Advice on a 1970s dynamo

[fetimo]

Hi all,

I've recently started commuting to work and picked up an older bike to get my bearings.

On inspection, I found that the rear taillight has some sort of lighting system. In my naivety I fitted a new bulb, spun the wheels and hoped for a brief spark of life. Instead I was met with a should-have-been-expected unlit bulb. There's a loose wire which looks like it needs soldering back on but the bit that I'm not sure of is how the thing is actually powered. I'm assuming some sort of dynamo system but I'm at a loss as to what. All the examples I can find seem to be bottle or hub and I'm not sure this is either.

There's an insulated wire that comes out of the taillight and into the rim of the fender. Does anyone know what is needed to power the light?

Apologies for the dirt underneath, my commute involves a bit of off-roading!

[Brucey]

it is a dynamo light housing, but if there is no dynamo fitted, it'll never work. Especially with wiring like that!

FWIW I wouldn't bother with that type of lamp because LED lamps are so much better.

cheers

[NUKe]

I am guessing but the light appears to rely on the connective earth of the bike.you might get the light working with a separate earth wire. Is it a1970 dynamo? Or a dynohub
I totally agree with Brucey modern leds are far superior. Especially if you intend to winter commute.

[[XAP]Bob]

Four places to look for a dynamo:
- Front hub
- Bottom Bracket (between that and the rear tyre)
- Alongside one of the wheels (Bottle style)
- Rear spokes, hub end (non drive side)

They should be fairly obvious...

You ought to be able to replace the bulb with an LED, but you'll also need to check the wiring.
"single wire" systems generally use the frame as a second wire.

Without a dynamo you could add a battery elsewhere, I use a PP3 (9V square battery) with modern dynamo lamps, which gives decent brightness and run time.

[Brucey]

also you could have/had a rear hub gear combined with a generator, e.g. SA models AG, FG etc

cheers

[andrew_s]

It's a dynamo light.
If it's '70s, it would have been a sidewall dynamo, most probably, or possibly a Sturmey Archer dynohub, either with or without a drum brake (usually front wheel).

Dynamos are now mostly hub dynamos, built into the front wheel, but sidewall dynamos are still available.
Other types are roller dynamos (running on the back tyre, just behind the bottom bracket) and spoke dynamos, clipping to the frame at the left end of the rear hub and turned by a peg in the spokes. These are either no longer available, or would need a bit of hunting for.

You would either have the dynamo connected to the frame, the rear light also connected to the frame, via the mudguard bridge and stays, and a single wire running between, which may sometimes be hidden inside the frame, or two wires running the whole way (more reliable). It was also sometimes the case that the mudguard had 3 foil strips inside, one central (which connected to the frame as above) and one either side, and the wires from the dynamo connected to the foil strips via small rivet fittings, usually just behind the bottom bracket and next to where the rear light goes.
Front lights would have been on the fork crown or RH fork blade.

If there's no front light and no dynamo, it's not worth trying to use the rear dynamo light. If you want dynamo lights, start from scratch with modern stuff. the lights are far better, sidewall dynamos not so much.

[wjhall]

I have a 1970s bottle dynamo on one bicycle, and an early 2000s version on another, so that probably shows me to be addicted to the bottle. They are backed up with two modern rear LED battery lights and one rear front light on each.

My advice for your application, a cheap commuting bike, would be to buy a set of cheap, bright LED battery lamps, or better, two sets for redundancy, and fit those, leaving contemplating dynamo lighting as something you can do at leisure.

WJH

[[XAP]Bob]

I would reiterate that many Dynamo lights can be run from a PP3, so one of those sets could reasonably be a dynamo-ready set.

Meaning that the switch to 'true' dynamo lights is merely adding a dynamo - and modern bottles are less bad than their reputation. I abandoned mine when it died after a summer's rain without being turned over at all...

[fetimo]

Thanks for all the advice, it's really appreciated.

I've got front/rear LEDs under the saddle and on the handlebars. Getting this working, as wjhall said, is more of a leisure thing. Having said that I'll see if the bike makes it through the summer/autumn and look at digging deeper if it does!

For those that mentioned attaching a PP3, is that just via something like http://www.maplin.co.uk/p/pp3-snap-battery-clip-hf28f?

If there's no front light and no dynamo, it's not worth trying to use the rear dynamo light. If you want dynamo lights, start from scratch with modern stuff. the lights are far better, sidewall dynamos not so much.

There's evidence that a light was once mounted there but no longer exists (I'm looking for something that'll fit the existing fork crown bracket but should probably just replace it, possibly the B&M Eyro and abandon the dynamo aspect).

[[XAP]Bob]

Yes - Worth a read:
http://mccraw.co.uk/battery-powered-dynamo-lighting/

[wjhall]

Interesting reference. It might be safer to use a 6 V battery pack, rather than a 9 V PP3, bearing in mind that 6 V is the usual nominal voltage for a dynamo system. It will depend what electronics are in the lamp, and whether you can find out the manufacturer's voltage spec. I have an LED front lamp in one system and in operation this shows up to 8.2 V rms at the lamp, with a reasonable light appearing a little above 3 V, suggesting that the lamp in question contains an appropriate regulator. At 6 V DC it drew 0.38 A, what you would expect as the nominal condition for a dynamo front lamp.

Yes - Worth a read:
http://mccraw.co.uk/battery-powered-dynamo-lighting/

I am not convinced about the advantages of modern bottle dynamos, the modern one I have is electrically good, but uses rubber traction rings that seem to have an unacceptably short life. The LED front lamp is actually driven from a Miller. I would nominate the Miller with hex nut lead and pulley fixings as the best, but I do not have a stock of spare pulleys, so any views on reliable modern bottle dynamos would be welcome.

Bearing in mind the much higher cost of dynamo lamps, I feel it is something that could be put off until you actually decide to fit a dynamo system. Cheap, bright, redundant LED battery lamps are practically in the financial noise.

[tatanab]

Running modern LED lights from a battery - a way to do this may be to use lights intended for e bikes because they are designed for DC use over a wide range of voltages. https://www.athleteshop.co.uk/spanninga ... s-xe-50-mm https://www.athleteshop.co.uk/spanninga ... -light-led

[[XAP]Bob]

The 6V nominal output from a dynamo is AC, which is about 8.6V peak.

BUT - a dynamo is a current source (500mA usually) rather than a voltage source. If lightly loaded then a dynamo will happily provide tens to hundreds of volts. Dynamo lamps therefore tend to have capacitors and regulators after the rectifier, so the circuitry is designed to deal with relatively high voltages.

I am therefore happy to recommend a PP3, or a set of AAs (targeting ~8-9V).


Personally I use a B&M Lyt at the front most of the time, which is available for <£16 and a toplight at the rear - total cost <£30 (and that's taking SJS prices which are normally a bit high IME).
The Lyt is an excellent light for town riding - you don't need to light the road, but it does put a decent patch down that way, and it provides a large visible light for 'being seen', enhanced by the built in retroreflector.

I have a Cyo? on the trike, which is used for winter commuting along unlit country roads, and that works very well - but I have used the Lyt in similar circumstances quite happily...