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  1. #1
    Mr. cost-benefit analysis
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    Need help with my DIY rechargable halogen.

    Well it's back to the drawing board on my DIY rechargable halogen project. I hope someone can help me understand where I went wrong.

    I started with a 12 volt 20 watt halogen bulb from Home Depot, wired straight into the male plug for a 14.4V 5000mAh rechargable Ni-MH battery from batteryspace.com. http://www.batteryspace.com/index.as...OD&ProdID=2462 It took about 1.5 hrs. to charge the battery as instructed on the rapid smart charger.

    Initially I was estatic with the intensity of the light, as well as the distance and pattern. Unfortunately, within .5 hr. the heat from the halogen bulb had melted the front of the housing I constructed out of PVC. Not such a big deal. It was super cheap to fabricate and version II woun't cost much either.

    My main concern is that I only got about 45 minutes of rideable light on this initial charge. That just isn't going to get me home from work. Frankly; I was expecting more out of this bulb/battery combination, since batteryspace.com recommends it for HID and halogen bicycle lights. I'm hoping that someone here has some experience with this or a similar battery, and wouldn't mind answering a few questions.

    1: Should I expect a 20 watt halogen to run longer on this battery?

    2: If not, can you recommend a bulb which will give me a better burn time? I really need 2 to 3 hours.

    Thanks in advance. DanO
    Last edited by Bottomfeeder; 10-26-07 at 11:36 PM.

  2. #2
    Mike
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    New NiMH batteries need 3 or 4 cycles to reach their full potential. I would recharge and run again. Secondly, 5000mA is to small a pack to get 2.5 hours out at 20 watts (100% capacity). I believe that the best you can do will be a conservative 60-70% at that amount of current. The quicker you discharge the battery with a large current draw, the less of the rated output you will get. A smaller current draw (say 5 watts) will get closer to the rated capacity (maybe 85%), but you will never get 100%.

  3. #3
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by mjww View Post
    New NiMH batteries need 3 or 4 cycles to reach their full potential. I would recharge and run again. Secondly, 5000mA is to small a pack to get 2.5 hours out at 20 watts (100% capacity). I believe that the best you can do will be a conservative 60-70% at that amount of current. The quicker you discharge the battery with a large current draw, the less of the rated output you will get. A smaller current draw (say 5 watts) will get closer to the rated capacity (maybe 85%), but you will never get 100%.
    The first part of your post is correct. Batteryspace even sends an information sheet with information about how to treat your battery new. The battery should be given 4 cycles before it reaches capacity.

    The second part of your advice is off. A 20W bulb run at 14.4 V draws 1.4A. That less then half of the batteries capacity...5A per hour would be maximum capacity. Ni chemistry and Li chemistry batteries can easily handle a full capacity discharge at 70F. SLA can't.

    The battery should give around 3.6 hours run time with a 20W bulb. I've found, using a similar bulb with a lower capacity battery, that the run time is within 10% of the rated time...after the battery reaches full capacity.
    Stuart Black
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  4. #4
    Mr. cost-benefit analysis
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    Thanks for the quick response guys. I did read the info that came along with the battery/charger combo and am aware of the initial 4 charge/full discharge cycles when the battery is new. I was just a bit concerned with even a first burn time of 45 minutes. I will proceed with the 'break-in' procedure this weekend using the 20 watt bulb.

    But I have another question - naturally, I'm new at this. Since I am off to the Home Depot to buy supplies for a new housing, to replace the plastic one which couldn't take the heat, should I consider a 15, or even 10 watt bulb? How do you think that might improve my burn time once the battery is 'broken in'.

    Thanks again. DanO

  5. #5
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by Bottomfeeder View Post
    Thanks for the quick response guys. I did read the info that came along with the battery/charger combo and am aware of the initial 4 charge/full discharge cycles when the battery is new. I was just a bit concerned with even a first burn time of 45 minutes. I will proceed with the 'break-in' procedure this weekend using the 20 watt bulb.

    But I have another question - naturally, I'm new at this. Since I am off to the Home Depot to buy supplies for a new housing, to replace the plastic one which couldn't take the heat, should I consider a 15, or even 10 watt bulb? How do you think that might improve my burn time once the battery is 'broken in'.

    Thanks again. DanO
    A 15 W would be a good compromise and give you a slightly longer run time. To figure the run time use this formula

    Hours = (Ah * V)/W

    where Ah = battery rating amp hour rating (divide by 1000 first)
    V = voltage of system
    W = watt rating of the bulb.

    For your system, for example

    H = (5 Ah * 14.4V)/20 W
    = 3.6 hours

    if you change to a 15 W bulb you get

    H = 4.8 hours.

    These are best case scenarios. Your actual run time will be slightly less...maybe 10 percent.

    The big difference will be in light output. A 20W bulb overvolted by 20% (14.4V vs 12V) will put out 29 lumen per W or around 700 lumens. A 15 W bulb will put out around 28 lumen per W or about 420 lumen. Still a bright light for cheap

    Go over here to learn more about lights and output. Try the MR16 bulbs. I'm not sure I agree that the output of the MR16 (it's about the optics) is as much greater as he suggests but it might be worth a try for a DIY light.

    I'd suggest you look at the landscape lighting for the head. The plastic used is more resistant to the heat then PVC. Nylon melts about 60 F higher than PVC (around 360F vs 420F).
    Stuart Black
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  6. #6
    Mr. cost-benefit analysis
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    Thanks again Stuart. I'll definitely cruise the landscape lighting section when considering the new housing design. But that's the fun part, actually.

    I was more concerned about battery/charger performance. And regarding that, you're calculations for 15 and 20 watt bulbs are encouraging. I would be happy with 2.5 to 3 hour burn time. So I will continue the break in charge/discharge sequence in good faith. I am presently keeping track of the 2nd discharge.

    I am definitely going to find 15 and 20 watt bulbs which will fit the same housing so I can compare.

    Now I gotta git down to the Depot.

    DanO

  7. #7
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    I am running a 20W halogen off of a 14.8v Li-Ion pack. I find the current draw to be more like 2A than 1.4A. I get 2-2.5 hours from my 4.8AH pack.

    For a housing I use a 4" piece of 3/4" copper pipe. I drill a hole in the side for the wires to come out. I solder the wires to the terminals of a MR16 bulb and then Gorilla Glue the bulb into the pipe. I add an endcap and seal around the wires to make it all water tight. I then spray paint the outside of the bulb to keep the light from leaking out. A Two-Fish handlebar connector is used to hold it in place.

    I have been using this light for the past year with no problems. I actually built a backup but have never used it.

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