicker because thick filaments have higher thermal mass than thin ones. Though I've not noticed much difference myself, I guess 50Hz flicker could have been a problem on a large shop-floor lit entirely with filament bulbs all flickering together at the same time.

Agree care is needed, especially with lamps in a workshop. The cheap magnetic 2-pin work-light my daughter added to her sewing machine is safe enough because the sewing machine is double insulated and operated on a table in a dry indoor room. I wouldn't use the same lamp in my workshop because the risk of a serious shock in there is much higher. My lathe isn't double insulated, I stand on a concrete floor that might be damp and sometimes splash water about. The lamp is exposed to higher levels of vibration and  falling into the chuck could break the insulation. The environment has all it needs to make an electric shock much worse than it would be in a dining room. Special rules apply to bathrooms, which are dangerous for similar reasons. Mains electricity in a workshop requires a few more precautions, like avoiding cheap 2-pin work-lights!

Dave

Edited By SillyOldDuffer on 21/08/2023 11:32:15

The simple solution to flicker is three co-located lamps, each fed from a different phase of a three phase supply!

Is all this worrying about strobe effects justified? Apart from the neon light illuminating the strobe marks around the outside of a record turntable and a specialised strobe gun, I can't say that I have ever seen this in practice. It has to be a neon as this is one of the few lighting technologies easily available that does not have any significant "inertia" in the light output. Well, maybe LEDs driven off rectified but not smoothed AC, but even then I'm not sure how powerful an effect it is. Filament bulbs surely have so much thermal inertia in the filament that they can't flicker to any meaningful extent.

Even fluorescents do not give out light directly from the internal discharge which presumably is at mains frequency but stimulate a phosphor which glows - and I'm pretty sure that the phosphor will continue to glow for the few miiliseconds between excitations. Certainly when my workshop overhead lighting was fluorescent I never came close to seeing stroboscopic effects on my lathe chuck. That wasn't the reason I swapped over to LED striplights fed by DC from a SMPS.

Is the whole thing really a bit of an old wives' tale?

The machine shop I worked in had a mixture of mercury vapour lamps and tungsten filament to combat strobe effects, they invested a lot of money in the design of a lighting system to address an old wives tale. It was a long time ago now but was regarded as the best design for machine shop lighting at the time.

Mike

I have occasionally used strobes as a student and later at work. The effect, with the correct light, is very obvious. As for workshop lighting I am not sure. I have never seen a strong strobe effect with incandescent, tungsten, fluorscent and LEDs. Years ago there was an article in the ME where someone had studied the stroboscopic of various lights. Surprisingly he observed the effect with incandescent lights. I feel it is just something that people like to worry about.

Safety wise I would be more worried about machine lights clamped onto milling machine tables, lathes cross slides etc. (shown at the start of this topic). They are always in the way and give far too concentrated a light. Industrially I only every saw them in badly lit workshops. Surely it is far better to floody the area with general lighting (LED strips these days).

JA

No, it's a real issue. The phosphors in fluorescent tubes vary depending on type, colour and make, but most do not have significant persistence. So they will cause strobe effects. LED lights will too. IT's all dependent on the design of the light(s), what other light is present, the speed and optical proerties of the moving part.

Trouble is that the conditions for "freezing" a moving part don't happen often so we forget about it until an accident happens.

Robert.

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It could be very noticeable where long fluorescent tubes were installed, without baffles.

[ The flicker is out of Phase at the two ends … so if both ends are comfortably within the field of view, they ‘cancel out’ ]

Good practice in big rooms was to run groups of lamps on each of the three available phases.

… same smoothing effect as having a three-phase motor on your lathe.

MichaelG.

my machine lights are 12v domestic downlights in a bean tin. never had a problem after all i switched the machine on so i know its running and it makes a noise so cannot forget its running. however if it was a problem i would use a 12 volt battery

Yes, they have a vested interest … but this is a reasonable overview: **LINK**

https://www.airius.co.uk/all-resources/the-dangers-of-stroboscopic-effects-in-the-workplace/

MichaelG.

Strobe effects are very real.

Anyone who has used a strobe light will know that depending upon the frequency of the strobe, relative to to the rotating or vibrating item, it can appear to be moving forwards, stationary or moving backwards!.

We used to trigger the strobe with a signal generator, so that when the item appesared to be stationary, we knew the frequency at which it vibrated (often the rersonant frequency. We could then take steps to damp the vibration or to tune things so that the resonance was outside the normal running range. (Not always easy with low frequencies )

My shop has mixed illumination. Fluorescent on the ceiling, LEDs on the Mill, LED and Quartz Halogen on the lathe, and have never been aware of any strobe effects, but that may be because of the mixed lighting.

Certainly, before failing LEDS can flicker. I have put this down to failure of one half of the bridge rectifier circuit., so that it only strikes on one half of the cycle..

A smoothing capacitor will reduce the risk of flicker, as long as the lamp can stand the resulting peak voltage.

Probably just over 33 with a nominal 24 volt supply?

Howard.

Howard

Edited By Howard Lewis on 22/08/2023 08:05:11

Certainly not arguing that stroboscopic effects do not exist; although it's a long time since I had occasion to use one, the strobe lamp I remember used a xenon discharge tube (I think) that gave well-defined pulses of light directly from the discharge rather than via a phosphor which must at least soften the rise and fall times of the light pulses.

I am querying whether, in practice, in a home workshop, it's a significant effect. After all, not many of us are going to install a three-phase inverter just to run a set of fluorescents! And definitely not when a set of replacement LEDs would do the job at lower cost. Rather than install "LED tubes", I removed my workshop's fluorescents altogether and installed low-profile LED strips. Like most commercial LED lighting, I suspect, these are fed from a cheap SMPS that is not likely to produce any meaningful flicker. I accept that those who reuse a surplus 12V or 24V transformer plus bridge rectifier might generate some 100Hz flicker but the SMPS boxes intended to drive LEDs are probably a lot cheaper than buying a transformer and get over any worries about overvoltage with or without smoothing caps. Even with my 12V LED lathe light replacement, the cheapest PSU was a repurposed "wall wart" which might not be the cleanest DC but must be better than transformer+rectifier.

Thanks for further comments. In a moment of madness (as it turned out) I pressed 'buy now' on a pair of 12-30V spotlights - the sort of things people mount on their SUV's to dazzle oncoming drivers help with off-road activities - £16 the pair. Taking on board comments about damp environments (I sometimes use suds) the IP68 rating sounded good too. They are advertised as 48W 4800 lm so I was a bit worried they might be a bit too bright. However:

The regulation is actually pretty good in that power consumption is 15-15,3 W from 12 to 30V , but obviously not as advertised. So they'll go back and I'll order the Sealey.

Robin.

Yes, that's all very well until the day when you are distracted by something or someone walks into the workshop to ask you something then you turn back to your lathe and absentmindedly place your hand on the apparently stationary chuck, saying to yourself, 'right, now where was I ?'..........ooops! That's what an accident is.

Aircraft and airliners land with their wheels up from time to time, but you would think that pilots would know that they were airborne and about to land, wouldn't you ! It happens due to distractions.

Having said that, to really 'freeze' a rotating object with light you need quite an intense strobe light with very short 'on' pulses, e.g a xenon car timing light.

As I mentioned earlier, it also depends on the nature of the moving object. A facetted item like a hex bar or the jaws of a chuck can be frozen by much lower light levels if the pulse coincides with a reflection in the irection of the viewer. Yes even less likely but still a problem when it does happen.

Nealeb,

Yes you would think the phosphor would broaden the pulse of a white LED. However it's not the case. Some time ago I was looking at alternatives to short gap xeon strobe tubes for a new analytical instument. Out of dilgence rather than expectaion it would work, I tried some phosphor type white LEDs. I was shocked at how fast they were. The turn-off was much faster than even an electrically quenched xenon tube.

Note that a lot of LED lights specifically use pulsed outputs. The human eye responds to peak light levels so for the same power consumption a LED operated at a 50% duty cycle with twice the current will appear brighter than if operation on all the time.

Robert.

Well I had to give it a go. 12v angel eye array running off a 12v rectified AC, no smoothing. No other lighting in the room apart from displays on DRO etc. I couldn't actually freeze the chuck, but it had strange effects, I wouldn't be happy if that was all the lighting I had. LED striplight (like a fluorescent tube, but LED, couldn't replicate the effect at all. Angel eye and striplight same strange effect, the L angel eye is a lot brighter close up. My normal machine light is tungsten filament, and will remain so until it pops. Then I'll see what effect a switch mode supply has

Most current quality mains powered LED lights have some internal smoothing to prevent flicker as it makes them more pleasant and less tiring to use, even without strobe effects. Even an incandescent bulb has a slight strobe effect. My dad had card circles with markings for adjusting auto changer record players and they worked under a normal lamp although they effect was not extreme you could see if the pattern was moving.

Many record players were supplied with a multi sectored disc, so that the speed (33.3, 45 and 78 rpm ) could be checked and adjusted until at each speed the appropriate circle appeared to be stationary, evn under filament lamp illumination..

On motor vehicles the "Timing Light" is a strobe triggered by the ignition circuit so that the crank pulley appears to be stationary relative to the timing mark, allowing the ignition timing to be adjusted until the mark on the pulley coincided with the mark on the timing pointer. Early ones were neons, but the later mains powered Xenon one gave a much brighter light, making the job easier.

Howard

Well the "27W" Sealey unit has arrived and it consumes about 18W over the advertised 12-30V range. Probably bright enough for my needs though.

I made a simple full wave rectifier with a 1000μF capacitor across the output and there is negligible ripple according to my manky old oscilloscope. 34V as expected, but that can be taken down - I remembered that I have some buck convertors left over from a previous project, might be more efficient than a resistor. It's getting a bit complicated for a lathe lamp I know, but I would like to use the lathe's power supply rather than a free-standing mains lamp if I can.

I did wonder if the 34V output would be enough to run one of the nominally 40V Plessey modules which MichaelG tipped us onto a while back albeit with a reduced output (they are eye-blisteringly bright at 40V). Sadly not, they don't turn on until about 38V.

I think the electrics are now sorted and I'm pondering on the mechanics. A gooseneck rather than an articulated design might be good. I was wondering about this item. It's meant for phones/tablets, but some reviewers complain that it's too stiff/strong so maybe OK for this application? Any suggestions welcome!

Robin.

In the interests of scientific enquiry, I had a careful look at my own lathe under normal working conditions last night. I have LED strip lights fed off a cheap smps nominally designed for the job, plus the lathe worklight which is a cheap eBay car spotlight in the original worklight shade fed off a repurposed "wall wart" 12V PSU rescued from a defunct internet router. My lathe has a mechanical continuously variable speed arrangement; over the range 300-1500rpm I could see no stroboscopic effects. And even wearing my Bluetooth headphones/ear defenders with the radio on, there's no way I would not hear it running!

So, whatever the theoretical risks, I'm happy that they do not apply in my case. I'm more likely to do something a mischief by turning the wrong handle...

Edited By Nealeb on 26/08/2023 08:00:57