Fuses and wiring help

[Baf05]

I am building a mega tree using Ruprects guide so all the specs are pretty much the same, 1344 12v lights, 42 lights per string 32 strings, 8 strings per universe, 4 universes.

I have a block of 4 fuses set up, 1 for each universe, and I am using 18AWG speaker wire. I have done some reading and found that the max amp for the speaker wire is 7amps, trouble is, 7.5amp fuses blow!

Should I try 10 or even 15 amp, and over power wire, or should I move to an 8 block fuse holder?

 

[mborg10]

I'd get thicker wire. You want the fuses to blow before your wire fails and you see magic smoke.

 

[AussiePhil]

There are a number of issues with this, all with power wiring and fuses.

1344 pixels divided between 4 fuses is 366 per 7.5A fuse, no wonder they are blowing.

Baf: as your in Canberra you could drop around and chat or I could head out to your place over the weekend if it would help.

Cheers
Phil

 

[Baf05]

Thanks Phill, I think you are north? And I am deep deep south. Working this weekend too. 6a To 4p, But maybe we can arrange something, I am much better at visual work than reading? So your help would be greatly appreciated.

I have just added a second fuse block to give me 8, that' helped and I got stronger white before one went. the trouble is as the power line is continuous one fuse goes, they all go, I am wondering if severing the power line at the "top" of the tree would help. Might isolate any problem areas?

 

[lizardking]

sounds like you need to do separate power injection from another psu and another fuse block not connected thru the controller , with that in mind NeVER let any PSU positives join as you will get back feed and blow the PSU up of maybe your controller i have had the same problem i have one PSU connected to the controller and 2 psu going just for power injection connected to 2 fuse blocks hope this helps

 

[Baf05]

I don't know about that, the PSU I have is rated to cope with the current draw I need (I think); its a 600 watt

I think I have worked out I am now trying to draw about 20 amps across the fuse? Does that sound right?

1344 lights / 8 fuses = 168 (12v)lights per fuse / .72 watts = 233.33 / 12 volts = 19.44 amps....

Is that right?

 

[lizardking]

are you using just the one output on the PSU you may need to just add another fuse block or 2 and run 1 fuse block for each output to separate some of the load

 

[AussiePhil]

Thanks Phill, I think you are north? And I am deep deep south. Working this weekend too. 6a To 4p, But maybe we can arrange something, I am much better at visual work than reading? So your help would be greatly appreciated.

I have just added a second fuse block to give me 8, that' helped and I got stronger white before one went. the trouble is as the power line is continuous one fuse goes, they all go, I am wondering if severing the power line at the "top" of the tree would help. Might isolate any problem areas?

No worries, I'm up in Flynn and working in Gungahlin now.... I'll pm you my phone number, even a chat might sort this out for you.

I don't know about that, the PSU I have is rated to cope with the current draw I need (I think); its a 600 watt

I think I have worked out I am now trying to draw about 20 amps across the fuse? Does that sound right?

1344 lights / 8 fuses = 168 (12v)lights per fuse / .72 watts = 233.33 / 12 volts = 19.44 amps....

Is that right?

numbers are high and real world measurements will show then to be lower, however you are on the right road.

 

[scamper]

Just to add a little to the conversation
A fuse is meant to protect against a major problem and usually is around double what you would expect to draw (current)
therefore, the wiring and supplies should all be able to handle much more than that.
If you expect a current draw of 7 amps, then the wiring should be able to supply 15amps or more and the fuse can be up around 10 to 15 amps.
What should happen is at a constant current, the wiring should not be overloaded as it will create heat and in turn create more resistance and drop more voltage.
If you have a problem, such as a short, the instant high current will cause the fuse to blow.
I am sure this will only make sense to half of you as after reading it I am getting confused myself

 

[Benslights]

I think that is well said scamper. only issue I see is if your had your fuse at 15 amps as you say it would do nothing. I always try to keep the fuse as close as possible to what im trying to protect

eg I have P2 fused on input at 1amp.

3 strings of 5v pixels I have 10amp fuse on as they will pull 9.5amp from memory on white so I use a 10amp fuse

 

[lithgowlights]

While I would say 9.5A, what is the rating of the wire you are protecting. It's not just the total load. The fuse is there to stop the wire burning in the event of a failure, so you have to think about the placement of injection points and even how you are going to fuse them as well, especially for the longer runs of pixels

 

[AussiePhil]

Fuses MUST protect wiring, if they are not sized based on the wiring used you may as well not use them. I am completely happy to demonstrate this to anyone if needed.


any fuse will carry at least %110 constant current and is exactly the reason fuses must be sized appropriate to the wire size.

 

[Benslights]

agreed but no point protecting the wiring if the controller at the end of it does not handle the amps that the wire can.

so I guess in general the best way of putting it is that I fuse to what is the lowest rating for that item.

I also place my fuses close to the power supply so it is only about 10cm of wire at most to the fuse

 

[ԆцряєсϮ]

Baf for what its worth, I have my tree protected by only 4 x 15A fuses.
All my cabling is rated at 15A continuous load so I structured my injection to run off 4 feeds.
The fuses are only there to protect the cabling in the case of a fault. If a fault occurs and any of the cabling draws more than 15A then the fuse will blow.
If the fuse wasnt there the cable would melt and most likely catch fire.
As your using considerably lighter guage cables you will need more fuses.
I'd recommend using a heavier cable myself, Im using 26/0.30 fig8. When you run them now does the wire get warm?
[/size]You'd be best to take up Phils offer and let him come down and have a look see.
[/size]
[/size]Cheers
[/size]Rod