Issues with MR16 Halogen Lights.


Postby xoom3 » Mon Jan 05, 2009 7:28 am

Hi,
I have recently moved into a house where the kitchen lighting is supplied by 8 x 12 V MR16 halogen lights in a false ceiling.
Three of these do not work, despite testing with working bulbs for the working lights.
I'm assuming the cablings ok with it being in a circuit back to the light switch on the wall. Would there be a transformers somewhere inline between switch and first bulb to take the voltage from 230V down to 12V?
Is it possible that the bulb holders are faulty and can these be replaced?
Doug.
xoom3
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Postby ericmark » Mon Jan 05, 2009 12:43 pm

The two pin connection do seem to have limited life maybe due to heat. The low voltage GZ10 and GU10 will not allow GZ10 (Dichroic) lamps to be fitted in GU10 holders but both lamps can fit in the GZ10 holders however with the extra low voltage MR16 lamps dichroic lamps can be fitted into non dichroic fittings and so over heat the sockets. My attempts to buy replacement sockets at a reasonable price have failed and normally I end up buying new complete lamps and where matching is required cannibalise the new one to repair old one.
The extra low voltage do not always have transformers some have inverters which work on a switch mode system and are a lot lighter but these often will show no output if tested without a load. They work on a range between X watts and Y watts and will switch off with zero load.
So use test lamp not a meter on the extra low voltage side. Being careful of course not to connect to low voltage side which at 230 volt would both blow test lamp and likely cause danger.
Note:- Low voltage AC is classed as 50 volt to 1000 volt so all house electrics are classed as low voltage the MR16 are normally classed as separated extra low voltage (SELV).
As to how many transformers it was common at one time to power many lamps off one unit I have seen 10 spots at 10W each being powered from one 100W unit which caused a problem when the owner replaced them with 20W lamps and burnt out the transformer. Especially when the floor access point was now under fitted carpet. OK when electrician fitted but then house was empty moving furniture to be able to lift carpet was not my idea of fun.
Today most the inverters are designed to fit through the hole where lamp fits and it is common to fit so they can be accessed through the hole with enough slack cable but strictly speaking laying the inverter on the plaster board is not correct method.
Most electricians shy away from SELV spot lamps one big problem today is the withdraw of tungsten lamps and although cold cathode lamps at around 11W each can be used with GU10 fitting with the MR16 the only option is 3W LED lamps which to be candid are like Toc H candles. Plus often they do not draw enough current for the inverters to work.
If you ever replace them for GU10 type be careful on how they will take the longer cold cathode lamps as those with fixed power connectors tend to leave to bulb sticking out of the holder, those which fix to rim of lamp and have a free power connector although more of a fiddle to change bulb will take cold cathode and LED bulbs without them looking unsightly.
Eric
PS dichroic lamps allow heat to pass through the reflector and it only reflects the light so not heating what it lights too much. But of course there must be free air behind them to allow the heat to leave the unit. Building inspectors however often insist on hoods etc to be used to stop fire in lower floor affecting upper floor too quickly and these stop the heat escaping and overheat the unit. The dichroic when used in food displays of course works very well but not in the ceiling of a domestic house but many people are unaware of the different types and fit them in error.
ericmark


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