what fuse for accesory socket/line?

[Ribenapigeon]

What fuse should I use if I fit a socket for electrical accesories.

Also am I right in thinking that such a line would simply be connected at the positive output from the rectifier in parralel with other fuses?

How can I work out what load my bikes electrical system can cope with for accesories? My bike is a Yamaha WR 125 X.

Cheers.

[janner_10]

What is it you are fitting?

Usually things mention the power consumption in W on the box / instructions which would give you a fair indication on what fuse to use.
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Yamaha FZS600 (Now gone to heaven) > CBR600F4i (SOLD) > '99 YZF-R1

[Ribenapigeon]

Its just for general purpose stuff like GPS or mobile phone charger etc maybe heated grips though not sure about that as my gloves are doing alright evn on freezing days.

[Teflon-Mike]

Ok, lets look at the feed first.

Do you want the accessory socket permenantly 'on' or switched by the ignition key?

If you T off the feed from the regulator to the main harness, that is normally direct to battery, so you would have permenant 'battery' live.

If you want it ignition switched, you would need to work out what the common ignition switched live is. Look at wiring diagrams, it will be the wire that comes out of the ignition switch and goes to all the others.

If you are going ignition switched; then, you are limited to the current that can go through the ignition switch, which over and above everything else it's supposed to feed, might not be much.

Main supply will probably be fused any-way, probably something like a 10 or 15A ratiing.

Head-Lamp, tail-lamp, stop-lamp, indicators, and idiot lamps, and you are probably drawing something in the order of 90-100W, or about 8A... which doesn't leave you much, and take another amp off that, papping the horn at a junction with full load on teh loom could be enough to blow the fuse!

Also means, that if you want to indipendently fuse the accessory socket, you will want something eff off low, like under 1A,m which is enough to run a phone charger or a GPS supply, that draws maybe 1/4A, but you wont be able to run heated grips off it, which could draw perhaps 8A on thier own.

So, if you go ignition switched, through the ignition circuit; and want to independently fuse it, you are probably going to have to look at micro-fuses rather than conventional automotive blade fuses, as they only go down to about 3A commonly.

If you want to run higher current devices; then really you will have to go straight off the battery, and to relieve load on the main loom, and keep things simple, I would make up completely independent accessory loom, with ring terminals to T in straight off the battery terminals for + & -.

Then you can use wire rated to whatever ampage you anticipate drawing, and fuse accordingly with a water-proof inline blade fuse.

If you want it ignition switched, you can then switch with a relay, off the ignition switched circuit, which will draw mili-amps in itself.

BUT, how much power you can take off the battery to power accessories, IS going to be limited.

Snowie wanted loads of electrical gadgets on the Pup; but 125's tend to not have particularly generouse generators. 125 Super-Dream though is one of the more generouse, Honda wanting to belt & braces the e-start only engine, giving it, I think a 150W genny and 9Ah battery, which is like about double the power rating of many contemprary 80's bikes, and still pretty impressive for modern tiddler.

To get the standard equipment current draw down sufficiently for her to have an upgraded head-lamp, heated grips, phone charger, GPS & alarm, we had to go to LED's for almost everything light-wise, and a solid-state electronic indicator flasher.

Did you know that the peanut bulbs in the dash-panel that provide the back-lighting, and tell-tale lights like neutral, indicators or hi-beam are 3.8W a piece? With the head-lamp on main-beam, two are back-lighting the clocks, one illuminating the tell-tale.... thats almost 16w of light, MORE than the frigging tail-lamp bulb is drawing, just lighting up the dash!

Replacing the dash-lamps with LED's freed up about 16W or 1A of peak current draw.

Replacing the side-light bulb, tail-lamp bulb and indy bulbs for LED equivilents, probably another 40W of 'peak' load, about 3A.....

Upgrading the headlamp, going to a 35W HID actually gave more light AND a 10W current saving!

THAT was enough I reckoned to run the heated grips and accessory socket on a 3A fuse.

Its also enough that after starting she can pump the tyres up from the accessory socket with a fag-lighter pump! (provided the heated grips aren't on!) But not from 'flat'. Generator wont make enough juice to supply that draw with the engine on idle, so it will depleat the battery; even with the lights off.

SO... with a 'good' electrical system, and a lot of efficiency savings found, there is 'just' enough electric being made to keep a small 1/4a GPS charger powered and the heated grips on intermittently.

We used Oxfords on her bike, as they have smaller grips, for her little hands and one of the better and more efficient (if reputably less reliable) power management systems.

So far its worked OK, but neither of us have run the system hard, using grips on higher settings, with the lights on 'main' for any lenth of time; using side-light only for DTRL, and head-lamp only when its dark..... and Snowie doesn't ride much in the dark!

SO... bit of thinking to do, as to what may be the best way to do it, depending on what you intend to run and when.
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Ribenapigeon]

Thanks Tef, I'm not going to bother with heated grips but I think a igniton swith to relay setup will do for GPS and the occasional mobile phone charge.

[Casper]

I stuck a fag socket in my bike. Took the live feed from the brake light switch so it goes of with the ignition and use a 3A fuse. In the socket is a double USB socket with a small light and that runs the SAT NAV software in my Android phone. Its been fine and well used.

[stinkwheel]

The simple answer to the initial question is the next commonly available size fuse below the rating of the cable it is attached to.

So 7A cable would want a 5A fuse. 13A cable would want a 10A fuse and so-on.

Providing the fuse is rated lower than the cable, you will avoid electrical fires.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Islander]