My bike gave me a buzz!

[Butterfly]

When I was riding back from the shops yesterday, I was braking on a descent and got a sensation like a mild electric shock in my hands. It stopped once I stopped using my front brake. Could it be worn pads on the disk brake causing friction, or something to do with my dynohub which is not currently working?

[Kim]

Since I last adjusted the pads, the front brake on the Red Baron has developed a squeal.  Interestingly, this vibration propagates back up the cable to the lever, which can then be heard squealing in sympathy (maybe this is normal, and it's just the Baron's geometry putting the brake levers close enough to my ears that I've noticed it).  Anyway, I can imagine the same effect at a lower frequency feeling a lot like a mild electric shock.

That said, being zapped by a dynamo hub feels an awful lot like an electric shock too (DAHIKT), but I'm struggling to imagine how a current path through the brake lever would happen.

[Butterfly]

I couldn't think how it could either. It felt like the rather beautiful violet wands they had at the London alternative market. Beautiful but very much not my thing.

[Kim]

Oh, and I also got a 50Hz tingle from my bike frame wile standing on the platform at Peterborough one time.  I assume leakage from the overhead lines.

[Brucey]

you can indeed get zapped by the dynamo when braking; if the wiring is a particular way and your headset bearings don't conduct very well, when you apply the brakes you may become part of the circuit.

The reason is often that

a) the frame is working as an earth return
b) the headset doesn't conduct very well
c) the brake cables provide the earth return
d) when you apply the brakes the levers are connected to the brake cables but the levers are pivoting on plastic bushes which are insulated
e) you get some fantastic voltage generated between the brake levers

I suspect you have a wiring fault (eg the live wire on the front light is connected to the ground on the rear light, which would also stop the lights from working).

Years ago a chum had a dodgy ground on a single wire system and sometimes when descending the lights would go out whenever he used the brakes and he got the full benefit of everything that the generator chucked out, which caused him to scream loudly. The headset had plastic parts that made sure that there was no circuit there.

cheers

[Butterfly]

Thank you Brucey. I'm going to try to get it into the bike shop in York today, since they're one of the few that cope with both hub gears and dynohubs.

[Butterfly]

Thank you Brucey. I'm going to try to get it into the bike shop in York today, since they're one of the few that cope with both hub gears and dynohubs.

So Cycle Heaven couldn't find a problem, but it worked when we left there, which it hadn't been doing. And then it stopped again. I've taken it in to Bache Brothers in Stourbridge to see if they can tidy the wiring up again. If not, I'm not sure of the solution.

[Butterfly]

Bache Brothers seem to have sorted it out again, hopefully it will stay sorted this time. 

[Brucey]

did they say if they found a particular fault?

cheers

[Butterfly]

did they say if they found a particular fault?

cheers

No, I think they just tidied up the wiring.

[Butterfly]

It's started happening again, although the lights seem to be working fine now. I assume it is a slightly different fault, as I've had a frame transplant so it has been totally rewired. It's the rear brake that is causing the problem now. Fortunately, on the tandem it is pretty safe to use just one brake - an e-assist tandem is unlikely to flip - but it is worrying and quite nasty when I forget.

Does anyone know of any bike shops that are happy to look at dynamo wiring?

[Brucey]

it would help to know where you are and also what parts you have in your system; some have earth return connections and some don't.

Mad thought; as a temporary measure you could simply provide insulation as necessary; tape over the brake levers, wear rubber gloves, that kind of thing....

cheers

[Kim]

It's a Shimano hub with a Cyo (which is electrically isolated from its mounting) of some flavour mounted on the bars.  The cable's been extended to reach.  Last time I looked, the wiring at the lego brick was a bit of a mess (having been yanked out and bodged in the field a couple of times), but presumably that's now been tidied up.  IIRC there's also a rear light of some DToplightish flavour (which do usually earth to their mounting).

There's now a STEPS system, but that's not connected to the dynamo lighting and can likely be ignored.

I'd start by scrutinising the wiring to the rear light, with attention to polarity and earthing.  I'm guessing it might be the classic frame return as short circuit configuration, with sufficiently bad conduction through the headset that the lights still work.  The brakes and rider are presumably providing an opportunistic path for a slightly better short circuit.  Cure would be to <the_doctor>reverse the polarity</the_doctor>, preferably at whichever point it's currently wrong at to avoid future confusion.  The convention is that the wire with the stripe (or the outer conductor of coaxial cable) connects to other wires with stripes (at the Cyo) or the terminal marked with an earth symbol (⏚) at the rear light and dynamo.

I'm not sure I'd trust a bike shop to troubleshoot dynamo wiring problems, unless their bread and butter was touring bikes.

[mrcharly-YHT]

Take the rear light off and alter the mount so that it is electrically isolated from the frame?

Does that rear light have a standlight, probably a capacitor?

[Kim]

Take the rear light off and alter the mount so that it is electrically isolated from the frame?

That's a lot more involved than getting the polarity right.

[Brucey]

at one time all shimano hub generators had an earth return. However more recent models don't, and some models have changed configuration whilst retaining the same model designation.

BTW I agree with the basic idea that the earth return from the rear light is the most likely cause of the problem.

Note that if the rear light has a standlight, that may keep the rear light lit well enough during times when the connection is dicky and the brakes are being used.

cheers
 

[Butterfly]

Thank you all. I'll get clarion to have a look at it and see if he I can do that. Insulating tape on the brakes may be something I can do, at least  .

[Kim]

If you get really stuck I can have a proper actually-paying-attention-and-with-a-decent-meter-to-hand look at it for you, if you like.

[Butterfly]

If you get really stuck I can have a proper actually-paying-attention-and-with-a-decent-meter-to-hand look at it for you, if you like.

Thank you 

I'll have a look and get clarion to have a look and if that fails, I'll take you up on that 

[clarion]

Hmm... no obvious shorts, cable in good condition.  I swapped the polarity of the rear light, and all seems to work OK, but can't give it a proper test till Butterfly gets to ride it.