Hub Dynamo efficiency comparisons?

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Tony1951
Posts: 18
Joined: 11 Nov 2015, 4:38pm

Re: Hub Dynamo efficiency comparisons?

Post by Tony1951 »

Brucey wrote:re the magnet issues; if you have a spare stator you can simply slide the magnet onto that and it will 'keep'. If you don't have one, it is OK (or at least not terribly harmful) to slide the magnet half-way off the stator. You can do this in both directions and therefore clean, measure and correct the stator all over its working surface.

BTW folk have replaced the magnets with modern types and indeed the output goes up considerably; more volts and (surprisingly) more current too. More drag also, obviously...

cheers


Thanks for the info Brucey.

I was thinking vis a viz the voltage doubler that if I could have got hold of some Schottky diodes instead of using 1n4001 silicon diodes, I could have saved a whole VOLT in losses on that Raleigh Twenty set up that I gave to my daughter in law. I just looked up the price of 1 amp Schottky diodes and they are dirt cheap and the saving would be worthwhile as with an extra volt the lights would come on at a lower speed and be brighter at riding speed.

I can't really use the idea of 12v LEDs on the Superbe as the battery backup unit rectifies the hub output, but I might use my bike to make a testbed for the idea. If I simply switched off the installed lights and connected a doubler and a pair of wired in 12v LEDs to the hub directly. I could test the current and voltage available with the bike on a stand or upside down by turning the pedals and taking the measurements. On my six volt system I made new measurements and with 2 parallel connected 6v leds which I think are about 1 watt, I just got a max output of 210mA out at 8 volts with a hard pedal thrust in top gear from the Superbe. This equates to 1.68 watts. Maybe running flat out down a hill with the rider doubled over the bars it might reach the stated 1.8 watts capacity, but it could be that the difference between measured and stated output are down to the rectification in the Filter Switch Unit. The disparity looks to be about what might be expected.
Last edited by Tony1951 on 25 Nov 2015, 11:40am, edited 2 times in total.
Tony1951
Posts: 18
Joined: 11 Nov 2015, 4:38pm

Re: Hub Dynamo efficiency comparisons?

Post by Tony1951 »

Just found some posts from Edocaster, and Sa_sa from Nove 20th which I had missed. Thanks for the points about forward voltage and nicad / nimh overcharging and trickle charge rates. I'm not sure if I mentioned that I'd bought a six pack of D size alkalines for about £7. Each set of three ought top last about 40 hours on standlight duty for £3.50 a set..... Less than £0.10 an hour. At that rate, it probably isn't too worthwhile to buy a set of three Nicad or NIMH for about £12 and start butchering my original battery rectifier unit. The FSU doesn't look too easy to take apart and it is not the kind of thing it would be easy to replace with another working unit, so I might just leave it as it is for now unless my system goes wrong. The other alternative would be to just fit NIMH cellls in due course remove them for charging now and then.

Thanks for the info though. I am learning a lot from the inputs you made.
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