Dynamo failure for the second time

[FV43576]

Hi everyone, I have a Radleigh Touring 1957, I used this cycle everyday to work, I have used the Miller dynamo that touch the rear side tyre. For some reason the first has stop working last month so I thought it must be old so I bought a new old stock same Miller for £45. Now 4 weeks later yesterday return from work a bit dark dusk and I come down the hill I am not sure how fast probably under 20mph all the lights went off! This morning test the Dynamo with multimeter it runs on 0.3volts max it should be the max of 7volts. Do you think the speed that cause to damage the Dynamo? I am not really sure why it happen, I have old instruction of Miller dynamo it does not say what speed is max I thought it can go any speed. Do you think I better get dynamo on alloy hub?

[Jdsk]

This morning test the Dynamo with multimeter it runs on 0.3volts max it should be the max of 7volts.

What scale are you using on the meter... magnetos like that generate AC.

Jonathan

[Jdsk]

Do you think I better get dynamo on alloy hub?

Yes. Much better.

Start here:
https://www.cyclinguk.org/sites/default/files/document/migrated/publication/feature-hub-dynamos.pdf
then search the archives for recent discussions of models and lamps.

Jonathan

[FV43576]

Jdsk thanks for your relpy much appreciate.

[FV43576]

Jdsk my multi-meter on AC volts 0.1 to 0.4 is broken! what a rubbish I will go for hub dynamo!

[mercalia]

I have had a B&M bottle dyno for 20 years and never let me down - The only issue was the need to lube the inards a bit as they were getting a bit seized up with stiff action. Also once the cabling broke some where ( not the dyno fault).

[rjb]

Are you using incandescent bulbs. I would check those first incase they have failed and shorted internally.

[mercalia]

Are you using incandescent bulbs. I would check those first incase they have failed and shorted internally.

good point. originaly I had old fashioned haolgen lights then moved over to a led light over the last 20 years

[Brucey]

some old dynamos have a brushed construction and do actually produce (ripply) DC. Until the brushes wear out.

Old miller generators would originally be wired using an earth return. Twin-wire connections are potentially more reliable, especially if the dynamo is on the fork and the lights are not, or vice versa.

The best way of testing the dynamo is using a test lamp. Even something simple like turning the wheel by hand with and without a dead short on the output (which should make it stiffer to turn) will tell you something.

cheers

[Jdsk]

some old dynamos have a brushed construction and do actually produce (ripply) DC. Until the brushes wear out.

I didn't know that. Thanks.

Any idea why they'd do that in an era of incandescent filaments?

Jonathan

[Brucey]

...Any idea why they'd do that in an era of incandescent filaments?...

why?

No, not really.

Unless someone pedantic (what in the world of electronics, surely not....?... ) decided to take their manager seriously when they were asked to design 'a dynamo'. You know, just to show them. And maybe they didn't even notice, either....

cheers

[Jdsk]

Unless someone pedantic (what in the world of electronics, surely not....?... ) decided to take their manager seriously when they were asked to design 'a dynamo'. You know, just to show them. And maybe they didn't even notice, either....

Thanks

: - )

Jonathan

[cycle tramp]

As a bottle dynamo user myself, I think its unlikely that the dynamo would have failed. Personally speaking I would firstly check the dynamo by wiring it into a circuit which contains a small filament bulb which I knew to be working (something like a bulb in a bulb holder with an earth and live lead running from it, with both leads ending in crocodile clips).
If the dynamo is fine, then I would check the bulbs, by replacing them with new ones, and if that doesn't work I would then check the wires to the bulbs.
The thing about electricity generated by forward motion is that it's very easy to get cause and effect mixed up - yes, I suspect that going down hill at 20 mph may have blown the bulbs, but it could have been a coincidence and that by chance, as you were going down hill, perhaps one of the wires detached.
Be methodical- as someone once wrote, don't twist the facts to suit the theory, just collect the facts and allow them to suggest the theory.

[bgnukem]

I remember the lights going out once when I was descending a steep hill with a bottle dynamo on. Then later the lights came back on. I believe there is some kind of voltage regulator in some systems to protect the bulb in the light?

I know it's not the question, but would highly recommend using a hub dynamo instead. Much less effort required to pedal and no issues with tyre wear, dynamo slippage in wet/icy conditions and less chance of water getting into the dynamo causing failure.

[Jdsk]

I know it's not the question, but would highly recommend using a hub dynamo instead. Much less effort required to pedal and no issues with tyre wear, dynamo slippage in wet/icy conditions and less chance of water getting into the dynamo causing failure.

Yes, but that was a question!

Do you think I better get dynamo on alloy hub?

: - )

Jonathan