Dimmer rating not making sense

[mhar]

Went to a house the other day as dining room lights not working. 4 x 40/50w gu10's on a dimmer, dimmer faulty.
Looking round the house there was an incredible amount of incandescent lighting mostly on dimmers so I suggested to customer that it may be worth spending an extra couple of £'s on the dimmer to get one capable of dimming led lights, they agreed.
Went to cef (the nearest wholesaler) with the faulty dimmer (40-400W rated) and asked for a dimmer that would work on LED's ultimately but on the gu10's now. A couple of phone calls later the guy produced a 60-600W dimmer that he said would be fine. When I questioned him saying that ultimately the load would only probably be 4 x 6W so how would this be suitable he made another call, was put through to a technical department who told him that the dimmer would work with 2 x 7W or 6 x 4W led's and was definitely suitable for led lighting.
Could someone explain the logic of this to me please and how a min 60W rated dimmer would be more suitable than a 40W min rated one. I would have expected something like a 15-200W one!

 

[Richard Burns]

CEF can provide interesting information (using interesting in a variable sense!).
Dimmer design is very much variable and different manufacturers may make a similarly specified dimmer in different ways.
Normally for halogen downlights you would derate the dimmer by at least 25% possibly 50% depending on manufacturer and so you should be looking at about a 400W dimmer for the halogens he has.
Normally for LED dimmers there is no minimum wattage specified only a maximum so if you have a minimum wattage I would be surprised if it worked for anything lower than that minimum.
However it may be that the manufacturer has modified the design of the dimmer but not the labelling!
Possibly the instructions require an additional load resistance in circuit when using low loads?

 

[mhar]

Thanks for the reply.
I did read the instructions before posting (!) and there is absolutely no mention of LED dimming but they assure me that they will work with LEDs however they did specify the minimum loadings / configurations as stated in the original question.
Summarising the statements and specs this unit requiring a min 60W load will work on a 14W load if a minimum of 2 x 7W LEDs are used or a 24W load if a minimum of 6 x 4W LEDs are used.

 

[Richard Burns]

I would tend to set up a test bed and connect up a few LED downlights to the dimmer and see if they dim properly.
Do the instruction state that the dimmer must not be under loaded? If so then you are a bit stuck despite the quality advice from CEF:confused5:.

 

[mhar]

To be fair to the bloke from cef he did make 3 calls to get info and what he reported to me was from the manufacturers technical department. If it was just a counter assistants statement I would have taken it with a very large pinch of salt!
There is nothing in the instructions re loadings, the loading info was on a sticker on the rear of the dimmer.
I am asking mainly out of curiosity's sake. I won't be held to it by the customer as the couple were out and my discussions were with the Romanian mum who couldn't speak English so we were communicating in French (grade C at O level in 1976!!)

 

[Richard Burns]

Hopefully you are going to be OK and maybe someone with better knowledge of dimmer design would be able to provide more information.

Good luck with it, since you have been informed (indirectly) by the manufacturer it is suitable you are following the manufactures instructions!