Author Options:

Dynamo charging charging circuit for AA NiCd/NiMh? Answered

I've just got hold of a Union 6V 3W dynamo with lights. I'd like to charge 4/5/6 x AA batteries during the day then switch to the batteries for the lights at night. I'm switching out the old bulbs for LEDs. Any pointers or relevant 'ibles would be great. Thanks in advance people.


1N4001 or better diode (minimum) 4 diode bridge (recommended for 2 X the efficiency) diodes should be capable of atleast 1 A current resistor in series with battery if the batteries feel like overheating charge batteries in series links of 2 - 4 per link. multiple links can be charged together each with its own diodes

So, let me get this right. 1. AC from dynamo thru 4 diode bridge (FWR). 2. Resistor in series - what value would you suggest for 4x 2300mAh NiMh? - or 4x 660mAh NiCd? 3. 2-4 batteries in series per bridge. Sound right?

How about a Zener to stabilize the voltage?

no need. there is need only to reduce current with resistor if its too high and batteries overheat

I have a similar problem, except imp using a "Shake/faraday torch" concept. so to charge a NiMH battery I only need to limit the current going through? so the voltage can fluctuate between positive values? Second: what current do I use? I read elsewhere that "the efficiency is 66%" ie. I need to supply 1500mAH for a 1000mAH AA battery. Is this true? Thanks in advance

batteries like to be charged with limited and constant current etc for max lifetime

but nimh do stand quite well intermittent charging so yep you can charge it with fluctating positive voltage

current limiting is not allways required - fir example in a shake torch i dont think youll get to the currents that make problems (except momentary splashes which are ok). limit the currnt only if you see that the battery heats more than in standard charger

charge efficiency = you have to give the battery about 1.5 - 1.6 X more electricity than you gonna get from it. the battery has to be charged to the maximum whenever possible so you give it electricity 1.5 - 1.6 times more than its capacity

yep first try without resistor. you need one only if the batteries heat more than in standard charger if they do then experiment untill you find the correct one usually its up to few tens ohms max but should be high power resistor so that it wont overheat itself 2-4 batteries per link. 4 batteries to charge with high efficiency. works only if you spin it with high speed most of the time so there is enough voltage. 2 to charge with lower efficiency but works with low / interittent speeds too