6v 2.4w dynamo - can it run two lights?

Althusian

I've recently picked up a Dawes Geneva gents bike with a Shimano DH-2N30-E 6v 2.4W dynamo hub on the front wheel. At the moment it powers a front light, Basta 9430/2925 wiht 6v. 2.4w halogen.

Q.1 I'd like it to power the rear light too (I have an Axa Riff Steady, an LED light) but I've been told the dynamo won't have enough power. Is that true, or - if I got an LED front light - would it run both? This'd be my favourit option. But ...

Q.2 If I can't have my cake and eat it ;-) and can only run one light off the hub, I'd like it to be the Axa rear light. But I've read that if I only plug the rear light in, it'll blow from too much current.

Any comments/suggestions gratefully received!

lesfirth

Your dynamo output will be AC ( alternating current). LED bulbs need DC ( direct current). AC can be rectified to give DC but I am not aware of a bit of kit you could buy off the shelf to do the job on your bike.
The" blowing the rear light from too much current" is rubbish. You could run a rear lights of any wattage up to 2.4W or a front 1.2W bulb and a rear 1.2W bulb.
The best plan is to give the dynamo to a local museum and get some LED bike lights.

Althusian

Thanks for the info. Good suggestion about LED lights - just a shame to bin a working widget and replace it with more widgets if I could have got it working!

monkimark

You can get LED dynamo lights - I guess they have the rectifier built in to them. But I think the ones I have seen have the rear light connected through the front light so you'd probably need to buy 2 new lights to make it work.

Althusian

Thanks both - things are looking a bit clearer now!

andrew_s-2

You can run two lights off your dynohub, but it would be considerably better if you also replaced your existing halogen light by an LED version.
A halogen light would go pretty dim if the rear light sucked too much power, whilst the effect on an LED light would be relatively minor.

Suggestion:
https://www.sjscycles.co.uk/lighting/busch-muller-lumotec-iq-avy-nplus-headlight-for-hub-dynamos/

A rear light would normally be connected to the front light so that it can be turned on & off.

The great advantage of dynamo lights is that they are always bolted to the bike, so you don't need to take them off when you park the bike, or decide in advance whether you'll be out after dark or not.
Not needing to charge them or swap batteries is a subsidiary advantage.

Althusian

Thanks andrew_s-2, that's very useful. Got an LED front light on order, we'll see how it goes. I totally agree with the advantages you mention about dynamo lights - there's times when I don't have the time/space to ponder decisions on lights, they just need to be there.

Althusian

So I now have an Axa 606 Steady Auto Dynamo Headlight, Axa Riff Steady Rear Light fitted (both LEDs), powered by a Shimano DH-2N30-E 6v 2.4W dynamo hub. All works fine, and you only have to cycle thirty yards and you have four minutes (at least, on my rig), of backup light if you stop. Cabling was a bit of a faff, these things all use dinky spade connectors wot you cannot buy at Screwfix. And of course there's a bit of a question mark over how durable the cabling will be, and how well it'll work in the pouring rain! But for the moment it's great I'm a happy bunny. Thanks for all the advice!
Update: the Axa 606 Steady front light is switched, 'on' and 'auto'. On 'auto', it'll come on in the dark (or just poor light, it doesn't take much). In bright light, it'll go off, of course. The rear light however, stays on whatever the switch at the front says. Not a problem - there's lots of times when a rear light is a good idea, even in daylight.

Althusian

UPDATE: front light still works fine, Axa rear light has failed :-( I checked the wiring 'n' all, should work OK.
so, either:
-- Like everything else these days it's made in China and QA isn't great, or
-- The AC from the Shimano hub killed it (front LED still fine though)
Any opinions/advice before I get another rear light?

andrew_s-2

Almost all bike dynamos are AC, and almost all bike lights that are meant for dynamo use are designed for use with AC. This includes both your dynamo and your lights.

Most dynamo lighting problems are due to wiring faults.
Both the front light and the rear light should have two connections for wire and/or spade terminals. One will be marked with a symbol for "live" (usually a lightning bolt zigzag), and one will me marked with a symbol for earth/mass (usually a bent 3-prong fork). You've got to make sure that the same wire core is connected to the same symbol at each end.
If the wires are crossed over, it may work, but you are relying on a bad contact somewhere to prevent a short. An example of a bad contact may be between the body of one of the lights and the bike frame, and repositioning the light a couple of times, or road vibration, may make the previously non-conducting join conduct, and short the light out.

By way of a test, you can connect the problem rear light directly to the hub using two wires, having previously disconnected the front light.
If it doesn't come on when you spin the wheel, it's dead. LED light failures are uncommon, but they do happen sometimes.

Althusian

Thanks very much - could well be a wiring problem, I'll update after some more ferretting about ...