# Simple electricla question?!

• posted on November 19, 2003, 12:02 pm
Just looking at buying some low voltage lighting from TLC, it says:
http://www.tlc-direct.co.uk/Products/LTYT150.html
"The circuits can be loaded up to the total value of the lamps, not to the transformer rating as is usual."
What does that mean? The transformer is rated @ 150w does it not mean i can connect 3x 50w lamps to this circuit using just one transformer? Im confused!
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• posted on November 19, 2003, 12:07 pm

I think it means you could use 2x 50w lamps too. A standard transformer might overvoltage if underloaded, causing other lamps on the circuit to blow quickly.
Christian.
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• posted on November 19, 2003, 1:00 pm

They are suggesting that with their premium transformers you count the mains circuit requirement as the total (low voltage) lamp load, say 100W for 2 bulbs or 150W for 3, but on an inferior transformer the circuit should be rated at 150W irrespective of the lamp load (1, 2 or 3). Unless you have a ceiling full of LV lighting in each room then I don't think it will make much difference to you and I don't think it affects your application.
However, I would not use any piece of electronics at 100% of its rating for extended periods as it tends to last faaaaaaaaaaaaaaaaaar longer if it is say 20% derated. Thus, I would use a 105W transformer to power 2x50W bulbs, but not a 150W transformer to power 3x50W bulbs.
HTH
--
fred

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• posted on November 19, 2003, 1:12 pm

Ok, that's not even 5%, but you get the idea . . . .
--
fred

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• posted on November 19, 2003, 5:05 pm
Ahaaaa many thanks Fred!
:o)

blow
should
have
much
for
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• posted on November 19, 2003, 1:46 pm
Thanks Christian, maybe i smoked too much last night as im not entirely sure what you mean! So you're saying if one lamp blows there may be a voltage surge to the other two lamps, im not sure how this is relevant to my question :o( Are you saying i should only use 2 x50w on this 0-150w transformer?
cheers

blow
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• posted on November 19, 2003, 1:59 pm

Not on this transformer, although you may do so if you wish. It claims that you can underload it without ill effects. I think it means that some other makes or designs of transformer must be fully loaded to prevent damaging overvoltage.
Christian.
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• posted on November 19, 2003, 5:06 pm
Thanks Christian im getting there !

that
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• posted on November 19, 2003, 5:43 pm
Christian McArdle wrote:

FWIW as a fully qualified electrical engineer, tho not of the electrician variety, it made no sense to me at all.
Probably written by IMM....
It might be voltage stability, it might be power factor...who knows?
Maybe its translated from the Japanese. "Be sure of connecting the terminal for the rug"
Took me a lot of lateral thinking to work out that in japan. floors are covered in rugs, and floors are sort of what ground is near, not to mention earth..or perhaps in japan, they have proper steel mats under the houses...to do their earthing.
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• posted on November 19, 2003, 6:20 pm

OTOH, when I had to design a basic switch mode power supply from first principles at university, we had to produce very precise output voltages and all sorts of input voltages and output currents without wasting much energy. That's the main point of SMPS.
Christian.
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• posted on November 19, 2003, 7:00 pm

And how was it's regulation at zero load . . . .
btw that's really zero load, without the 'zero load' load resistor you had to put in the box to make it stable ;-)
--
fred

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• posted on November 19, 2003, 7:19 pm
fred wrote:

effin useless usually :-) Many SMPS'S won;t even produce voltage at all unless SOME load is applied :-)
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• posted on November 19, 2003, 7:27 pm
writes

Yes dear, that was the pint I was trying to make to the enthusiastic one :-)
--
fred

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• posted on November 19, 2003, 8:03 pm
fred wrote:

Never mind the pint, cos IMM doesn't believe I haven't been drinking anyway. he POINT is that even one lamp represents enough load to pull and SMPS PSU into decent reg.
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• posted on November 19, 2003, 8:37 pm
writes

Yup, fairy snuff and I did laugh when I saw my freudian slip after IMM's attempt at a dig . . .
We did eventually answer the OP's question didn't we . . . .
--
fred

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• posted on November 19, 2003, 9:35 pm
fred wrote:

Dunno. Who cares?
Its national beat about the Bush and come up IMM day isn't it?
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• posted on November 19, 2003, 7:18 pm
Christian McArdle wrote:

Precisely, in more ways than one. You cannot rely on an open loop SMPS system very easily. Not that regulation on 12v LV lamps is particularly important.
Toroids, wound to sensible magnetic flux levels are remarkably good at regulation tho.
In fact so is any transformer, which is why it's rare for all the bulbs in your house to go when your neighbours switch theirs off and sneak upstairs for a bit of nookie while you are stuck reading UK.d-i-y.