computer PSU for landscaping lights?

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richms

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#949286 11-Dec-2013 12:20

Those ones for down lights have a high frequency output so are not suitable for long wires like with landscape lighting.

Richard rich.ms

SepticSceptic

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#949305 11-Dec-2013 12:32

Is the length restricted to minimise RF, or do the PSU's don't like driving inductive / capacitive loads ? The max length specced was 3m, which is half the distance I needed, but nevertheless, working well :-)

SepticSceptic

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#953095 16-Dec-2013 14:31

Last weekend's foray into landscaping was 5 x 20w Halogen bollards, spaced 1.6m apart, with the central connection, or 3rd lamp, feeding a 5meter cable ( like a long-tailed "T") to a 105va electronic transformer. Used a standard 10amp extension cord for the wire - it's cheaper to buy a 25meter extension cord than purchasing dedicated landscaping wire - same diameter of 1.0mm ... , and then cut up and connect as required.

The result is dimmer than expected, but not disappointing actually - I do prefer the reduced light output, but I do know that it will be detrimental to the halogen lamp life expectancy ... my brief calcs show a 3.5volt voltage drop to the halogens - so from 11.5 v rated at the transformer, to 8v at the lamps ..

It's a moot point as I was not planning on running 100w worth of halogen ( actually 200w, as I have another 2 x 50w general illuminating lamps) for multiple hours during the evening - every 5 hours = 1Kw/h :-(

Will be hunting down some G4 LED equivalents, that work on AC - there are a few that purport to be direct plugin replacements for outdoor lights, but are probably designed to work with 12v 50Hz outdoor systems, but may not work with the 30-40Khz AC as output by the electronic transformers.

BTR

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#953102 16-Dec-2013 14:48

Going by what GregMCC has said my installing of data cable in the weekend to run POE equipment was illegal? It works by a device that is plugged into 240V which steps down to a lower voltage.

I don't agree with you there on that one sorry otherwise half of the people of this forum who have installed their own networks have broken the law....

Also the mention of using common sense does't sound right. Everyones perception of common sense is different therefore I don't think anyone in their right mind would write something like that into electrical regulations....

gregmcc

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#953166 16-Dec-2013 16:32

BTR: Going by what GregMCC has said my installing of data cable in the weekend to run POE equipment was illegal? It works by a device that is plugged into 240V which steps down to a lower voltage.

I don't agree with you there on that one sorry otherwise half of the people of this forum who have installed their own networks have broken the law....

Also the mention of using common sense does't sound right. Everyones perception of common sense is different therefore I don't think anyone in their right mind would write something like that into electrical regulations....

Have a closer looks at the regs, exempt work includes telecommunications......

The POE unit is desgined as a stand alone device, not as a component of an appliance, and therefore meets the requirments and an appliance that can be unplugged by means of a plug and socket which exempts it.

richms

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#953206 16-Dec-2013 17:50

Go dc if you are using led as the ones that say ac just have a diode bridge so flicker on 50 hz ac and it is annoying to be around.

Richard rich.ms

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Niel

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#953384 16-Dec-2013 22:22

There are some G4 LEDs that have a proper LED driver IC. They are spec'ed to run off both 12V and 24V. Most other cheap(er) ones are just a diode bridge and resistor, so when run off an unregulated supply the voltage can go too high and the LED burn out.

You can never have enough Volvos!

richms

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#953408 16-Dec-2013 23:41

The ones I have tried have a constant current drive to be indifferent about voltage but in order to be dimmable by pwm they cannot have a smoothing cap in them. An ac transformer and a conventional phase angle dimmer gave terrible results with all lamps I tried both mr16 and g5.3 capsule replacements. Ugly cheap ebay sourced "led dimmer" in line pwm controllers work great and give very close dimming curves across a variety of lamps.

Richard rich.ms

Aredwood

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#955393 20-Dec-2013 11:16

richms:
Aredwood:
larknz: One thing people seem to be missing here is that a PSU is a switchmode power supply and not an isolating transformer. Therefore the output is not isolated from earth.

Every single computer power supply I have seen is isolated. If they were not then swapping the phase and neutral connections would make the output live. If you open up a broken one you will see a transformer in the middle of the circuit board. This provides the isolation. Look at the solder side of the board and you will see a line down the middle with no tracks on it and the transformer bridging both sides. This is the division between the primary side and the secondary side.

Every single one I have seen has the 0v line connected to the chassis ground so they are not isolated as is needed to prevent a fault to ground.

What I was referring to is isolation between the incoming phase and neutral conductors and the outputs. This means that a fault on the mains side like open circuit neutral or swapped phase and neutral wont cause mains voltages to appear on the outputs.

Only downside I can think of from not having the earth isolated as well is a fault in a buried cable causing crossion damage to the cable. Anything else that I haven't thought of?

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