Now here is a real "nuts and bolts" or rather "volts and amps" question.
I am in the process of arranging a power system for auxilary units in the shack to get rid of noisy "wall warts." It will be run off a separate power supply from the one that is used for the transceivers (which I have been told is very important for digital interfaces).
Is there a "rule of thumb" for the amperage of fuses that provides a safety factor for the equipment without being too sensitive. For example what fuse would you use for a piece of equipment that draws 750mA?
The other question would be: is it really necessary to have each bit of equipment with individual fuses or is it ok to add their power together and use a single fuse between the equipment outlets and the power supply. We are only talking about very low power items here - antenna switches, a scanner, keyer, digital interface and the like, all of which run on 12v.
73
Wayne VK4WDM
"Rule of thumb" for fuses?
Re: "Rule of thumb" for fuses?
Hi Wayne,
As Justin pointed out the main purpose for using fuses in your distribution system is to prevent overloads which can cause wiring fires.
If I were wiring a new distribution system, I would employ a main fuse straight from the source, be it a battery system or decent power supply, then the line to the distribution point is protected.
I have seen poorly installed equipment in cars where heavy cabling was run direct from the battery, through a hole in the firewall (with no gromet) to the vehicle interior, with no fusing. (Boy racer doof doof sound systems). A fire waiting to happen!
I would fit a fuse from that point to every device being fused, to protect the smaller cross-sectional cable feeding each device.
To work out what would be a sensible fuse rating to employ, I usually look at the current draw of the device, and double it, and make that the fuse rating, so if your device draws say 5A, use a 10A fuse. This will mean that your cabling should be adequately protected, and you should eliminate any nuisance failure of the fuse from things like switch-on inrush currents. For your 750 mA device, I would probably use a 2A fuse.
It's also worth ensuring that your cabling is of sufficient size not only to minimise voltage drop, but be able to easily handle more current than the fuse without risk of failure.
As Justin pointed out the main purpose for using fuses in your distribution system is to prevent overloads which can cause wiring fires.
If I were wiring a new distribution system, I would employ a main fuse straight from the source, be it a battery system or decent power supply, then the line to the distribution point is protected.
I have seen poorly installed equipment in cars where heavy cabling was run direct from the battery, through a hole in the firewall (with no gromet) to the vehicle interior, with no fusing. (Boy racer doof doof sound systems). A fire waiting to happen!
I would fit a fuse from that point to every device being fused, to protect the smaller cross-sectional cable feeding each device.
To work out what would be a sensible fuse rating to employ, I usually look at the current draw of the device, and double it, and make that the fuse rating, so if your device draws say 5A, use a 10A fuse. This will mean that your cabling should be adequately protected, and you should eliminate any nuisance failure of the fuse from things like switch-on inrush currents. For your 750 mA device, I would probably use a 2A fuse.
It's also worth ensuring that your cabling is of sufficient size not only to minimise voltage drop, but be able to easily handle more current than the fuse without risk of failure.
Tim, VK4TIM.
QG62MM, Brisbane.
QG62MM, Brisbane.
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VK2CBL
Re: "Rule of thumb" for fuses?
Having spent 20 years in the power supply business... Google "fuseology" and download the pdf's.
That will keep you busy for a few days. Cheers.
That will keep you busy for a few days. Cheers.
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VK5ACY
Re: "Rule of thumb" for fuses?
Further to VK5ZD's helpful post.....aluminium potentiometer shaft offcuts fit 3AG fuseholders perfectly !
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VK2XSO
Re: "Rule of thumb" for fuses?
+1 with Justin's comment.
Only where I work engineers see a 10 amp fuse and then find a cable to over rate the fuse.
Even if the equipment only requires 2 amps.
And I'm impressed with 5zd's ratings chart of the various supa-fuses
Only where I work engineers see a 10 amp fuse and then find a cable to over rate the fuse.
Even if the equipment only requires 2 amps.
And I'm impressed with 5zd's ratings chart of the various supa-fuses