Schimdt and B&M

[Chris Land]

Can you fit the extra Schmidt light in line with a B&M Oval Tech first light, running off a Schmidt hub?  

I want the extra light, but am not good at wiring and don't want to have to replace the B&M I already have fitted - partly cost, but also I don't think the Schmidt lights don't have a standlight.

[Dave Whittle Thorn Workshop]

Hi, you can run any primary light but it must be the Schmidt secondard light to work properly.

Dave dave@sjscycles.com 01278 441542

[Chris Land]

Cool - I'll pick one up with my next pay cheque then.  Starting to get a bit too dark on sections of the commute home...

[Dave Whittle Thorn Workshop]

Also note unless you travel @ high speeds, i.e. above 20mph you are better off with 2 2.4 bulbs rather than 2 3W bulbs, this will reduce the load and make you go faster.

[Chris Land]

quote:Originally posted by Danger Mouse

Also note unless you travel @ high speeds, i.e. above 20mph you are better off with 2 2.4 bulbs rather than 2 3W bulbs, this will reduce the load and make you go faster.

Thanks for this.  I was assuming, in my complete ignorance of things electrical that the energy for the extra bulb was already being produced at higher speed.  But you are saying that switching the extra light on increases drag on the hub?

I run a rear light, so have a 2.4 front bulb anyway.  I guess that you couldn't add a 3w to a 2.4w first light?

Sorry for my complete ignorance [:I]

[Dave Whittle Thorn Workshop]

The hub responds to the loads put on it, so if you put 2 x 3wt bulbs on it then the load will be harder to pedal and more effort will be required to get to your usual speed and maintain it.  If you lower the load i.e. 2 x 2.4wt bulbs it will be easier to get and maintain your usual speed. In your case 2 x 2.4wt and 1 0.6wt bulb you will end up with 5.4wt of load which shouldn't be too bad.

As the secondary light is switched you can turn it on when you need the extra light.

Also note this is only aplicable to Schmidt dyno hubs up to 6wt, if you load any other hub or rim dynamo up this much you will probably burn it out.

P.S. Lightspin generators will run @4.8wt acording to Lightspin.

[PeLu]

DangerMouse:

Have you tried this with a SON?

The SON is more a constant current source, not a constant voltage one (as most bicycle generators). It 'wants' to deliver a little more than 500mA. When you use a rear light with it, you take the 2.4W bulb, otherwise the 3W. There is no joice. The second bulb has to be a 3W one (because it has no rear light in parallel).
Using just a 2.4W bulb alone will result in a much brighter light at a very low lifetime. And as the voltage goes up, the generator needs more input power, but you will not be able to tell it.