Cabling and fuses

Julian De Jong

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Jan 5, 2019
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Hi everyone
I am completely ignorant when it comes to power, cabling etc and am looking for some advice on cabling and fuses running between the power supply and the controller board. I am using a f16v3 with 2x 350w 12v psu’s each running once side of the board. Per the advice I’ve seen on this forum I will be running the psu’s at 85% capacity. From my calculations the total draw of the pixels running from the board will be around 80amps (980watts) at full brightness but will be running them at around 75% brightness. However for the purposes of my setup I am basing the calculations on running the lights at full power. I understand I will need power injection as the 2x psu’s won’t be able to power that many pixels.
I recently bought some power cable to run between the psu’s and the controller but only just noticed tonight that the cable is only rated at 25amps (it is 12awg cable).
I also plan on fusing between the psu’s and the controller. I have seen this one at jaycar
https://www.jaycar.com.au/automotive-fuse-box-6-blades/p/SZ2002 and would have one power line from each controller running through one fuse each on the board using 2 fuses on the block (I will also have another couple of psu’s running to distro boards through the fuse block)
But from what I understand each fuse is rated at maximum 15amps. I like the idea of using a fuse block as opposed to in line fuses as it sits neater in the enclosure.
My questions are, is the cable I have bought rated high enough for the draw from the pixels and will I need to look at using another fuse block which can handle fuses with higher amperage? Or am I completely off track in my setup?
I have had a good look on this forum for other similar questions and have read the 101 manual but just can’t seem to wrap my head around this!
 

TerryK

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Hi Julian. Quite a few questions there. OK, first 12 gauge; I would not suggest running 25 amp through it. It is used quite a bit here in the states and I have always kept current at 20 amp which is its 80% de-rated value. At 25 amp it will heat and there will be significant voltage drop. As a side note, it is used in US home wiring and is fused at 20 Amp.
Fuse block; the description indicates each circuit is 15 amp max with a total on the entire block (all individual circuits summed) of 45 amp. So while I see no reason why it will not work, circuit draw will need to be calculated and implemented carefully. If you know the draw will be around 80 amp I would suggest splitting that 80 amps across at least 3 blocks even though 2 should suffice. The block also uses spade connections and they will loosen and burn at high currents which is likely a reason why the block has a circuit limit of 15 Amp.
You mention running at 75% brightness, is that calculated at white? And no, I do not think you are off track. I do feel that it would be a good idea to re-think how to divide the current load between supplies and the power feeds. Also check the site's Wiki; good information there too.
 

AAH

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It isn't really necessary to fuse between the power supplies and boards that have fuses on their inputs.
Do you have a link for the specific cable that you bought? There's often a big difference between specs quoted on sites and what the real specifications are. There's some info in the ACL101 on cable sizing and http://www.da-share.com/misc/wire-size-chart/ and https://www.da-share.com/calculators/wire-cross-section-area/ are both handy.
I have 2 fuse boards that are made especially for displays. The first is the Hexfuse which has 3 30A (max) inputs to 6 15A (max) outputs. The second is a power distro fuse board particularly handy for power injection and that is the Power8. It has 2 30A (max) inputs to 8 7.5A (10A max) outputs.
 

orchidman33

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As you are using a 12V system, be very careful of the volt drop. This link may help you work out what size cable to use
https://www.windynation.com/jzv/inf/choosing-right-wire-size .
I am using 6mm (10 awg) wire from all my 30A power supplies, on a 230V mains , its rated at 32A, some would say its over kill, but with our low voltage any volt drop can mean power injection or its not possible to run the briliance wanted.
 

Julian De Jong

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Thanks everyone
Yes I believe I have calculated the brightness at 75% on full white.
The cable I bought was from here
From reading the specs on the page it seems to be 12 gauge wire which going off the 101 manual can be rated at 29amps but the manufacturer could be being conservative.
Al, when you say you don’t need to fuse between the controller and the psu, I didn’t think that the F16v3 had input fuses or am I completely wrong. I would also be worried about power spikes from the psu that could potentially damage the board.
Going off the advice here I think I will go with a larger gauge wire both in terms of safety and to reduce voltage drop as much as possible.
In terms of distributing the load, am I correct with my following thinking?
Let’s say I have a string of pixels with a draw of 6amps attached to one falcon output with no power injection. Going off what I understand at maximum brightness this could potentially break the fuse. However if I power inject at the end of the string the load would be shared between the two power inputs, theoretically 3amps at the power injection point and 3amps at the board output point. Is that correct?
 

AAH

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That cable is pretty decent and is certainly good enough for 25-30A connections within an enclosure.
Fusing doesn't do anything for power supply spikes. Fusing actually relies on a voltage drop across the fuse so each additional fuse that you are adding there will be an increased voltage drop.
The F16 has fuses immediately after the input terminals so it doesn't really need any fusing between it and the power supply.
You should only (really) power inject from the same fuse. You can generally get away with using the same power supply and not separating the positives on a string of pixels but it's best practice to do so.
Scribbling up a picture of how you want to wire things up and pop it in here if in doubt or after advice.
 

TerryK

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The higher strand count is what allows the cable's amperage rating to be higher. 12AWG THHN as an example has a typical strand count of 19. 'Skin-effect' applied to a greater number of conductors essentially.
As AAH mentioned, fuses do not stop surge/spike damage. As fuses are thermal devices and spikes are typically high and short (narrow) a spike will go right through them. Strategic application of MOV's and surge suppressors will help but even then those can't or won't stop everything. A Google of thermal fuse misconceptions will provide some information to help understand what, when, and how fuses work or don't.
I am going to offer an alternate opinion (and it is a tiny one) to AAH's mention of fusing inputs. I would add that it depends upon precisely what one is attempting to protect. And which like a number of other scenarios is not always easy to ascertain.
 

Julian De Jong

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I think it’s all a starting to make sense now. I think I had seen other people use fuses to the power boards and thought I needed to use them but didn’t actually understand the purpose. It’s interesting because this discussion has made me completely redesign the power management across my display because I realised I was loading too much against each controller and output so it has been extremely useful!
Rather than ditching that cable I think I will use it in another area of my display for one of my diff receivers with fewer pixels and save the larger cable for the f16v3.
Thanks again everyone!
 
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Bigwillystyle

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One thing to remember the length off the cable will change the current capacity or the cable.. A longer run will reduce the current capacity, however a shorter run will Increase that capacity.. If your running cable inside an enclosure and you use a decent size you should be fine.. 10 or 12ga automotive is massive for a run of 200mm at 30amps.. good to have headroom and saftey but i wouldn't go any bigger than that for that purpose.. To give you an idea, 8ga automotive (car stereo cable) will safely support 50amps (70 dynamiclly) over 6m of run.. 4ga pushes that out to 100-120 amps however if i was running 100amps over 1m or less i would feel more than comfortable running 8ga to do the job.
 
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