Vistalite NiMH battery - Battery Pack

Discussion in 'Cycling Equipment' started by tross45, Nov 4, 2003.

  1. tross45

    tross45 New Member

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    I have a Vistalite NSP Hyp 15 light that has two of those long, heavy, battery sticks. The light is a few years old and will need battery replacement at some point. I really don't like the batteries that Vistalite supplies. I have seen battery packs unsed for a lot of other appliacations. What I am wondering is, can you make up a battery pack out of C or D cell NiMH batteries and come up with the voltage or amperage that is needed to run this 15 watt light for a couple of hours. I don't know how to calculate what would be needed to do this.

    Let me know if this is doable and if so how to do it.

    Thanks for any help.
     
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  2. Duckwah

    Duckwah New Member

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    Yep its definitely possible and actually very easy if you know a little about electronics

    its also much cheaper than buying new manufactured packs

    what you need

    1. your system is probably 6 volt so you will need 5 NiMH cells (1.2V each) for each battery pack.
    2. Hook up wire
    3. Plugs that will fit your system, take your current lights to an electronic store to get matching bits
    4. 50mm tube shrinkwrap
    5. electrical tape
    6. Soldering gear, wire cutters etc
    7. Multimeter (not essesntial)

    The vistalite battery pack should have a rating of 2200 mAH or something like that and i used 2700 mAH NiMH cells to make up my pack (you can get 4000 mAH cells to)

    the 2700 cells give me 1 hour 45 mins for a 10 watt glode and 3+ hours on a 5 watt

    to make the packs you need to connect the cells in series and then connect them up to a plug (middle of the plug should be positive)

    If you need any more info let me know, i'll try to post some photos of the packs i made for our 24hr mountain bike race

    I had it down to about 20 mins to make each pack
     
  3. tross45

    tross45 New Member

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    Thanks for the advise. I would really like to see your pictures of the packs that you made.
     
  4. 143paul

    143paul New Member

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    OK - I did this, but I used NiMH 9000mAH D cells.

    The problem I'm having is recharging them - what do you use to recharge? - The stock Vista light charger seems to be overheating.
     
  5. cachehiker

    cachehiker New Member

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    Rapid charging NiMH cells is a bit of a technical challenge.

    A rapid charger for a 9000 milliamp-hour will fry a 2100 maH battery. The amperage being delivered will just boil away the electrolyte. Some of the less expensive chargers for 2100 maH batteries could be used to charge a 9000 maH battery if you watch the time and pull the battery pack before it overcharges.

    The rapid charge function is terminated by a knee in the cell voltage. When charged at an ideal amperage, NiCad and NiMH cells will hit a point where the cell voltage actually decreases in spite of your continually pumping amperage into the cell. The properly designed rapid charger detects this knee and shuts off at this point.

    If the battery pack has a much lower maH rating than the charger was designed for, it just overheats. If the battery pack has a much higher rating, the knee never occurs and it will just overcharge the pack if you don't remove it at the proper time. Better chargers will just time out and shut off under the assumption that you have an old, ruined, or otherwise defective battery pack.

    I use NiCad and NiMH everywhere and I have one bicycle headlight that uses simple AA cells and another that uses D cells. I probably own around two dozen NiMH AA cells and a dozen C and D cells. I also work in an industrial environment where we occasionally test charging circuits. This career has effectively sentenced me to a life of geekdom where I'm continually reading application notes involving subjects not intended for normal people.

    I'll look around a bit this week and see if I can find a generic charger that can be adjusted and built by the average electronics novice. Bother me and I might keep looking for a second week. :D
     
  6. 143paul

    143paul New Member

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    Thanks Bri - your Geekdom has once again proved it's greatness. I on the other hand have only one circuts class and it makes me more of a danger than anything else ;) Let me know what you find.
     
  7. Weisse Luft

    Weisse Luft New Member

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    Electric powered radio controlled model airplanes are growing in popularity. You can find good chargers for NiMH and NiCd packs for about $30, prices are dropping because everyone wants to use the newer LiPolymer packs (lighter but more problematic). The advantage to these "delta peak" chargers is they are FAST.


    I have some 8 cell Sanyo 4/5FAUP's at 1950 mAH for my "birds" that are GREAT for cycling light use as they are light (1.375 oz per cell) and deliver good amperage all the way to complete discharge. They charge in about an hour with the above mentioned charger.

    BTW, stay away from Li-ion/polymer packs as they have a habit of catching fire when damaged, over charged or over DISCHARGED.
     
  8. jasong

    jasong New Member

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    Hi, glad to see a battery expert is around!

    Sounds like the price point for all of this is using AA 2200 mAh batteries.

    Several of the less expensive systems use a 6V 4.5 Ah seal lead acid pack.

    This would be constructable easily using 10 AAs like

    +
    +
    +
    +
    +
    + with each + representing a parallel AA pair

    design, giving off 6V at 4.4 Ah. What do you see as being any different in what a cyclist would see in this approach versus a SLA pack (temperature, discharge characteristic, etc.)? 10 AA's is only about $24 at WalMart. Chargers are fairly cheap. If each AA weighs about one ounce, then your looking at ~300 g, which is right inline with the weights advertised. A 4.5Ah 6V SLA weighs about 1 kilo.

    Why buy a $200 system when it seems like building one would be pretty easy? It doesn't seem like there are any other electronics in these systems? No over voltage worries really?

    Anyone wear these packs in the cold to maintain battery life?

     
  9. jasong

    jasong New Member

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    I've done a lot of reading in the past hours about homebrew systems where they address all kinds of these things. Am off to build a halogen lead acid design tomorrow.

     
  10. cachehiker

    cachehiker New Member

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    I've looked around but haven't found a simple NiMH or NiCAD rapid charger design suitable for anything in the 2-4 Ah range or higher. I was hoping to find something with maybe 6-8 parts that could be customized by changing only one or two parts. I will keep looking.

    So far, discharging completely and then recharging for exactly 10 hours at exactly 10% of the rated capacity, 440 mA for a 4.4 Ah pack, is the best option I've found. You would only need a big wall transformer, a timer, and a constant current regulator that consists of about five parts and a big heat sink on a breadboard.

    The only home-brew battery pack I have uses 4 "D" cells to run a 6V MR-11 lamp. It isn't robust enough to use on the mountain bike, but does OK for commuting purposes. The batteries fall out of the holder too easily and the lamp flickers everytime I hit a big pothole. This will be the major hurdle for the 10 AA cell solution. You could order a custom battery pack from http://www.digikey.com where the cells are welded together in series. Unfortunately, you still have to find or build a 6V charger that matches the capacity and chemistry of the battery pack.

    All batteries suffer in the cold. I know the carbon-zinc type suffer the most and alkaline suffers less than NiCad's or NiMH. I'm unsure but I think SLA's are in the middle as well. The cell voltage actually goes up while the capacity goes down. Slightly brighter light but shorter life. I don't have much for comparisons, but I think my Petzl Zora has only lasted two hours instead of three on a couple of really cold, 5-10ºF XC ski outings in the moonlight.
     
  11. Weisse Luft

    Weisse Luft New Member

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    There are plans available for rapid charging (2-3*C) of NiCd but AFAIK, NiMH should not be charged faster than 2*C (30 minute charge). I fly hotliners which are electric powered high performance sailplanes and use both types of batteries. My 1300 mAH, 8 cell NiCd packs charge in 20 minutes and deliver 35-40 Amps at very short duration. My 1950 mAH 8 cell NiMH packs take 30-45 minutes to charge, depending on the temperature, and deliver about 35 Amps. Both types get my sailplanes to "speck height" (400-500 feet AGL) within seconds thanks to a 350 Watt brushless DC motor.

    NiCd wll take faster charging because the majority of the charge is an endothermic process and any heat generated by ohmic losses (internal resistance, which in Ni is very low) is more than offset by the absorption of thermal energy by the charging process. Not so with NiMH. The charging is exothermic, generating heat from both ohmic and chemical reaction. Since NiMH requires hydrogen to be stored in the metal "sponge", too much heat slows this absorption and recombination of the hydrogen releases the energy as heat.
     
  12. gubaguba

    gubaguba New Member

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    Check out www.batteryspace.com I have ordered from them and had no problem. They have chargers and shrink wrap and of course batteries. Don't worry about the connector. I just cut mine off and soldered on a new one that was easy to find. I had trouble finding the original. Good luck.
     
  13. Weisse Luft

    Weisse Luft New Member

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    http://www.angelfire.com/electronic/hayles/charge1.html

    This is a DIY charger although the PIC will cost you a few dollars as the programmer has not released the firmware but will sell you a pre-programed chip, excellent for the folks who can solder but lack the PIC hardware/knowledge.
     
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