I originally posted this in the LED forum, but perhaps this is better suited here as I am asking about handling current and not overloading a power supply.
I posted previously (in the LED forum) about driving LED strips (5050 60 led/ M) from an Arduino through RGB amplifiers vs building a board with MOSFETs .
My question now is centered on safely powering the strips. I purchased a 600W atx power supply that has 2 dedicated 12v rails, each supplying 24A (48A total) of power. I am looking to power 45M total of RGB strips. As I understand this each strip can draw a max of 1.2A per meter (6A per 5M strip).
I have purchased 9 of the above amplifiers and plan to wire between 5M-10M to each power supply. For the most part they will be synched to music so they won't all be totally on at the same time. I have read (and verified) that through PWM each strip seems to use about 1/2 to 1/3 of the highest amperage they could require.
Is there any safety concerns I should take into account when creating a setup like this? From my observations I appear to be under the required wattage and amperage, and, I have taken steps to power each RGB strip independently where I can.
From my experience with ATX PSU even if they wrote 600W on it it can't reliably sustain that power consumption without being stressed: consider it for supplying about 80% of its nominal power. That should still be within your parameters.
On top of that, from a non LED expert, is your current requirement considering all the three colors? I mean, if you light them al white you should absorb about 60mA (3 x 20) per LED which seems to be around (60 x 60) 3600mA per meter... As I said I'm not an LED expert and I haven't read the 5050 RGB datasheet, may be they have lesser current requirements or share the same 20mA current among the three LEDs...
So, max if all on is 6A per 5m strip. That is from what I gather the highest it can ever draw.
I am thinking through PWM and not too often having all strips max whiteness/ max brightness I should stay below the current draw.
I have attached the datasheet link that I hope you can review and ensure I didn't read this wrong
The datasheet you linked doesn't list any RGB LED, it is listing separate LED per color, each one reported at 60mA typical current consumption, three times my guess of 20mA per color. If I were you I would check the current limiting resistors values on the strip itself
I Think power source needed depends on the length that you cut the LED strip. Let's use the 150 LED RGB strip light as an example: Each foot uses 2.2 watts. Add the amount of feet together, multiply by 2.2, and you have the wattage used. You should add 20% more room in the power supply so take the wattage, and divide by .8 to get the power supply needed.
I was able to find the specifications, and they are listed below. This would be for each LED on at the same time for the entire strip (which will not happen)
Specifications:
-Led Strip
-Color: RGB
-LED Type: 5050 PLCC-6 SMT SMD LED (IP65 Waterproof)
-LED Quantity: 300 leds/5 Meter or 60 leds/Meter
-Size: L500cm (5M) x W1.4cm x T0.3cm
-Package: 1 X 5 Meters / Roll
-View angle:120°
-Working Input Voltage: 12VDC
-Output power: 72W /5 Meter
-Working Tempreture:-20° to 50°
-Drive Mode:Contant Voltage
While digging around some more this week, I found a post from another board that ties into this topic.
From this exchange it appears that the lights will not draw close to maximum watts/amps even while full on. This has helped ease my mind with regards to the maximum amount of power I could possibly see.
At this point I have connected all 45M of LED's for short periods of time. I am still hesitant to let this run for longer periods until I ensure it is safe - but, it was nice to see it all working as intended even for a brief period of time (less than 2 hours).
JLairson:
From this exchange it appears that the lights will not draw close to maximum watts/amps even while full on. This has helped ease my mind with regards to the maximum amount of power I could possibly see.
Complete rubbish.
He didn't get the full current draw because he was connecting them up with crappy wires and the strip wasn't getting enough volts.
45 meters of LEDs at 60 LEDs/meter is 2700 LEDs.
At 60mA per LED (they're RGB color) that's 162 amps if you set them all to white.
Luckily for you they're connected in groups of 3 so the current is a third of that, 54 amps.
You shouldn't run a power supply at 100% rating if you expect it to last so you need a 75A, 12V power supply.
Next you need to think carefully about how to wire it.
You can't just connect 12V to one end of a 45m strip and expect 54 amps to go down it. It simply won't work. You need to connect it in sections and make sure you're not getting much voltage drop anywhere along the strip. If you see voltage drop ("droop") you need to chop it up more and run more power cables. This is how you figure out how to wire it - measuring the voltage along the strip and make sure it stays at 12V. If you see (eg.) 11V anywhere then you need to chop it up more and run more power cables.
Once it's wired up with little power losses you need one of those "amplifier" boxes for each section of LEDs, all hooked up to a central controller.
If the strip is in one long line you'll either need very thick power wiring to run alongside it,
(copper isn't cheap) or could have a number of smaller power supplies and controllers for
sections of the strip, since the thickness of mains wiring will be much more managable.
I took a look at the thread and they couldn't figure out why full power (72W) could never be achieved, even when dual-feeding (connecting the controller at each end of the strip). When connected at one end only, there was a 3V drop in voltage measured at the other end.
So, for example, if the series resistance of the strip itself is 2 ohm, then using P = V2/R we get P = 144/2 = 72W
At the other end we have 9V, so P = 81/2 = 40.5W representing a 44% loss in power or brightness.
With the dual-feeding approach, there would be 1.5V dropped in the middle of the strip. The loss of brightness here would now be (144/2)-(110/2) = 17W or 24%.
So the only way to get full power out of the strip is to cut each segment apart and connect them in parallel.
Another consideration: Note that red leds are typically more efficient (output more mcd), so if the series resistance for the red led is higher than for blue and green, full red led current (therefore power) could not be realized. See below:
Suggestion: Check the label(s) on the ATX PSU for the max amps @12V. Older types wouldn't have a very high 12V power rating, newer models can deliver 80-90% of its rated capacity to the 12V terminals.
Great point about the power supply ratings. I am connecting them up to 2 separate power supplies now (A 600w and a 500w) power supply. The max load is well under the power supplies watt/ amp ratings.
Please note that power supplies come in a wide variety of qualities.
A "480w" Logisys brand PSU will die (likely to due to a switching transistor exploding) at around 180w load.
A "450w" Corsair brand PSU will shut down at around 500w of load, and restart happily.
Bobnova:
Please note that power supplies come in a wide variety of qualities.
A "480w" Logisys brand PSU will die (likely to due to a switching transistor exploding) at around 180w load.
A "450w" Corsair brand PSU will shut down at around 500w of load, and restart happily.
"Watts" is also a bad measure of power supplies. You have to look at how it's distributed between 5V and 12V. Some cheap supplies put a lot of amps on the 5V rail to boost the overall wattage rating. You need 12V for these strips so that's the number you should look at, not "watts"
I am using 2 high quality power supplies. Both will only need to supply 2/3 of their rated amps on the 12v rail at full on maximum.
The lights will rarely be fully on as they are reacting to music.
Since each strip is only 5M and powered on its own so far no wires feel hot, the power supplies are running cool.
