Powered Head Stem on my bike

Discussion in 'General Electronics Chat' started by Julian Jane, Jun 10, 2016.

  1. Julian Jane

    Thread Starter New Member

    Jun 10, 2016
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    Hi All,

    New to the forum and I am developing a powered head stem for my bike.

    I'm on the second iteration (pics attached) and it works well.
    The objective is to have power to my camera for around 6-8 hours.

    I can ft 1 x 18650 2500mah battery in with the circuitry however I'm thinking 4xAA batteries would be better.
    However, I see there is no commercially available 4xAA USB rechargeable battery packs on the market, there's clearly a reason for this but could someone explain in layman's terms why?

    the 1 x 18650 battery works fine but only lasts for around 4 hours (along with the camera inbuilt battery)

    Thanks
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are rechargeable AA batteries and there are 4 cell battery holders.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Lol, I thought you were talking about a steam powered bike.
     
  4. Julian Jane

    Thread Starter New Member

    Jun 10, 2016
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    LOL......steam, now that would be novel.

    tracecom - thanks for the reply, I realise I can buy separate batteries and a holder however I want to be able to recharge them in suti like I can at present, otherwise I'd have to remove my bars after every ride to change the batteries.

    I suppose my question is:

    Why can't I buy a 4 x AA USB power pack which I can recharge by USB?
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Four AA batteries in series would be over 6 volts. I presume the camera runs on 3.7V, which seems to be the output from a single 18650 battery. To increase the run time, you would want to put multiple 18650 batteries in parallel so that the voltage remains at 3.7V. An arrangement of two 18650 batteries in parallel would approximately double your run time; adding another two 18650 batteries also in parallel would almost double it again. Keeping the voltage at 3.7V would enable charging with 5V from a USB source. https://www.amazon.com/SmartLive-50...&sr=8-3&keywords=18650+batteries+and+chargers
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Not with Ni-cads. Aren't they 1.2V nominal? Or you might consider using 3 and just a short across the 4th position.
     
  7. Tonyr1084

    Active Member

    Sep 24, 2015
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    First, welcome to this forum.

    Judging by the pictures you don't have room for additional batteries inside the stem. So you'll have to modify it somehow to allow an external power source. Without knowing how your batteries are presently charged all I can do is guess that additional batteries will be charged through the internal charging circuit.

    I would be concerned that the charging circuitry might not handle the extra load. It could burn out. On that assumption your external batteries may need a charger of their own. Hence, probably the need to be able to plug in and remove the external power source.

    Also consider recharge time. If it takes 4 hours to recharge then double the capacity would take twice as long to recharge. Having an external - detachable - power supply with its own charger will cut that time considerably. Assuming twice the capacity - it would take twice the time to recharge. Meaning 'as soon as you get back from your ride you'll need to put the camera batteries on recharge.'

    Also a benefit of an external PS, you can have extra batteries being charged while you're on your ride. If for some unexpected reason you find you may be riding for 12 hours (I've done that before - a very long time ago) (Whittier CA to Laguna Beach CA and back - as well as knock-around riding in Laguna), you can have the extra batteries charged and in your backpack.

    Food for thought.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    4 AA NiMH batteries in series have a output of over 4.8V when charged so can't be charged from a 5V USB unless you add a boost switching regulator to get more than 5V.
    Why do you want to charge them from a USB source? You can buy wall-powered chargers to charge any number of NiMH batteries, such as one of these.
     
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