Dean Heighington wrote:
Ah, OK wall warts then...
YEP... nice metaphor 
probably a uk.d-i-y special, but it seems to capture the essential
qualities l-)
OK looking at your specs from the other post, the LED lights both have a
12DC Supply, the ordinary halogen ones use a 12V AC supply. There is
nothing to stop you running the AC lights on DC since they should just
be ordinary incandescent bulbs (the reverse is not true since the LEDs
won't like having AC stuffed up em!)
OK, I can sort of understand you on this. My knowledge of electrical
theory and principles is somewhat weak. I studied Technology at school
but had a boring teacher and other, more appealing, distractions at the
time. I take your word for it, but FMI, is it that the LEDs need a
'steady' (direct) current as they are very sensitive, whereas the
halogens would prefer alternating current, as they rely on heating of an
element, but will withstand DC through not being so sensitive???
Sort of... the halogens are ordinary light bulbs which are not at all
fussy about what you feed them. Hence for garden lighting applications
it is cheaper to feed them AC since all you need is a transformer and
nothing much else.
LEDs (Light Emmiting Diodes), are electronic components that in most
respect behave like ordinary (i.e. non light emmiting) diodes - they
have a one way valve type of effect - they will only let current flow in
one direction. So when you connect them the "right" way round to the
power source they conduct, and emit light. When the wrong way round they
don't.
So best case on an AC supply (i.e. one that keeps swapping its polarity)
is that they would flash on and off at mains frequency (i.e. 50 times /
second). Unlike a light bulb they have no persistance of light output -
so when you turn them on of off, they react immediately. You may not see
this flicker when you look straight at them, however it would be
distracting as you move your eyes around since you would catch it in
your peripheral vision.
The worst case is if the supply voltage is higher than what is known as
the maximum "reverse bias" voltage of the diode. Ordinary dioes are
quite robust in that you can stick quite high voltages accros them in
the reverse direction and it does them no damage. LEDs however are a bit
more fragile and don't usually like large revers voltages. On some more
tahn 5V will kill them.
So you need one 12V DC supply that can handle a total current.
OK... A 'daddy' transformer then?
Yup.
No need for a dedicated circuit here - we are talking about a tiny load
overall - less than 100W in total.
Not wrong then, but would be overkill?
Basically yes.
suggesting that I add a new circuit to the consumer unit, using one
of the spare 'ways', and fit a PSU which converts 240V to LV (replacing
the kit supplied transformers) and suitable for providing LV to all
3 lighting circuits in unison? And then interrupting the LV supply to
each by installing the desired switches?
Yup that would be a solution...
OK... Need to source 'external' switches that would suffice for LV. Or
would I have to use ones intended for 240V, because that's all is
available on the market? Again, I want to keep costs down, so would
External switches designed for 240V will tend to be fine for 12V also.
Something like:
http://www.tlc-direct.co.uk/Main_Ind...hes/index.html
consider any switching solution... would you employ 1 master switch for
ALL 3 circuits, or control them individually? Do you have a URL so that
I can see the full range of components available for 'external'
installations for LV (if they exist)?
If you end up connecting to a socket to feed the daddy PSU then that can
be your master switch. See the TLC site above for a good range of stuff.
Also look at:
http://www.cpc.co.uk/
Personally I would start by measuring the actual current draw of each
set of lights (with multimeter if you have one)
I have some such device from RapiTest... I need to did it out, but I'm
sure I remember it being a multimeter... might have been for cars though.
Should I have one (or buy/borrow one), I have no idea how/where to take
the readings from... can you advise?
Multimeters are dead cheap anyway. See CPC above or
www.maplin.co.uk.
To take a current reading you need to place the meter in series with the
circuit. i.e. you need to disconnect one of the wires to the PSU and
connect it to one of the MM leads. Then connect the other MM lead to the
PSU so that the current is actually flowing through the meter. (This is
different from using it to measure volatage where you can simply connect
it across the terminals of the PSU)
Is this an alternative to the above or in addition? It sounds
It was a continuation of the above - just suggesting a cheap and
available source of power supply - but now we know two sets require DC
it is not such an attractive solution since the output of lighting
transformers are AC and not DC and hence unsuitable for the LED lights.
Should I now disregard this then?
You can disregard the bit about the LV ligghting transformer since the
output of this will not be suitable for the LED lights.
That's why I'm concerned about choosing the wrong device. Would you
assist me with the selection and point me to a source where I can obtain
all that I might need?
The CPC link above is a good choice for PSUs. I can advise on a model,
but will need to know how much current all your lights are really going
to need since that will affect how much you need to spend!
Have I understood you correctly? Which do you think is more
appropriate and cost-effective?
Using the ones you have is the most cost effective, however it may not
be the most appropriate.
What's your 'ballpark' figure on the cost of going the CPSU route? It
Assuming you need a 5 to 10A supply, then then cheapest PSU would
probably be a computer one. These start at about 10 quid. If you went
for a nice neat small boxed unit however you could easily end up
spending 30 to 40.
may be that, ultimately, it would be prudent for me to use the supplied
"Warts" in a hidden location in the house (say the understairs cupboard)
and then just buy 1 (or three) external switches and fit them to the LV
cables at the deck. Again, available components dictating what I can
There is alot to be said for that. You will often need to extend the
wires for these things anyway...
do... I assume that a 'single master switch' would have to be '3-pole'
(is this the correct terminology?). Also, would it be sufficient for me
No need for 3-pole, single pole would do. (you split the supply to the
three lights after the switch, not before)
to construct/purchase a 'waterproof box' at the house wall, into which I
could install a 4-gang, 240V extension block, with the 'warts' attached
and contained within?
Someone posted a link to such a thing the other day - it may have been
on the TLC site...
--
Cheers,
John.
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