Overhauling a Shimano DH-3N71 Dynamo Hub

[Cpt Sisko]

I have a confession to make. I've been running a Shimano hub for the last four year, excellent all worked well until about four weeks ago when it stopped working. Now it could have been the B&M light itself, but as I was washing the bike I also thought, Mmmm these bearing are a bit rough and then noticed the rotation mark on the hub and saw I'd been running it backwards for, well forever.

So before I dive inside to see if I can replace the bearings (which previous posts say is posible) what's the collective thoughts about whether or not I've buggered up the internals as well. 

Also, and excuse my ignorance here, how do I check the light is okay? Is it just as simple as wiring it up to a 6v battery?

[Oaky]

I also thought, Mmmm these bearing are a bit rough
Also, and excuse my ignorance here, how do I check the light is okay? Is it just as simple as wiring it up to a 6v battery?

Just bear in mind, in case you weren't already aware, that dynamo hubs can naturally feel "notchy" when turned by hand, as if they have rough/dodgy bearings, owing to the magnets.

[Cpt Sisko]

No these are well past that, they have always felt a bit notchy even when the hub was new, but they are seriously bad with a bit of side to side wobble as well. Definately passed their sell by date.

[Brucey]

if you have had the terminals on the left side of the bike, running the hub backwards, there are two dangers;

1) that the cone on the RH side will loosen, precess inwards and wreck the bearings

2) that the whole stator assembly will try and unscrew itself from the hubshell, again via precession.

If neither thing has happened then the installation hasn't affected anything, I'd have said.

BTW with DH-3N71 the fatal exception is running the bearings too tight; this usually causes the RH (terminal side) cone to disintegrate. The correct adjustment is to have a little free play that just disappears when the QR is tightened properly.

To test your lights, it is probably easiest to attach a load of some kind (eg the rear light) directly to the generator, and test that first (at very low speed else you might blow the rear light). Once you have done that, you can test the front light on the now 'known good' source.

cheers

[Cpt Sisko]

Thanks for your reply Brucey, it sounds like I haven't got a lot to lose by having a go at looking at the internals.

[Brucey]

yes, but I would suggest that you

a) confirm that the generator is electrically sound first (else there isn't much point in fettling the bearings....) and
b) troubleshoot the lights with your (hopefully functional) generator before stripping it down.

If the front light and the generator are bad, it might be that it is worth getting 'a package' including lights and generator; these often work out a better deal IIRC.

cheers

[Kim]

A working hub should:

Illuminate a 6v torch bulb or known-good bicycle light when spun.

Have a lowish reading when a multimeter on the ohms range is connected across the stationary hub.  Infinity is bad, <10Ω is suspicious.

Give a reading of a couple of tens of volts on a multimeter on the AC volts range when the wheel is spun without a light connected.

[Brucey]

A working hub should:

Have a lowish reading when a multimeter on the ohms range is connected across the stationary hub.  Infinity is bad, <10Ω is suspicious.

IME <10Ω is 'normal' with many hub generators.

Maybe we should start a thread with measurements so that info on different models can be pooled?

cheers

[Kim]

IME <10Ω is 'normal' with many hub generators.

Cor, there's less wire in them than I guessed.  (It was bedtime, and I wasn't going near bikes.)

Maybe we should start a thread with measurements so that info on different models can be pooled?

I've just measured:

SON28: 3.6Ω
SON Delux: 3.2Ω
Shimano DH-3N80: 4.2Ω  (Manky contacts, may be lower.)
Shimano Capreo: 3.4Ω

Which puts them all well within the miscalibration of a typical household multi-meter.  So there isn't an easy way to tell the difference between a working hub and an internal short.

[andrew_s]

A working hub should:
Have a lowish reading when a multimeter on the ohms range is connected across the stationary hub.  Infinity is bad, <10Ω is suspicious.

I think that Brucey was pointing out that you should has said ">10Ω is suspicious"

[Kim]

A working hub should:
Have a lowish reading when a multimeter on the ohms range is connected across the stationary hub.  Infinity is bad, <10Ω is suspicious.

I think that Brucey was pointing out that you should has said ">10Ω is suspicious"

That wasn't what I meant though.  I was assuming a coil resistance of over 10Ω, so a lower reading would imply an internal short.  But it's much lower than that, so you can't discriminate by resistance.

Agreed that higher non-infinity resistances are bad.  Probably indicative of a corroded contact.

[Dave_C]

Oh dear, I'm also guilty of leaving my aydax wheel in the garage unused for months on end.... I'd better take a look before audaxing commences. I rode a 200 a couple of weeks ago on my winter/tourer.

I hope I don't have to take the thing apart to regrease. I CBA at the mo....

[Splurge]

Hi All,

First post here, but have been a mid-term lurker/knowledge sponge (sounds so much better than lurker!)
I have a question hopefully someone here can help with...
I've been running a DH-3N80 for a little over 3 years in all weather conditions for audax, tours etc. The hub is still spinning nicely, no added sounds, no extra play or anything but is not putting out anywhere near as much electricity as it used to.
I run a Sinewave Cycles Reactor from the hub and use the USB to power lights/phone/power bank etc.

Previously, electricity would flow very nicely at around 4kph - easily enough to charge my phone (Nexus 4, now a 5x) running OSMAND and I would finish any length of ride at 100% battery.
Now, the phone lights up at around 12-13kph and does not actually charge (measured using an ampere meter app).

I have changed the Reactor to an older version of a dynamo->USB converter, which previously worked fine but the issue persisted.
I changed my phone (for other reasons) and the problem persists.
I have cleaned the wire and contact points on the dynamo, but still the problem persists.

Any thoughts on what the problem is? Anyone had anything like this? I don't mind trying to take my hub apart and clean/regrease it, but will that have any effect?

All advice/insight is welcome!

Greg

[Dave_C]

Try replaying the USB to microUSB lead. Could be something as simple as a few broken strands of copper in the cable which allow a small amount of current to flow, but not enough to trigger charging.

So far
- The dynamo is ok, I assume,
- You changed the Generator for the older version,
- You said you tried the older phone,

The only other thing it could be it the wiring.

- Its simplest to swap over the USB lead and if that does not help, try rewiring the hub/generator etc..

[Splurge]

@Dave_C

Thanks for replying 
I have tried with different cables (same result) and the original cable (USB to USB-C), which works just fine plugged into a wall socket.
I guess it will have to be an afternoon in the sun taking apart the generator and making sure that little copper wire hasn't been damaged somehow......

Greg

[Dave_C]

@Dave_C

Thanks for replying 
I have tried with different cables (same result) and the original cable (USB to USB-C), which works just fine plugged into a wall socket.
I guess it will have to be an afternoon in the sun taking apart the generator and making sure that little copper wire hasn't been damaged somehow......

Greg

Good luck. Start with junctions which are exposed to the elements and also likely to flex. The ones you /shop installed. These things (dynamo and Sinewave Gen) are designed with outside in mind, so more often than not its a simple broken wire between two bits.

I'd start with the 'lego' brick connector. The wire is exposed there and will be dark if it has corroded. I always wrap my cable round the fork so I have plenty of spare to uncoil for when I need to strip back the wires.

Dave C

[Brucey]

there is absolutely no point in stripping the generator down unless you are 100% certain that there is a fault of some kind. DH-3N80 has an aluminium winding so I'm not sure what you could do with that anyway.

If you want to test the generator there are some very easy tests you can do

1) test current output
2) test winding resistance
3) test generator using a dummy load

These tests require a cheap multimeter, some wire, and a dummy load.

So; test #1 just requires a multimeter with an AC current setting that will handle 1A.  Just connect the meter to the hub and spin the wheel. You ought to see between 600 and 800mA at reasonable speeds.

 If it is lower than that, test #2 is to check the resistance of the windings and compare with the figures elsewhere in this thread. If the resistance is higher than quoted then maybe there is a bad contact in the generator.

Test #3 requires a dummy load. A 12 ohm resistor (with a 5W rating) is suitable.  You can compare the generator output (as AC voltage across the resistor) with the StVZO specification and the published test data for DH-3N80 available online.

in the grand scheme of things I'd expect there to be a fault with the wiring or the charger you are using before the generator would fail. If the generator has a fault, it is likely to be either a bad joint somewhere or possibly a short to ground. Both are pretty rare things, unlike USB chargers going flakey, which is commonplace.

cheers

[Splurge]

Thanks a bunch, chaps! I really appreciate it
I'll pinch a multimeter off a friend this afternoon and get to it.

[Splurge]

Righto, so a quick test showed that spinning the wheel as fast as I could by hand shows no current at all, which is a little odd.
I am by no means an electrically minded person (I deal with people usually, not electronics ) but the multimeter is set to AC in a reasonable range, the contacts are plugged in properly and in contact with the hub (where the two wires would connect via the 'Lego box'.
Using Brucey's post below..... how on earth would I go about testing the resistance of the windings?!

Complicated (for me) but fun, all this...

[Kim]

Most multimeters require the positive probe to be in a different socket in order to use the current range.  I'd expect a 10A range and associated socket, and a few-hundred-milliamp range and another associated socket, along with the usual socket for measuring voltage, resistance, etc.  The negative probe uses the same socket at all times.  You'll probably need the 10A range to measure the short-circuit current of the dynamo.

Also, if the meter cost more than a fiver, there will be fuses on the current inputs (accessed via the battery compartment, of by taking the back off the meter).  A standard multimeter rookie mistake is to attempt to measure the voltage of something capable of producing a decent amount of current (eg. a battery) with the probe still connected to the current socket.  On a decent meter, this will immediately blow the fuse and leave you scratching your head at a reading of zero, before the realisation that you're going to have to fork out for some expensive new HRC fuses slowly dawns^[1].  With a cheapo, unfused meter, this will briefly result in a nonsensical reading, while the realisation that the meter and/or the probe leads are in the process of catching fire slowly dawns^[2].

To measure the resistance of the windings, you'll put the meter into the lowest value resistance mode (200Ω would be typical, if it doesn't auto-range), with the positive probe in the volts/ohms/etc socket, and probe the terminals of the stationary wheel.  I'd expect a reading of about 3-6 ohms.  The meter may helpfully beep while you do this (handy for working out what wire goes where, when you aren't fussed about the precise resistance).  Coincidentally, this is the same procedure you'd use for determining whether a fuse is blown...



_{[1] You'll then forget all about it, and lend the meter to an electronics n00b trying to troubleshoot their dynamo, who will inexplicably get a reading of zero on the current range.
[2] I made this mistake on a car battery once.  I realised as the smell of the melting probe lead reached my nose.  Impressively, the two-for-a-fiver Maplin multimeter was undamaged.}

[mmmmartin]

On YACF, every day's a school day.
I can't remove the black plastic seal on the right hand side of the hub. Does anyone know which size of spanner I need? I doubt have one big enough. Today I took it to Homebase but none of their spanners were big enough. Needs to be a ring spanner.

[Splurge]

I feel rather dense here, so if someone can shed light on this then that'd be ace!
This multimeter is a clamping variety for measuring amperes, which makes measuring current impossible with the wires I have to hand.
However! The multimeter app on my phone will happily read current. Here's the strange thing though:
When the phone is plugged into the mains charger, it displays the battery as "Charging, AC charger" with 1870mA, which would be right for a wall charger on a modern smartphone.
When I run the app while the phone is plugged into my dynamo and spin the wheel, it reads as NEGATIVE mA relative to speed, with the app saying the battery is discharging.

I have reversed the leads on the Lego block, thinking that was causing the issue - no difference.
What on earth would be causing that?! (probably it is something simple I am overlooking...)

[Kim]

That just means that the battery is discharging (in order to power the phone), doubtless because your spinning of the wheel is inadequate to provide enough power to put a net charge into the battery.

The output of the hub is AC (it's really a magneto, rather than a dynamo), so reversing the polarity won't affect that.

[Splurge]

@Kim, I know that a dynamo is AC and reversing polarity won't affect things; it was more to stop someone else saying it.
I don't understand how resting (not plugged in to anything), the phone is discharging at -260mA, plugged in to a wall it is charging at +1860mA and cycling at 14kph it is discharging at > -1000mA (by which I mean less than -1000mA, of course).
Why is that? Why would being plugged in to a power source seemingly increase the rate of discharge? Or am I looking at things completely the wrong way?

[Kim]

Because the phone sees external power and decides it can turn all its power saving features off.

It's an occupational hazard of connecting some devices to current-limited sources.  If you're lucky they give up after a while of no net charging of the battery and ignore the external power until it's been removed entirely (Androids tend to say "Not charging").  If not, they sit there merrily draining their battery at an accelerated rate.  The only way to win against such a device is with something that can supply the required charging current (which it sounds like your charger usually could, before this mysterious fault happened), hence some devices need a cache battery to charge properly from a dynamo charger.