Voltage drop at headlights - SV650.org

14-07-05, 08:22 PM

The headlights on my 99 bike have always seemed **** poor so I've bought some Philips 150% brighter jobs. Before changing them I thought I'd check the voltage at the bulb and found that with a battery voltage of 11.8 volts I am only getting 7.6 at the headlight main beam. Looking at the route to the headlamps (through both handlbars) and the spindly wiring it's not surprising there is a big voltage drop when passing over 10 amps.
I'd be grateful if a few more people could carry out the check and see if it's just my bike. If it is I'll check all my connections, if it's common to all I'll put in some heftier wiring and a couple of relays.

14-07-05, 11:15 PM

I've just ordered some philips bulbs too.

I dont think its the volts you need to be concerned with its the watts the majority of automotive bateries are 12V. Its the watts that determins the strength of the light and the heat emitted.

I'll check mine when i change them.

ophic · 14-07-05, 11:15 PM

10 amps? is it really that much? i'd say without some seriously thick wires you're lucky to get what you've got.

thinking now. 12V electrics... P=IV... does that mean your headlights are 120W? *thinks more* 2x60W bulbs -yeah i spose it would. I hate low voltage electrics...

BillyC · 15-07-05, 08:40 AM

As Ophic correctly points out, Wattage is directly proportional to voltage, so a 55W, 12v bulb, will only produce 55W of light, when fed 12v.

With the lower voltage suggested, it could be said that you're only getting about 38W of light!

You've already done a visual inspection of the wiring loom, and I would perhaps go with that a bit further. I suspect that there is either a worn wire, or a partial ground somewhere.

If nothing is obvious, then you may have to trace the wire back along the loom with a voltmeter to see where the problem is.

A couple of other thoughts before you do this; firstly check what your battery's voltage is; and secondly measure the bulb voltage while your engine is running at 3000-4000 RPM.

I'm sure Mr Squid will be along soon with his experienced suggestions on the subject.

Sid Squid · 15-07-05, 02:00 PM

If there's no one connection/switch that your wiring investigation reveals as obviously lacking, then it may just be easier to re-feed the headlights direct via relays as you say

The voltage is important, any resistive parts of the circuit will cause volt drop, and thus rob you of light output.

Yours is not an unusual complaint, out in all weathers and alternatively heated and cooled, moist atmospheres and vibration often takes a toll on automotive electrics, as said above a careful look round might reveal one connection that is corroded or loose, but it's not always true, as most commonly the fault is cumulative between a number of connections.

Happy hunting

17-07-05, 11:00 PM

Couldn't find any dodgy connections so put in some new 2.5mm wiring and some relays and now have blinding headlights.

14-07-05, 08:22 PM	#1
streetos Guest Posts: n/a	Voltage drop at headlights The headlights on my 99 bike have always seemed **** poor so I've bought some Philips 150% brighter jobs. Before changing them I thought I'd check the voltage at the bulb and found that with a battery voltage of 11.8 volts I am only getting 7.6 at the headlight main beam. Looking at the route to the headlamps (through both handlbars) and the spindly wiring it's not surprising there is a big voltage drop when passing over 10 amps. I'd be grateful if a few more people could carry out the check and see if it's just my bike. If it is I'll check all my connections, if it's common to all I'll put in some heftier wiring and a couple of relays.

14-07-05, 11:15 PM	#3
ophic Member Mega Poster Join Date: Jan 2004 Location: Whyteleafe Posts: 3,395	10 amps? is it really that much? i'd say without some seriously thick wires you're lucky to get what you've got. thinking now. 12V electrics... P=IV... does that mean your headlights are 120W? thinks more 2x60W bulbs -yeah i spose it would. I hate low voltage electrics... __________________ Silver SV650SK3, Fuel exhaust

15-07-05, 08:40 AM	#4
BillyC Moderator Mega Poster Join Date: Nov 2003 Location: The exiles of Kent Posts: 2,184	As Ophic correctly points out, Wattage is directly proportional to voltage, so a 55W, 12v bulb, will only produce 55W of light, when fed 12v. With the lower voltage suggested, it could be said that you're only getting about 38W of light! You've already done a visual inspection of the wiring loom, and I would perhaps go with that a bit further. I suspect that there is either a worn wire, or a partial ground somewhere. If nothing is obvious, then you may have to trace the wire back along the loom with a voltmeter to see where the problem is. A couple of other thoughts before you do this; firstly check what your battery's voltage is; and secondly measure the bulb voltage while your engine is running at 3000-4000 RPM. I'm sure Mr Squid will be along soon with his experienced suggestions on the subject. __________________ SV650 K3 - Gone. Now a member of the SV650.org Kawasaki brigade!

15-07-05, 02:00 PM	#5
Sid Squid No, I don't lend tools. Mega Poster Join Date: Jul 2003 Location: Skunk Works, Nth London Posts: 8,680	If there's no one connection/switch that your wiring investigation reveals as obviously lacking, then it may just be easier to re-feed the headlights direct via relays as you say The voltage is important, any resistive parts of the circuit will cause volt drop, and thus rob you of light output. Yours is not an unusual complaint, out in all weathers and alternatively heated and cooled, moist atmospheres and vibration often takes a toll on automotive electrics, as said above a careful look round might reveal one connection that is corroded or loose, but it's not always true, as most commonly the fault is cumulative between a number of connections. Happy hunting __________________ If an SV650 has a flat tyre in the forest and no-one is there to blow it up, how long will it be 'til someone posts that the reg/rec is duff and the world will end unless a CBR unit is fitted? A little bit of knowledge = a dangerous thing. "a deathless anthem of nuclear-strength romantic angst"

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
RST Voltage Leathers	DarrenSV650S	Bikes - Talk & Issues	9	22-06-10 12:25 AM
Low voltage relays	DarrenSV650S	Bikes - Talk & Issues	21	16-03-09 09:16 PM
are fuses voltage rated?	Stu	Idle Banter	21	02-02-09 02:36 PM
Low voltage at headlights 10V right 12.5V left?	F16Falcon	SV Talk, Tuning & Tweaking	21	11-08-08 03:30 PM
Voltage regulator / rectifier	Alpinestarhero	SV Talk, Tuning & Tweaking	6	16-08-07 03:53 PM

14-07-05, 11:15 PM	#2
Vtwinlover Guest Posts: n/a	I've just ordered some philips bulbs too. I dont think its the volts you need to be concerned with its the watts the majority of automotive bateries are 12V. Its the watts that determins the strength of the light and the heat emitted. I'll check mine when i change them.

17-07-05, 11:00 PM	#6
streetos Guest Posts: n/a	Couldn't find any dodgy connections so put in some new 2.5mm wiring and some relays and now have blinding headlights.