110v lamp on 250v dimmer

[david.elsbury]

No, they were 12v AC halogen lamps- MR16's. Same as for birdies.

 

Thanks for explaining, I thought I may have been right, just wasn't sure why.

David

[skdean]

You could always hire one of the new Jands racks, you can vary the output of each dimmer channel, from 110v or 240v, and also I believe 80v

[mattwright15]

Hey guys think we all maybe missing out a big point here, its an incoming show. If it was my gig going into a venue I would want to know 100% that everything was done the last thing I want is bubbles popping in a gig. just hire the transformers. don't take a risk that big.

 

only my 2 pence.

[dbuckley]

Clearly some misconceptions here in basic electricity.

 

a) You can happily run transformers off dimmers, provided the dimmer is rated for inductive loads. I havent seen a dimmer in years that isnt. Probably have to go back to mini IIs era.

 

b) If the dimmer is set to 50% output on a linear 'curve' then the triac will turn on at the peak of the half-cycle, so the instantaneous voltage (as seen on either a peak hold meter or a scope) will be something like 330V. The RMS voltage, as read on a meter capable of reading true RMS will be half the mains voltage. Ordinary meters (including an Avo 8) will read average voltage, which is something else again. It is the RMS voltage that is important for this aplication, as RMS is effectively heating power (misuse of word power, but it'll do for this level of discussion), and thats what makes lamps glow. Thus you can operate a 110V lamp off 240V through a dimmer quite happily, providing you keep the RMS voltage at an acceptable level.

 

c) The frequency out of a dimmer is the same as the frequency in, it doesnt change as you dim, the waveform chopping occurs on both half-cycles.

 

The issues as has been pointed out are insulation (which I forgot about - oops - and the clue was in the question) and curve, both from the perspective that 50% may not be 50%, and the actual rate given that one would compress 100% of range into 50% of control, and that lamps themselves are not linear.

 

As we did this just a week or two ago, I'll repeat it - you can also stick an appropriately rated doide in series with the lamp, which will chop every other half cycle.

 

Anyone else here old enough to remember pin patches with resistor pins for running single 110V bubbles?

[Schultz]

Woops... ok, David. Sorry if I seemed a bit overbearing and patronizing: reading your profile I realize you probably know quite well if a lamp is powered by AC or DC... sorry again!

 

I've finally found the link to some interesting divulgative articles on the IES/ETC website.

 

Dimming

 

They're fairly basic but give a good idea on the principles of dimming. Anyone in the forum who is interested in learning more about it might find them useful. The graph really explains it all. There are other, more technical ones on the web but these should prove useful.

 

Now let's see if I get beaten to this too...

 

Roberto

 

EDIT: for dbuckley. I have unfortunately more than once come across ancient dimmers not rated for inductive loads. Not knowing anything of the venue I just gave the safest advice... :)

[j_b]

Oh dear - many misconceptions here of how dimmers work, how physics works etc.

 

There's a lot of duff info in this thread. Best advice I've seen is from Mark Powell - i.e. do it the way everyone else in the indusctry does when cross touring the US and the UK.

 

Quotes like "Not linear, even at 100%" and "lamps on DC, rather than AC" (filament lamps, yes?) make me worry - lots.

 

Give Mark a call if I were you, 'cos he does seem to have his facts straight, and by following his advice, you're likely to end up with

 

1) a show that works

2) no damaged equipment

3) no dead people

 

I assume this is the result you're after?

[Schultz]

Quotes like "Not linear, even at 100%" and "lamps on DC, rather than AC" (filament lamps, yes?) make me worry - lots.

 

Many people think things on the line of "Dimmer at 50%: same as half 230V". When some of the posters gave the impression of thinking like that I pointed out that it's not so and highlighted some of the facts of SCR dimming: it's a chopped wave, it has a choke, the output isn't as simple as that, etc. I didn't want to get into a paper on wave forms, triacs, transistors, describing variable currents and potential differences with trigonometric functions, etc. I wanted to point out the risks. Maybe I was too brief. Sorry.

 

When David talked about popping 12V lamps, and me having not long ago come across some "expert" who plugged a 12V DC apparatus (not lights) in a dimmer outlet and raised the fader at a "low" setting, thinking it would work, I instantly jumped to the conclusion that something similar was happening. Didn't read the post or user's profile correctly and excused myself publicly. I'm really sorry about this.

 

Give Mark a call if I were you, 'cos he does seem to have his facts straight, and by following his advice, you're likely to end up with

1) a show that works

2) no damaged equipment

3) no dead people

 

Believe me, I agree. If you're not sure, don't do it, ask someone who knows. Platinum rule.

 

Roberto

[Ilthigore]

surely if you restrict the output on a dimmer it's just half power not half voltage

 

I'm pretty sure that Power is proportional to the Voltage squared (because P = IV = V*V/R = V²/R) - or [more voltage = more current = more more power]. That's why scalings for dB are different for power and voltage.

 

Therefore, P/2 = (VI)/2 = (V*V/R)/2 = V²/2R = ±V/√2√R

 

In other words, by halving the power, you would be dividing the voltage by the square root of two times the square root of the resistance (which in lighting is probably variable depending on power). It would be directly proportional to the square root (in this case, of 2), but also dependant on resistance. I doubt you will ever apply that, but now you know...

 

This rule does apply to rms voltage too I presume... although I haven't done the calculations (once you start talking about rms things always get complicated... I was reading a book and it started talking about imaginary numbers!!! :) )

[foh_al]

Thus you can operate a 110V lamp off 240V through a dimmer quite happily, providing you keep the RMS voltage at an acceptable level.

 

An interesting thought, and on the whole, I agree. Two things crossed my mind though:

 

1. 110V lamps/fixtures/accessories are rated for 110V RMS (~155V Peak Sine). I'm not saying that sticking 325V peak at the same 110V RMS (from a dimmer at ~50% duty cycle) will do any damage - it really, really shouldn't. From a legal point of view, though, it probably ain't brilliant. No doubt if something, anything, were to go wrong on that show, some twisted individual could use that "lethal practise of wiring 110V equipment into 230V circuits" against you!

 

2. Pure speculation here: Possibly this might shorten the lamp life due to the much higher slew rate - 46kVs-1 compared to 26.4kVs-1 - causing mechanical stress in the filament. Or possibly I've just been drinking too much lately :).

[Jivemaster]

Wether a filament lamp integrates a part loop pulse and gives a representation of a lamp properly run at half voltage depends on the thermal mass of the filament. Low wattage (small filament) lamps will mare accurately respond to the applied waveshape and "see" the instantaneous voltage, than will a larger lamp.

 

The method needed here (OP) depends on the wattage of the practicals and their lamp type.

 

Can the lamps be changed to UK lamps

 

Dropper resistors need to be matched to the load to get correct volt sharing

 

Individual transformers may or may not like being dimmed

 

Running a suitable dim pack off a 110v transformer and having a complete 110v domain (with earth referenced the same way as your theatre install) is the route that should provide optimum reliability and safety. If the company are going elsewhere in the UK they will need to take the hardware with them!

 

The NJD dimmer boards as in their DP10000 and the 8000 controller (all analogue -sorry) are split powered the control ccts run off mains but the power control will take a transformer feed for low volt lamps. I have a 8000s with four faders on the front if you want to use it (£neg Hire/sale +transport) I also have a 110v Tr

[JimWebber]

Just a thought to go with the above...

 

However you derive your 110 Volts, I would also use a non-standard connector for the 110V practicals as far as possible. If there is a standard 15A/16A/13A plug on them, there is a risk that it could be plugged in to a 240V supply.

 

I realise that at some point in the chain, you will have to use a standard connector, but the more you can keep this to a minimum, the less danger.

 

For example.....

 

Crowded, hectic backstage environment, person or persons unknown kick plug out of socket. (It is always some-one else, "I didn't do it....")

 

Said person plugs plug into socket they assume it came out of....

 

You catch my drift.

[Wilf dLampy]

However you derive your 110 Volts, I would also use a non-standard connector for the 110V practicals as far as possible.

<{POST_SNAPBACK}>

Even better, use the standard connector for the job.- A 110V yellow c-form.

 

We use bars of 4 PAR36/46 ACL strings, four 28V lamps in each bar wired in series, resulting in a 110V bar. The bar is fitted with a yellow 16A connector, and then a series split from a 240V connector to two 110V connectors is used to connect them into the dimmer. IIRC rubberbox can provide the inline cable split to do this nicely. i.e. One blue socket to two yellow sockets.

 

If you only want one bar in your rig, the other one can be located backstage somewhere, or replaced with a suitable 110V parcan (again fitted with a yellow plug) to act as a dummy load backstage.

 

If the correct connectors are used then things can't get plugged in wrong- the keying on 110V c-form differs from the 240V versions so you can't mate the two together even if you are blue-yellow colour blind.

[Jivemaster]

To avoid connector problems the Maplin UK to USA auto transformers have the US standard three pin plug -two flat blades and one round earth pin. Guess the practicals will have this anyway. They simply dont fit a UK outlet.