Dimmer Capacity

[Greenside]

Four 12V 50W halogens, each with a transformer: 300W or 500W?

I know you have to over-rate them but had hoped 300W would do as I don't have sufficient room on the wall for an additional box. The Sparks Who Overspecifies (SWO, from now on) is telling me to go for the larger ones but one of his mates (quietly) disagrees.

[InterestedObserver]

Unless I am missing something, four 12V, 50W halogen lamps should be ok with a 300W dimmer. That is allowing 33.3% overcapacity for transformer and dimmer losses.

[InterestedObserver]

Unless I am missing something, four 12V, 50W halogen lamps should be ok with a 300W dimmer. That is allowing 33.3% overcapacity for transformer and dimmer losses.

We are talking about a solid-state dimmer, aren't we?

[Crossy]

Assuming you have dimmable transformers the 300 should be quite adequate.

[Greenside]

Unless I am missing something, four 12V, 50W halogen lamps should be ok with a 300W dimmer. That is allowing 33.3% overcapacity for transformer and dimmer losses.

We are talking about a solid-state dimmer, aren't we?

One of these:

The kind that fits in the regular switch box on the wall.

Edited September 7, 2011 by Greenside

[Greenside]

Thanks. I'm sure the transformers are dimmable or at least that's what I asked for when I ordered them.

One other minor question: Can you use a three way light switch in regular one way and two way configurations? The Panasonic catalogue shows plain single pole switches only as three way (WEG5002K) - all the other variations have fancy neon lights on them which I don't particularly want.

[luudee]

Since you are actually dimming the transformers, they should be

considered in the calculation.

Depending on the quality of the transformers, they have a certain

loss when they down-convert 220V to 12V.

I have no idea what the efficiency of your transformers is.

Lets assume it's 90%.

Your total load is 200W from the lights (4 x 50w), so the transformers

would add an additional 20W making the total load around 220W. So

yes the 300W dimmer would be ok.

Most modern transformers will be better than 90% efficiency, and

even if you get a really crappy one with 70% efficiency, the 300W

dimmer will be just fine. Also, the Triacs in the dimmers are usually

under-rated and can provide higher currents for short periods of time.

Std. Disclaimer: I have extremely simplified the above example ... but

it gives the basic idea.

Cheers,

rudi

[Crossy]

One other minor question: Can you use a three way light switch in regular one way and two way configurations? The Panasonic catalogue shows plain single pole switches only as three way (WEG5002K) - all the other variations have fancy neon lights on them which I don't particularly want.

OK, let's sort a little terminology here, as a Brit I'm often confused by American terms when it comes to light switches and circuit wiring, a problem compounded here in LoS because some manufacturers use US terms and others UK when describing their products.

A quick comparison.

UK - One way switch, US - Two way switch. This is the plain vanilla on/off switch.

UK - Two way switch, US - Three way switch. This is a change-over switch, usually used in pairs to control stair lights from top and bottom.

UK - Intermediate switch, US - Four way switch. Much rarer than the above, you use one of these to add a third (or fourth or moreth) switching point to the above stair lighting arrangement.

The simple answer to Greenside's question is, yes, you can use any switch to replace one with fewer 'ways' with no issues whatever other than working out which terminals you need to connect to.

[electau]

Australia/NZ.

Switches. C-1 or C-2. ON/OFF, used as a normal switch or as a two way switch. Switch may have a looping terminal for a neutral.

Intermediate switch. position 1. 1-3, 2-4. position 2. 1-4, 2-3.

With intermediate switching the first and last switches are 2 way switches, the others inbetween are intermediate type.

Source. Clipsal, HPM, PDL.

　

　

　

[Greenside]

Crossy, the electrician and I had an extremely long and awkward conversation in Tingish with him trying to convince me that 3 way meant two way and me telling him it meant 3 way. In the end I gave up, much to my wife's relief and just let him amend my lovingly drawn up specification.

Thanks for showing me the error of my (three) ways

Actually got power in the house today but no fittings yet so can't use it for much.