How to stop 6v bulbs blowing?

[SpannerMonkey]

So when I actually GET to ride my '72 pc50, I have this nasty habit of over-revving the engine some-what.
Being a 6v direct lighting system with no battery or fuses, every time I go downhill and do anything over 33mph-ish my back light will blow... which then leaves a heavy load on the headlight, which follows within the next 15 minutes.

I understand the theory that goes into engines really well... but I seriously struggle to comprehend electrics as I cant picture whats going on. So how the hell do I stop these lights from blowing? besides using less throttle

Would a 6v battery wired between the power source (Dynamo? magneto? I dont even know what you call these things...) smooth out the current? Also maybe keep my lights brighter at low revs?
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[Willson]

In short: No. Without a wiring diagram I couldn't say for certain, but there should be a Regulator/Rectifier between the alternator (correct?) and the rest of the electrical system which converts AC to DC (the Rectifier bit) and smooths out the voltage/current (The regulator bit). If that's not working correctly it could be the problem, but I have no knowledge of these bikes.

That's at least how I understand it.

Willson
____________________
Benson: Wouldn't life be easier if we were all turtles?
Me: Pig on bread = The way forward.
Riding: '00 Suzuki SV650S. Previous: '99 Kawasaki ER5 - sold, '02 Suzuki GZ125 Marauder - sold

[G]

It's probably running AC. (Confusingly the c90 runs both AC and DC through the rear bulb.)

I'm sure there is various ways (probably just a resistor in the right place, etc?) but I'm too rusty on such things to give good advice.

[SpannerMonkey]

I seem to remember it being 6v AC... I'll have a check when I get home and have my manual to hand.
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[stinkwheel]

Make sure you get a motorcycle specific bulb. They tend to have and extra "leg" supporting the filament. It might be vibration rather than overload that's making it blow.

Another option would be to fit a higher wattage bulb in either the front or rear light. They'll be more dim at lower revs but it's really just a position light anyway. I certainly wouldn't try riding inthe dark with it.
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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.

[SpannerMonkey]

[kramdra]

try fitting some small orings on the headlight mounting bolts. Stops all vibration. I went through 6 bulbs from november to feb, and havent used any more since.

[Teflon-Mike]

Vibration is a bulb killer, but 6v bulbs and direct lighting are notoriouse.
Old fasioned way of dealing with it was to fit lower wattage 12v bulbs.
Power = Current x Volts
Volts = Current x Resistance
So 15w 6v bulb, current would be 15/6.... call it 3 Amps. Resistance would then be 6/3 or 2 Ohms
A 15w 12v bulb, do the same you get 15/12 for 1.5A and Resistance 4 Ohms
So fit a 4Ohm 12v bulb to a 6v system, and it would draw, Volts / Resistance, 6/4 1.5Amps
So, Power = Volts x Amps, you'd get 6x1.5 or 9W from it instead of 15...
So you crunch some numbers to find out what 'sort' of 12v rating gives 'similar' lighting power...
Then you try it, and see how it works.... becouse often the 12v bulb at lower revs wont get enough juice to make it glow.... and you then go down a rating..... but, should find one that works acceptably, and that wont 'blow' when high revs over voltage is applied to it.

Alternatively..... yes, you want a little regulator circuit and battery, which can easily be wired up from components, and Maplins do some quite small, sealed lead acid 6v 'alarm' batteries that would do quite a nice job.....

HOWEVER...... your bike, PROBABLY has a regulator already..... and it's fucked!

6v direct systems often had a 'zenner diode' regulator. Its a diode working backwards, so it clips voltage over threshold, to prevent over volts... not very efficient, but they do work... and that's teh first place to look... do you have one? and is it working?

On Hondas often looks like a blade fuse in the headlamp, black, with a diode symbol on it ->|- if not, could be on the fork yoke or head stock, or under the ignition key, and possibly have a bit of heat sink around it.

If you dont have one, a 6V Zenner of suitable rating might be a solution, rather than full regulator circuit... and a nice descrete mod, it can be wired 'in line'... but, I think I'd go for a small sealed lead acid and a regulator circuit, hidden away somewhere, for 'reliable' lights for modern roads.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
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[stinkwheel]

I think you overestimate the complexity of these bikes Mike.

It has a headlight and a tail light that run on single phase AC direct lighting. It's a 7 wire loom (see attached picture, that's ALL the wiring).

No brake light, no flashers. The speedo back light is cunningly arranged by having a hole in the headlight reflector directly under the speedo. Similar arrangement for the hi beam (to make laughing noises) warning light.

If you want to sound the horn at the same time as you have the lights on, you have to pretty much redline it.

I very much doubt there is any form of regulator at all. It produces about 5A top whack and that's AC output. Start trying to rectify it and you have no chance.
____________________
“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.

[ThoughtContro...]

If it's 6V AC that it's producing, then you can't wire a battery or capacitor to smooth out the voltage to the light. That nominal 6V is RMS BTW, the peak Voltage will be nearer 8.5V.

As mentioned, the best way is to upgrade the bulb to cope with any increased current at high speeds. You'd be best sticking a meter on the output to the light, and measuring it with the engine revving at the sort of rpm your getting when you're going downhill and blowing bulbs. Don't forget to switch your meter to AC tho, or you won't get an accurate reading.

Once you know what max voltage is the problem, then you can start messing around with equations to figure out what bulb you need (or suitable resistor if you can't find a bulb with the right rating.
____________________
Prize cunt
--
"In a world of universal deceit telling the truth is a revolutionary act" - George Orwell

[Teflon-Mike]

[ThoughtContro...]

Mike, if you're using a Zener regulator you'll usually use a shunt resistor too, see https://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

It's not the most efficient way of doing things.


If you use a 4 diode bridge rectifier, then you'll drop around 0.6-0.7V across the diodes, so you'll lose about 1.4V max across each diode pair, during each half cycle.

Also if you'd be better using an electrolytic capacitor to smooth out the output from your bridge rectifier, since it's smaller lighter and cheaper than piddling about with the complication of extra batteries, if you want to do it that way.
____________________
Prize cunt
--
"In a world of universal deceit telling the truth is a revolutionary act" - George Orwell

[Teflon-Mike]

[ThoughtContro...]

[SpannerMonkey]

[Teflon-Mike]

[ThoughtContro...]

[SpannerMonkey]

Right, I really dont understand any of this electrical bollocks... what am I supposed to be fitting? what fits between where? I need someone to either educate me in electrics so I can make my own decisions, or for someone to make my decisions for me, and justify them lol
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[ThoughtContro...]

OK possible suggested circuit diagram attached (MS Paint)

Components
----------------

1N5401 Diode x4 Maplin Code - QL82D, 29p each

(Rated 3A, 100V, so fine for any 6V bulb up to 18W, Any of the 1N5400 series will do really)

Optional
-----------

470uF 25V Electrolytic Capacitor Maplin Code - DT60Q, 31p each

(Not critical at all as long as rated voltage is well above 10V it'll be fine. Large uF value is nice for smoothing purposes, tho it's no big deal since we're running a filament bulb not a logic circuit. The one above is a High Temp Cap too. The only thing to make sure with Electrolytic Caps is make sure you solder them in the right way round, as they are polarised. Negative lead will be marked)
____________________
Prize cunt
--
"In a world of universal deceit telling the truth is a revolutionary act" - George Orwell

[finpos]

[SpannerMonkey]

[ThoughtContro...]

[finpos]

eh... stick a bigger bulb in it! You can even try using 12V bulbs.

You could possibly put a vespa regulator (https://beedspeed.com/product_info.php?products_id=1663) in it, the worry being that the alternator won't put out enough power to operate that and the lights - in much the same way that simultaneous horn and lights can only be a dream. May be worth trying at £20.


f.

[finpos]

[kramdra]

Schottky ftw. double them up, 15A rating is plenty for that bike.'


https://www.rapidonline.com/Electronic-Components/Discrete-Semiconductors/Schottky-Diodes/Power-dual-Schottky-rectifiers/78105

https://www.rapidonline.com/Electronic-Components/Discrete-Semiconductors/Rectifier-Diodes/High-power-dual-Schottky-rectifiers/76074

https://www.rapidonline.com/Electronic-Components/Discrete-Semiconductors/Schottky-Diodes/Power-Schottky-rectifiers-TO-220/78104



For DC to work, you need some REALLLY big smoothing caps. Small ones wont just not work, they will rapidly dry out and go bang... or something.... smells really bad anyway. Capacitors do disipate power = voltage x ESR (AC resistance).

https://www.rapidonline.com/sku/Electronic-Components/Capacitors/Radial-Electrolytic/Low-profile-snap-in-105-deg-C-2000hr.-electrolytic-capacitor/80204/11-3152

they dont do anything bigger... 2 or 3 of those in parallel.