Power two taillights with one dynamo?

[RonS]

So, I have a B&M IQ Cyo headlight and a toplight line taillight powered by a Shimano 3N72 hub dynamo. The toplight line supposedly makes it easier for motorists to judge distance. I think it would be easier still if the bike had two, separated lights, the toplight on the rack and perhaps the new Secula on the fender.
I have no idea how much current the new LED lights draw. Do the German regs require  LED lights to draw 2.4 and .6 Watts like the old incandescents, or would a 3W dynamo be up to the task?

[martinf]

I have a 3W hub generator, it powers two rear lamps (B&M Line Plus on the rack and Seculite on the mudguard) and one front lamp (B & M Cyo 60).

My generator is a SON Klassik, any other 3W generator ought to work as well.

With the extra rear lamp, you might need slightly more speed to get the lamps to the same level of brightness, but I haven't noticed any difference.

[Aushiker]

I am pleased I decided to check in and use the search function

I am thinking of running two Busch & Muller Busch & Muller Secula Plus for Seat Post or Stay (331/2ASK) rear lights in-combination with a Busch & Muller Lumotec IQ2 Luxos U front light.  All of which will be powered by, a SP PD-8 dynamo mounted in a 20" wheel.

Sounds like this might be a go.  Fair call?

Regards
Andrew

[Danneaux]

Fair call?

Hi Andrew!

While I have not used this exact combination myself, I'd say it falls firmly into the "should work" category.

Worst-case, you could sell-on one of the Seculas and substitute an LED blinky if the two didn't work, but I think you'll be fine.

Best,

Dan.

[Aushiker]

Hi Andrew!

While I have not used this exact combination myself, I'd say it falls firmly into the "should work" category.

Worst-case, you could sell-on one of the Seculas and substitute an LED blinky if the two didn't work, but I think you'll be fine.

Best,

Dan.

Thanks Dan.  I think I will give a shot. I have read but that the Secula does draw "high power" so I may loose a touch of front light I guess.

Andrew

[RonS]

Just got my shipping notice from Bike24 that the Secula is en route. I should be able to report in a couple of weeks how well a Secula / Toplight Line Plus / IQ Cyo combination works. If two taillights draw too much current, there is a battery version of the Toplight Line.

[Aushiker]

Just got my shipping notice from Bike24 that the Secula is en route. I should be able to report in a couple of weeks how well a Secula / Toplight Line Plus / IQ Cyo combination works. If two taillights draw too much current, there is a battery version of the Toplight Line.

That would be great.  I don't have a rack on the bike so the likes of a couple of Secula appeals.

Andrew

[Hirtshals]

I have to IQ Cyo headligts on my bike and a flashing batterylight.
http://www.flickr.com/photos/bicycletour-dk/11407643984/in/photostream/
Best infoside
http://www.peterwhitecycles.com/wiringinstructions.asp

[Danneaux]

Good news from your practical experience and usage, Andreas; thanks. For a long time, Thorn/SJS Cycles made a very nice mount for dual headlights that proved helpful with those mounting needs, but it appears they're down to just the single light version now: http://www.sjscycles.co.uk/thorn-alloy-dynamo-headlamp-bracket-m5-fork-crown-mounting-black-prod12373/?geoc=us

I'll miss the availability of the double headlight bracket if it is now truly gone; it was a beauty!

Best,

Dan.

[mickeg]

I am guessing that two tail lights in parallel would work ok.  But if you find you are draining too much current from the head lamp, then try running the tail lights in series.  They might be dimmer in series however so I would try parallel first.

My thoughts above are only a guess, I have run two headlights in series without a tail light.  (My taillights are battery powered.)

[martinf]

I am guessing that two tail lights in parallel would work ok.  But if you find you are draining too much current from the head lamp, then try running the tail lights in series.

On the two bikes I have with two rear lamps powered by the hub generator they are connected in parallel.

I haven't tried series connection, but suspect that it wouldn't work well with LED lamps.

[Aushiker]

I have two of the Secula lights on order from Bike24.net so I guess I will find out soon enough if they will work or not

Andrew

[Andre Jute]

On the two bikes I have with two rear lamps powered by the hub generator they are connected in parallel.

I haven't tried series connection, but suspect that it wouldn't work well with LED lamps.

LED bicycle lamps are designed to drop or to be made up in sets to drop the 6V nominal that a hub dynamo produces. This could be one lamp dropping a notional 3W, or a headlamp at 2.4W plus a tail lamp at 0.6W. In the filament and halogen days, BUMM lamps used to tell you in the specs and also in the serial number whether the headlamp was 3W or 2.4W, and all rear lamps were 0.6W. Today you may assume that a front BUMM LED lamp with an outlet for a tail lamp will drop 6V with or without the tail lamp attached. An additional lamp or set of lamps must thus be fitted in parallel. There may be exceptions (perhaps where the LEDs are supposed to do double duty as rectifier diodes, in which case they would be wired in opposed series-parallel, recommended for DIYers who know what they're doing) but I don't know of any in the sort of commercially sold lamps we would normally consider. These considerations are slightly, but only slightly, complicated by the knowledge that almost all common dynamos running without load will rise at the output to at least 7.2V and some higher, because the nominal 6V rating presupposes full load. But modern LEDs are quite strong, quite possibly today more sensitive to overheating than to moderate overvolting, so breakages are likely to be rare.

SUMMARY
The safe thing to do with LED lamps in the absence of hard information, knowledge and instruments, is to series one headlamp with one tail lamp, and to parallel the next lamp or set.

[martinf]

SUMMARY
The safe thing to do with LED lamps in the absence of hard information, knowledge and instruments, is to series one headlamp with one tail lamp, and to parallel the next lamp or set.

With a headlamp designed to work with a hub generator (i.e. with a manual or automatic switch), is the tail lamp connected to the headlamp output working in series or in parallel ?

I thought the only reason not to connect the tail lamp directly to the generator (so in parallel) was to benefit from the on/off switch in the headlamp.

With bottle dynamos, I always connect the headlamp and tail lamp in parallel, three of the family bikes still have this setup.

[Andre Jute]

With a headlamp designed to work with a hub generator (i.e. with a manual or automatic switch), is the tail lamp connected to the headlamp output working in series or in parallel ?

I thought the only reason not to connect the tail lamp directly to the generator (so in parallel) was to benefit from the on/off switch in the headlamp.

With bottle dynamos, I always connect the headlamp and tail lamp in parallel, three of the family bikes still have this setup.

Well, you would mount two filament lamps, 6V each, in parallel. You would also mount in parallel two LED lamps, one 6V, one a lesser voltage but with a built-in circuit to reduce 6V form the generator to whatever voltage the LED requires.

In each case it depends on what protection circuit for the lamp is already in place.

The advantage of a series connection, if the voltages of the LEDs add up to generator voltage, is that no energy is wasted in heating dropper components. But, if there are other circuits already built into the lamps to control the voltages, then parallel connection would work best.

At bicycle voltages/current you are unlikely to do much damage if you get it wrong.