Garden lights and watts

[Jim]

Hi All

I currently have 3 x 21W 12v garden lights supplied by a 96w transformer. I'd like to add another 2 lights but obviously this will take the total wattage up to 105W. What will happen if I go ahead and add the lights as is ie.

1. Will none of the lights work
2. Lights will work but be dimmer than normal
3. Transformer blow up due to excess demand
4. Something else entirely

I know I could use lower wattage bulbs all round but I can't seem to source

18w wedge bulbs anywhere so have moved up to the 21W (these ThanksJim

[John Rumm]

What sort of transformer is it? (i.e. electronic or an iron cored jobbie)

[The Natural Philosopher]

3 probably. Or a fuse will go.

[BigWallop]

The extra demand will burn the transformer. Transformers are cheap from most of the DIY Sheds, so it might be better if you go for something like a

150W supply and allow yourself to go with brighter lights in a couple of places in the garden.

Like this from Bite and Chew

it's dimmable to create real mood lighting. :-)

[Jim]

Thanks for the responses so far

No idea what sort of transformer it is, it's fairly bulky and weatherproof with a built in dusk to dawn sensor if that's any indication.

Are transformers generally safe up to their max wattage, ie if the add on lights were a different style with a couple of 15W bulbs, a total of 93W would this be OK to run up to 12hrs a day

Cheers

Jim

[meow2222]

If its bulky its a 50Hz iron cored transformer. Running such a transformer 10% over its ratings has less than 1% chance of causing failure. The effect on the transformer is it will reduce its life expectancy marginally, but since normal life expectancy of these items is several decades its not an issue. The other difference it makes is to output voltage, 10% drop of the (circa) 10% regulation is a 1% voltage drop, which again is a non-issue. For filament lamps efficacy is proportional to voltage to the power of 1.9, so this will lose you

1.9% of light output, and increase lamp life by about 13%, so all round a non-issue.

NT

[Owain]

The lights flash on and off slowly as the thermal cutout resets?

Still, it is nearly christmas. You could pass it off as decorations.

Owain

[Kevin]

that's assuming it has a re-setting cut-out

[meow2222]

and assumes its an unusually accurate one, with a set point unusually close to working temp, and the transformer is housed in conditions that create maximum operating temps. Amusing, but unlikely.

NT

[Man at B&Q]

More Big Bollocks.

It's 9W over budget on a 96W transformer, or less than 10%. What exactly do you think is going to happen? At what power demand does the transformer suddenly burn? 97, 98, 99W...?

Do you know anything about the way electrical items are specified, made and tested? Are all the bulbs taking exactly 21W? Is that nominal or worst case? What is the OPs mains voltage? Does that have an effect? What's the ambient temperature around the transformer? What's the temperature spec for the transformer?

MBQ

[meow2222]

I once did an experiment before the days when a mains smpsu would have been practical. I needed power with much smaller than usual size and weight. I forget just how hard that transformer was pushed, but something like 2.5x rated output, and though it ran hot its still working fine.

There's a lot more to transformers than just a nameplate rating.

NT

[Man at B&Q]

Indeed.

MBQ

-- He who knows not and knows not that he knows not is a fool; avoid him. He who knows not and knows that he knows not is a student; teach him. He who knows and knows not that he knows is asleep; wake him. He who knows and knows that he knows is a wise man; follow him.

[Bob Mannix]

-MBQ

[dave]

Other MBQ's found so far...

Acronym Definition MBQ Mohawks of the Bay of Quinte (Ontario, Canada) MBq Megabecquerel (SI) MBQ Metal Boat Quarterly MBQ McBurger Queen (comic) MBQ Muhammad Bin Qasim (Pakistani general) MBQ Message-Based Queuing MBQ Modified Biquinary Code MBQ Minimum Base Quantity (inventory/sourcing) MBQ minimum batch quantity

I like the sound of a "Megabecquerel" myself. :-)

[Bob Mannix]

The Becquerel is the only commonly used measure that is dimensionless. Not a lot of people know that. Usually used in GigaBecquerels.

A.N.O'rak

[Rod]

The gravitational coupling constant? I find I use that far more often... :-)

[Bob Mannix]

No doubt, but it is a constant not a measure

[Rod]

True - I had pasted that by accident and then, meanning to paste what I wanted (rather than what was in my paste buffer), I sent it before correction. :-(