Are bottle-dynamos directional?

[glasgowcyclist]

I hear what you are saying and I am sure that quality modern set-ups are 'light' years ahead of the stuff most of us are basing our opinions on but, how much does such a set-up cost (including having a wheel built with the dedicated hub)?

My SON hub was £150, including wheel, over two years ago. You can get an excellent B&M Cyo front light for around £30 and a tail light from £6 upwards. Considering the dynohub is guaranteed for 50,000km this represents a solid investment that will probably outlive my bike.

GC

 

[Tim Hall]

I hear what you are saying and I am sure that quality modern set-ups are 'light' years ahead of the stuff most of us are basing our opinions on but, how much does such a set-up cost (including having a wheel built with the dedicated hub)?

The OP sounds as though he is struggling with a product straight out of the 70s or 80s and based on that assumption I will stand by my advice to chuck it in the bin and get some 'light' modern LED lights.

I'm kind of with you. That bike over there has battery powered LEDs, from B&M. New and shiny and very good.
That bike over there has a mounting bracket for a bottle dynamo but I now use a hub dynamo with five or six year old shiny LED light.
I don't know how long the batteries will last as I've only had the light a week. I'm hoping for a whole Friday Night Ride's worth, but will take spares. The dynamo just goes. It doesn't have a standlight (due to an ordering mix up when I first bought it) but such things are available.

To the OP, my bottle dynamo was mounted on the right fork even though it was a left fork dynamo. This meant the bracket was on the rear face of the fork, so the spinning action of the wheel tended to pull the dynamo into the tyre. It could be this is what you're experiencing. (note that dynamos mounted back to front as I had it must be done up securely. If it comes loose, it'll jam between fork and wheel, stopping the bike dead).

 

[Richard A Thackeray]

Double-post

Sorry, now edited


'See below'

 

[Richard A Thackeray]

Don't be daft - all the electricity would fall out.

On the bright side, as when it falls out, it's just smoke - well that's what normally happens with car electrics

Therefore, Lucas (the Princes of Darkness) sell replacement smoke. In a Jar!

 

[Windassisted]

I suppose the scientific crux of the issue is that spun backwards a dynamo will generate CD current instead of DC. This will no be efficient if your light bulbs are DC , you will need CD light bulbs and also you must reverse the light cabling.

 

[themosquitoking]

If that's the case could a switch of positive and neutral wires somewhere solve it?

 

[Drago]

If you're running regular bulbs it makes no difference with most of them.

 

[tyred]

I suppose the scientific crux of the issue is that spun backwards a dynamo will generate CD current instead of DC. This will no be efficient if your light bulbs are DC , you will need CD light bulbs and also you must reverse the light cabling.

A bicycle dynamo is actually an AC device so it would infact produce CA current. If you feed CA current to an AC halogen bulb, the bulb will explode in a puff of pink smoke whereas traditional vacuum bulbs will explode in a puff of green smoke.

DOn't try this at home kids

 

[themosquitoking]

But you make it sound so pretty.

 

[Soltydog]

I hear what you are saying and I am sure that quality modern set-ups are 'light' years ahead of the stuff most of us are basing our opinions on but, how much does such a set-up cost (including having a wheel built with the dedicated hub)?

The OP sounds as though he is struggling with a product straight out of the 70s or 80s and based on that assumption I will stand by my advice to chuck it in the bin and get some 'light' modern LED lights.

Probably not as much as you think. The OP has the lights, so would only need a dynamo hub - http://www.spacycles.co.uk/products.php?plid=m2b0s170p1793

 

[Gravity Aided]

If that's the case could a switch of positive and neutral wires somewhere solve it?

No, the electrocity would fall out of the switched wires. This is called a voltage drop. That's why some trucks have those strips trailing off the chassis, so they can pick up the dropped voltage from when they fiddle with the wires. In answer to the OP's actual question, I think the idea would be to fit the dynamo a bit tighter to the tire, but that may cause increased tire wear. They used to make some sort of little cover for the wheel on the dynamo, that functioned sort of like a tire. Maybe a piece of tubing would do the trick.

 

[Chris S]

Last night I dropped the dynamo to the bottom of it's slot so different parts of the tyre/friction wheel made contact. There was much more light when the wheel was spun forwards but no difference when it was spun backwards. It does seem to be some sort of wear problem

 

[Richard A Thackeray]

I think the idea would be to fit the dynamo a bit tighter to the tire, but that may cause increased tire wear. They used to make some sort of little cover for the wheel on the dynamo, that functioned sort of like a tire. Maybe a piece of tubing would do the trick.

SJS have a range of Dynamos & spares (including roller-covers)
http://www.sjscycles.co.uk/dynamos-dept880_pg1/

 

[Pale Rider]

I have a working Brompton bottle dynamo which any dyno fan on here is welcome to.

There's a break in the cabling somewhere - often happens with the fold - but the bottle churns out power.

The soldered terminals are visible underneath, so anyone reasonably handy could rewire it.

 

[Cyclopathic]

I hate dynamos and seem to kill them as soon as I touch them. Leds all the way.