Maximum number of lights connected to Dynamo hub?

[flake99please]

I am in the process of deciding on what lighting to fit to my recumbent trike. I already have the Son Dynamo on order, and would ideally like to fit numerous LED lights (2 front, 3/4 rear). I would also like to have a spare power output for charging mobile/gps or other USB device.

Would a single hub have the output capacity to power all of this? If not, would 2 hubs have the capacity? Failing that, is there a commercially ready & available 'power bank' which could supply the necessary output needed, which the 1/2 hubs could keep topping up, or do I need to build something from scratch myself?

 

[mjr]

I think they're 6V 3W nominal, with front lights being 2.4W and rear 0.6W but many LED rears are much lower and so the fronts take advantage of any spare. I can understand a trike wanting to have two rear lights, but why two front and 3 or 4 rear?

Dynamo lights tend to be much better-designed than battery ones, so it's realistic to just fit one good one of each and leave it at that.

 

[Ian H]

The more you connect, the higher speed you have to attain before the lights come on. You would also have to check that the front lights would play along. Probably wire them in series rather than parallel. You might be better off having back-up battery lights. The SON runs up to about 18v at high speeds.

 

[flake99please]

but why two front and 3 or 4 rear?

Im considering using the front mudguards for the front and rear lights as opposed to the front mount. Additional rear lights for rear mudguard and possibly behind the neck rest.

 

[DRHysted]

On the Boardman I have 2 B&M front lights mounted on the lower forks, a rear rack light, and a rear mudguard light. All running from a single Shimano hub without issue.
I think that there is a slight difference in light output from the Allez which is fitted with 1 B&M front, a rear rack, and a rear seat stay light. But that difference could also be explained by the Allez having the light on the crown, whereas the Boardman has the 2 lights slightly higher than the brake discs (I had issues fitting them and had to adapt some mounts).

 

[andrew_s]

A dynohub will give 3 watts at 5-6 mph, and something like 6 watts at 13-14 mph, and maybe 7 or 8 watts at 22-23 mph, PROVIDED THAT there's a suitable load attached to it. If there is a suitable load, the hub will supply up to a maximum of a bit over half an amp, at a voltage that's determined by the speed.
The 6V 3W for a bike dynamo is what you get when your suitable load is a 12 ohm resistor, such as old-style bike light bulbs, rather than a property of the dynamo

If you connect lamps in parallel (i.e.direct to the hub), the current is split so that you hit the current limit before requiring a higher voltage, and with a second light you effectively get 2 lights running at half power rather than one light running at full power. If the lights are different models, the power split probably won't be even.

If you connect the lights in series, you can get them all to light up fully provided that you are going fast enough and there aren't too many of them, and they may also be subject to a minimum speed as Ian H notes. If you aren't going fast enough, they won't be at full brightness.
Series connection also means that if any one light is turned off, none of them will light up. Senso switching one more than one lamp may give problems in this respect.

I'd expect that one hub will be usable for your lights, but that if you want USB power at the same time as lights, you'll need the second hub for that.

The general report is that having one front/rear light pair and an eWerk running together has a noticeable impact on both light output and charging rate.
There have also been reports that the cache battery in a USB-werk or Luxos-U will supply any shortfall between generated power and required output power, but that when the cache battery runs down, the USB charging gets cut off until the cache battery is sufficiently recharged