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6 Volt system and headlights from battery power?

Discussion in 'Technical and Troubleshooting Torque' started by krabi, Oct 13, 2009.

  1. Hi folks,
    I just restored a 1974 Honda C90 step through for my wife (see image below), but I'm having slight problems with the electrics as it has a magneto. I put in a brand new battery and new rectifier. I found this little folt finder flow diagram http://www.electrosport.com/technical-resources/library/diagnosis/pdf/fault-finding-diagram.pdf and used it to check out my problems. However, it assumes 12 volt systems rather than 6 volt.
    There are a number of things that I noticed from my observations with a multimeter.
    I have a 6 volt battery but when I put the multimeter on it while bike is running it shows a charge fluctuating between 10-15 volts, this also occurs when I test the output from the rectifier (it's a brand new rectifier).
    I did a resistance test from the the 3 wires coming from the engine, of the four possible test combinations, one resistance rating is low. The one that fails is the white and pink wire combination. The white wire is the one that goes directly to the lights.
    The c90 coughs and splutters when the white wire is connected to the lights, but when I take the white wire off and connect the lights directly to a battery source (I used the horn active) the bike runs smooth and as a bonus the light shines bright and constantly.
    Now, is it a bad idea to keep the light connected to the battery source on this old 6 volt system rather directly from the stator? Is there anything that you experienced people with old 6 volt systems can offer me in terms of advice, like if I put a rectifier between the white wire coming from the stator (if so how?) would that help, or is the stator packed in just for the the white wire? Can I repair the stator just for the white wire? or do i replace the whole stator?
    thanks in advance!


    Attached Files:

  2. My own C90s were later models with different charging systems (still 6V tho') so I can't offer direct practical experience.

    However, I do have the Haynes manual for the range and can scan the relevant wiring diagram and send it to you if you PM me.

    The charging level doesn't sound outrageous to me. The C90 has a fairly primitive system in which the battery is expected to act as the voltage regulator as well. All the rectifier does is convert AC to DC. It has no regulating function.

    Looking at the wiring diagram, I would expect the White-Pink connection to have a lower resistance than the other paths. As a ballpark figure, I'd expect maybe half the Pink-Yellow. Not zero though.

    You might want to check all the connections and switch contacts in the lighting circuit. On 6V systems without much surplus output, it's quite possible for lights to rob enough juice to stop the engine if everything isn't in top condition. One of my (later) bikes would proceed in a series of kangaroo lurches when the indicators were switched on, alternating between feeding the globes and supplying the ignition coil. Very exciting in heavy traffic on a wet night :eek:.

    Bottom line, double check everything, hook it up in accordance with the wiring diagram and proceed from there.

    If the stator is buggered, it should be possible to have it rewound. I've heard of it being done as a DIY job but wouldn't fancy it myself. Chances are, an electrical specialist (there's at least one outfit advertises in Just Bikes IIRC) could do the job for considerably less than Honda would consider reasonable for a new one.

    Good luck. Fully sorted they're an excellent little bike.
  3. Make sure the connections are clean and properly connected - extremely important for this type of system.

    If possible replace some of the wiring with decently thick wire. That can help since the low grade of electrical wire used in some of the older 6 volt systems is not wonderful. This particularly applies to the earth wire to the frame.
  4. Thanks for the advice folks.

    Pat B, I have a wiring diagram for it from someone on the net who scanned the entire Workshop Manual so thank you any way. I also ordered an old Haynes manual off ebay just last night.

    TonyE, I'm thinking just that, doing a complete rewire and replacing all the connectors.

    An interesting thing is now happening to the bike. I moved the lights on to the horn active, if the lights are NOT on, the bike kangaroos, but if I turn them ON the bike runs smoothly!
    Sounds like old 6 volt systems are temperamental and I just have to get everything right.
    I might just replace all the electrical components, I can buy them on ebay. I just want the bike to be reasonably reliable for my wife.
  5. At first glance, that suggests that the coils of the stator that supply ignition and battery charging current are not doing so, or not much. Hooking up the lights into that circuit may be allowing the lighting coil to feed the other systems via the globes. Maybe not the full 6V but enough to keep them working. I'd bet quite substantially that you'll find that the lights are very dim. Well, dimmer than a 25W, 6V headlamp normally is anyway.

    Get a new or rewound stator. I reckon that's your problem.
  6. Wow, Haven't seen one of these in decades. Apart from it not being red, it could have come straight out of a "You meet the nicest people on a Honda" ad.
  7. That's the plan, thankyou very much for your input, I was hoping to get out of it simply
    It took me three months to restore this puppy and hours to colour match it at an auto paint store. My wife wanted a postie bike, but I told her she needed something cooler :cool: