Testing a Nexus HB NX23 Generator Hub
I recently bought a bakfiets with a Nexus generator hub. Interestingly, when you search for "Nexus" on this forum, a thread from someone else who bought a bakfiets with a Nexus generator hub comes up. He also seemed to have a burned out bulb and it war recommended that he gets a new light rather than just a new bulb. OK, I'm on board with that.
Hub is HB-NX23, and a Google search didn't turn up much. It's a single wire design with a spade connector. Shimano's website found doucmentation, but only in Japanese, and it wouldn't let me download it anyway. I turn the wheel, and there's no light. The bulb has a frosted, knobbled texture, so I can't see the filament, but it looks intact, I'm just making the assumption it's bad because that's the most obvious. However, before I invest in a new light, I'd like to be sure. How do I test to make sure my hub works, first? What do I put the little tester leads onto? |
if you have a voltmeter, you should be able to measure between the spade lug and some point on the frame that doesn't have paint. Maybe a brake bolt?
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Got it. So the ground goes through the frame. Thanks.
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Dyno hubs are alternating current, if your meter is set for direct current it might not give you what you need to know.
A dynohub that is not supplying current to anything other than your meter can run high voltage. Going down a hill at 25 mph I measured over 30 volts AC on my hub. Many Shimano hubs (possibly all?) ground to the frame. |
Originally Posted by bajajoaquin
(Post 20391038)
Got it. So the ground goes through the frame. Thanks.
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Thank you. That's what I planned on doing, but the extra detail is helpful. I had planned on waiting for my multi-meter to arrive, but I think I'll grab a couple pieces of wire and do a jump test to see if I get light. Of course, the light bulb might still be bad! :)
Yes, a new LED light is coming. I want to get the generator sorted first, then buy a light. If this generator doesn't work, my caliper brakes aren't very good either, so I'll be buying a Sturmey-Archer XL-FDD 90mm drum brake Dynohub. |
You said bulb, a bike headlight bulb is 2.4w. what is the hub output?
typically a bike generator is 3w, with an 0.6w bulb rail light and a 2.4w headlight bulb, one burns out the other is overpowered.. Now, LED lights get an IC, with a rectifier (AC to DC) and an overvoltage regulator in the circuit.. |
That is correct. The light is also a Nexus, but it's an older bulbed version. I reassembled it all, and I don't have the model number handy, but it was a 2.4w bulb. There's a taillight, but the wire was just run into the rubber grommet on the rear drum brake linkage.... in other words nowhere. My guess was that the bulb was burned out, but I decided to try to get a light on the bulb by running a ground wire from the light bracket to the axle. It didn't work.
So I'm back to waiting for Amazon to deliver my multi-meter, and I'll test the output of the hub by touching from the spade connector (for the light to hook up to) and to the axle or other parts of the hub. If I find that the hub puts out it's 3w at 6v that I expect, I will probably keep it and add a new LED light/taillight. If the hub doesn't work, I'll probably buy a Sturmey-Archer XL-FDD. |
If you get a 3 watt bulb at the hardware store, then skip the taillight. A good Ace hardware store or a True Value hardware store should have an assortment of flashlight bulbs.
Some people have wired in 7.5 or 8 volt Zener diodes to reduce the chance of blowing out an incandescent bulb on downhills. But since almost all bike lights now are LED with over-voltage protection it is getting hard to find the instructions to do that, but googling zener diode bicycle dynohub might give you some help. WIth the demise of Radio Shack it is getting harder to find things like Zener diodes. |
Thanks. I may try that. Theres very little danger of my blowing out bulbs on any downhills on this bike! |
The 3 watt rating on dynamos is nominal. Power output varies a lot with speed.
Modern LED lights have very good over-voltage protection, so there is virtually no worry of damaging them with too much. |
I am glad I read this thread, I was planning on building a new front wheel with a Nexus dynamo hub but now that I know it is a frame ground I need to rethink, carbon front fork. Even though unrelated to the OP's issue I still learned something that will save me a bunch of time and money on something I wouldn't get to work. Thanks.
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I think I would check on that first, they probably have made different versions.
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Don't most of those hubs have two wires coming out of them?
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Originally Posted by WheresWaldo
(Post 20394093)
I am glad I read this thread, I was planning on building a new front wheel with a Nexus dynamo hub but now that I know it is a frame ground I need to rethink, carbon front fork. Even though unrelated to the OP's issue I still learned something that will save me a bunch of time and money on something I wouldn't get to work. Thanks.
Where you can get in trouble is if you have a metal fork and a hub grounded to the frame, and a light also grounded to the frame. In that case, there is a 50/50 chance that when you wire it, you will get the wires reversed and the light won't work. In that case, switch the wires.
Originally Posted by noglider
(Post 20394452)
Don't most of those hubs have two wires coming out of them?
I tried an experiment, I wired in a headlamp that was grounded to the frame. Shimano hub, so it also was grounded to the frame. I only needed one wire from the hub to the light, see photo. I no longer run the light on the fender mount, the light worked fine but was too low to the ground and I got weird shadows from tiny little things sitting on the ground, it was a short term experiment and I decided I needed the light up higher. But that was the easiest wiring job I ever did, less than a food of wire. https://cimg7.ibsrv.net/gimg/bikefor...72cc33b17f.jpg |
Yeah, great wiring, bad lighting. I tried that mount point, too. No good at all. However, the fork crown is a perfectly good height for me. I love my headlight there.
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This is an old model Nexus hub. I don’t know the age, but I’ve posted the model number above if anyone can use that to find out better than I did. In other words, don’t take my hub description to be the current state of the Nexus art. |
Doing a google image search of your part number, it appears that Shimano did indeed make some hubs that have connections for only 1 wire instead of the normal captive-wire 2-connector clip... :-(
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Yes, this is a single wire hub. I also found that I didn’t actually order a multi meter but it was sitting in my cart. Then I went in vacation then I had month-and quarter-end to get through at work. I had another family over tonight for dinner and offered up a ride since the husband is a former racer but had never ridden a bakfiets. Imagine my surprise when the light worked! The bulb is pretty dim, I think a product of being on a 20” wheel and being pedaled slowly uphill. But it works. I'd like to convert to LED, but I understand that the difference between a conversion bulb and a new light isn’t that great. What are my reasonably priced options? Is there a good $30 light or should I just suck it up and spend $80 on a B&M? |
Originally Posted by bajajoaquin
(Post 20420539)
I'd like to convert to LED, but I understand that the difference between a conversion bulb and a new light isn’t that great. What are my reasonably priced options? Is there a good $30 light or should I just suck it up and spend $80 on a B&M?
https://www.rosebikes.com/b-m-lumote...eadlamp-683821 |
Originally Posted by bajajoaquin
(Post 20420539)
...
I'd like to convert to LED, but I understand that the difference between a conversion bulb and a new light isn’t that great. What are my reasonably priced options? Is there a good $30 light or should I just suck it up and spend $80 on a B&M? While looking at it I saw that he had an LED flashlight bulb in his vintage headlamp unit. He complained that if flickered at low speed, I assured him that was normal for most LED lights because the hub puts out AC, not DC. But I told him his might flicker much worse because an LED uses DC, not AC. Thus, his bulb might only use half as much power as the hub puts out. I told him that if he can find a Radio Shack that has not closed yet, for a few bucks he could try a rectifier to change the current to DC. I have no idea what the voltage rating on his bulb is. If you want to try something like that, some LED flashlight bulbs have a wide range of voltages. But I have found LED flashlight bulbs sometimes do not play well with the reflector because of the bulb design. |
Originally Posted by znomit
(Post 20420558)
For city riding the eyc is fine, about 40US$
https://www.rosebikes.com/b-m-lumote...eadlamp-683821 |
In addition Planet Bike offers a Dynamo version , with a wire, and a disconnect plug in the middle of the twin lead wire
So like their battery headlights, the light comes off the handlebar mount and can go in your pocket , when you lock up the bike , and pop it back on, with the convenience of the plug.. leaving your wiring to the hub itself intact.. |
+1 on Eyc. You can further look at offerings from xxcycle. Trelock lamps are OK , below B&M but sufficient for city riding. Axa Pico is very inexpensive. Make sure you buy a lamp with a standlight function. You are likely not going to save buying a no-name Chinese lamp on Ebay. The beam pattern may be lacking and the light may die in the rain - too much risk in my opinion.
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I have an AXA Echo 30 that I bought some years back that I bought to replace another lamp. I've been happy with the performance on my "please don't steal me" city bike.
I wish there more choices for a bright, durable light with only a standlight and a simple on/off switch. It seems like many of the lights these days incorporate features that I don't need that seem more like liabilities. /old man |
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