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Help with motocycle lighting project

  1. Oct 16, 2008 #1
    I am in the middle of a project, building an on road bike from an off road model and I am to the electrical system the coil I am getting is 200w I will be running probably 80w of lights and some led signals maybe 160w of lights if I feel the need to double the headlights , anyway my Question: with the 200w coil rectifier and regulator I would like to keep the battery VERY small I thought of using the RC type batteries in a pack to 12v are these or is this small battery pack going to have enough capacity / will it handle the 200w coil , maybe I could run 2 packs in parallel . P.S. I only need power when the bike is running , it's kick started and what’s listed above is all the draw.

    Comments better ideas?

    Rick
     
  2. jcsd
  3. Oct 16, 2008 #2

    berkeman

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    200W is a lot of drag for you to push! So yeah, having the battery do the work makes more sense. The battery is rated in Amp hours -- that is, the energy stored is listed as current multiplied by time. So a 1Ahr battery can put out 1 Amp for 1 hour, or 1/2 Amp for 2 hours, and so on. Figure out how much current will be drawn by your load, and use that number to see how big of a battery you need.


    EDIT -- I just noticed that the title of the thread is "motorcycle". Duh. When I read your comment about a road bike, I thought you meant bicycle, so that's what lead to my comment about "pushing" the 200W (which is a lot for a bicycle!). Sorry for the confusing comment.
     
    Last edited: Oct 16, 2008
  4. Oct 16, 2008 #3
    Ok , sorry but I understood about half of your reply, how do I figure the current draw? I will be running 4 20 watt lights (80w) and some led's (not much draw).

    rick
     
  5. Oct 16, 2008 #4

    mgb_phys

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    Power is volts * amps so the current draw is just the total watts / 12V
    Note that a typical car battery is designed for high current not deep discharge - you will typically only be able to use half the amp-hours of a car battery without damaging it.
    NiMH or lithium ion wil give you morecapcity for less weight/size but are expensive.
     
  6. Oct 16, 2008 #5
    Ok then I guess I have a 2 part question are the RC type batteries stacked up to 12v going to have a problem with the 200w input from the coil thru the rectifier? and am I going to have problems drawing that amount from those batteries?

    Rick
     
  7. Oct 16, 2008 #6
    Would a capacitor be a better idea?

    Rick
     
  8. Oct 16, 2008 #7

    mgb_phys

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    200W at 12V is 16A, no problem for a lead acid car battery and your engine should be able to handle recharging (200 is around 1/4hp). If you need the lights when the engine isn't running a small car battery 80Ah would be abdle to run them for 2-3hours.

    You would typically only want to pull about 4-5A from a small NiMH/LiIon battery so you would need a few of them (one per lamp).
     
  9. Oct 16, 2008 #8
    Hi agent141,

    This page may help,

    http://nordicgroup.us/s78/

    I used it as a guide to build a very bright bike light set for little money.
     
  10. Oct 17, 2008 #9
    Ok , thanks for the replies BUT I guess I am not asking the question correctly. I will try again. I have an off road bike, I have an aftermarket upgraded coil 200W, I will be adding 80w of lights and some led signals maybe 160w of lights if I feel the need to double the headlights, I have NO room for a lead acid battery, I need to use a very small battery / batteries, the system only needs to power the lights NO starter ect. My question is will the 200w coil, rectifier and regulator fry the RC type batteries (4500 mAh 35A Rate NiMH),(3300 mAh NiMH) bundled together to 12v, or NiMH Battery Pack: 3700 mAh, 12V if it's to much for one pack could I reduce the draw by running 2 packs in parallel. Or is there a better option.

    Thanks

    Rick
     
  11. Oct 17, 2008 #10

    mgb_phys

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    If it says it can take 35Amps then yes, although a 4500mAh @12V would only run a 200W light for 10-15mins
    Check that the 35A figure is continuous not just for a fraction of a second at startup and consider where you are mounting them so they can be cooled. Don't bolt them under the fuel tank on top of the engine!
     
  12. Oct 17, 2008 #11
    mgb thanks for the quick reply, I do not need any storage , just running the lights when the motor in running, and am I correct in saying that if I run 2 battery packs in parallel it will cut the draw for the individual pack in half?

    Rick
     
  13. Oct 17, 2008 #12

    mgb_phys

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    If you only need them to run when the motor is runnign - why not just use the bike's battery.
    If the bike electrics are 6v and the lights are 12v you will need a dc-dc converter, but you would need that to charge the 12v battery packs anyway.
     
  14. Oct 17, 2008 #13
    The bike does NOT have a battery... I am adding that system to it.

    rick
     
  15. Oct 17, 2008 #14

    mgb_phys

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    Ok, I used to have an old British 2stroke like that, kick start and then everything ran from the alternator - the ligths dimmed when you stopped unless you revved the engine!

    The alternator is probably 6v so you would need to boost it to 12V to run the lights or charge the NiMH battery. I don't know if it would put out 200W, I imagine weight is the main concern in an off-road so it is going to be as small as possible.

    If the alternator doesn't have enough power to charge the lights then you need either a big battery or more efficent lights.
     
  16. Oct 17, 2008 #15
    I guess what I really want to get across is I know what I want to do I just don't know or understand the formulas/ numbers , I have 200w ac from the coil going to a rectifier then regulator to the battery pack / s to a switch to the lights max 170w, my question is will one of these http://www.trailtech.net/040-BATT3.7.html (NiMH Battery Pack: 3700 mAh, 12V) going to work or will I overload it if so can I run 2 in parallel to cut down on the draw. Sorry if I am just not getting it.

    Rick
     
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