I'm feeling a bit dim.... - help with dimmer derating needed

[sparkybird]

Hi all

Done a bit of search but just wanted to confirm what I think I found. Adam will probably know the answers!!

Tungsten filament - no need to de-rate. Is is OK to say use a 400W dimmer on a 100W single lamp? Would 250W be better?? If so, why (apart from cost)?

Mains halogen - need to derate by 50%. ie 400W dimmer would do 4x50W=200W

ELV/12V - need to use electronic transformers with a dimmer suitable for ELV (but I have also read somewhere an ordinary one will do?). Then add up the VA on the transformers plus 25%. So a 400W dimmer will do 6x50W = 300+75=375. OR, so you not have to de-rate as it is an ELV dimmer???

When I get this right, it would make a useful 'cut out and keep'....

yes, sad I know

Thanks

SB

 

[securespark]

Yes, 400W is OK, but no need, unless you want to future-proof it as much as you can. You can always buy a 1 kW dimmer!!!

Most dimmers have a minimum too, usually 60W.

Yes, GU10's, derate by 50%.

With SELV, you need to look at both the dimmer mfrs and tx mfrs. Some tx's have "can be dimmed with regular dimmer" on them. If not, use a dimmer designed specifically for SELV.

 

[ban-all-sheds]

And read the small print of both tx & dimmer, in case there is a leading-edge/trailing-edge issue...

 

[sparkybird]

Thanks folks!

Ban - what's that in english? Annoyingly City and Guilds deleted lighting from the replacement 2360 course - so now I have to educate myself elsewhere...

Cheers

SB

 

[ban-all-sheds]

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//www.diynot.com/forums/viewtopic.php?p=325205#325205
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[sparkybird]

I dimmers couldn't be that simple!

Thanks Ban!