Forum

[jefrs]

Adding a relay means you have to find somewhere to hide it and run extra wiring to and from it; complicated and not needed. You can pull the supply from the brake light switch circuit in the casquette, through the heaters (fuse and switch) and back to ground in the casquette. The casquette will have a ground point from which a black wire should run back to the bike frame either near the battery or hidden on the seat tube near the rear engine mount where the alternator grounds. Anywhere on the main frame makes a good ground but the steering head bearings are not the best conductors, so although the head lights ground in the casquette, there's a thick black ground wire back to the frame, use that.

[papasmurf]

A relay sufficient for the purpose only measures 30mm x 13mm x 27mm

[jefrs]

papsmurf, I do the calculation in me head mate, it's really quick.



That Solar Power calculator link results with overly thick wire. 17.5A only needs 2mm², that's only 1.5mmØ.

Typical down&dirty linky showing sizes http://www.autoelectricsupplies.co.uk/p ... ategory/11

What's sold as 15A is generally 17.5A for safety margin.

[papasmurf]

I provided a link for those who can't do mental calculations.

[NicoV]

Papasmurf: a very interesting and useful link ! (to me the uninitiated )

[jefrs]

Papasmurf, it was good of you to provide a link. Unfortunately the Solar-Wind calculations are too thick, by a factor of 3. Solar-Wind gives 6mm² for 17.5A cable but it should only be 2mm² as shown on the (randomly selected) sales site I gave. There are other calculators out there, or you can grab a reel of the stuff off a shelf and measure the core diameter.



We don't want the thinnest cable capable of doing the job, it needs to be physically strong enough to withstand being pulled about; bike wiring tends to be overkill.

[papasmurf]

Jefrs a few years ago when clearing a relatives house after they had popped their clogs I found enough reels of suitable wire to last me and several other people a lifetime.