Dimming Fluorescent Tubes

[Ike]

Neon might not be such a bad idea. Most neon sign shops have loads of used 'straights' and transformers kicking around and cable and clips are cheap enough. You need the transformers to match the tube but they'll probably sort that out for you and while the tubes and cabling are at high voltage it's current limited and usually protected against earth faults so even touching an exposed contact would most likely just be really painful. Neons can be flashed, dimmed or whatever. If you're dimming them you may need to add a dummy load/lantern to the circuit like with low voltage transformers and you can't dim them completely to nothing but they do go a lot further than normal fluorescents.

 

Neons are far better looking (in my opinion) than any neon alternative ever could be.

[Tomo]

There are basically three kinds of dimmable fluorescent ballasts:

 

1) Two-Wire. These have a Live and a Neutral, and you simply connect them to the output of any SCR-based dimmer and they work.

The best I've seen recently was a Photon Beard softlight, which struck at 20-25% on the upfade, and doused at around 15-20% on the downfade.

There are some Varilite dimmable CFLs opn the market as well which have similar characteristics, but have very visible (and quite pretty) flicker effects below around 30%.

 

2) "Three-wire" ballasts.

These use one neutral, one 'switched live' and one 'dimmed live', plus protective conductor.

 

To start them, the switched live is switched on, and then the dimmed live is faded up.

These tend to be able to go much lower than two-wire dimmable fluorescents.

 

However, they're pretty difficult to deal with in a touring situation, as it's difficult to arrange circuit protection due to the two lives.

 

3) Internally-controlled ballasts.

You give them a switched power supply, and control the brightness with a control protocol such as 0-10v, DSI or DALI. I've not seen any DMX ones, but they may exist.

These are often the cheapest, especially the 0-10v ones.

However, you can't connect them to just any 0-10v demux - these units actually create 10vdc inside the ballast and must be 'pulled down' by the demux to dim.

The reason for this is twofold - it means they could be controlled by a simple variable resistor with no PSU, and also it means they 'fail safe' - if the control wire is cut, they turn on.

 

I've also found that many 0-10v ballasts won't actually dim to nothing - they drop to very low (maybe 10-15%), but you have to isolate the switch supply to properly turn them off - using a switchpack set to "Full at 10%" patched to the same DMX channel as the demux is a really effective way of controlling them. Very power efficient as well, as you're not powering the device when it's off!

 

Most dimmable fluorescents are aimed at the architectural or TV markets though, which can make them expensive and often complex to install.

 

Other than that, actual neon is great.

It strikes almost instantly, even at low levels, and most 'standard' neon ballasts don't flicker until around 25-30%.

See what you can find locally - used neon kit is generally fairly cheap as it's difficult to recycle and there isn't a huge market for it secondhand.

[pscandrett]

Hi - many thanks for your comprehensive reply.

Other than that, actual neon is great.

It strikes almost instantly, even at low levels, and most 'standard' neon ballasts don't flicker until around 25-30%.

See what you can find locally - used neon kit is generally fairly cheap as it's difficult to recycle and there isn't a huge market for it secondhand.

That's interesting; I'd sort of written neon off but I'll get back to the guys we've used before (Image of Blush Sign) to see what they say. My concern for all of this is durability, to be honest, but we'll see how we get on!

 

Thanks.

[Ike]

Durability wise they aren't as bad as you might imagine. We've toured Europe with some doing pretty much what you want, used nothing more than a bit of bubble wrap and a few bits of waste pipes for protection and not a single one got damaged.

[AdrianW]

Hi All,

 

Reading with interest about the use of Ballasts with a 0-10V control signal, since a similar problem has just landed on my bench!

 

I'm needing to control some 4' 36W UV tubes and have 'come across' a source of Philips HF-R dimming ballasts at a very reasonable price. I now need to create a control unit for these.

 

I hear what Tomo has said about the 0-10V control signal..... it needs to be pulled down towards 0V to control the intensity of the lamp. A quick Google suggests that the commercial units use a pot across the 2 terminals, and reading between the lines seems to suggest that open circuit (high resistance) = full intensity, short cicruit (ie. low resistance) = min, intensity. However, Google hasnt suggested a value for a suitable pot. Anyone got any ideas? I have found that this is detailed in the European Standard EN90929 but dont really want to buy that just to find out the relationship between the control current & the intensity!

 

Has anyone come up with a circuit to drive these from standard 0-10V demux output? I was thinking about maybe a basic current mirror configuration of two transistors & a preset ? Any body tried it? What about isolation?

 

Your thoughts would be appreciated!

 

Adrian

[dbuckley]

Without having tried it...

 

The control element is just a pot, and the control line will be fed from a 10V source by some pull-up resister. A voltage and current reading would enable one to calculate what value that resister has, if one wished to know...

 

An external voltage source will be able to override that pull up resistor quite easily, if it has a low enough impedance drive.

 

So, for a demux with a flimsy output drive, perhaps a unity gain opamp would be all that is required?

 

The other thing that occurs to me is that in the Zero88 Chilli dimmer range, there is a fluoro dimmer, the HF series, which isn't actually a dimmer at all; the normal mains outputs are relay switched rather than triac dimmed, and there are a series of additional 10V control outputs to let the ballast know how bright to go. But, in the Chilli manual (1.3MB PDF) there are all sorts of dire warning about these 10V outputs not being ground referenced, so I would make very sure you understand just where the 10V control signal from the ballast is referenced to, or smoke may be released, or even worse, cries of pain...

 

Edited to say: Years ago I did a installation which had 16 dimmable fluoro fittings, using ASCR15 dimmable ballasts, no longer available, and having fluoros dim, flash and strobe is a very powerful look...

[Tomo]

Has anyone come up with a circuit to drive these from standard 0-10V demux output? I was thinking about maybe a basic current mirror configuration of two transistors & a preset ?

There are a few commercially-available DMX demux designed especially to drive such florries.

 

I have successfully used the Pathway Connectivity eDIN 16-channel demux to run 0-10v florries - they are very compact DIN-rail mounting units that can drive either 'standard' analogue dimmers, or 0-10v fluorescents.

They have a DIP switch per channel to select the kind of drive.

 

Unfortunately I don't know the cost of these units as it was a big architectural installation.

 

I expect there are quite a few other varieties designed for this purpose.

 

dbuckley mentioned the Zero 88 Chilli florry dimmer, and there is also a Unison Dimming expansion module that does the same sort of thing.

- You fit a relay module into the rack for the mains, wire the 0-10v lines to a small expansion card, and then they 'dim' together.

[pscandrett]

Keith Owen and Dave Smith of Specialz have developed a dimmable ballast called the AtLast which plugs directly into the output from a dimmer. Very neat.

FWIW I emailed Specialz and got an email back from Dave Smith saying: "Sadly, we no longer manufacture the Atlast ballast in small quantities, Atlast 2 is on the drawing board, but with no release date planned as yet.

 

Depending on the application, ADDI of Austria manufacture a dimmable ballast that is DMX controllable, but there is a limitation of tube size. www.ldde.com"

 

Hope that helps someone.

[Racer_Rob]

hi, I need dimmable fluorescent tubes for a school production and so started to look into dimmable ballasts when I came across this topic. I've found this RS dim flo and wondered if it was any good. After looking at the data sheet (link on the product page) two things caught my attention

a. it says it uses a DSI signal which seems very similar to a DMX, could DMX not be converted to this?

b. the wiring instructions say some cables linking the tubes to the ballast can be a max 1m?!? ...this could cause some problems..is this really essential? and y is it...their only power cables!

 

anyway if anyone could help that would be great, or just update if there have been any developments in the 'dimmable flo tube' area since the last post ! thanks

 

Edit: alternativly I have just seen this Philips ballast which looks pretty good, it looks (from the data sheet) that control is given from a 0-10V DC supply ... could I not just build a seperate circuit which a variable resistor and a DC supply to control this? (..and this one doesn't have 1m max cables!)

[musht]

DSI is Trichronics own protocol, probably can get DMX to DSI somewhere but wouldn`t bother.

 

Tube to ballast lead lenght of 1M is probably pretty universal, at the high frequencies lead length becomes a real problem.

Electronic ballasts are quite slim and light compared against wound iron ones.

 

Personal prejudice would choose Philips over Tridonic,there was some new Osram ballasts on ebay recently, should be fine with whatever source of 0-10v you can rig up.

[Racer_Rob]

ok, thanks for that :up:

 

do you know what is needed for connection to the tube. I.e Tube fitting something like one of these at either end?

 

..and does any special type of cable need to be used? (or if the ballast outputs 58W then just a cable that can handle that)

[musht]

Tube fitting should be fine, as to cable they`re usually meant for assembly with solid core wire, it just pushes into the cage clamps on the lamp fitting.