C15 wassell Lucas led headlight bulb

[rhyatt]

Hi all,
Just run this by you all.
1960 C15 with a 12v conversion and I'm trying to preserve as much voltage as possible by using led bulbs.
Strangely , the Wassell/lucas bpf headlamp bulb works fine with the engine off , nice and bright, but the moment I start the engine, it flickers on and off.
This is not a bad connection issue as everything is soldered and earths are good etc but I'm wondering if the led circuit is getting upset by spurious pulses of AC coming through the reg/rec.

The same bulb was in my other C15 with a 12v conversion and it suffered exactly the same issue , flickering when running and fine when engine off.

I gave up eventually and found the bike would just balance with a 36w dip bulb at 30mph in 3rd.

Failing that , I'll have to buy a later encapsulated stator as both my bike's have the earlier open coil stator which I think was about 60w output.

I have a few reg/recs all simple 4 wire , 2 x yellow and red and black , and tried  a couple of them but still the same result

Any help or ideas anyone

[scifi]

I had the same flickering with my C11.   Had to revert to the Incandescent lamp.
Hope you get an answer to the problem.

[V500]

I think rhyatt has nailed it when he said it's down to voltage pulses/spikes.
Good old incandescent lamps obviously are more forgiving of the waveforms from old alternators.

[rhyatt]

So, not just me then.
If I had 60w at 6v and now converted to 12v , I'll assume 60watts still ,
Tail is 6 , stop occasionally 18 , pilot 6 and head on dip is 36 (forget the 42 main)

Forgetting the stop , I have a total of 48 (pilot, head , rear) leaving 12watt @ 12v =1 amp left for the ignition.
Just leaving the ignition on , running through a 12v coil with about 2ohms primary consumes 6amps, but bearing in mind the dwell angle of 40 odd degrees it won't be drawing this whilst running , so let's assume 2 amps or 24 watts whilst running.

Now I'm on borrowed time defecit , pulling out more than is going in.

If I could use led tail and pilot might work leaving an incandescent dip.
Or maybe just use a 10watt pilot running light .
So much fun

[scifi]

I tried putting a 10,000 uF capacitor across the battery, but that had no effect.  It was a bit too difficult to wire it in place in the headlamp shell.

[rhyatt]

if the current 4 wire reg/recs are 1/2 wave then the little £5 rectifier blocks with 4 diodes must be FULL wave, and may smooth out the DC supply.
the only thing then is to regulate the top end , so a zener or similar may let me use this fancy led bulb

garage time i think !!

[idie]

Can you try a diode in the feed to the bulb. Failing that try a bulb designed for a cam-buss system as used on modern cars

[rhyatt]

I've tried a diode but didn't fix the issue
The wasell led bulb was 12 quid or so, there are other led hlamp bulb but crazy prices , too expensive to buy on a guess

[DAVE BRADY]

Hi,

Is it worth speaking to Paul Goff?  He specialises in LED lights.

Dave.

[rhyatt]

Yes maybe, but at 33 quid an expensive gamble especially if it's the reg rec being half wave.
I'm trying the little square rectifier which I know are full wave - an easy trial - and prove to myself where the problem is.

It is a very defined issue , engine off led headlight fine.
Start it up hlamp goes intermittent with charging

[V500]

Those little four terminal solid state rectifiers are good at rectifying but poor at smoothing. Worth a go at £5 a time but it'll still be a fluctuating voltage.

[rhyatt]

ah , thank you, I'll bear that in mind

[scifi]

I've been thinking about it...!   Why don't mains LEDs flicker, when they are supplied with 240v a.c..?
The reason I came up with, was that they use very high frequency switched mode power supplies, working from the 240 volts.
 
We only have 12v to play with, so even 5 volt of ripple is noticeable.   Maybe if we used a 100,000 uF smoothing capacitor that would solve the fault...  Problem then is, those size of capacitors are bigger than the 12v battery.

[DAVE BRADY]

Hi,

Is the Podtronics type reg/rec better at smoothing out the voltage?

Dave.

[Jim S]

I have a 1951 C11 (6V coil) with a flashing LED headlamp also. With the engine not running, I turned on the headlamp and the ignition, then opened and closed the points. The headlamp brightened and dimmed each time the points were opened and closed. I saw the same results even with a battery charger connected.

I also have a B50T (12V coil) and the LED headlamp does not flash.

Based on the above, I wonder if the excessive current draw from a 6V coil is causing the LED headlamp to flash.

Rhyatt, when you did the 12V conversion, did you install a 12V coil?

Jim