Bicycle project - Need help designing circuits and advice on the project.

FixedG3ar · Oct 23, 2012

Hi all, I'm new to this forum, I joined because I need help with a little project of mine.

I am interested in Bikes, single speed/fixed gear bikes are a favourite of mine. I have always wanted to build a custom fixie bike and I may get the chance soon. I would like to make it stand out so have been coming up with a load of ideas which may help make my bike a little more unique. most of my ideas are inspired by what I have seen on the internet while looking for ideas for mine. I would like to make use of Dynamo hubs to power axillary lighting, which will be functional as well as interesting to look at.

I would like to install a neon effect light underneath the frame, I will be trying to conceal the light by using car body filler to visually thicken the down tube whilst leaving a channel down the middle of the down tube to fit a neon effect light. I would like to be able to switch on/off this light via a push button on the end of my handlebars.

Another feature I would like to add is functioning indicators, these will probably be orange LED strips. I would like to control the indicators via a sliding switch with three settings, the middle setting being off and the left or right setting controlling the LED's on the left/right hand sides of the bike.

From my research I understand that Dynamo hubs provide a consistent amount of power at a consistent speed, and that axillary items such as lights will slowly die out when you stop. I would like the lights to remain illuminated for a little while longer when I stop at traffic lights or crossings. I suppose this could be done by using a capacitor somewhere in the circuit. That is one thing I will need help with from people on this forum.

I have made a simple diagram displaying the ideal location for the LED's, neons and switches.

http://www.flickr.com/photos/[email protected]/8116898679/in/photostream

Any help/advice you can give will be much appreciated!, I would also like to know how practical this project will be and if it is easily completable.

Thanks all for any input, Jordan.

KJ6EAD · Oct 23, 2012

You're probably going to need a battery to run your lights and effects. The dynamo alone won't be enough. You should also consider using only LEDs for all lights and effects since they're efficient and shock resistant.

Raven Luni · Oct 23, 2012

KJ6EAD said:

You're probably going to need a battery to run your lights and effects. The dynamo alone won't be enough. You should also consider using only LEDs for all lights and effects since they're efficient and shock resistant.
Click to expand...

I agree. A small sealed lead acid battery is probably the way to go. You would need several farads worth of capacitance to keep things running for any meaningful length of time and the bigger the capacitance, the more work would need to be done to charge them. You can still use dynamos to charge the battery not unlike a car alternator.

As for the neon effect. EL wire is probably the best bet for that. I know they use high voltages and require special inverters but I've no idea how power efficient they are.

Another way to keep power requirements down is to pulse the LEDs at high frequency. This works well for standard and high / super bright types but not for the big multi-watt ones (I learned this when trying to make a super efficient torch with 3 3W LEDs only to have it complately outshone by a single LED off the shelf torch )

FixedG3ar · Oct 26, 2012

Thanks all for your replies, I have re considered and might change my design slightly, I need to start building a parts list soon.

What effect would running two dynamo hubs have? I can run a driverless dynamo on the front and freewheeled dynamo on the rear, it would mean I cannot ride fixed anymore but will consider it if it means I can have the features I would like.

Laplace · Oct 26, 2012

I use a Shimano 6-volt/2.4-watt hub dynamo to power a Hi/Lo-beam LED headlight & taillight on my bicycle. The Lo-beam is an array of 16 superbright white LEDs each driven by its own 20 mA current source. The Hi-beam is a one-watt LED in series with the Lo-beam array and mounted in a reflector sending out a focused beam to punch through the dark of night. At low dynamo voltage (low speed) a power MOSFET shorts out the one-watt LED so the LED array gets all the voltage. When a sufficiently high generated voltage is sensed the MOSFET is switched off so both the Lo-beam & Hi-beam LEDs are powered on.

The issue with the hub dynamo is that it has a high internal resistance. With no load I have measured 70 V (rms) on the terminals - it's not a clean sine wave; more like a distorted square wave. With a 400 mA load the voltage drops to 6 volts, more or less depending upon speed. Also have a one-farad supercapacitor that will keep 10 mA flowing through the Hi-beam and taillight for about one minute after the bicycle stops.

Bicycle project - Need help designing circuits and advice on the project.

FixedG3ar

KJ6EAD

Raven Luni

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