1.5v dynohub

[NUKe]

Anyone have any experience of the new generation of 1.5v hub dynamos for example the shimano deaore Xt dh T&85
or the SP series 8,
Main reason is to use with a small wheel bike. I assuming they will power modern LED lights no problem as they 6v, but less surplus power for phone/ gadget charging not an issue for me.

[james01]

I've had no experience of the low wattage dynamos but on the basis that the standard 6v dynamo front and rear lamp set requires a nominal 3 watts, you should expect poor performance unless you specify lights which have been downgraded accordingly. In view of limited choice of such lights, I don't think low wattage dynamos make a sensible choice at the moment. Incidentally, the slight gain in drag from the lower wattage outfit must be almost immeasurable.

[Mick F]

No real answer to this question, but a small observation regarding modern LED torches.

We've had an LED torch for some years and it takes three AAA batteries in series = 4.5v nominal. LED Lenser is the make.

Bought a new one a week or so ago and it takes one single AA. LED Lenser also.
It's FAR brighter than the old one ever was and only needs 1.5v nominal. The beam appears to go well over 100yds. £20odd well spent IMHO.

Therefore, why not have a 1.5v bike dynamo?

[gloomyandy]

I don't know much about these but I assume this is actually 6V 1.5W not 1.5V?
https://www.rosebikes.com/article/shima ... aid:742795

[Brucey]

Anyone have any experience of the new generation of 1.5v hub dynamos for example the shimano deaore Xt dh T&85 or the SP series 8, Main reason is to use with a small wheel bike. I assuming they will power modern LED lights no problem as they 6v, but less surplus power for phone/ gadget charging not an issue for me.

I think you perhaps have a misunderstanding; low power hub generators produce 6V, 1.5W, not '1.5V'.

Thus these generators produce a nominal 6V, 250mA into a suitable load, where a standard 6V, 3W generator would produce 500mA into a suitable load. The output is usually tested using a simple resistive load.

Having said this, it isn't as simple as that, in that most hub generators will produce more power than their nominal rating at speed, provided they are presented with a suitable load (that isn't a simple resistor). However you can expect less power at all speeds with a '1.5W' generator vs a '3W' generator, and (depending on the design of the lamp electronics) some 3W lights won't ever get fully bright at normal speeds using a 1.5W generator, even on a small wheeler.

cheers

[tatanab]

Yes, the unit is Watts not Volts, the dynamo is still 6V. It is intended to be paired with 1.5W headlamps such as https://www.sjscycles.co.uk/lighting/0- ... b-dynamos/ I believe that these are intended a lights that are more than adequate for city riders.

[NUKe]

Sorry that was a typo 1.5W not 1.5v, its still six volts nominal.
My mistake the SP is 3w after all.

So the question is slightly different, why do say the 3N80 have a minimum wheelsize?

[Brucey]

possibly the output becomes too much and this would then blow the bulbs in a 'standard' tungsten bulb setup. Remember that the '3W' generators are built to meet a now-archaic DIN standard.

Modern lamps generally handle excess power differently (better) than that; for example many modern LED front lamps just draw more and more current if the voltage gets to about 5V, and most hub generators won't produce more than about 700mA even into a dead short. This can then limit the power to about 4W regardless of speed.

The same generator might be capable of producing over 50V into an open circuit, and likewise might be capable of powering two or more 6V,3W lamps in series.

The primary advantage of the shimano 1.5W generators is reduced weight. But they are not appreciably lighter than a 3W SON anyway.

cheers

[Mick F]

Well, that makes my post looking a little stupid.

However, I wonder what power our little torch consumes?
One single AA Duracel.
It's really really bright, and small and light too.

If 1.5v can produce a good bright light, why can't a bike generator be 1.5v to supply two of them .......... one front, one rear?

Ok, we have an AC/DC thing going on here, and AC voltage isn't the same as DC voltage.

[mercalia]

well I would like a bottle with the ops spec - the ones we have are a throw back to filament bulb days. over kill for my Axa pica30 I imagine it would run much smoother and offer less resistance to the wheel? shame wont get one now