Hub Dynamo Question

[Paulmh]

Hi, I wonder if any forum members can help? I have a bicycle with a hub dynamo, a Shimano Nexus Inter L, ref. HB NX10, 36 hole. It's probably about 12 or 15 years old. There are 2 electrical connections on it; one being a male spade connector, the other being a projecting blob of what looks like solder. It doesn't work when I connect up a new Busch & Muller Lumotec Oval Senso Plus light (6V 3W) although I was told by the people that sold me the light that it didn't matter which of the 2 wires from the light is connected to either of the terminals on the hub dynamo. The light itself has a separate earth wire.
The hub may not be working - I did take it to the shop where I bought the bike, some years after I'd bought it and they said they'd tested it and it wasn't working and sorry but nothing they could do.
As I can't find anything out from Shimano, I don't know if I've been given the correct info by anybody and wonder if one of the terminals from the dynamo should go to earth and the other to the light. But then why would the light have 2 wires plus an earth terminal (that I've connected to the forks)? Think I've answered my own question.
Next question is whether I should just fit a new hub dynamo and I can get a Shimano DH-3N20 for about £20 including postage and then spend a happy day fiddling with 36 spokes and trying to fit it into my wheel. Is that a good plan?
Any helpful advice gratefully received!

 

[tyred]

Could it be that there was originally a spade terminal attached to your blob of solder and it has got knocked off? If so, solder a wire directly on to it.

I don't know about the Shimano but the Sturmey Archer dynohub was always isolated from the frame and required two wires. Bottle dynamos will usually earth to the frame through the mounting bracket, as do most simple bulb type dynamo lamps so a seperate earth wire isn't required but I use one anyway for better reliability.

 

[Paulmh]

Thanks and yes, I expect the stump is the remains of a spade terminal that was knocked off. So if an earth is not required, I definately need to get a new hub dynamo.
Cheers,
Paul

Could it be that there was originally a spade terminal attached to your blob of solder and it has got knocked off? If so, solder a wire directly on to it.

I don't know about the Shimano but the Sturmey Archer dynohub was always isolated from the frame and required two wires. Bottle dynamos will usually earth to the frame through the mounting bracket, as do most simple bulb type dynamo lamps so a seperate earth wire isn't required but I use one anyway for better reliability.

 

[andrew_s]

The NX10 has only one connector (the spade).
The other connection is via the locknut/axle to the fork dropout and thence to the rest of the frame.
All Shimano hub dynamos earth to the frame, even if they've got two terminals.

The "blob" on my old NX10 has a plastic coating all over it.

 

[Paulmh]

Thanks Andrew. Does that mean I should connect the "blob" with a wire to the hub locknut? And if so, which of the 2 wires from the light connect to the spade terminal on the dynamo? Or can it be either? Or do I have the wrong light? And why don't Shimano have anything on the NX10? (Don't bother with the last question).

The NX10 has only one connector (the spade).
The other connection is via the locknut/axle to the fork dropout and thence to the rest of the frame.
All Shimano hub dynamos earth to the frame, even if they've got two terminals.

The "blob" on my old NX10 has a plastic coating all over it.

 

[tyred]

I have a few B&M lamps and the spade terminals will have a "lightening strike" symbol beside one and the ground/earth symbol beside the other (a number of horizontal lines, each one getting shorter and a vertical line perpendicular to it, google ground symbol to find a pic). The lightening strike symbol would be the positive and connects to the spade on the dyno. The other one needs to be connected to the frame since the hub is grounded. It would usually do that through the mounting bolt anyway. If you have a tail light as well, be careful that they both are connected the same. Incadesant lamps (I take it yours is the halogen version of the lumotec oval) are not polarity sensitive but you need both the headlamp and the tail lamp to be connected in the same manner or otherwise it will be a short circuit.

So for now, I would disconnect the tail lamp if you have one, run the wire from the lightening strike terminal of the lamp to the spade on the hub, run the earth wire of the lamp to the axle nut and see if that works. Just do it with a few bits of loose wire for now. You can tidy it up later. In theory (assuming a steel framed bike), it should connect the earth through the frame but my preference is to use a separate earth wire for reliability.

If this works, and you want to add a dyno powered tail lamp, most traditional type dyno tail lamps will have one terminal which you need to wire to the spade on the hub and it should earth through the mounting point so run another wire from the mounting bolt of the lamp to the front axle nut.

 

[Paulmh]

Thanks, Tyred,
There are spade connectors on the light; a pair are for connection to a rear light (which I do not have) and one is for earth, which I have wired to the frame head. That leaves a pair of wires emerging from the light as supplied, which are not marked in any way (except they are black and one has a white stripe down it) and there is nothing in the instructions or marked on the light to say what they are for, but they are obviously supposed to go to the power supply, i.e. the dynamo. Why are there 2 wires when my dynamo only has one terminal, plus the bump referred to earlier? Can I choose any wire to go to the dynamo and ignore the other? Or connect both wires to the dynamo spade terminal? The bulb is a 3W halogen, by the way. The bike frame is aluminium. Sorry to be going around in circles on this but it's hard to get a definitive answer and I don't want to embark upon experiments that stuff up the expensive kit.

Best wishes,
Paul

 

[tyred]

I would expect the solid coloured wire to be positive and the negative wire to be the striped one. Ignore the spades for now and try it with the striped wire connected to the hub axle and the solid wire connected to the spade. Ideally, try this first of all with the headlight not attached to the bike (alluminium conducts electricity too) and just spin the wheel to see if it lights. If it works, fit it to the bike and try again. If it has stopped working after fitting to the bike, swap the wires around at the hub end.

 

[Paulmh]

Thanks, Tyred - I'll try that when I get some free time and let you know what happens. There's always the chance that the dynamo is cream crackered.
Cheers,
Paul

 

[Paulmh]

Well, I did as you suggested, Tyred; wired the white striped wire to the hub and the all black wire to the spade and it works! Why oh why don't the light manufacturer's instructions say anything about that? Why is there an apparently meaningless solder blob on the dynamo and why don't Shimano have anything on their website for my dynamo? And why did the bike shop declare that the dynamo wasn't working when it clearly is? Don't bother with answers!

Your reply on the forum has saved me a good few quid, so I'm dead chuffed.

Thank you.

Paul

 

[tyred]

No problem. Glad to be of service.