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LED Lights and NiMH batteries

fishywebfishyweb Posts: 173
edited June 2007 in Road beginners
Can anyone let me know of a reasonably priced front light that works well with NiMH AA batteries, suitable for use on lit and some unlit roads (though not at fast speeds!)?

I bought a Blackburn light set consisting of Quadrant front and Mars 3.0 rear lights. The Quadrant takes 4xAA batteries and the Mars takes 2xAAA. I've tried using rechargable NiMH batteries and had some problems, especially with the front. Although they are all fully charged, using a good quality charger, I find that the light only works with particular batteries. Maybe I have some faulty ones, but they work perfectly well in other demanding gadgets (digital camera etc).

Any thoughts on this, or recommendations of another light?

Is this the right forum to use, or should this be on the Techie forum (I'm a first-time poster on here)?
http://app.strava.com/athletes/287459
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Posts

  • biancobianco Posts: 78
    What mah are the batteries.

    Remember that they are only 1.2v instead of 1.5v so I've always had to get batteries with a higher mah to compensate.
  • fishywebfishyweb Posts: 173
    bianco - I've tried 2300 and 1800 mAh. It won't work with 4x2300, nor with 4x1800, but is OK with 3x2300 + 1x1800, but they have to be certain ones. I know it sounds like faulty batteries but, like I say, they are OK in other demanding gadgets, and it is a very high failure rate as well!

    I'm mindful of the lower voltage of NiMH, and was sceptical about whether they would work at all with LED lights - I guess there must be some regulator circuitry.
    http://app.strava.com/athletes/287459
    Member of http://www.UKnetrunner.co.UK - the greatest online affiliated running club
  • peterbrpeterbr Posts: 2,076
    Here goes:

    Cheap lights will simply protect the LED with a series resistor, so you will lose some output with a lower input voltage. More sophisticated lights will have a proper constant current controller and it won't matter at all providing the total voltage exceeds the forward voltage drop of the LED and a small overhead for the controller. It sounds to me that some of the cells you have have a slightly lower voltage than others and hence can't drive whatever control circuit you have.

    You won't notice this in other high-drain applications for the simple reason that 1.2v or 1.5v or whatever are simply the nominal terminal voltages. If you apply a load on normal cells, they have a high internal resistance, which leads to a rapid drop in cell voltage as the current increases. NiMH cells have very low internal resistance and hence when delivering high currents, the voltage still stays high, even if that is a little lower than expected to start with. If you drive a halogen lamp for example, the voltage on a NIMH cell will probably be lower than an alkaline when off but higher when on.

    The simple solution is borrow a volt meter from somebody and check them - if somebody you know also has a more sophisticated battery charger, you can measure the actual capacity of each cell (that stated on the cell is a nominal, engineered capacity, chemistry can produce varying results) - use cells with the closest matched capacity and voltage together in pairs or fours. For rear lights I'd recommend you use lithium primary cells. These last me around a year anyway.

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    "Europe\'s nations should be guided towards a superstate without their people understanding what is happening. This can be accomplished by successive steps, each disguised as having an economic purpose, but which will eventually and irreversibly lead to federation"
    Jean Monnet, founding father of the EU.
  • fishywebfishyweb Posts: 173
    Thanks very much for that explanation. Very useful indeed.

    Are you able to recommend any lights that have a constant current controller, that don't cost mega-bucks?
    http://app.strava.com/athletes/287459
    Member of http://www.UKnetrunner.co.UK - the greatest online affiliated running club
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