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  1. #1
    Russian Troll Farmer
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    Wiring bike lights together

    OK, I know there are lots of rechargeable lights out there, but none of them have very good battery capacity, and some are a pain to remove and charge. I prefer the big-@$$ flasher lights which generally take 2 AA batteries, since these give great light, and don't just die at the worst moment. Even so, when a battery gets low, it will still give you little warning before going dark.

    Recently, I've bout a couple of those rechargeable LED headlights on Amazon, which come with rechargeable strap-on batteries with really great capacity, all for less than $30. I decided to take the smaller battery pack, and wire both my front and rear flashers to it. Bought some 2-wire 22ga cable, a male plug to connect to the female plug on the battery pack, and I soldered wire ends to the tops of the battery contacts.

    I drilled a hole through the backs of each flasher unit, and checked that the polarity was correct before soldering. Since these units are LED's, and since the definition of the term "diode" is a circuit component that only allows current to go one direction, it is imperative that polarity matches. Once soldered in, I filled the gap around the hole with sealer, and everything was ready to mount.

    Since the current is now 6v, compared to the 3v with batteries, the light is brighter. I do need to charge the battery every few rides, but that's an easy plug-in while mounted on the bike. I have an extension strip right by where I store the bike, so recharging is quick and simple.

    I think I'll buy another Amazon headlight set, just to have a spare battery pack....
    "L'enfer, c'est les autres"

  2. #2
    RoadBikeReview Member
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    Quote Originally Posted by No Time Toulouse View Post

    Since the current is now 6v, compared to the 3v with batteries, the light is brighter. I do need to charge the battery every few rides, but that's an easy plug-in while mounted on the bike. I have an extension strip right by where I store the bike, so recharging is quick and simple.

    I think I'll buy another Amazon headlight set, just to have a spare battery pack....

    I love DIY but you might wanna do something about that voltage as it could, "could" severely limit LED life.

    As batteries go, we've got lots more options than even 5 years ago.

    Here is a pic of my DIY that used a 12V power supply and high output LED. Currently working on "Mothership" system using automotive LED.




  3. #3
    RoadBikeReview Member
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    Nice job finding a solution that works for you...I'm all about doing it yourself/cheaper, but for headlights, did you ever check out Exposure lights? I've got the Strada 1200, while pricey, it runs 3 hrs on high, 18-24 hrs on the low and flash modes. It also has a "time left" run time counter.

    Also, to solve the short run time issue for tail lights, I went with Orfos. Their design allows you to use your own USB battery.

  4. #4
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    Quote Originally Posted by No Time Toulouse View Post
    OK, I know there are lots of rechargeable lights out there, but none of them have very good battery capacity, and some are a pain to remove and charge. I prefer the big-@$$ flasher lights which generally take 2 AA batteries, since these give great light, and don't just die at the worst moment. Even so, when a battery gets low, it will still give you little warning before going dark.

    Recently, I've bout a couple of those rechargeable LED headlights on Amazon, which come with rechargeable strap-on batteries with really great capacity, all for less than $30. I decided to take the smaller battery pack, and wire both my front and rear flashers to it. Bought some 2-wire 22ga cable, a male plug to connect to the female plug on the battery pack, and I soldered wire ends to the tops of the battery contacts.

    I drilled a hole through the backs of each flasher unit, and checked that the polarity was correct before soldering. Since these units are LED's, and since the definition of the term "diode" is a circuit component that only allows current to go one direction, it is imperative that polarity matches. Once soldered in, I filled the gap around the hole with sealer, and everything was ready to mount.

    Since the current is now 6v, compared to the 3v with batteries, the light is brighter. I do need to charge the battery every few rides, but that's an easy plug-in while mounted on the bike. I have an extension strip right by where I store the bike, so recharging is quick and simple.

    I think I'll buy another Amazon headlight set, just to have a spare battery pack....
    Cool. I believe you are an engineer aren't you? Well done.
    A point of small correction or oversight. In bold what you wrote above.

    I am sure what you meant is current has increased because for same level of resistance, Voltage is proportional to Current because of Ohm's law: V = I * R.
    So I believe you meant, Voltage in now higher because you wired the batteries 'in series' which makes net battery voltage additive.

    Well done and enjoy the bright light.

  5. #5
    ngl
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    When you connect two identical (3 volt) batteries in parallel, you double the output capacity (milli-amp hours) while keeping the output voltage the same as either battery (3 volts). In other words the battery pack will last twice as long but the light brightness will stay the same.

    When you connect two identical (3 volt) batteries in series, the output capacity (milli-amp hours) stays the same while the output voltage doubles (to 6 volts). In other words the battery pack will last the same time as just using one battery but the light brightness will double.

    Applying 6 volts to a 3 volt lighting system will ultimately damage the lighting system.

  6. #6
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    Ngl beat me to it.

    You aren't increasing the run time with the batteries wired in series and I'd be concerned about blowing out the circuit board or bulb at 6v. I can pretty much guarantee that will happen very quickly.

    I think rewiring it as a parallel circuit would be a smart decision. If you want a brighter light you need to find one with more lumens and keep it at the correct voltage.

  7. #7
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    Quote Originally Posted by ngl View Post
    When you connect two identical (3 volt) batteries in parallel, you double the output capacity (milli-amp hours) while keeping the output voltage the same as either battery (3 volts). In other words the battery pack will last twice as long but the light brightness will stay the same.

    When you connect two identical (3 volt) batteries in series, the output capacity (milli-amp hours) stays the same while the output voltage doubles (to 6 volts). In other words the battery pack will last the same time as just using one battery but the light brightness will double.

    Applying 6 volts to a 3 volt lighting system will ultimately damage the lighting system.
    Exactly. Voltage divides in series, current divides in parallel. Not advisable to increase nominal voltage as the LEDs were rated at a certain voltage. It will shorten their life if not blow them immediately.

    I have Cygolite head and tail lights with self-contained rechargeable batteries. The battery life is awesome. I get 5 or 6 rides out of them before I need to recharge.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



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