Hitchcocks Forum

I am a fairly new owner of a 2004 sixty-5. I have been looking at improving the headlight.
As far as I can ascertain the AC regulator is a pair of back to back zener diodes.

That would imply that:-

At low revs with the lights on, they do nothing and the lights see a sinusoidal voltage at whatever the alternator can deliver into the bulb

At high revs with the lights on, the lights see a heavily clipped sine wave, almost a square wave with the peak value being the zener voltage. Presumably the zener voltage is chosen so that the RMS value is about 13V.

At medium revs with the lights on, the lights see a flat topped sine wave with a RMS voltage significantly lower than at high revs.

At high revs with the lights off, the zeners are absorbing all of the power of the lighting coils making them highly stressed.

I am considering fitting a LED headlight bulb ditching the AC regulator and installing a separate rectifier, capacitor and series regulator just for the headlight.

With the lower current taken by the headlight (1.6A as opposed to 5A) it should be far brighter at low revs and as LEDs are resistant to vibration and last a long time AND I may as well keep the headlight on all the time.

Has anyone done anything similar?

I think if I was going for DC lighting, I'd just use all the alternator output to charge the battery with. There is an established way of doing this, I think it involves pairing the orange and yellow wires onto one each of the violet wires and running them into a replacement reg/rec that can cope with a higher output. There's a bit more to it than that because you need to get overlapping AC waveforms and you can't tell by looking which violet you want to pair up to. Others will be able to advise more specifically. You'll probably need to use a different headlight switch (eitherr off an older model or a jap bike) to deal with DC lighting, the existing one that deals with both AC and DC is... complex.



There is a chance you may be able to use the AC through an LED headlight bulb. I am currently experimenting on just this, watch this space as I have a (cheap) bulb in the post as we speak to try out. Not something I want to experiment on with a £50 bulb. My research indicates you need one with a non-polarity or positive earth design which has an extra bit of circuitry that feeds it power the correct way regardless of how it's connected.

The “convert to DC” seems to be the usual suggestion. But here is a lot of stuff between the battery and the headlight


Battery

Wire to fuse

Fuse

Fuse to harness

Harness connector to ammeter

Ammeter

Ammeter back to harness connector

Harness connector to ignition switch

Ignition switch

Ignition switch back to harness

Harness connector to lighting switch

Lighting switch

Lighting switch back to harness

Harness connector to dip switch

Dipswitch

Dipswitch to harness connector

Harness connector (finally) to bulb


I measured the volt drop to the 4W pilot light and I got 0.73V. That indicates about 2 ohms in the path above (excluding the dip switch). If I put a 55W bulb on the end of that I’d only get about 7V. I guess that is why folk start adding in relays or doing a full scale rewiring job.

If the original alternator is getting a little long in the tooth you can always replace it with a Lucas RM21 or a Sparx 005 and a modern single phase reg/rectifier unit. If it's still in good nick I don't see why you can't convert the AC headlamp feed to DC with its own reg/rectifier unit and a capacitor. Our hosts sell the Boyer Powerbox in a single phase version which will do the trick, though you can get other reg/rectifiers with built-in capacitors cheaper. I'm planning to use one, no, two of these with one of my project bikes which has the CDI ignition (6 wire) version of the AC headlamp alternator.



A.

If the original alternator is getting a little long in the tooth you can always replace it with a Lucas RM21 or a Sparx 005 and a modern single phase reg/rectifier unit. If it's still in good nick I don't see why you can't convert the AC headlamp feed to DC with its own reg/rectifier unit and a capacitor. Our hosts sell the Boyer Powerbox in a single phase version which will do the trick, though you can get other reg/rectifiers with built-in capacitors cheaper. I'm planning to use one, no, two of these with one of my project bikes which has the CDI ignition (6 wire) version of the AC headlamp alternator.



A.

Don't know why that duplicated, read whichever one you prefer. A.

What Aethelric says is true. HOWEVER you can just use the switch output to trip a relay, thereby powering the light direct from a fused feed from the battery with minimal/no drop in power. This works well on many bikes with shitty switchgear (and enfield switchgear IS shitty, I've owned one long enough to know).

Hi Stinkwheel, wouldn't you need two relays, one for main and one for dip?. Unless you still send it through the LH switchgear

The main reason for the mod though is because I suspect AC regulator is not ideal. I believe it only produces a clipped sine wave and the rms power (which is all a filament lamp cares about) will vary with speed.

If I installed the DC regulator arrangement I'd be putting it close to, maybe in, the headlamp assembly. All would be AC then rectified, regulated, and sent to the dipswitch.

OK, I can't get more than the alternator gives out, but maybe I can make better use of it.

It will be a job for the winter though.

Just a thought, Aethelric - if you're talking about 5A current being drawn for the headlights at the moment, presumably you have a 60W H4 headlamp bulb fitted.



If the alternator struggles to power a 60W H4 at lower revs, why not fit a lower powered H4 bulb which will actually glow more brightly at lower rpm? A 35/35W, which you CAN get in 12V H4, needs just under 3A. Unless you do a lot of night riding I'd give it a try. A very quick mod which saves fundamental changes to the bike's electrics and cheaper than the cost of a LED H4 replacement and a DC reg/rectifier. If that doesn't meed your needs you've not wasted a load of money, and you can still carry out the DC/LED conversion during the winter as planned.



A.

I'd have thought using "clipped" ac was about as efficient as you'd get? If you rectify a single phase, you'll just be getting the top half of the waveform.



There are all sorts of ways of doing relays. I'm actually looking at a way of getting AC to the headlight and DC to the position and taillights from a single switch output due to unusually narrow power supply constraints of my chosen alternator. "Dual filament" LED stop and tail bulbs don't work well on AC (they will work, it's just there is no difference in brightness between stop and tail) but I have so few Watts to play with, I pretty much have to use the AC output for something. It will involve DPDT relays.