Question for electrical types!

Darth_1100S · Post by **Darth_1100S** » Tue May 11, 2004 12:15 am

My Lads XJR400 is a grey import. The dipped headlight is permanently on which is a pain, because some mornings when it's being a bit difficult to start the battery runs down very quickly. I was going to put a switch in so it can be turned off. Will it be advisable to put a relay in the circuit or will a decent switch by itself be ok to handle the current? Alternatively any suggestions for a disconnection circuit while the starter is operating? I've got no circuit diagrams for the bike as nothing of that sort is available in the UK - can't even get a workshop manual for it.

Dave

Delpel · Post by **Delpel** » Tue May 11, 2004 5:24 am

If you can work out the current the bulb is using and get a switch that handles the current you would be OK. But the switch might be a bit large.

Best way to acurately measure the current is to place a multimeter in series with the dipped beam bulb. Just pop the headlight cover of and you'll find the right wire. A relay is used to switch high currents so that the manufacturers can use cheap low current switches.

I can draw you a circuit diagram if you want but you will have to put in the wire colours for the bulb.

Hope that helps.

mdouglas · Post by **mdouglas** » Tue May 11, 2004 7:09 am

55Watts at 12V. That'll be about 4.5Amps then. (P=VI, wake up those at the back of the class!)

There's a whole range of switches that will comfortably handle this.

Try Vehicle Wiring Products at this web site:

http://www.vehicle-wiring-products.co.u ... tch-1.html

As you'll see, they even have splashproof ones that'll support 10A or 20A at 12V DC.

Darth_1100S · Post by **Darth_1100S** » Tue May 11, 2004 8:26 am

Thanks for that guys, whenever I've wired up lights on my cars in the past - eg spotlamps etc I've always put them thro' a relay. With the bike just having the one headlight I wondered if it was still necessary to use one. Rather than have a huge switch I think I'll pop a relay in.
Thanks for the offer Delpel but I think I should be ok. If I get into bother I'll give you shout if that's ok

Dave

Delpel · Post by **Delpel** » Tue May 11, 2004 10:17 am

(P=VI, wake up those at the back of the class!)

I knew it was something like that, Far to early in the morning for ohms law

minivin · Post by **minivin** » Tue May 11, 2004 1:09 pm

ah kay, since alot of the modern alternators can kick-out alot of current at engine cranking speed's some people have been putting relays in to cut the alternator out of the circuit so it doesn't load the engine at starting.

This is done such that a "break when set" relay is put in the circuit so that as the starter button is set, it sits in parallel and breaks the contacts in the relay thereby seperating the alternator output or sensing circuit.

I'll email a picture to you in a bit since I got the "luvly" croc-clips here which is perfect for doing shitty piccies

minivin · Post by **minivin** » Tue May 11, 2004 1:17 pm

Delpel wrote:(P=VI, wake up those at the back of the class!)

I knew it was something like that, Far to early in the morning for ohms law

<cough> don't forget (I*I)*R and (V*V)/R