Front and two rear lights from one dynamo?

[Trikeyohreilly]

Hi. I have a Shimano dynamo hub from which I have been running a B+M Cyo T and a rear light. I would like to try and run a second rear light at the same time. I have no idea what this may do. I'm guessing that underpowering won't damage them and I already have them.

Unless I really shouldn't experiment with this how would I wire it? Just spilt the front light output from one wire to two and run it to the rears?

[Trikeyohreilly]

All three lights seem to be working perfectly, at least as much as I can tell from spinning the dynamo hub wheel by hand in a dark room. If I actually rode it though for a decent distance am I going to break something?

[alexnharvey]

Are you running a single wire or a double wire to the rear currently?

The easiest way to me seems to be splitting at the rear of the bike, by connecting two new pieces of wire to the current end(s) and then connecting these to each light.

Assuming they're both led lights it should work just fine.

[slowster]

If one of your rear lights is a B&M Toplight Line Plus*, it has two sets of connection points - one which accepts spade connectors and another which accepts bare wire. With that rear light I think you would be able to use the spare set of connection points to power a second light.

* I guess that other B&M rear lights designed for mounting to a rear pannier rack bracket may also have two sets of connection points.

[rjb]

Increasing the number of leds just increases the power output from the dynohub to supply the connected load.
from this site http://pilom.com/BicycleElectronics/DynamoCircuits.htm

[Trikeyohreilly]

That's great news. Thought I might brake something.

I do have a toplight line brake version that does have two sets of connectors. But I using the mini line rear lights that are just the 50mm mount with a small LED in the middle.

As these don't have double connectors I have mocked up, to be done properly later, the double wire leaving the front light running to the back of the bike. Then joined one each of those wires to one each from both the rear lights, so three wires joined together. Seems to work.

Who knew a dynamo would put out more power when more LEDs were added? Magic.

Thanks for the information

[MikeF]

If one of your rear lights is a B&M Toplight Line Plus*, it has two sets of connection points - one which accepts spade connectors and another which accepts bare wire. With that rear light I think you would be able to use the spare set of connection points to power a second light.

* I guess that other B&M rear lights designed for mounting to a rear pannier rack bracket may also have two sets of connection points.

On one bike I have three back lights on a rear carrier; two B&M secula on each side and an obsolete Philips in the centre All wired in parallel and powered from aShimano DH3N80.

[Trikeyohreilly]

I surprised this is not more common knowledge. Why not have a second rear light? Perhaps it is and I'm just not very knowledgeable. Perhaps the extra output reduces the life span of the dynamo?

[CXRAndy]

You can happily run 3 led lights from a Shimano 3W hub. You can even charge a phone with a usb adaptor

[nigelnightmare]

I've been running 2 rear lights from a dynamo for over a year now with no problems (one on the trike & one on the trailer).
I have plenty of light output from 3mph with the trailer & from 2mph without.
HTH

AS shown above
As the power output rises with more lights in the circuit so does the resistance.
I.E.
It get's harder to turn the wheel.
I only notice it when turning the wheel by hand, not when riding the trike.

[rjb]

And did anyone notice that the minimum speed to light the LEDs increases with the number fitted. so if you had 6 LEDs they wouldn't start to illuminate until you reached 8 km/hr and wouldn't reach full brightness until 25km/hr.

[MikeF]

....... Perhaps the extra output reduces the life span of the dynamo?

It shouldn't make any difference with a hub generator as there aren't any moving parts apart from the hub which will turn anyway with cycling. More lights need more power (from you) and the light output might be slightly lower at low speeds, but I haven't noticed much difference. It seems to take slightly longer for the standby capacitors to fully charge, but that might be expected.

[Trikeyohreilly]

This is all great news. I'm going to do it for sure. Just one question left... I having problems with my dynamo hub wheel build again so might need another. I think I remember that there is a difference in the polarity? or something between Shimano and SON. Is this true or will swapping the hub make no difference to the system or the wiring? Thanks again those who have help me with this.

[Brucey]

some (not all, not most of the recent models) shimano generators have one connection grounded. You can't substitute a SON for one of these if the earth return is used, not without modifications to the wiring. Nor can you use a shimano generator (of this type) instead of a SON if there are ground connections in the lamps (which is often the case), not without taking account of it, anyway.

If it is a groundless shimano generator, you can swap it for a SON no worries.

Easiest thing to do is to fit the alternative wheel and to try it. If the lights don't come on, you know there is a problem.

cheers

[Brucey]

Increasing the number of leds just increases the power output from the dynohub to supply the connected load.
from this site http://pilom.com/BicycleElectronics/DynamoCircuits.htm

worth noting that rear lights have a nominal power of 0.6W (0.1A @ 6V), but very many LED rear lights use a lot less than that. Thus the curve for one front light and one rear might be most like the orange curve above, and if you add another 0.6W rear light the load is only 20% more so the speed at which you get good light will be barely affected. In reality an extra rear light will probably use a lot less than 0.6W; some use just 30mA or so. You could have three or four of these together with a front light and it would all still work fairly normally.

cheers