Fuse rating

[B Button]

I've upgraded the horn on my Bandit 650 hopefully to penetrate any cloth-eared, phone-talking twatface's senses https://www.valkmotive.com/webshop/sales-great-prices/horns/valk-motive-extra-loud-replacement-horns-black-twin-set/1290
Installation instructions do not give the amperage, but advise increasing the fuse rating by 5A - 10A. I've used the circuit the original horn was on which also covered instruments, brake light and indicators and had a 15A fuse. I changed this for a 20A, but yesterday it blew.
I'm hesitant to uprate the fuse even more, in spite of the advice. Can anyone advise whether it ought to be safe to do this?
____________________
BSA Sunbeam 250 scoot (1965), Van Van, Bandit 650 SA

[chris-red]

That is atrocious advice.

Fuses are designed to protect the wiring. The fuse size is primarily determined by the gauge of the wire it is protecting. i.e. the thicker the wire the more amps it can handle. Uprating this without uprating the cable could cause the wires to melt and catch fire should you have a short.

You should use a relay to power it.

A relay is a switch that is triggered by current, it lets a lower powered circuit operate one that uses higher power. You'll put the existing horn wires onto the switch pins on the relat and then run a fused wire from the positive side of the battery to another pin and another wire from the other pin to the horn. You then connect the other side of the horn to an earth.

When you use the horn button it will trigger the relay to allow current from the battery through to the horn.
____________________
Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.

[B Button]

[Tankie]