power supplies in parallel?

Discussion in 'Power Electronics' started by camilozk, Oct 24, 2016.

1. camilozk

116
4
Apr 20, 2014
hi!

I need to provide current to 91,2 meters of 12V LED strip. This is 2736 leds, each 60mA at full brightness = 164,16A

I have 3 12V 60A power supplies, and I thought that if I connect them in parallel, I would obtain 180A, However, looking around, I saw that this may not be the case. Could you share your knowledge on the subject, and perhaps give me some recommendations on how to achieve my goal with this material?

I attach a photo of the connected power supplies, which I still haven't plugged, just in case

thanks!

File size:
139.7 KB
Views:
112
2. duke37

5,364
769
Jan 9, 2011
You would be better to split the LEDs into three so there is no argument between supplies.
You will need a very, very thick cable to pass 160A with low voltage drop and low heating, even 50 or 60A is a lot.

dorke likes this.
3. Harald KappModeratorModerator

10,069
2,150
Nov 17, 2011
How do you think you are going to connect the 91 m of LED strips anyway? In series? I doubt the strips support 160+ A of current as this would be the current along the first few centimeters. You will have to connect power at regular intervalls so each section of LED strip needs to carry only as much current as it supports. This will require multiple supply connections in any case, therefore you can as well make three segments, each 30.4 m long, and supply each segment by its own supply. You will still need multiple power connections to each 30.4 m segment.

May we have a look at the LED strip's datasheet?

4. camilozk

116
4
Apr 20, 2014
Good point. I should have pointed out some more details before jumping into the issue.

The led strips are distributed in 16 groups of 5,7 meters each, all of which are connected straight to the power supply with a cable not longer than one meter.

5. Harald KappModeratorModerator

10,069
2,150
Nov 17, 2011
That makes sense.
Now make that 2 groups of 5 and one of 6, each with it's own power supply and you're set.

116
4
Apr 20, 2014
I will!

7. camilozk

116
4
Apr 20, 2014
what does this mean anyway, "fighting power supplies"?

8. Harald KappModeratorModerator

10,069
2,150
Nov 17, 2011
No two (or three) power supplies will have the exact same output voltage. Each power supply has a built-in regulator that tries to keep the output voltage a the nominal value and thus the regulators of paralleled supplies will worka against each other:
The one with the higher voltage will try keep a higher voltage on the shared power bus than the one with the lower output voltage. This will force current back into the output of the one with the lower output voltage.

116
4
Apr 20, 2014
danke Harald

10. grumps

12
1
Jul 11, 2015
long as your various power supplies are fairly close - in voltage - they will all power your loads :

same as jumping your car battery from another battery ( how the national power grid works ? )

i assume all the leds , have the same current and voltage ratings .

11. Harald KappModeratorModerator

10,069
2,150
Nov 17, 2011
When jumping a car's starter battery, a high current will flow from the good battery/car to the bad one. In this case this is desired to boost a bit of charge into the bad battery.
The national grid works a tiny bit differently: teh different power sources aka power plants are closely controlled to avoid reverse power flow. Otherwise a generator would become a motor. Various mechanisms are used to control this effect at each transformer station, generator etc.

12. Audioguru

2,869
644
Sep 24, 2016
12V LED strips have 3 LEDs in series, not parallel and each series group is probably 20mA or less. Then the total current for 2736 LEDs is 18.24A or less, not 164.16 Amps.

13. grumps

12
1
Jul 11, 2015
for AIR flow from / to another location ( typical weather systems , etc . ) there needs be a phase / pressure

difference ... between ... them ; alternating current busses probably ? require similar differences , for power

flows to combine ( have watched side - by - side motor generator / converter , AMMETERS , swing wildly !

as phase differences ( reflected by internal regulator ... corrections ) ) were reduced ;

as a field engineer for large UPS systems - whether solid state or motor / generators - the sounds of multiple

power generators ' adjusting ' to real loads ? required internal sobriety and ... calmness ;

the power grid here in puerto rico recently cascaded a shutdown , caused by a substation fire - for 3 days :

my empathy for support personnel , during that catastrophic event ? guarantees ! they deserve their pay .

14. Kabelsalat

125
24
Jul 5, 2011
I'll suggest a little modification/addition to the suggestion of using 3 separate power supply.

On each of the 3 splitted segments, put the power supply in middle, so that you feed 2x 30A from each power supply. That will cause less voltage drops along the cable and you can use a smaller cable too.

15. camilozk

116
4
Apr 20, 2014
The strips are either ws2811 or ws2812b or ws2813b. In all of the each led is 60mA (20 per color).
2376 * 60 / 1000 = 164.16A

16. camilozk

116
4
Apr 20, 2014
This mainly depends on having the phisical possibility of connecting the supply in these different points. In my case, I didnt!

17. camilozk

116
4
Apr 20, 2014
And what is happening if I am feeding a Led strip, lets say 15mts ws2812b 60led/mts. This is 54A

I would then use for example 2 power supplies, each 30A, one connected to one end of the strip, and the other connected to the other end.

Is this ok?
Wouldn´t the power supplies regulator anyway be fighting to keep things regulated?
Or why would this work with no problems?