Dynamo battery charger

[vonnieglen]

Hi Eric

thanks for the help, it makes sense now

Well I am glad that the posts make sense to you, but to me, someone who has experimenrted a lot with these little dynamos the posts seem confusing and less than helpful. These dynamos behaive in a way that is far different from what persons who are unaware of their electrical characteristics are assuming. The voltage / wattage ratings are only relevant when used with the original resistive loads that they were designed for. Even the smaller 6v 3w dynamos will output 9v at slow speeds. It all depends on the amount of load you put on them. With an open circuit many 6v dynamos will put out up to 50v at around 20mph... with any kind of load the voltage drops off dramatically. The size of the bulb regulates the AC voltage in an unmodified system. A 6v 3w bicycle dynamo with a full bridge rectifier can easily charge a small 9v battery, without any extra circuitry even at fairly low speeds. I know, I have done it. Depending on the type of battery it might not be a very good idea.

I use a 12v 6w bicycle dynamo and a full bridge rectifier from Radio Shack to charge a battery and run bicycle lights. I prefer the larger size because they are more robust and I use a rubber cap that goes over the small wheel that rides against the sidewall of the tire which reduces the internal speed of the dynamo at a given speed and causes the entire system to run much quieter and cooler. I isolate the dynamo from the frame of the bicycle, hook the DC output from the rectifier to a small 6v SLA battery. It charges the battery even at low speeds. I monitor the voltage of the battery, but the battery acts as my voltage regulator and with the load from the lights I have never had any difficulty with over-charging.

Personally I feel that SLA (sealed lead acid) batteries are the most robust in this type of application. NiMh, NiCad, Li-ion, are all easier to damage. Even the SLA's should be monitored to make sure you are not over-charging although this would be very hard to do using a small bottle dynamo. I am switching over to dynamo hubs and LEDs but the principles are the same.

 

[elect89]

hi im new here.

i want to build a dynamo battery charger that can power rear and front LED and maybe power other things like charge hp etc. i wanna use the bottle dynamo 6V 3W. and for the battery maybe a 6V2.3Ah seal leaded battery (or can anyone suggest any other battery that more suitable).

if anyone can give the circuit diagram and explain the process it would be helpfull.

thank you.