Correct way to calculate the Fuse values in a multi-inject continues loops

[TPK]

Would like to get a feedback on a build please.

I have 2 outputs connected to 10 x 2m pixel strips.
If the strips are on a individual closed loop I can calculate the Fuse values required easily.

But it has 2 multi-inject loops and wanted to know how to calculate the required fuse values for each 6 fuses.

Please see the picture attached.



Each LED is 0.3W.
Each strip = 0.3 x 120 = 36W
Amps for each strip = 36/12 = 3A

The hard part is to find out the loop on each section as it is connected continuously.

From my understanding the fuses would be (from Left to Right): 6A, 6A, 3A, 3A, 6A, 6A

Please let me know what are the values you think right for 6 fuses from left to right.

 

[AAH]

I would personally run 7.5A fuses for them all. Or if I wasn't being lazy 7.5, 7.5, 5,5,7.5,7.5. You could probably also get away with 5A fuses across the board and never have an issue. Fuses don't blow exactly at the rated current and in order to blow they have to exceed the threshold for a time that's dependent on how far over the current you go.

 

[Srmorgan]

I thought that the point of a fuse was to protect the wire. So the size of the fuse would be based on the gauge of the wire that is behind the fuse. Assuming that the smallest gauge wire would be the pixel wires that would be the size fuse you need.

 

[TPK]

Do I need to put a 40A fuse at the very start of the power cable as well?

Thanks

 

[AAH]

Do I need to put a 40A fuse at the very start of the power cable as well?

Thanks

Ummmmm. The individual connectors on power supplies are rated at 30A so distributing 40A from there would mean combining 2 lots of + and 2 lots of -.
You'll actually get better voltage results at the far right hand side if all 6 fuses were connected directly at the power supply or alternately 2 separate busses ran back to the power supply (and fused there) to supply the 2 separate sides of the receiver. Ideally the power supply would be right at the receiver.

 

[TerryK]

I would begin with your 6/6/3/3/6/6 arrangement and see what happens based on an assumption that full amperage will be less than calculated from running less than 100% white. If the display is illuminated at that level and a fuse or fuses open, up them a bit in size. Not knowing exactly the physical layout what I see though is a design leading to cascading fuse failure (which is not necessarily a bad thing). A possibility is to route v- (ground/common) and Data only in the dotted lines at the top of the drawing. This logically 'daisy chains' the pixels but gives each fuse it own string.
Because of the rather large current in the supply buss lines, as Alan just mentioned it would be better I think too if the fuses were brought back to the supply individually.

I thought that the point of a fuse was to protect the wire. So the size of the fuse would be based on the gauge of the wire that is behind the fuse. Assuming that the smallest gauge wire would be the pixel wires that would be the size fuse you need.

In most situations that would be correct. There are designs however where one must determine which component to sacrifice or which to protect typically based on either cost or difficulty to repair. To sum, fuse sizing is one of those scenarios never easy to answer.

most people fuse at the power supply as its to protect the wiring not the LEDs. If a fuse is blowing while running, the leds have already gone or the wiring has been shorted. In your design if there is a wiring short on your main bus lines your power supply is going to let the magic smoke out.

Depends upon the supply. Quite a number of supplies have some type of built in protection. Most Mean Well supplies use either what they call a 'hiccup' mode or current limiting. Granted, something downstream is either most likely already destroyed or in the process thereof. The power supply though, if it has some type of protection designed in will try to protect itself.

 

[Dreamin]

fuses are there to protect the wire, not the lights, so you need to factor in the wire between the fuse to the lights etc as well.