Author Topic: Two rear dynamo lights  (Read 1638 times)

Two rear dynamo lights
« on: 17 February, 2018, 07:46:40 pm »
Hi all,

I’ve recently become the proud owner of an awesome secondhand George Longstaff upright tricycle. It’s predominantly for icey days, although it’s great fun so I’ll be doing a few audaxes and tours on it as well.

Anyway, I’ll be sticking my SON dynamo hub front wheel on it with a Cyo premium on the front and in an ideal world I’d like a matched pair of rear dynamo lights on the back. My first choice would be toplines or alternatively a pair of seculas.

Would they be significantly dimmed? Does the dynamo kick out enough juice? Has anyone done this?

Thanks!

John

Re: Two rear dynamo lights
« Reply #1 on: 17 February, 2018, 07:52:57 pm »
fitting them in parallel will work fine and will only slightly raise the speed at which all the lights achieve full brightness.

However it may be worth trying the rear lights in series and seeing how this goes; it might work OK for you.

A little research may reveal which rear lights work well at lower voltages and which draw less current than the 100mA 'standard'. This may influence your choice of series or parallel configuration for two rear lights.

cheers

yorkie

  • On top of the Galibier
Re: Two rear dynamo lights
« Reply #2 on: 17 February, 2018, 07:53:01 pm »
I'm running a topline and a secula in parallel on the back of my audax bike (Cyo premium on the front) without any problems. I certainly don't notice any difference between the topline on its own and the pair together. Given the current drain of LED lights, there shouldn't be any major issue with this.

ETA: x-posted with Brucey.
Born to ride my bike, forced to work! ;)

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Kim

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Re: Two rear dynamo lights
« Reply #3 on: 17 February, 2018, 08:03:24 pm »
I've got two Spanninga Pixeos in parallel on the ICE trike (wired through an original B&M Cyo on the front).  They're currently powered from the electric assist battery via a voltage regulator, but originally ran from an AXA bottle dynamo.  Works fine.

With LED lights, the steady-state draw is generally less than the dynamo can supply, so I wouldn't expect a loss of brightness.  It might take a little bit longer for all the standlight capacitors to fully charge.

Series wiring would seem to turn the entire rear light system into a single point of failure (and potentially introduce grounding issues) for little if any benefit.  With parallel wiring, there's a level of redundancy.  Also, series wiring is a really bad idea if the lights aren't identical.

Re: Two rear dynamo lights
« Reply #4 on: 17 February, 2018, 08:24:48 pm »
Sounds promising. I was thinking parallel wiring seemed sensible for redundancy.

Thanks all.

John

Re: Two rear dynamo lights
« Reply #5 on: 17 February, 2018, 08:34:06 pm »
....Series wiring would seem to turn the entire rear light system into a single point of failure (and potentially introduce grounding issues) for little if any benefit.  With parallel wiring, there's a level of redundancy.

Re redundancy, true, but it depends how the wiring is configured.  I would be surprised if separate wires are run all the way from the headlight to each rear light in parallel operation on a trike; I think they would have to be commoned somewhere, eg at the headlight, which is perhaps the most likely point of failure.

Regarding ground faults IIRC the current topline model does not have a bolt that is a ground connection. Dunno about the secula but I think that also does not have a ground connection built into the bracketry.

Because of the low voltage required for red LEDs, if you were going to DIY an efficient setup, series operation for two rear lights would be the best  (simple) way. For example I have a nice bright DIY rear light that only draws 30mA and I could have two in series quite easily.

IIRC at any given wheel speed if you reduce the current draw the voltage output goes up and using some headlights (with clever circuitry) this typically  does increase the light output at modest triking (eg 12-16mph) speeds.

cheers

Re: Two rear dynamo lights
« Reply #6 on: 17 February, 2018, 08:50:24 pm »
Dunno about the secula but I think that also does not have a ground connection built into the bracketry.
It doesn't.
The bolt has a square plate on the end that just sits in a recess in the back of the light body, unconnected to anything else.

Kim

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Re: Two rear dynamo lights
« Reply #7 on: 17 February, 2018, 09:08:13 pm »
Re redundancy, true, but it depends how the wiring is configured.  I would be surprised if separate wires are run all the way from the headlight to each rear light in parallel operation on a trike; I think they would have to be commoned somewhere, eg at the headlight, which is perhaps the most likely point of failure.

Indeed.  You tend to notice failure at (or upstream of) the headlight, though.

Re: Two rear dynamo lights
« Reply #8 on: 17 February, 2018, 10:35:48 pm »
I wouldn't run off-the-shelf rear lights in series without knowing their exact circuit design. There's a fair chance they wouldn't be running full brightness, or the standlight capacitor wouldn't be charging properly/fully, etc.

Re: Two rear dynamo lights
« Reply #9 on: 19 February, 2018, 09:32:26 pm »
I run a couple of home-brew rear lights with supercaps, and it's best done in parallel. Taken together they're designed to consume 0.5W of power. It's 9x 8mm super-bright red LEDs in a new Lucas 525 motorbike light on the rack, and a single one behind a flare lens in any old housing on the mudguard. Either one can run with the dynamo, I just tap off the power cable direct from the dynamo for each of the 3 lights so anything can be disconnected and the others don't care.
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