Power injection best method. And Fuses
- Thread starter cdjazman
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Fing
Full time elf
ԆцряєсϮ said:the leader of the opposition.... or minister of finance
otherwise know as the "Circuit Breaker"
Fing
Full time elf
Hi,
When thinking fuses, draw your circuit and then imagine what would happen if a fault developed. Where the fault is also important, but a bit of logical thinking can narrow this down. For example if one of your trees in the parallel example shorted, then the fuse blowing would take the other 4 trees out as well. perhaps individual fuses would be better in this example?
My megatree is split into 6 separate sections, each individually fused so a fault can only take out one part.
By using individual fuses they can be smaller rated which may help to limit the fault current and potential damage.
Cheers
Fing
When thinking fuses, draw your circuit and then imagine what would happen if a fault developed. Where the fault is also important, but a bit of logical thinking can narrow this down. For example if one of your trees in the parallel example shorted, then the fuse blowing would take the other 4 trees out as well. perhaps individual fuses would be better in this example?
My megatree is split into 6 separate sections, each individually fused so a fault can only take out one part.
By using individual fuses they can be smaller rated which may help to limit the fault current and potential damage.
Cheers
Fing
cdjazman
Full time elf
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- Apr 24, 2012
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- #19
djgra79 said:
Hey Graham,
So in this example you have 3 pos from psu to hex fuse then how many are power injection gong out?
I have 8 points of power injection in my mega tree - two lots of series - wondering if two hex will cover converting them to 8 direct injection cables.
Craig.
Sorry Craig, forgot to respond the other day.cdjazman said:
In this example I have 6 power leads coming out of this box, 4 from the left cable gland and 2 extra to the right. This was my 5v box that powered a BBB for a 4x1 P10 matrix, powered a P2 and then 4 PI points for 5v pixel nodes from memory.
Being a designer for mining products (intrinsically safe) there is a lot of validity to the above.
Keep in mind the positioning of the fuses (ie a fuse is of little use at the end of a 100A cable) and it's type (slow/fast blow etc). For our purposes generally we aren't driving inductive/capacitive loads so a fast blow is fine.
However there are posts where guys have had their main cabinet with psu's in their garages and the fuses at the display. It may be commonsense to most of us, but always have a fuse on the psu regardless. As Rup said, worst case scenario is not a problem with the display but with the cable shorting out to itself (being cut,crushed etc).
And although most modern switch mode psu's have a decent crowbar on their output to reduce the output current upon a short, it's not something to rely on. Don't do it, bad practice.
Not too relevant here but we also have to use encapsulated fuses to minimise the risk of an ignition source, however if in a plastic case keep an eye on temperatures. I have seen the cheaper ANL audio fuse holders literally melt and smoke under full load.
As an aside also take into account the vdrop across any fuse in the circuit they are essentially just low ohm fusible resistors.
Keep in mind the positioning of the fuses (ie a fuse is of little use at the end of a 100A cable) and it's type (slow/fast blow etc). For our purposes generally we aren't driving inductive/capacitive loads so a fast blow is fine.
However there are posts where guys have had their main cabinet with psu's in their garages and the fuses at the display. It may be commonsense to most of us, but always have a fuse on the psu regardless. As Rup said, worst case scenario is not a problem with the display but with the cable shorting out to itself (being cut,crushed etc).
And although most modern switch mode psu's have a decent crowbar on their output to reduce the output current upon a short, it's not something to rely on. Don't do it, bad practice.
Not too relevant here but we also have to use encapsulated fuses to minimise the risk of an ignition source, however if in a plastic case keep an eye on temperatures. I have seen the cheaper ANL audio fuse holders literally melt and smoke under full load.
As an aside also take into account the vdrop across any fuse in the circuit they are essentially just low ohm fusible resistors.