UKH

I've changed all the lights in the house to LED apart from the kitchen, which has halogen downlights currently.

I've been putting it off because I suspected it'd be a nightmare.

My first foray was to just put in some MR16 LEDs (6.1W each) into the existing low voltage tails.  Mostly they don't light at all; one flickered sickly.

First question.  My googling suggests that's because the transformers won't drive LEDs...or do I just need to find different MR16s?

Next step has been to remove a fitting and see what's above the ceiling.  Bulb is pressed into tail; tail is wirded into mini connector box; other side of connector box wired to transformer; transformer wired to a bigger connector box that I've not had down but I think receives mains power.  The bulbs are in three sets of six each; controlled on a 3-knob dimmer switch.

Second question.  I think I should be able to contain the messing about to the transformer/bulb end of the equation and not have to change the dimmer switches?

Next the current transformers (I assume one per bulb?) are 240V AC to 12V AC T02 dimmable.  There are lots of other data and symbols I don't understand. 

Third question.  There's a bewildering array of things purporting to be LED transformers.  What do I need for 6.1W M16 bulbs?

Fourth question.  Should I take the opportunity to change to GU10?  If so, do I just wire the larger box to the GU10 lamp holder and throw away the existing transformers?

Finally, if I was switching to GU10, should I go integrated?

If the answer to 1-6 is "get an electrician" then they'll just stay as halogen, which is a shame.

Thanks in advance for your help

Presumably you have 3 transformers, one for each set/string of lights? Hard to grasp exactly what you have but it doesn't matter too much. 

To get the MR16 LEDs to behave you'd need to swap out the existing transformers and connectors for three 12v LED drivers that can do your load plus 20% overhead. By your numbers, you'd need 1.2*(6 * 6.1) = 43.9. 45W is the closest standard option.

The three new transformers should be wired straight from the main box to the feeds in from the dimmers, and into each string of bulbs. 

Something like this should suit -  https://www.seratechnologies.com/shop/dimmable-led-driver-constant-current/

Personally I'd switch to GU10 with changeable bulbs running at mains voltage if you are happy to do so, and there isn't a specific safety reason for the LV setup in the first place. This would require running new some cable with earth's etc as I'm sure you know, but simplifies the system and makes it more flexible in the future. 

Not all dimmer switches are compatible with LEDs, and yours are likely 'leading edge' (rather than trailing edge) so they may or may not work. Given you have a highish load it should be ok with decent bulbs/transformers that are specifically dimmable.

Thanks very much.

As far as I can see there seems to be one 60VA transformer per bulb.  Is that possible?   I can't see much because it's all in the ceiling!

Yea, that's possible as halogens can be up to 50ish watts. VA is equivalent to power in watts in DC circuits, which the 12v low voltage lights are. 

In that case if it's only easy to access directly where the lights are, you could fit a small LED suitable transformer in the place of each existing one without needing to change the fittings or change how the circuit is wired.

In that case something like this with a wattage rating of 0-50w. 

https://www.tlc-direct.co.uk/Products/LTYT50.htm

Ignore the link in my first post, it's for higher voltages!

Are the LED lamps you bought dimmable? Not all LED lamps are.

Hi Damon

Thanks fo rthe advice.

The link is page not found?

They are

If the thought of unqualified (no part P) "fixed electrical installation" hasn't put you off, but the idea it might be a nightmare still concerns you.... Just go for GU10.

https://www.tlc-direct.co.uk/Products/LTYT50.html

Lost an l at the end. 

Ah, perfect. And re the dimmer switch I should do all the swaps and see if it works?

FWIW, I used these - https://www.lighthubdirect.com/products/cct-led-fire-rated-downlight-ip65-6... - and it was imho much preferable to rip out what was there and start fresh.

I would swap the dimmer to a trailing edge type. With dimmable LED lamps they sometimes hold a little voltage at the end of each half of the mains cycle (they are capacitive and the electronics don’t conduct all the way to 0V). Leading edge dimmers switch on some time after zero crossing so there can suddenly be a significant voltage of the opposite polarity meeting it, which can cause a very short high current spike which can exceed the triac’s rating, leading to failure. Trailing edge start very near to 0V so the effect is far less. Although it’s dependent on the bulbs and the dimmer so it may work or it will quickly kill the dimmer.

Assuming the bulbs you bought are dimmable, maybe! Explained well by mark above. Otherwise the approach suggested by Dave to replace the whole fittings (assuming the holes in the ceiling match) may be a cheaper approach if you need a new set of mr16s as well.