2nd battery

Discussion in 'Tech Area' started by tarkus4, Jun 8, 2018.

  1. tarkus4

    tarkus4 New Member

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    If i were able to cram a second battery in my ct70 and used the yellow wire feeding the headlight with a rectifier to charge it, would I be able to power the headlight this way?
     
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  3. racerx

    racerx Administrator
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    The answer is a clear-cut, "it all depends/maybe".o_O This setup has been used, by our very own Fatcaaat...on a 12v system. The voltage, alone, doesn't make any real difference. However, 6v stuff is antique technology; translation: far fewer options in reg/rec units, bulbs and...especially...LEDs. That last one hurts the most. Replacing the HL bulb with an LED of similar wattage would deliver a no-excuses-required HL output; unfortunately, nearly all are 12v flavor and there's hardly what I'd call enough of a market to encourage manufacturers to enter the game.

    So...the only real option is to give it a shot, then test charging voltage with the engine running, HL illuminated. If you see ~7V, or better, you're good-to-go. Below about 6.5V, you'd have a partial-loss charging system; that may be "good enough" (really) if the battery takes hours of continuous HL use to discharge. You could slap a charger on it at the end of the ride, or forgo DTRL. I did that for years.
     
  4. tarkus4

    tarkus4 New Member

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    Thank you for the answer and I shall give it a try and report the results.
     
  5. racerx

    racerx Administrator
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    I wish you luck with this, seriously. If you use a half-wave rectifier, you'll reduce total current available (as DC) by slightly over 50%. This type of rectifier converts half the AC waveform into waste heat and thus, is not very efficient.

    Warning, way off-topic: If you know your way around electrics, it is possible to custom-wind a "6v" stator coil using a single (continuous) length of wire, float the ground (the stocker is split into two windings, each with one output...and their other ends run to ground) and use a full-wave bridge diode reg/rec unit. It should be possible to convert to 12v this way. However, this is "terra incongita"...IOW, roll-your-own hobbyist experimentation. Thus, I'd suggest staying away from this option unless you either really know what you're doing or are a sufficiently hardcore experimenter...or both.
     
  6. tarkus4

    tarkus4 New Member

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    I have plenty of old coils to experiment with, I may just try to make a 12 volt coil after I experiment with the two battery idea.
     
  7. b52bombardier1

    b52bombardier1 Well-Known Member

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    If you are going to wind yourself a 12 volt coil, I urge you to reach out to Jon Pardue here on LiLHonda. He has done this before and he understands the science behind using thin gauge enameled wire here or thick for wrapping these charge coils - its a volts versus amps discussion here. I would not attempt to re-invent the wheel for winding coils when Jon already has experience with this.

    Rick
     
  8. racerx

    racerx Administrator
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    I don't recall Jon ever mentioning having done this. Still...he knows his way around electrics and knowledge is power, in this instance electrical power.:rolleyes:

    That said, there's some DIY "failsafes" built into this. First off, while it is a volts vs amps balancing act, Ohm's Law sez that there's constant...watts. Volts x amps = watts, i.e. total electrical power. (Just to further illustrate, 1 horsepower = 746 watts.) Best guess is that a 2-pole (6v type) CT70 alternator can generate maybe 40W total output, max...regardless of volt + amperage balance. There is, imho, an optimal balance, of those two parameters, which segues into the other "failsafe". Thinner wire should increase voltage...more turns; however, it'd be at the expense of amps. Thinner wire has higher impedance...a.k.a. ohms. It's also more fragile. OTOH, thicker wire being the opposite, would likely tend toward low voltages at lower rpm. Fortunately, Honda engineers did us a favor; they selected a wire gauge that has proved viable. Thus, I'd start there. Any further experimentation would be using wire diameters no more than 1-2 gauge numbers higher or lower.

    Since we're already wa-ay out on this limb, I'd start with one gauge number lower (next larger wire diameter), winding the coil to the physical limits of the stator assembly. That extra metal (total amount of wire) should balance-out the impedance (and peak voltage) and provide maximum total output...watts.
     
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  9. b52bombardier1

    b52bombardier1 Well-Known Member

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    If I remember correctly, he did this rewind on a 90 CC stator coil. Yes, fundamentally different animal than what's on a CT70 but he's still got more experience in this neighborhood than most of us. I'd still seek him out here.

    Rick
     
    #8 b52bombardier1, Jun 10, 2018
    Last edited: Jun 10, 2018
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  10. allenp42

    allenp42 Active Member

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    Racerx and B52 (Rick) make excellent points and provided great advice. No matter what you do, you're only going to be able to extract "x" number of watts from the lighting stator. Bob is spot on with ohms law. Watts is watts regardless of the voltage. If the source is only capable of so much power (i.e.: watts), then you have a limitation regardless of the voltage. For sure, I would take Rick's advice & contact the Pardue Brothers. No need to re-invent the wheel or suffer pain and agony if he's already been down this bumpy road. It may save you some time and tylenol.
     
  11. fatcaaat

    fatcaaat Well-Known Member

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    you can usually find the 6v CDI conversions and plates on ebay. Those generate about 50 total watts of power. You can then get a good rectifier/regulator and rewire slightly but then you only get 25 left. Not much you can do with only 25 total volts unless you swap to LEDs... That should do it. All in all, if you want real lights, the only choice is to convert them to 12v systems.
     

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