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Old 06-08-07, 12:12 AM   #1
gnome 
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Computers & Hub Dynamos?

I am building up a Raleigh twenty as a fixed gear commuting bike for winter. As it is going to be for winter I am putting a hub dynamo on the front. The dynamo will either be a S-A Dynohub or a Shimano DH3N20 dynamo hub. I want to run a basic computer so that I can accurately log my distance and speed. Will the magnets in the hubs interfere with the computer sensor?
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Old 06-08-07, 05:30 AM   #2
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Not being familiar with the product here's my question - does the dynamo go only on the front wheel? If so can you place your sensor for the computer on the rear?
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Old 06-08-07, 06:13 AM   #3
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Quote:
Originally Posted by gnome
I am building up a Raleigh twenty as a fixed gear commuting bike for winter. As it is going to be for winter I am putting a hub dynamo on the front. The dynamo will either be a S-A Dynohub or a Shimano DH3N20 dynamo hub. I want to run a basic computer so that I can accurately log my distance and speed. Will the magnets in the hubs interfere with the computer sensor?
No, there should be no problem with that. If you're worried, put the computer sensor as far from the hub as possible. If you don't already have the computer, you might consider one that puts the sensor on the rear wheel. I have one with two sensors, for example, one for speed and one for cadence; and to combine the wires as much as possible, they put the wheel sensor on the rear wheel.

Changing the subject slightly.... I built up a Raleigh Twenty using the new Sturmey Archer dynamo hub / drum brake combination, which is nice because it's hard to put decent caliper brakes on the R20's fork. If you don't already have the hub you're going to use, check it out:
http://aebike.com/page.cfm?PageID=30...ils&sku=HU2200
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Old 06-08-07, 07:39 AM   #4
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Quote:
Originally Posted by gnome
I am building up a Raleigh twenty as a fixed gear commuting bike for winter. As it is going to be for winter I am putting a hub dynamo on the front. The dynamo will either be a S-A Dynohub or a Shimano DH3N20 dynamo hub. I want to run a basic computer so that I can accurately log my distance and speed. Will the magnets in the hubs interfere with the computer sensor?
if it's a wired connection, it won't. I have a Schmidt dynamo hub with a Cateye Mity 8 computer and the two play together just fine. The Mity's sensor is on the front wheel.

I've heard of flakiness with wireless computers as interference can cause the computer to either stop registering your speed or tell you that you're going 50 mph while stopped at a red light; but that can occur even if you don't have a dynamo. I don't know if adding a dynamo will increase the likelihood of that, but I've never had a problem with a wired bike computer.
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Old 06-08-07, 08:06 AM   #5
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Peter White's web site claims that you can use the hub dynamo in place of the wheel magnet to provide data to your computer, which seems like a pretty elegant solution to the problem.

Considering how close I have to keep the wheel magnet to the sensor to get my bike computer to work, it should be pretty easy to mount the computer pieces far enough away from the hub generator to eliminate interference. I have a Schmidt hub generator on one bike and a Shimano 3N-71 hub generator on another bike, with computer sensors on the back wheels of each bike, and there's never been a problem.
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Old 06-08-07, 07:08 PM   #6
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Originally Posted by markf
Peter White's web site claims that you can use the hub dynamo in place of the wheel magnet to provide data to your computer, which seems like a pretty elegant solution to the problem.

Considering how close I have to keep the wheel magnet to the sensor to get my bike computer to work, it should be pretty easy to mount the computer pieces far enough away from the hub generator to eliminate interference. I have a Schmidt hub generator on one bike and a Shimano 3N-71 hub generator on another bike, with computer sensors on the back wheels of each bike, and there's never been a problem.
I haven't looked at that page for a bit, but I think that he was referring to a specific computer that has the magnet for the computer actually on the hub. Mine goes out near the wheel so that wouldn't work for me. Like I said, I think be depends on what kind of a computer. This is something I'm researching as well though since I want to get a dynamo hub on my commuter eventually.
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Old 06-08-07, 10:13 PM   #7
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I have three bikes with Shimano dynamo hubs and computers, never had any issue.

Unrelated to the dynamo hub, one of my computers is very picky about the alignment between the magnet and pickup. If either gets knocked out of place much the computer will not receive data. I happened to have some quite strong, small rare earth magnets; placing one on the wheel magnet effectively boosted its signal and the pickup's reception is much better.
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Old 06-08-07, 11:07 PM   #8
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Also no problems with a Sturmey Archer DynoHub & front wheel magnet/sensor setup on a wired computer
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Old 06-10-07, 02:50 AM   #9
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Thanks for the help

Thanks for the help. Now I just have to build the bike before winter is over.
Does anyone have any recomendations on what light I should get to go with the dynamo hub? I have settled on using my Shimano hub.
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Old 06-10-07, 10:00 AM   #10
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I like my B&M Lumotec Senso Plus. I have the oval one. It will stay lit for about 2 minutes after you stop pedaling.
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