12v Transformer

[Adam09]

Hi guys,

I have 2 x Wickes decking light kits, both containing 8 LED bulbs, and a 230-240VAC 50Hz 15VA wall wart transformer.

I would like to use these as kitchen plinth lights instead, and run all 16 off one transformer wired into my lighting circuit.

I have a spare 12v transformer, and was wondering if this would be ok to use.

The transformer is a RING : DET-105 240V ~ 50Hz 105 VA max.

Cheers,
Adam

 

[ericmark]

A LED lamp is typically 1.2 volt and the reverse bias is limited so normally feed with DC. When these lamps are fitted into a package often components are added so the whole lamp will run on for example 12 volt AC. But without details of lamps no one can answer your question.

If we assume the 15VA wall wart transformer is matched to lamps then you will need a 30VA transformer. Because most quartz lamps use inverters which in turn contain a transformer not only is there a maximum but also often a minimum current as well. Likely 30VA will draw the minimum current but it would need checking.

Very likely your lamps will run on the transformer you have. But without all the details no one can tell you for certain if the two components do match.

Looking at the Wickes instructions it states "2 core DC Cable" which makes one question if these using will work from a inverter likely giving a HF AC supply.

It does not call the unit a transformer but a driver which would make one think likely a switch mode power supply (Inverter) but other than reference to DC cable (Only DC cable I have used is compensating cable for thermocouples) which seems it's self suspect as most cable is same for DC and AC there is really no information as to what supply they require other than being 12 volt.

 

[Adam09]

Hi ericmark.

Thanks for the information above. I have taken some photos.

This is the wallwart transformer:

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• Adam09
• 3 Jun 2011
• 1

This is the transformer I would like to use if suitable:

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• Adam09
• 3 Jun 2011
• 1

These are the instructions for the decking lights.

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• Adam09
• 3 Jun 2011
• 1

Although the instructions state the supplied transformer is 10VA, its actually 15VA.

Each deck light uses about 0.3W/0.3VA. If I use all 16, I would be drawing 4.8VA?

Do I simply need to check what the minimum VA I can draw from the Ring transformer?

If not, could you give me a link to a new transformer? Preferably on Screwfix.

Cheers,
Adam

 

[ban-all-sheds]

Although the instructions state the supplied transformer is 10VA, its actually 15VA.

Each deck light uses about 0.3W/0.3VA. If I use all 16, I would be drawing 4.8VA?

Yes, you would, which is less than 10VA, let alone 15, so you can use one of your wall-warts without worrying about compatibility, and keep the other as a spare.

Don't forget that however you do it, installing these lights will be notifiable.

 

[Adam09]

hi ban, I would like to use a transformer I could use on my lighting circuit, so they can be switched with the main kitchen light, rather than having to use a plug in wallwart, which I would have to switch on at a socket.

Cheers,
Adam

I will press thanks once I get back on the computer guys.

 

[bernardgreen]

The transformer supplied appears ( from it's size ) to be a true transformer and not a switched mode power supply that the white one most definately is.

The true transformer provides sine wave 12 volts.

The SMPU produces "12 volts eff" ( effective ) which can be rapid short pulses of maybe 24 volt (or higher ) that average out in the lamps to be 12 volts.

Most filament bulbs will work on the 12 volts eff as they will average out the voltage,

LEDs supplied by 12 volts eff may be destroyed by the pulses that are more than 12 volts sine wave AC.

 

[Adam09]

Thanks guys.

Would I be looking to buy a LED constant voltage driver then?

If so, are any of these good?

Cheers,
Adam

 

[bernardgreen]

Would I be looking to buy a LED constant voltage driver then?

That would not be a good idea.

The LED element ( the bit that turns current into light ) is best driven by constant current.

But the LED lamp units that you have ( which are one or more elements fitted it into a holder ) will almsot certainly have the necessary current controller{s} included as part of the fitting. Other wise they would not be able to run on 12 volts AC that the recommended transformer supplies.

 

[Adam09]

Ok, so is there not a transformer I could buy which I can use?

If not, looks like I will have to wire a plug socket onto the lighting circuit, for the wall wart to plug into underneath the kitchen units and label it plinth lights only?

Cheers,
Adam

 

[bernardgreen]

If I was doing this then I would use one of these

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=5405179

installed in a suitable case or protected location with fuse and thermal protection.

It is a job that needs some knowledge to do it properly and safely.

Other sources of similar transformers are available

 

[ban-all-sheds]

hi ban, I would like to use a transformer I could use on my lighting circuit, so they can be switched with the main kitchen light, rather than having to use a plug in wallwart, which I would have to switch on at a socket.

Why not install a socket on the lighting circuit?

 

[RF Lighting]

You beat me to that.

Never mind all this fannying about trying to run two sets off one tx, or finding replacement bits and whatever else.

Just have a twin socket wired off the lighting circuit through the switch and plug both sets in.

 

[Adam09]

You beat me to that.

Never mind all this fannying about trying to run two sets off one tx, or finding replacement bits and whatever else.

Just have a twin socket wired off the lighting circuit through the switch and plug both sets in.

Hi RF,

I will do this, but with a single socket and one transformer, as the kit states I can purchase extra deck lights and have up to 20 lights on one kit.

Thanks guys!

Also, whilst I'm here, I'm looking to purchase a flush ceiling occupancy pir.

Has anyone used a MK K5015?

Or a CP ELECTRONICS Green-I?

Cheers,
Adam

 

[bernardgreen]

I will do this, but with a single socket and one transformer, as the kit states I can purchase extra deck lights and have up to 20 lights on one kit.

If running close the the rated output allow for the transformer to run warm which means allowing free air movement around the unit.
Most of these have an internal fuse which "blows" if the unit gets too warm. The internal fuses are almost always non reseting and often non replacable as they are buried in the windings of the transformer.

I'm looking to purchase a flush ceiling occupancy pir.

There is a difference between a motion detector and an occupancy (or activity or presence ) detector. You can sit working at a desk in a room with a motion detector and it will not detect you ( after it times out from you entering the room ). Occupancy detectors are sensitive to arms moving across the desk.

http://www.steinel.de/en/produkte_fuer_fachkunden/praesenzmelder/koenigsklasse ( it is in English )

EDIT This is a better link http://www.steinel.de/en/produkte_fuer_fachkunden/unterschiede_bewegung_praesenz ( also in English )

There are other sources of PIR presence detectors ( but I think these are the best )

Consider also a means to override the unit both to OFF ( a cat in the room will not need light ) and to ON if the unit fails or you need light when the sensor considers it is already bright enough