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Charging system advice, battery is overcharging, sulphur smell...

Discussion in 'The Garage' started by djMaldoror, Jul 22, 2022.

  1. djMaldoror

    djMaldoror XS400 New Member

    Hi gang!
    Newbie here, first post so go easy on me ;)
    I'm a metalsmith, not an electrician, and I bought an '81 XS400 Special just a few months back. Just getting familiar with using a multimeter (i.e. check the battery for voltage).

    Background -
    It was partially modded to a cafe / rat racer by the previous owner so the wiring does not follow the original harness in any way, shape or form. It is stripped down as much as possible: kick-start only (no electric starter), with just an LED headlight and brakelight (no turn signals) and a back-lit speedometer so the peripherals that need electricity are next to none.

    The Issue -
    The current battery (an ES4LBS Walmart special) seems to be overcharging (smell of sulphur comes on strong after a ~12 min ride).

    My question(s) -
    1) What is the smallest battery that'd work on this build?
    2) How many amps does the xs400's charging system produce?

    Thanks in advance for any thoughtful replies!

    PS - One fact I learned recently is that I could install a small lithium batt with internal BMS, since the BMS will automatically prevent any overcharging of the batt...
    PPS - Including a few pics of my '81 CR Mod as well as my other ride, just to introduce meself! 278286021_4902609743128247_3042816187520590391_n.jpg IMG-0649.jpg IMG-0691.jpg Beast00.jpg
    Last edited: Jul 22, 2022
  2. CaptChrome

    CaptChrome XS400 Addict

    Welcome to the forum! I suspect you will learn a ton from the bike as it is already getting you out of your comfort zone. It sounds to me like your voltage regulator is not operating.

    To answer your questions, I don't know how small a battery you can use. It depends on how much load you have (max amp draw). But it doesn't sound like you have much, so theoretically you probably don't need much. However, it should have some safety margin and also be able to "soak" up what the charging system is putting out. The alternator on your '81 puts out 12A at 14.5V at 5000rpm. So, 174 watts of power.
    djMaldoror likes this.
  3. djMaldoror

    djMaldoror XS400 New Member

    Thank you very much for the insightful reply, Cap!
    I've gone ahead and ordered this lithium compatible RR from ricks motorsport electrics and this tiny 4 cell battery from AntiGravity.
    Fingers crossed I can get 'em wired up correctly and be back on the road sooner than later.
    I'll drop an update here at that time, just for reference if others have the same / similar issue.
    BambinoFan likes this.
  4. CaptChrome

    CaptChrome XS400 Addict

    Yeah, do update us on how it goes. Lot's of folks seem to have this issue, so having some good product review info will be more than welcome. Good luck on the repair.
    djMaldoror likes this.
  5. BambinoFan

    BambinoFan XS400 Member

    Any update on this?
  6. djMaldoror

    djMaldoror XS400 New Member

    Hey BF,
    Update - I got both the aforementioned lithium battery and compatible RR installed. In fact did much rewiring of the harness, in general. All electrics work buuuuut.... now bike won't start.
    So while I'm sure I fixed the problem from my original post, I have as of yet been unable to test it.
    Carbs were rebuilt just 1 month before the Sulphur battery smell / regulator issue began, so that ain't the problem.
    Since the summer months are flying by I will probably swallow my pride, admit I don't know how to fix her and take her to the local garage.
    Maybe I'll get to ride her before the weather turns bad.
    I'll post another update at that time!
    BambinoFan likes this.

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