Dynamo on way out ?

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ianpallen
Posts: 70
Joined: 12 Nov 2014, 10:43am

Dynamo on way out ?

Post by ianpallen »

I have removed my bottle dynamo and front light.. I have wired up the rear dynamo light to a battery pack and put an led bulb in so the batteries last longer. The front light works ok with the bottle dynamo as does the back, but when I have them wired together, the front is hardly lit. It seems the rear light is taking all the power. I have checked the wireing and there are no shorts and both lights are wired the correct way. If I change the polarities over, the light will not work at all. Is this an indication the dynamo is on its way out as it cannot power both lights at the same time ? At least, there will not be any whirring or pressure or load on the back wheel. The front light is a halogen and the back light is a nornal 6v bulb.
tatanab
Posts: 5033
Joined: 8 Feb 2007, 12:37pm

Re: Dynamo on way out ?

Post by tatanab »

Sounds like the wrong rear bulb. It should be 6V 0.1A (0.6W). Dynamo sounds fine.
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Dynamo on way out ?

Post by Brucey »

I think you need to check carefully that

a) you have the grounded connections correctly wired; (each lamp will have a ground connection in it which is to allow single-wire wiring instead of twin-wire wiring, but the latter is a better idea) and

b) that you have the correct bulb ratings in each lamp.

The rear light needs to have a 0.05A or a 0.1A bulb in it if you are intending to use it with a headlight as well. An LED rear light is a much better idea; they can draw less current, leaving more for the headlight.

cheers
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ianpallen
Posts: 70
Joined: 12 Nov 2014, 10:43am

Re: Dynamo on way out ?

Post by ianpallen »

Thanks. The wires were the correct way fitted as when I tried them the other way, they would not light up. The lights light up perfectly on their own on the dynamo, but not together. The rear bulb is a Philips 6v 0.6w. My sons bike has the same lights and bulbs but a different dynamo. My dynamo is a single connection with earth on the mounting / body of the dynamo. One thing that is strange is I dont have to have the earth connected to anything, just to the other light earth. If I twist the earth wires together and leave them, the lights work, but if I connect the wires to an earth (dynamo mounting bolt to frame), the lights will not come on. I think I will convert both lights to battery pack. The led in the rear light now is so bright, it makes the light look pink. lol.
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gaz
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Re: Dynamo on way out ?

Post by gaz »

If you have a powerful white LED behind a red lens it will turn pink. Red LEDs are a better choice.
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ianpallen
Posts: 70
Joined: 12 Nov 2014, 10:43am

Re: Dynamo on way out ?

Post by ianpallen »

gaz wrote:If you have a powerful white LED behind a red lens it will turn pink. Red LEDs are a better choice.



It is a white led. I will have to look for a red one. :D It will do for now though. I have other red rear lights to use too.
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Dynamo on way out ?

Post by Brucey »

ianpallen wrote: One thing that is strange is I dont have to have the earth connected to anything, just to the other light earth. If I twist the earth wires together and leave them, the lights work, but if I connect the wires to an earth (dynamo mounting bolt to frame), the lights will not come on....


hang on, I've just read this post..... I think you have effectively wired the lamps in series or something mad like that, instead of parallel.

cheers
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ianpallen
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Joined: 12 Nov 2014, 10:43am

Re: Dynamo on way out ?

Post by ianpallen »

If I go positive to positive wires and place them in the dynamo connection (there is only one under the bottle) and twist the earth wires together, but not put the wies to an earth, the lights work. If I ground the wires on the dynamo mounting bolt, the lights dont work. If I change the wires, earth to positive and put one lot on the dynamo connection, one light works but not the other. If I swap the wires around on the connection, the other light works. I can get the lights both working at the same time, but the front is dim and the back is bright as normal as if it was wired on its own to the dynamo. Front wired up on its own is bright. Connect rear and front goes dim again. :? strange but back light is ok both with or without front light wired up.
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Dynamo on way out ?

Post by Brucey »

I still think that in one of the configurations you have wired the lights in series. In the other configurations you may only get one light working because not all LED bulbs draw current at the same voltage; if the white LED bulb contains a simple overvoltage protection it may limit the voltage to the front bulb perhaps?

When neither light works you have probably wired the dynamo live to ground via the ground connection in a lamp housing.

If you fit a tungsten rear bulb what happens?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
mercalia
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Re: Dynamo on way out ?

Post by mercalia »

I think the only way a bottle dyno is likley to fail is if the bearings go
tim-b
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Joined: 10 Oct 2009, 8:20am

Re: Dynamo on way out ?

Post by tim-b »

Hi

I'm no expert on dynamos, and frankly I prefer battery lights, but prejudices aside I'm interested in this...

Are you running the LED rear light while all of this is going on? They have a polarity that must be followed if they're to work in this application, and will generally only allow current to flow in one direction. LEDs can take a reverse voltage, however they can be damaged if a large enough voltage flows the wrong way; replace the LED with a bulb while you experiment

If I'm reading your description correctly, "If I go positive to positive wires and place them in the dynamo connection (there is only one under the bottle) and twist the earth wires together, but not put the wies to an earth, the lights work"
You're connecting a loop from + to + and in the absence of another connection nothing can flow, there must be a short to earth somewhere if this arrangement works

Regards
tim-b
~~~~¯\(ツ)/¯~~~~
ianpallen
Posts: 70
Joined: 12 Nov 2014, 10:43am

Re: Dynamo on way out ?

Post by ianpallen »

All of the testing on the dynamo was while it was with its proper light bulbs. The led is now fitted and running off battery power. After not getting the front light to run bright with the back light connected, I decided to remove the dynamo set and I thought about converting the rear light to battery. This is when I thought obout putting the led in. I will be getting a red led soon so the back light is not pink. I have other rear lights for bikes, but the 'dynamo' one is a rack mount light. :D
I will just have to suffer and keep buying batteries instead of running on dynamo's. The dynamo was on the back wheel. There is a purpose brazed on bracket for it. If I can find a decent bracket so I can put it on the front, I might have the front halogen light running off it. The front works perfect without the back light.
I was told before, or I read it somewhere, led's cannot work off a dynamo as a dynamo is AC and batteries are DC. I dont know if this is true, but i have never tried it. :?
ianpallen
Posts: 70
Joined: 12 Nov 2014, 10:43am

Re: Dynamo on way out ?

Post by ianpallen »

tim-b wrote:Hi

If I'm reading your description correctly, "If I go positive to positive wires and place them in the dynamo connection (there is only one under the bottle) and twist the earth wires together, but not put the wies to an earth, the lights work"
You're connecting a loop from + to + and in the absence of another connection nothing can flow, there must be a short to earth somewhere if this arrangement works

Regards
tim-b



This is what is puzzling me. If I put the 'earth' wires to the earth, the lights dont work.
When I first got the bikes, there were two wires off from the lights near the dynamo. On each light, there are two connections, positive and earth. These wires are the same as speaker wires (black and a black with white tracer). Black wire is to the positive, joined together and to the connection under the dynamo. The black / white wires were twisted together but not ground on the bike or dynamo body. So I ground them to the dynamo bolt, this should 'earth' them, making a circuit. I learned that much in collee on a vehicle mechanics course. :wink:
The lights did not work with dynamo running at fast speed. I disconnected the 'earth' wires from the dynamo mounr bolt. The wires still wired together. They worked with dynamo running fast. Front was dim and back was bright (normal). Strange.
If I seperated the wires, front connected to connection under dynamo and to the earth, the light worked bright. If I swapped the wires over, the light did not work. Same as the rear light.
The two main things were,
1) How can lights work without a circuit (but they would not work if it was + to - to make a loop circuit)
2) why would front light be bright on its own but dim when back light wired as well.
This is why I was thinking the dynamo was on its way out.
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Dynamo on way out ?

Post by Brucey »

the wire 'colours' potentially mean nothing; the usual convention is not universally applied.

For the third time; you have connected the lights in series when they both light up and your 'earth' wires are not 'earthed'.

Note also that one (or possible both) of your lamps will almost certainly have their own built in ground connection.

cheers
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tim-b
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Joined: 10 Oct 2009, 8:20am

Re: Dynamo on way out ?

Post by tim-b »

Hi
I would consider a couple of things, but only one at a time:
If you think that the dynamo is the problem, try a temporary swap with your son
Take both your front and rear lamps off their brackets so that they can only make a connection through their cables, wired normally to earth
EDIT: What make/model is everything?
Regards
tim-b
~~~~¯\(ツ)/¯~~~~
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