Battery issue
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Thread: Battery issue

  1. #1
    Junior Member Dwhiting24's Avatar
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    Jun 2017

    Battery issue

    Hey guys sorry have another newb question, sorry if it's been answered before I can't seem to find exactly what I'm looking for. On my 92 tw i can't seem to get the battery to stay charged, I have bought two new ones just in case and they both don't hold the charge. I know it has something to do with the bike and what makes me think that is because on my dad's 91 tw if the battery is out the lights with still turn on once the bike is started. But on mine if I take the battery out and start it the lights don't turn on like his. So that makes me think it's the same reason my battery isn't staying charged. Does a bike have something like an alternator like a car?? Thanks for the help guys!

  2. #2
    Super Moderator Purple's Avatar
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    Mar 2015
    Ynys Môn
    The TW has a “magneto” or generator (another word for alternator) which produces current from the rotation of the crank

    There are a few wires that come from the “magneto” — that provide power to the battery, and also separately to the CDI (ignition/spark thingy) — so it’s possible to supply to one, but not the other (the two circuits work on different coils)

    However, the cost of a replacement magneto is high, so first you need to get “testing” — there’s a chance the solution will not require replacing the magneto

    The first thing to do, is to locate the “regulator / rectifier” unit — it’s about the size of a cigarette packet, and has fins on it, and it should be close to the battery. The electricity comes out of the magneto, travels up to the regulator / rectifier unit, which then controls the flow. The AC power from the magneto is turned into DC (rectified), and limited to 14V (ish) eg “regulated”

    (The magneto is located on the left hand end of the crank, and the wires from it come out near the front sprocket)

    So - the electricity come out of the magneto in AC form, goes through the regulator / rectifier, and 14V (DC) goes into the battery — if your regulator / rectifier is defective, it would explain your battery problems

    The good news is that a replacement regulator / rectifier is fairly cheap, so check that first

    You should have AC going in one end of it — and have DC coming out of the other (to the battery), but it could be something simple like the connectors, so check them before doing the test

    You’ll find a copy of the manuals here - make sure you’re looking at the right one for your year

    They will help you locate the component parts, and guide you through the test procedure

    If by any chance the front sprocket has been replaced recently, there’s always a possibility that the wires coming from the magneto have been “pinched” by the crankcase, but as that’s a messy job, we’ll cross that bridge when we come to it …….
    cowboyjeff likes this.
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  3. #3
    Junior Member Dwhiting24's Avatar
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    Jun 2017
    Okay that makes sense and helps a lot, I went ahead and ordered a new rectifier / regulator to be safe. It very well could be the wires in the crank case as well because I have a leaking seal there from previous owner. So he was clearly in there doing stuff, I ordered a new seal for that so I'll make sure to check the wires while I'm in there fixing that.
    cowboyjeff and Purple like this.

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