Can I use 1 transformer for multiple lights?

[ban-all-sheds]

Just go to your nearest pound store and buy some torches - they will work just as well as your idea.

 

[Steve]

 

[mikhailfaradayski]

Can you clarify where you got the 1 tx for 1 lamp recommendation from?

Probably from me, as that is what I recommend.

fair dos, maybe we should re-name the big red joke book to RF7671:2008

 

[mikhailfaradayski]

Can you clarify where you got the 1 tx for 1 lamp recommendation from?

Probably from me, as that is what I recommend.

Listen to that man, he

downlights!

yea, man, dig the downlights, sod the Polar bears

 

[mk2phil]

thanks for the replies guys, but I think i'm more confused than before.

To be honest I'd prefer to use mains voltage, but the section where I'm placing these lights is a feature point and they need to be very small - hence an mr8 20w bulb. From what I can tell, these are only available in LV applications.

mikhailfaradayski - Thanks for that link. So I could use one of these to power the whole lot, and they'd still be dimmable too? Someone else mentioned voltage drop also - should I be worried about this, and if so what can I do to help the situation?

I was thinking perhaps of using one of these transformers (http://www.tlc-direct.co.uk/Products/LTYT105.html) to power 2 lights each. As its rated from 0w - 105w this would also allow me to use 35w lamps at a later stage. And from what I can tell, regardless of whether I use 20w or 30w lamps, I'd be able to dim them with these transformers....?

N.B Because the lights are so small I can only use transformers that will fit in side a 42mm diameter hole.

Thanks for all the replies so far.

 

[johnnykc]

mk2phil......the transformer that mikhailfaradayski is pointing you towards is manufactured by a company that specialises in dimming so you should have no problems there.....

If you check out the technical section of the TLC website you will find a voltage drop calculator that will give you the correct cable to use depending on the length of run..

Cheers

 

[mikhailfaradayski]

HI MK2Phil,

AFAICT, you shouldn't have a problem with dimming, if you bought this TX, print off the description from TLC and then if there is any issue, ring 'em and moan like buggery.

Volt drop is a valid consideration, but if like you say its only a 4ish metre run of 12V it shouldn't be a big problem. But to make sure, you could position the TX in the middle of the run and feed the 12V both ways, this should overcome any potential problem.

Alternatively, as you say these are to be feature lights, if you have a robust wallet there are some nice LED options available.

 

[mk2phil]

Thanks guys.

Mikhail when you mention LED alternatives, other than the bulb itself, is there anything else that needs to be changed should I want to use LED instead? I'm assuming LED lights are Low Voltage too...?

I initially discounted LED's becuase form what I've seen of them they are bright white and dont look very 'natural'.

Thanks again guys

 

[mikhailfaradayski]

There are lots of solutions, all depending on what you hope to achieve in the space you have and how much cash you want to put into it.

I dont know what you currently have in place or what you want to do, so what needs changing is anyones guess

note the cash bit

try googling something like 'LED lighting systems'

 

[mk2phil]

Can you guys tell me if these transformers will draw the maximum rating all the time? This wording in the instructions has confused me:

"To calculate the toal load for dimming, add the wattages of all the transformers you are intending to dim and choose a dimmer with a rating to suit."

I've got the 0w-50w versions and will be using 20w lamps in them. But does the wording above mean that the transformer will always be drawing 50w regardless of the lamp wattage?

If I have 10 20w lamps (and therefore 10 transfomers - I'm using 1 tx per lamp) does that mean I need a dimmer that can handle 500w or 200w?

Thanks[/b]

 

[Taylortwocities]

If you are using transformers then you need to add up the total VA value of the transformers, not the lamps.

If you have 10 transformers each rated at 50VA then the total load (for dimming) will be 500VA.

Note that you may need to add a percentage to this for some dimmers. And some dimmers can only handle a limited number of transformers.
And some transformers are fussy and only like leading edge (not phase cut) dimmers
Here's TLC's guide to THEIR dimmers. http://www.tlc-direct.co.uk/Technical/DataSheets/Systems/DimmerGuide.htm

I have not seen many 50VA transformers, most are 60VA.
Per the above, you can economise by having one 60VA transformer to serve a cluster of three 20watt lamps.
that will be cheaper on transformers and dimmers.
Or forget transformers and go for mains halogen lights.
Or forget downlights and install some luminaires that will be useful for lighting.

Hey, this electrical stuff isn't as easy as it first looks, is it?

 

[mk2phil]

All the dimmer switches I've looked at rate them in watts though? Do I need to do some conversions to figure this out then?

eg 10 transformers, 50VA each. How would I convert 500VA into a wattage rating that I can use when buying the dimmer switch?

IS it easiest to just take the maximum rating of the transformer - in this case 50w. therefore 500w dimmer.

OR am I able to buy a 200w dimmer if I only use a 20w lamp in each transformer?

And yes, its definately more complicated than it first appears - if I could use mains voltage then i would, much easier!

 

[Taylortwocities]

The lamps are rated in watts because they are purely resistive.
The transformers are rated in VA which is a bit like watts but it takes into account other factors (inductive/capacitive).
If you want to understand it just Google "AC THEORY" - its great for insomnia.

The dimmers vary. You need to follow the makers instructions re dimming ELV transformers. That's why I gave you the link to TLC's site. You'll notice that their iQ dimmers will only dim a maximum of 5 transformers.

Just dont buy 10 transformers and a 500watt dimmer and expect it to work. It might, it might not. If its not designed right then the dimmer may die after a couple of days, or the lights may start to flash.

 

[bernardgreen]

The lamps are rated in watts because they are purely resistive.

And to complicate it more the rating is when they are at normal operating temperature. When they are cold the resistance is considerable lower so when switching a lamp ON the operating voltage is applied to a lamp that is cold and the resistance of the filament is much lower than when hot.

So the current immediately after switch on, known as the inrush current, can be many times the normal current and will be high until the filament is white hot. So the wattage taken by the lamp at switch on can be many times the rated wattage. Most transformers will tolerate this short duration but severe overload without damage, some will degrade a little each time the lamps are turned on and a few will go "Phut" and die immediately. Different types and makes of lamp of the same wattage have different cold resistances. So whether the transformer goes Phut immediately or lasts a while or forever depends not only on matching wattage to VA but also ensuring the inrush currents are compatible.

 

[johnnykc]

Can you guys tell me if these transformers will draw the maximum rating all the time? This wording in the instructions has confused me:

"To calculate the toal load for dimming, add the wattages of all the transformers you are intending to dim and choose a dimmer with a rating to suit."

I've got the 0w-50w versions and will be using 20w lamps in them. But does the wording above mean that the transformer will always be drawing 50w regardless of the lamp wattage?

If I have 10 20w lamps (and therefore 10 transfomers - I'm using 1 tx per lamp) does that mean I need a dimmer that can handle 500w or 200w?

Thanks[/b]

that particular transformer will only draw the total lamp load i.e 20w per tranny rather than the transformer rating...