Help : Cfl Lighting Circuits + Initial Current Draw

[Ackybang]

Hi everyone,

Have been planning lighting layouts for my home, and after ordering 1-4 gang touch / remote dimmers from England, (which are on there way) to create different levels of lighting for any particular room, I seem to have made a mistake, it would seem.

Now, the dimmers I've ordered seem to drop the amount of watts per channel, the higher number of gangs you go, for instance, a 1 gang can be 5-600 watts or more, but a 4 gang is 250 watts per channel, unless specially ordered, which I didn't think I would need to do.

The reason for this is, I am going to be using dimmable cfl's predominantly, aswell as led strips, who's transformers are controllable by these dimmers. The compatible size cfl's for most of my dimmable fiitings are going to be the 13 Watt variety.

I thought I would calculate the load by counting the number of watts per bulb, and divide them up by the appropriate amount of channels on my dimmers. Now, after going to look at light fittings again yesterday, and sourcing a supplier for the dimmable cfl's, and actually reading the box, it clearly states that you can't run anymore than 8 x 13 watt cfl's on one 500 watt dimmer - is this due to start up current draw for the ballasts ?

If this is so, then is it the same for standard cfl's - I mean, should we actually count a 13 watt cfl as consuming it's incandescent light equivalent, i.e. 60 watts ? Also the 20 Watt version as really 100 Watts ?

I might have to rethink my layout / switching if this is the case - for instance, in my lounge, I have 6 sconces I was going to put on one 250 watt channel, as one 'mood' setting, aswell as 6 wall washers on another, and I thought the maximum load / draw would be 78 watts per channel - but due to the recommendation of Philips, it would seem it's actually going to be 360 watts - and therefore can't be done.

In real terms, is this a real issue, and would it actually burn out a channel - I thought I had arranged for every channel accordingly, and well within it's individual limits, to help prolong bulb / switch life, etc - but now it appears I might have to correct my layouts, and add in extra switches, or subtract bulbs. These dimmers are soft start, if that would make any difference.

I also have planned for outside lighting effects on 1-4 gang induction switches, using standard non dimmable cfl's - if the same rules apply, I could get away with reducing the bulb wattage on certain circuits, I suppose - but the dimmable cfl's only come in these 2 possibly pickle inducing sizes.

Any way around this ? Would appreciate any feedback from people with multiple bulbs on one circuit (especially dimmable cfls), or comments from real sparkies.

Also, will I have to rethink my led layouts ? I'm thinking of using tape in certain rooms for cove lighting effects - these are controllable by dimmable 12/24 volt transformers - I've heard a watt is always a watt - but is a rated 75 watt 5m long led tape still drawing a 'real' 75 watts, after the transformer, and therefore, could it actually draw a lot more on startup, also ? Some runs will be having multiple tapes in parallel / series.

I have searched these forums to no avail, even though I'm sure I read a post about it before - possibly by electau, and looked on the net, and can only find reference to this 'inrush current' phenomenon, whereby many appliances can actually draw upto 50/100 times their specified rating for a short initial startup time, instead of specific cfl related topics. I would say, however this site did mention that modern cfls might only draw a large load for around 0.05 seconds - but still, it seems like a very real thing, and for something travelling at the speed of light, are we to perceive this as a very long time indeed, with the real compounded potential to damage circuits / switchgear ?

I'm not an electrician, and I'm confused.

Thanks for your time / any advice..

Edited May 4, 2013 by Ackybang

[Crossy]

This is not a simple issue, I'll try to explain without getting too technical but there's really no choice.

Incandescent lamps are a purely resistive load (although they are non-linear) such lamps have a power-factor of pretty near unity (1) [Google Power Factor]. They are dimmed by reducing the amount of power supplied to them by reducing the supply voltage or chopping up the mains supply using a some electronics (a triac) in the dimmer. The dimmers are designed to handle this type of load at their full rated power.

CFLs are electronic loads, and many (particularly cheap ones) have a poor Power Factor (some as bad as 0.5) they also generate all sorts of harmonics and general noise which gets shoved back into the power supply.

CFLs are also constant-power loads, if the supply voltage reduces then the supply current increases so that the light output remains constant up to a point when the electronics gives up and the lamp goes out. This is great if you have a fluctuating (Thai) power supply but of course this means that driving them with a dimmer has little effect on the light output (not the effect desired).

Non-dimmable CFLs units don't cause much problem because the electricity supply has a very low source impedance which is quite capable of powering these 'odd' characteristics (not so a UPS or genset, where you could end up with only about 50% of your rated output when driving CFLs).

Dimmable CFLs monitor the supply watching for the chopped up waveform provided by a dimmer, they then measure the amount of dimming requested and modify the tube drive power to achieve something like what is intended by the user. Unfortunately this electronic jiggery-pokery (along with the harmonics etc.) presents the dimmer with a load for which it wasn't designed and it requires de-rating in order to prevent blowing itself up.

The instructions of the CFL box are probably erring on the side of conservative so you don't fry your dimmer, you need to talk to the dimmer supplier as well to see what he says about dimming CFLs with his product.

Regular switches and breakers are quite happy with non-dimmable and dimmable units, and yes, a 10W CFL does indeed draw about 10W from the supply. When dimmed the dimmable units do draw less power, but they become less efficient too so a 10W dimmed to 50% is probably actually drawing 7.5W.

Dimming your LEDs with dimmable transformers is going to present similar de-rating issues, and mixing LED and CFL on the same dimmer could well be a recipe for disaster

Add to this mix the availability of 'leading-edge' and 'trailing-edge' dimmers, some LEDs and CFLs like one type better than the other.

Personally, we have no dimmers, if we want dimmed lighting we turn off the main lights and use lower powered (5W LED) uplights reflecting off the ceiling and an assortment of table and standard lamps with various LED and CFL lamps.

[Ackybang]

Thanks for your reply, Crossy.

I did a lot of research in the first instance, looking for dimmers, and found what seems to be a decent enough product (Varilight - British made since 1972) but by not having the appropriate knowledge I just took the specified bulb wattage as a real given, and worked out my layouts from it.

These dimmers are compatible with dimmable cfl's, mains voltage aswell as dimmable / low voltage transformers - which the same company supplies for a good price, and I was planning on using them for dimmable led tape, from a company that I found a good link to on this site. Actually, pertaining to the switch manufacturer, a lot of their quality products work out a lot cheaper than the limited selection you can find here, with the combined strength of the baht, and no V.A.T. on export orders to boot.

They are trailing edge compatible, soft start, short circuit and compensatively overload / thermally protected, aswell as having other features, such as less noise / buzz - aswell as being able to detect unsuitable inductive loads, such as a wire wound / torrodial transformers, and will protectively malfunction in such an event. It does say not to put transformers or lighting circuits on inductive circuits, as the spikes can damage equipment - but I believe all my lighting circuits would be dedicated, so this shouldn't be an issue ? Is anything that's not digital with a ballast actually inductive, to a point ? Outside of this, I can't find reference to cfl's, apart from the award winning ones they sell - and at no point do they say a 13 / 20 watt should be accounted for electrically as a 60 / 100 watt, apart from terms of comparible light / lumen output.

It's Sunday today, but I will send the company yet another email, and see what transpires.

Looking at their site again, they do have a returns policy, and everything is guaranteed for a Year, unconditionally - so, if need be, I will send back and change some of the dimmers if necessary, as they can build them to order, bespoke, from the factory, and I don't really want to use less, or incandescent lights - neither do I want to double up on switches. Looking at their 1000 w dimmers, it's interesting that the actual maximum rating they give them is 650 w (?). Then why don't they say 650 watts, instead of a 1000 ? This is the bit I don't understand. Anyway, do you know why dimmers are rated in watts, and normal switches in amps ?

On these multiple gang dimmers, is cross interference possible, Crossy ? They seem to be independent units for each gang - I thought in theory, on a 3 gang switch, I could run normal incandescents off one gang, dimmable cfls off another, and a low voltage transformer off another, if I wanted to ? Am I incorrect in assuming noise would go to earth, or remain on an independent circuit - or is it because they would share a portion of the same incoming current ? I'm not trying to find disagreement with you, I'm genuinely interested in learning something from someone that knows.

Looking at the normal impulse switches I've ordered, they are 6A per channel, which in theory means I can run upto 1320 watts off every channel - is this right ?

So, mate, assuming I didn't have a clue about all the technical jargon - and you said a cfl draws roughly the same as it's stated rating - in layman's terms, is a 13 watt cfl really going to consume 60 watts of power or not, and can I comfortably put 6 x 13 watt dimmable cfl's (which I 'thought' would be 78 watts) on a 250 watt dimmer, or am I limited to 4, allowing for Philip's recommendation ? Because these dimmable cfl bulbs are expensive (1 x 13 watt - 385 baht), I don't want to buy a load of them, just to realise I'm overloading particular lighting circuits I've laid out, and can't really use them.

The only dimmable cfl's I can find here are Philips - and only in 2 sizes. This is a brand name I 'trust' to have a fairly good build quality - dimmable down to 5%. I do realise it's a fallacy to think we are actually saving a lot more electricity by dimming bulbs after a certain point, but it all adds up, I'm sure - and I do love the idea of energy saving, aswell as more flexible control of lighting for certain rooms, instead of just on / off.

Thanks again.

Edited May 5, 2013 by Ackybang

[Crossy]

I'm afraid there really is no simple answer here.

This is why I said to contact the dimmer manufacturer, although those Varilight dimmers do look pretty well indestructible preferring to shut down rather self destruct as the cheapies would

Since you know which lamps you will be driving it would be interesting to know how many of the exact lamp Varilight say you can drive with each dimmer rating. Not sure why their 1000W dimmer is only really 650W a spot of specmanship perhaps, 1000W is a LOT of lighting even if conventional.

Only the dimmer manufacturer can answer your question regarding loading, I would say you'll likely be fine with 78W of CFL on a 250W dimmer but I'm not going to guarantee anything.

EDIT This page http://www.varilight.co.uk/leaflets/compatibility.pdf suggests that you should respect the bulb manufacturers recommendations for CFLs other than VARILIGHT DigiFlux Dimmable EnergySaver+ CFLs .

I doubt you'll get interference between gangs of such well spec'd units, never say never mind. Any electrical noise generated would have to be absorbed by the supply which hopefully is of a low enough source impedance to do so.

A 13 Watt CFL will draw 13 Watts from the supply, however it may not draw 13 VoltAmps (did you read up on Power Factor?). When looking at complex loads you cannot simply multiply Volts x Amps to get Watts.

With a cheap 13 Watt CFL (PF=0.5) it may well draw 120mA (26VA) rather than the 60mA (13VA) you'd expect. By the way, your electricity meter does measure Watt/Hours (not VA/Hours), so you don't get over charged for the energy used.

Switches are rated in Amps as that is what they switch, a 10A switch will control 2200Watts at 220V or 120Watts at 12V.

For your 6A switches, you can run up to 1320VA of load at 220V, that would be 1320Watts of incandescent lighting or as little as 600W of CFL (if poor PF).

[Ticketmaster]

I'm wrestling with a similar problem. Not with dimmers, but with the startup inrush current of CFL's, which according to my research can be anywhere from 50-100 times the steady state current! My particular problem all started when I designed and outdoor lighting system using 24 - 23 watt CFL PAR 38 floods on a 20 amp MCB. I planned to use a 16 amp rated manual household switch and some motion sensor switches. Only 552 watts, no problem, right?

Then I started looking at motions sensors and saw things like 2000 watt, but only 300 watts for CFL's. or 3,000 watts, but only 500 watts for CFL's. <deleted>?

I did some research and learned that while a 60 watt incandescent bulb draws a steady 0.27 amps of power (on a 220VAC system), a 23 watt CFL draws its steady state power in repeated short spikes of ~0.6 amps. Thus, though its overall power consumption is lower, it mimics a higher draw for purposes of system design. Okay, so I can only use 1/6 as many "watts" of CFL's as I can incandescents on a single circuit without throwing the breaker. In addition, there is the danger of burning up a switch. If i use 24 - 23 wat CFL's, through they consume current of 0.10 amps, I will be switching the equivalent of 13.8 amps. Okay, so far so good.

But then there is start-up inrush current headache. For incandescents, it is 12-15 times the steady state load, or 3.2-4.1 amps for 60 watts. But for CFL's it can be anywhere from 50-100 times the steady state load and manufacturers do not tell you what the inrush current ratings are for their products! That means a single 23 watt CFL could pose a potential start up load of 10.5 amps! Twenty-four of these babies give a potential startup inrush current of 250 amps!

According to my research a typical MCB will handle 8-12 times its rating for startup inrush (or for a 20 amp MCB, 160-240 amps) and a typical household light switch will handle 10 times its rating (or for a 16 amp switch, 106 amps).

If I put 24 - 23 wat CFL's on a single lighting circuit (0.105 amps each), that comes to 2.51 amps of steady state consumption, but a whopping possible 250 amps of startup inrush current, which would throw the MCB and weld my switch contacts in the "on" position. So after putting together my well thought out "552 watt" system, I would have destroyed the motion sensors and the regular switch the first time I turned it on -- UNLESS I was lucky enough to get CFL's with a startup inrush current of only 50x. In that case, this system will scrape by.

This is ditto for LED's

Does ANYBODY know of a supplier of CFL's and/or LED's in Thailand that discloses the startup inrush current of its products? If you are "close to the wire" (so to speak), this information is essential to system design.

This is a nightmare. I may be forced to use incandescent lights in the system which will cost four to five time more to operate. Of course I could split the system into two circuits, but that would defeat the purpose of the system as a security lighting system designed to light the whole place up instantly.

Another solution would be to put an inrush current limiting device into the circuit such as an NTC thermistor. The problem is, I am not an electrical engineer, and I have no idea how to do the calculations to determine the right specs for my system.

Any help would be appreciated.