A collation of dynamo/generator drag/efficiency data

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Brucey
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A collation of dynamo/generator drag/efficiency data

Post by Brucey »

Sturmey Archer marketed their 'dynohubs' from some time in the 1930s until about 1980 or so. I continued to use SA dynohubs through the 1980s and 1990s (the 'dark ages' ho ho); even though they were more feeble than other generators, that was made up for by the reliability of the whole arrangement. SA had a 3W generator which they could have made, but they didn't think it would sell, so it never reached production. Others picked up the baton that SA dropped, and using modern magnets and better design details, this resulted in smaller, lighter, more efficient generators. These more modern hub generators have been with us for about twenty years or so, during which time there has been a lot of testing and much data produced. They vary considerably.

Modern LED lamps make the most of even the most feeble generators so relatively low power outputs from generators are no impediment to being seen. 'Twas ever thus in fact; old SA dynohubs were rated at about 2 to 2.4 W or so; not much, but front lamps were still brighter than the BS -approved battery lights of the time. Across Europe there have been various bicycle lighting standards but one of the most widespread has been the German StVZO standard which calls for a 3W,(6V 0.5A) generator, giving 0.6W (0.1A) rear and 2.4W (0.4A) front, with defined low speed vs power requirements. Looming harmonisation with Europe (anticipating a 3W BS-EN standard similar to StVZO) arguably killed off the old SA dynohub; it simply wasn't powerful enough and probably didn't meet the low speed requirements even pro-rata.

This thread is intended to garner up a lot of the data that has been produced, with images of key results and links to other data sources. I've probably only seen a fraction of what is out there so please post links, charts etc. Only one request; there will inevitably be some but please try to avoid too much duplication.

Most of the test data (from various sources) is in broad agreement with other data but there are anomalies. One is that shimano hub generators are routinely shipped with the cones adjusted too tightly, and not by just a little bit; about a quarter turn on the adjusting cone is quite normal. Ad-hoc testing suggests that the 'lights off' drag of a typical shimano hub can be about halved if it is simply better adjusted and lubricated. I don't remember seeing any tests where they claimed to have done this, so I would view much of the available data as being a little pessimistic and somewhat variable on this point.

For starters;

Image
shows the StVZO boundaries. The 'Japan brand' generator is almost certainly a shimano model (DH-3N30/70/71/80 for example).

Image
the standard StVZO test is to drive a purely resistive 12 ohm load. This means that if you see a test output (with a 12 ohm load) expressed in Volts, then the power (in Watts) is related simply by

Power x 2 = Voltage [edit; it isn't, so ignore that, I was having brain fade... It is actually Power x12 = V^2]

More to follow.

cheers
Last edited by Brucey on 20 Nov 2019, 11:54pm, edited 1 time in total.
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Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: A collation of dynamo/generator drag/efficiency data

Post by Brucey »

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Brucey
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Re: A collation of dynamo/generator drag/efficiency data

Post by Brucey »

the Renak Enparlite is (was?) a clever hub generator with a geared drive (thus allowing the electrical generator parts to be very small) and an external clutch control.

Image

Not sure what the Achilles' heel is of this design, but one feature is that it isn't noticeably more efficient than (say) a tyre driven generator when it is 'on', and is thus pretty draggy at speed.

cheers
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ConRAD
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Re: A collation of dynamo/generator drag/efficiency data

Post by ConRAD »

Brucey wrote:... this means that if you see a test output (with a 12 ohm load) expressed in Volts, then the power (in Watts) is related simply by
Power x 2 = Voltage ...

.. or P[W]=0.5U[V]
Image
SA_SA_SA
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

I wonder how efficiency the enparlite would be if the hub shell diameter was increased to approx common (eg shimano style) generator hub size and only one set of (larger sized cogs) gearing used.

Waning possibly dumb idea (but there was a spoke dynamo reviewed in a velovision magazine that used magnetic coupling from spoke to spin a 'dynamo' https://www.envirogadget.com/lamps-and-lights/magtenlight-contact-less-dynamo-bike-lamp-kit/.)

Could the gearing be in implemented in a non contact fashion with gear wheels driving each other magnetically rather then with teeth?
Last edited by SA_SA_SA on 18 Nov 2019, 2:44pm, edited 2 times in total.
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ConRAD
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Re: A collation of dynamo/generator drag/efficiency data

Post by ConRAD »

Brucey wrote:... the Renak Enparlite is (was?) a clever hub generator with a geared drive ...

Q1: ... was the gear drive a 1:1 clutched transmission or was it able also to increase the rotor speed
Q2: ... there's something not clear at all, the shell is rotating with the wheel, the rotor seems to be geared, are there somewhere brushes?
Image
SA_SA_SA
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

Its definitely geared, Mr Swhs has a reviews of it:
https://swhs.home.xs4all.nl/fiets/tests/verlichting/dynamos/Renak_enparlite/index_en.html

I don't think MR Swhs would like brushes.

If one is going to use brushes wouldn't the SA patented idea of rotating the Stator the opposite direction from hub rotation would be all you need (effective rotation speed squared)?
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ConRAD
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Re: A collation of dynamo/generator drag/efficiency data

Post by ConRAD »

Brucey wrote:Image Image

in the two charts above it would be better to specify that:

1st chart is Dynamo-Hub-Drag-Light-Off [W]
2nd chart is Dynamo-Hub-Drag-Light-On [W]
Image
SA_SA_SA
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

From this it would seem no bushes, the magnet ring just spins on a 'plain bearing' on the axle but a 'thin-ring radial ball bearing' inside the hub shell:
https://translate.google.com/translate?hl=en&sl=de&u=http://www.enhydralutris.de/Fahrrad/Beleuchtung/node70.html&prev=search
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ConRAD
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Re: A collation of dynamo/generator drag/efficiency data

Post by ConRAD »

OK, no brushes.

Image
Image
SA_SA_SA
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

So how efficient could a one gear stage version but with the fatter diameter of a shimano hub dynamo with 28 its magnets be I wonder....?
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

Brucey wrote:...SA had a 3W generator which they could have made, but they didn't think it would sell, so it never reached production. ...

I thought Mr Hadlands book said they took it to a European trade show and that there was little interest shown (NIIGS: Not invented In Germany Syndrome? :) ).
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SA_SA_SA
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Re: A collation of dynamo/generator drag/efficiency data

Post by SA_SA_SA »

Ii does seem puzzling that there was so little interest shown in the XAG by dynamo-preferring-countries who otherwise had a choice of a bottle or a roller dynamo...
then Mr Schmitt comes along with a luxury 3w generator hub, and Shimano follow with value/affordable hubs and bottles and rollers fade away...

why .......

http://www.sturmey-archerheritage.com/index.php?page=history-detail&id=141
http://www.sturmey-archerheritage.com/images/photos/pic-142.jpg
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Brucey
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Re: A collation of dynamo/generator drag/efficiency data

Post by Brucey »

Last edited by Brucey on 20 Nov 2019, 12:07am, edited 1 time in total.
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ConRAD
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Re: A collation of dynamo/generator drag/efficiency data

Post by ConRAD »

SA_SA_SA wrote:... so how efficient could a one gear stage version ...

One or more gears it doesn't matter, gears in a hub are the most horrible things I could think about.
Image
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