I use a lead acid battery to power my bicycle lights. It is 6v & needs replacing (it is only working for 45 mins now instead of hours).
I have been pondering using a 6v Dynamo to put charge back in whilst I am cycling. Now would be a good time to test this as the battery is at the end of it's life span & dos not matter if I kill it completly.
My questions are;
I am guessing as a dynamo is basically, a motor, I will need something to stop electricity flowing back & powering the dynamo as a motor. I think for this I need a Diode - is this correct, and if so, what type of Diode do I need to ask for?
If I wire the dynamo to the battery in parrallel with the lights, If I have the dynamo charging whilst the lights are switched on, what happens? I am guessing this should not blow the bulbs in the same way an alternator is charging a caar battery all the time (unless some sort of regulator is involvd?)(6v rated) - is this correct?
It is doable within limits. Find out what voltage your dynamo generates under load and no load - presumably you'd do some peddling during the day and that could be used to recharge the battery.
Good solution if you are camping for months on end with your bike.
Dynamos output AC and the rectifier diodes you'd need to convert to DC to charge the battery would prevent discharge. A switch or two on the handlebar would give you some flexibility on whether to use battery or dynamo - or you could just use a steering diode - dynamo voltage goes lower than the battery and voltage flows from the battery to the lamp.
It can be made lots more complicated - but a switch(s) and diodes and you're home free at little expense with good control of the system.
Now - while you're at it reduce the current demands of your lighting system. Switch to leds if you can. I mounted 56 white LEDs under my motorcycle headlight and it is more than enough at night for bicycle speeds (50-75 feet) - uses a measly 3 watts and looks brighter than the headlight in daytime - just doesn't have the same beam spread only
20 degrees. Headlight consumes 50 watts. Leds set me back $7 and the resistors and potting compound works out to about 9-10 total for the lamp.
Consider Nickel Metal Hydride rechargeable packs or Lithium also - may be able to lower the weight some.
Finally if you haven't already bought a dynamo; consider an in-hub one. The thingees that rub against the wheels add a lot more drag and abrade the tires over time. The in-hub dynamos start producing earlier and are current regulated to some extent (not good for battery charging- but saves light bulbs on an all dynamo system) The friction types will pop a bulb at over 15 mph.
In-hub dynamos cost, but are well worth it if you drive in the dark a lot. Requires a new wheel or some new spokes and re stringing the wheel. Since you would have some bucks invested in the front wheel ditch the skewers and use rounded lock nuts so the wheel isn't stolen.
To get power from the dynamo to the battery the dynamo has to produce enough voltage to overcome the diode drops point six volts or so plus a few tenths of a volt over the resting battery voltage (6.3 volts for lead acid - so figure 6.6 volts - more is better) which works out to
7.2 volts. - a 12 volt system will be more efficient at around (14.5 volts for charging)
I was writing to some guy in France awhile back who has an automatic system for charging and lighting - he camps in the mountains and uses the battery for lighting the way and reading at night.
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Whilst I appreciate your name Homer, I dont belive the drag would be a problem - if for no other reason than that the dynamo would not be able to excert eenough pressure on the tyre before it skidded. I may be wrong, but i do not think that even a direct short across the dynamo would cause this - and I am just intereste din trickle charging.
Weight is not a problem. My interests lie in low cost & resiliant lighting which can be charged from my own power.
Thanks for all the Ideas, I shall spend some time trying find and price components - I like the Idea of a LED system, but I am in the UK & generally, we are ripped of for electronic components - but i shall investigate!
Its interesting to hear of the guy in France - thats the sort of thing I had in mind, I just have to get a bit of knoweledge to acheive it.
TO further the Idea, when I have nothing better to do I d like to buy a excersise bike, connect it to a a alternator from a car & attempt to use my excersising to cpower lighting and other things in the home - I know its a bit crazy & doesnt really save much, but it just sounds fun!
If I take the bike thing any further, I will post how I get a long, I havent got as much time as I would like though!
I bought the LEDs on line from Hong Kong, the shipping was free
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A set of three 1 watt LEDs at $30 would give a little more light and out to the sides, 120 degree beam spread - but this works for me I just don't want the guys at intersections to pull out and test my driving skills or brakes and the LEDs seem to be doing that.
He was rectifying the AC from a hub dynamo and regulating it with SCR's to charge the battery when there was excess power to be had.
I've used both hub dynamos and friction types. Hub has it all over friction style for performance, and friction over hub for price.
Another guy is marketing a flashing LED bike light that works off a frame mounted coil and a magnet affixed to the spokes - don't know if that can do much more then keep one from getting run over in the dark. Put a lot of very strong magnets on the spokes and it might equal a dynamo for less money.
What's crazy? - makes a lot of sense to power the TV while watching it, lot healthier. There's satisfaction, knowledge, bragging rights, in the project with exercise for a side effect - sound like reasons to me.
Good luck
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It is true that dynamo on cycle is AC type. So use a bridge rectifier not diode. That will kill dynamos magnet in long run.
If U have lights on while charging then not much happens than U will huffing and puffing within a KM of cycling. If U switch off lights (in day time) may be after 20-30kms U will overcharge battery if U haven't put a current limiter after bridge. By the way U havent mentioned what battery AHs are. I think it is mostly 4.5 AH used in most of bikes. It has limit of 1.2Amps of charging so U have to put small resistor like 0.5ohm in serries. As somebody else has mentioned it is better to use LEDs as they dont pop off with excess voltage but for that condition U have to get speed like going downhill. With battery bulb doesnt popoff but if it is old battery then with overcharge its voltage may go beyond
8Volts and kill both the bulb and battery.
I have seen that people using friction dynamo have to change tyres frequently and hope U better get those axle dynamo. Best way would be to use small car alternator with some attchment to enagage/disengage it. Alternator has battery charging regulator. U will also need smaller
12V 4AH battery or get a pack of LI-ion batteries which are better than lead acid type.
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