sparky question re: LED lighting transformers and switches

[mound]

It looks like that driver's rated output current is 2Ax3 (2A max per output, with 3 separate outputs). The switch you are looking at looks like it is rated at 250VAC@5A (that's RMS). So, that switch should be fine for 48VDC@2A. I wouldn't connect more than one strip to a single switch. I'm assuming you picked the driver knowing that it is rated to drive the LED strips you are using without overloading the driver.

Still a bit confused by all this. 

The power supply will be big enough to drive all the lights, but not all in series nor all on at once. Each box/drawer will have a short length (24-36") of LED being turned on/off by the switch, with the boxes all in parallel to each other. 

Here's another switch that lists:
Rated Power : AC:125V, 15A; 250V, 15A,DC:125V, 0.6A; 250V, 0.3A

For a 48v DC power supply, would that mean at DC:48v, amps would allow for roughly 0.12A?

How can I determine how much amperage a single short length of the chosen LED's is required?   (The LEDs in question list 4.4 Watts/ft)

Just want to make sure I get a switch that will work and not weld itself shut!


Thanks!

[dav]

This is only the way that I would approach this. Others may have a different approach.

For the 1st question, the switch spec's say:

125VDC * 0.6A == 250VDC * 0.3A,

Note how as the voltage doubles, the current is derated by a factor of 2.

So, using the driver voltage:

48VDC x I == 125VDC * 0.6A => I ~= 1.5A

For the same conditions (eg, humidity and other environmentals), chances of arcing go down as voltage goes down.

Personally, I wouldn't have an issue running that switch at 48VDC and currents significantly less than 1.5A. But, I don't know if there will be an issue with arcing without more information on the switch and maybe even some testing. One thing to note from the AC specs is that at 250VAC (RMS), the instantaneous sinusoidal line voltage is about greater than 48VDC for over 90% of a cycle. I did a calculation to determine that. What that says to me is that the AC specs are far more conducive to arcing than switching 48VDC occasionally.

For the 2nd question, you say the LED strip is rated at 4.4Watts/ft:

So, assuming 3ft:

48VDC * I_leds == 3ft * (4.4Watts/ft) => I_leds == 3ft * (4.4Watts/ft) / 48VDC ~= 0.275A 

This is about 1/5th of 1.5A.

So, the switch will be switching about 0.275A @ 48VDC if you only control 1 strip per switch.

Personally, this is within what I would consider safe limits.

One thing I would do is make sure the unused contact on the switch is not exposed. Otherwise, it would have 48VDC exposed on that contact at some times. 

Again, this is only how I would approach the problem. YMMV.

[mound]

Thank you dav that was very informative!

[Roly]

AC specs are far more conducive to arcing than switching 48VDC occasionally.


Again, this is only how I would approach the problem. YMMV.

Except the voltage drops to zero twice a cycle  or every 1/120 of a second (on 60 cycle) which extinguish the arc every time it passes zero. 
 I think the switch may work also but unsure as the design of the switch comes into play and also and how many feet of leds are needed for the 48 volt supply.     Can you put 48 volts on a one foot section  or does it need 8 foot ?    Roly
I would also test the switches when the leds are where you can see them that they do go out and not continue to flicker. Use the same number of leds as would be on a switch. I am assuming you want the leds in a drawer that turns off when closed. A link to the lights would be helpful or ask the led company what to use for switching.

[mound]

Except the voltage drops to zero twice a cycle  or every 1/120 of a second (on 60 cycle) which extinguish the arc every time it passes zero. 
 I think the switch may work also but unsure as the design of the switch comes into play and also and how many feet of leds are needed for the 48 volt supply.     Can you put 48 volts on a one foot section  or does it need 8 foot ?    Roly

Good question I'm going to ask the manufacturer. I would hope a short length could receive the full voltage since this is going to be all short-lengths inside drawer and cabinet boxes and such.

[mound]

I would also test the switches when the leds are where you can see them that they do go out and not continue to flicker.  Use the same number of leds as would be on a switch.  I am assuming you want the leds in a drawer that turns off when closed.  A link to the lights would be helpful or ask the led company what to use for switching.

Thanks Roly. 

These are the LEDs in question.  Correct, in drawers or cabinets, turn off when closed.   There were two configurations we were bouncing around, one using 48v strips and two power supplies, the other using 24v strips and one power supply.  (same LEDs linked above, only selecting 24v or 48v input)

Their recommendation for switching was these IR detectors which are expensive and bulky ($21 per drawer or door) and looking at the specs would only work with the 24v setup, and, oh, also out of stock with unknown lead time.

For reference, both 48v and 24v setups they recommended use the same LED strips (just picking the correct input voltage). The 48V setup would use 2 of this power supply   (48V, 288watt)  and the 24v setup would use 1 of this power supply at 24v/600watt

They arrived at both of these options based on the total lengths and color decisions I provided.  Pricing for both packages works out to be basically the same, they said the decision really comes down to my desired installation logistics for number/placement of power supplies and wall switches)

[dav]

I think Roly gave good advice about first testing the lights for noticeable flicker after the switch is toggled. If you have a multimeter with current measurement capability, you could measure the actual current load, too.

[mound]

I think Roly gave good advice about first testing the lights for noticeable flicker after the switch is toggled. If you have a multimeter with current measurement capability, you could measure the actual current load, too.

For sure. I do, and I will!