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I bought some dangerously cheap AC LED floodlights. Cheap flex, shoddy sealing, no screw terminal block, no earth continuity, etc... But the LEDs actually kick out a good light so I'd like to persist.

I have already rewired —and earthed— two of these and have mounted them on the house using their glued-in transformers. Now I want to run a string of these down a long stretch of fence panel. At least three lights, spread over a 40m (130ft) run from the house.

I could do that with AC but that requires armoured cable in the UK which is expensive. I'd like to see if I could power these from an external AC→DC power supply at the house end and running a little low voltage line out to the units in parallel.

My problem is I don't understand the output rating on this driver:

enter image description here

24-46V seems like a huge variance. My understanding was that most LEDs fub out with 20-30% undervolting. This is almost 50% and that seems mad.

And it also has serious implications on the voltage drop I'm going to get from the distance I'm running. 46V could go a fair way with a small percentage drop-off. 24, not so much.

But assuming you can make sense of this,

  • What would you replace this with to power 3 of these over a long distance? 48V 5A?
  • Is there any benefit to something more exotic like stepping down to unreferenced 48VAC and adding a bridge rectifier in each unit?
  • What wire thickness would are you basing that on?
  • These are going to be on fence posts. Should I earth these still?
  • Any chance they'd be dimmable?
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    \$\begingroup\$ Seems like it's a constant-current driver with 300mA constant output current and variable output voltage according to the load (i.e. LEDs). \$\endgroup\$ Oct 3 '16 at 9:15
  • \$\begingroup\$ You considered currents and voltages. Consider its level of ingress protections - it is IP66. This is very good level of protection from environmental issues! That's why it does not have any screws and terminals - it is ready to use in really harsh environments except under the water. \$\endgroup\$
    – Anonymous
    Oct 3 '16 at 9:33
  • \$\begingroup\$ @Anonymous It says IP66 but it also has a CE mark on it (as did the box) and it was an unearthed metal case. I'd wager all the safety marks are fake. \$\endgroup\$
    – Oli
    Oct 3 '16 at 9:40
  • \$\begingroup\$ The electronics appliance itself seems to have plastic casing. The casing the appliance is placed is metal, but these CE and IP are for plastic made appliance. If there's suspicion that it is counterfeit this question should be addressed to seller. I did not find "ZX-10W" device on the internet. \$\endgroup\$
    – Anonymous
    Oct 3 '16 at 10:17
  • \$\begingroup\$ Easiest would be to use three seperate power lines with the existing power supplies. Since they're constant current supplies they will automatically compensate for the additional line losses. You may even get away with three power wires plus one common return; depends on how the supplies are made. \$\endgroup\$
    – JimmyB
    Oct 3 '16 at 10:33
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LEDs tend to be specified as being fed by a constant current because of the unpredictable voltage characteristic: -

enter image description here

If you studied the above you would conclude that as you turned the voltage up on this particular LED, current would start to flow at about 1.7 volts and by the time you got to 2.1 volts this particular LED might have fried.

Of course there are plenty of different LEDs available but they all tend to have this sort of characteristic so, it's easier to control the current rather than try to predict what forward voltage is the "Goldilocks" value. It also changes with temperature so it's better to control current.

What your LED driver tells you is that providing the load has certain characteristics in terms of its resistance, 300 mA will be delivered. If the LED load resistance is 80 ohms then the terminal voltage will be down at 24 Vdc. If the LED load resistance is as high as 153 ohms then the driving voltage will be 46 Vdc and, importantly, if the LED load resistance rose above 153 ohms, the driver output will not be able to supply greater than 46V in order to keep the constant current of 300 mA flowing.

What would you replace this with to power 3 of these over a long distance? 48V 5A?

Replacing three of these to power 3 LED units is the wrong way to look at it. For a start you'd need 3 x 300 mA but the problem arises when one LED fails and the other two share 450 mA each. You could wire three LEDs in series and feed 300 mA but that then requires potentially a supply voltage of up to 3 x 46 volts (138 volts DC).

You might be able to get away with non-armoured cable providing you use an RCD at the AC feed point from your house after all, fish ponds only use rubber cable and they go underwater. You could bury some trunking to put the rubber cable in.

Any chance they'd be dimmable?

There is no guarantee that these devices are dimmable.

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You need to find a 300 mA constant current power supply, capable of possibly as high as 46 V compliance voltage. It also needs to match your mains voltage or like the one you have, be wide-range to accomodate all popular ones.

There are dimmable such supplies available, by normal TRIAC dimmer or by external PWM signal.

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