Marwi Bike Light Instructions and info |
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 Image of a single 18650 Lithium Ion battery |
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About the batteries: I build the battery packs using 18650 Lithium Ion protected cells. These batteries are used in most portable computer battery packs and are perfect for bike light battery packs. They are very light and have very high storage capacity. Lithium Ion batteries are very different than other battery types like Ni-Cad and Ni-Mh. Li-On cells can only be drained down so far. If they are drained below a certain voltage, they will be permanently damaged and they will not be able to be recharged. The Li-On batteries I use have tiny circuit boards on the the negative ends of the cells. These tiny circuit boards prevent the battery from going below the minimum voltage level. The circuit boards will shut off the battery current flow to protect the battery from permanent damage. If you would like to read more about Lithium Ion batteries, check out this Wikipedia page. There is lots of useful info on how to care for Li-On batteries on this page. http://en.wikipedia.org/wiki/Lithium-ion_battery |
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 Image of 4 cell square and flat battery packs |
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Battery run time: Most battery packs I build have 4 x Li-On cells inside. The run time on a fully charged battery pack will depend on the brightness setting you have the light on and the battery capacity. The two types of LED's I have used in my lights are the SSC P7 and Cree XML. Both LED types will have about the same battery run time because the maximum current is controlled by a driver board inside the light. I usually like to calculate the run times on the conservative side to make sure that the battery packs do not get drained down all the way and the protection circuits kick in. It's hard to calculate the run times exactly because usually the lights are switched to different modes during a bike ride. To be safe, I like to say that 3 hours on high is about as long as I like to run the lights. But, they can run longer than that. If you use one of the low settings for part of the ride, the run times will be way longer. Most riders I know don't ride 3 hours in the dark so the 3 hour figure works out well as a general guide line. If you used a half power setting all the time, the battery run time would be 6 hours. Some of the XML lights I build actually have a very low 20% mode and so the run time would be something like 15 hours if you ran the light on that low setting the whole time. Calculations for those that like math: mah = Milliampere hour The lights I build will typically discharge somewhere around 2.5 amps (2500 milliamps) average rate on the high setting If you put 4 x 18650 - 2500 mah batteries in parallel, you end up with a 10,000 mah battery pack. (2500 x 4 = 10,000) If you run the light at 2.5 amps or 2500 milliamps, each battery would give you 1 hour of light at that rate. So, you can say that a 10,000 mah battery pack should last for 4 hours at a 2.5 amp discharge rate. But, I don't trust battery manufactures figures any more than I believe gas mileage figures on a new car sticker. This is why I say to consider the 3 hour mark good enough, but there really is some run time left in the batteries. As the batteries get older, the maximum run time will decrease and the 3 hour mark may end up being the max run time at some point. |
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 My old trusty and dusty shop charger charging a single 18650 Li-On cell |
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Charging the battery pack: The chargers I use have LED's that light up Red when the battery pack is charging. The LED turns to green when the battery pack is fully charged. I always charge the battery pack as soon as I get home from my rides. To be safe, hook your battery pack up to the charger as soon as you finish using it. You can leave the battery packs connected to the charger full time. There is no need to disconnect the battery pack after it has fully charged. If the battery pack happens to drain down a bit while it is connected to the charger, the charger will turn back on and charge up the battery pack automatically. The Li-On cells do not get hot while charging like older battery types. Li-On battery chargers do not trickle charge like older battery types do. Li-On chargers charge the battery and then shut off. Once in a while I have seen the charger LEDs flashing when you hook up a battery pack. This usually means that the battery is kind of in a limbo zone, it is not drained down far enough to need a charge. Go ahead and use the battery some more and then charge it. The charger LEDs should light up Red once the battery has been drained down far enough. The chargers actually have two separate battery chargers inside. You can charge two battery packs at the same time, each battery pack will be on it's own charger. |
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 Image showing both styles of Marwi LED lights |
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Using the Light: The LEDs I use for the Marwi bike lights are very high powered and produce quite a bit of heat. The heat is not a problem if there is air moving across the surface of the light body. The air moving across the light body will dissipate the heat. Do not turn the lights on high and leave them sitting in still air or they may overheat and damage the LED. Most people use the lights in the winter for night riding when it is cold and so over heating is never a problem. If you use your light for bike commuting all times of the year, you may have to take into account the air temperatures during the hotter month. If it is 95 degrees outside and you come to a stop at a stop light, I would switch the light to low or off if you are going o be sitting at a hot stop light with no air moving for several minutes. If you are going to use the light in a still air situation, use a low setting. I have used my lights to crawl under the house, look at the back of a computer under a desk, etc. A low setting is all you need if you use your light for an around the house task. |
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A windows media player appears here You may have to approve a plug in to get the movie to play If the movie does not play click this link to watch it https://el34world.com/Misc/bike/Video/WireBending.wmv Here is the movie link on YouTube http://www.youtube.com/watch?v=cdxvxj9X-XM |
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Things to avoid: Avoid flexing the wires back and forth at the point the wire enters the light body, the battery pack and at the connectors. The tiny wires inside the cable may start to break if they are flexed in the same spot all the time. It's best to have the wires flex in a broad arc somewhere in the center between the connector and the light body or battery pack. Avoid submerging the lights and battery packs in water, they are not water proof. It's ok if water drops get onto the light and battery packs. Keep the battery packs as dry as you can by keeping them in backpacks or pockets. If you use some sort of water bottle cage container, make sure it cannot flood and fill up with water. Make sure you don't dent the battery packs, the batteries may short out internally if they get dented. Don't tape the battery pack down tight to your bike frame. If you do tape it down, use some sort of cushion between the batteries and the hard surface. Do not charge a bike battery pack and a single 18650 battery on the same charger side. Plug the battery pack onto the right side and insert the 18650 battery into the left side or the other way around. Do not get the battery packs hot! Lithium Ion batteries are very sensitive to high heat. |
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Questions and answers: Q: How come you don't use nice looking heat shrink tubing to wrap the battery packs? A: Li-on cells are very sensitive to high heat. Early experiments with heat shrink tubing resulted in battery packs self destructing on the work bench when heat was applied to shrink the tubing. The Vinyl tape I use may not look as nice as heat shrink, but the battery packs are not damaged which is the important thing. I also experimented with dipping the battery packs in a rubberized tool handle solution. They came out nice looking but it takes 3 days of dipping and drying each dipped layer to get a nice thick coating on the battery packs. 3 days of dipping is too much time and labor. I would have to charge allot more for the battery packs if I had to spend 3 days creating a nice rubberized out shell. Q: How long do battery packs last? A: I don't know exactly how long they will last. I replace mine every 2 years just because I like nice fresh battery packs. It gives me more peace of mind when out in the middle of Pisgah Forest at night. If I used my lights on trails where it was fast and easy to get out of the woods, I would replace the battery pack less often. There is more info on Li-On battery life on the Wiki page link at the top of this page |
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