Posted by Stuart on August 30, 2021, 8:44 pm, in reply to "fuses "
>What size fuses should i use on my Velo when i fit a new wiring ?
Add up the Watts of all the light bulbs, divide the total by 6 or 12 Volts depending what the bike's DC electrics are/will be, the answer is the Amps. Round it up to the nearest whole number and either remember or note that number.
Add at least a couple of Amps for the horn.
I'm guessing the Velo has a mag. for ignition? If so, the battery terminal connected to the frame requires a standard automotive blade fuse holder close to the battery terminal, fuse with a number equal to or just above the number you calculated above.
Otoh, if the Velo has Kettering coil-'n'-points ignition add four (Amps) to the number you've calculated so far, the fuse in the holder between frame and battery terminal needs to be the same as the new number or just above it.
This is the main fuse, final protection if a short-circuit happens in a way you never considered.
If you wish to fuse individual 'consumers' - e.g. headlamp, tail-lamp, brake lamp, Kettering ignition, etc. - the individual fuses should be rated either the same as the calculated Amps consumed by the component or just above that figure - blade fuses are available in 1A, 2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A and 40A.
Any fuses for individual or groups of components should go in the wiring between the battery terminal that isn't connected to the frame.
Fusing individual components is a nice theory but a pita in practice on a bike, given you need to site the fuse where you can get at it easily - e.g. if the ignition or headlamp fuse goes phut, you hardly want to be removing the tank at the side of the road to get at it?
>Fuses need to have a current rating lower than that of the wiring.
Sort-of. Wires are available in a very limited number of Amps ratings, and you have to consider the terminals you're going to use - not all wire types suit all terminal types. The single wire with the aforementioned 'main' fuse connected to the battery terminal should be rated the same or higher than the fuse rating; however, this wire size is not likely to be suitable - or necessary - for every wire on the bike.
>Especially on 6V systems, I use 16 gauge wiring
Lannis means No.16 American Wire Gauge, no equivalent in Europe. Here, we rate by Amps, number and diameter of strands, and insulation type ...
Fwiw, I use:-
. "28/0.30 thinwall" (28 strands, each 0.3 mm. o.d., special thin PVC insulation) for the (single) wire actually connected to either battery terminal. It's rated for 25 Amps;
. "9/0.30" (9 strands, each 0.3 mm. o.d., normal PVC insulation) for most other wires. It's rated for 5.75 Amps, which is more that big enough even for a 60W main beam headlamp. Btw, the formula that connects Watts, Amps and Volts is a simple Watts = Amps multiplied by Volts; from that you can see a 60W, 12V headlamp filament draws 5 Amps.
. However, sometimes I use "14/0.30" (rated for 8.75A) - some Lucas colour combinations aren't available in 9/0.30; 9/0.30 doesn't have a high-enough rating for a 100W headlamp main-beam ...
Apart from the aforementioned 28/0.30 thinwall, I don't use the smaller sizes (32/0.20, 24/0.20, 16/0.20), although their ratings look suitable, ime they don't 'work' with standard "Lucas bullet" terminals (which I use a lot without any of the legendary 'problems').
Lannis's "16 gauge" is about half-way between 14/0.30 and 28/0.30. in conductor cross-sectional area.
Hope answers to questions you didn't ask isn't too confusing ... Any questions arising, please ask away ...