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Thread: Fluctuating Voltage Readings at the Battery

  1. #1
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    Default Fluctuating Voltage Readings at the Battery

    I have a 83 GS1100G. When I put a voltmeter on the battery posts when the bike is running, I get voltage readings that jump all over. Within 5 seconds, the readings jump from 14.3, 7.5, 12.6, 14.7, 2.8, 13.2, .... on and on. I’ve been reading the forum for weeks trying to figure this out. The engine runs rough when it is on and back fires in “puffs”. First the bike wouldn’t start but it was turning over. I removed and cleaned the carbs. The Bike finally started when I added some starter fluid. Next I checked the coils and got 0 resistance readings. Bought and installed new coils. Removed the spark plugs which are new. They were black coated. Cleaned the plugs real well and had good spark. At this point, the bike would start but still ran rough with “puffs” in the exhaust pipes and fluctuating voltage at the battery. I installed a SH775 a few years ago. So I checked the stator. The AC voltage from the stator’s 3 wires were bad. 3 wires read 40-45V while the third read 5V. When I installed the SH775, I connected the 3 SH775 wires to the old R/R wires and connected the black and red SH775 wires to the battery. When I disconnected the stator wires at the original stator harness wires, the connectors were corroded and the ends of the wires were black and melted. When I checked the stator voltages the wires were disconnected from the harness. I checked the voltage at the battery and the readings were fluctuating still (I don’t understand that at all). I installed a new stator from RMSTATOR today and retired the SH775 directly to the stator output wires. I ran the SH775 to a ground on the engine block and connected the red SH775 wire to the original red wire that connects to the harness before the fuse box. Moment of truth, the bike started right up but still had fluctuating voltages at the battery and “puffs” in the exhaust!! The difference before the new stator the fluctuating voltages never jumped above 13.0. After I turned the ignition key off the voltage reading on the battery was 14.4V. I turned the headlight on and the voltage dropped to 12.6. Sorry this is so long but wanted to provide as much information as I can. Please share your thoughts and suggestions. Right now I’m thinking that I need to replace the SH775. This has turned into a quest.

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    My god, please reformat your text if you want some help. At least put some paragraphs in there.

    In any case, either your multimeter has crapped itself, probe leads are faulty or your connections on the bike are shot. Such wildly fluctuating readings are usually caused by intermittent contacts.

    You had coils with 0Ω, so likely something has shorted on the bike - which should be handled by a fuse. But somewhere in there you're writing "black and melted", so something bad has happened.

    Inspect, clean and replace as necessary all connections on the harness as a first step.
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    I second the art of sentence structure and paragraphs. I started to try and read that then just gave up. Two year olds construct sentences better than that.
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    Sorry about the text. Didnt know there was an issue with the format. I havent posted on the site in 6-7 years. Ill check my multi-meter before I try anything else.

  5. #5
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    Quote Originally Posted by Nash1100 View Post
    I have a 83 GS1100G.

    When I put a voltmeter on the battery posts when the bike is running, I get voltage readings that jump all over. Within 5 seconds, the readings jump from 14.3, 7.5, 12.6, 14.7, 2.8, 13.2, .... on and on. I’ve been reading the forum for weeks trying to figure this out.

    The engine runs rough when it is on and back fires in “puffs”. First the bike wouldn’t start but it was turning over. I removed and cleaned the carbs. The Bike finally started when I added some starter fluid. Next I checked the coils and got 0 resistance readings. Bought and installed new coils. Removed the spark plugs which are new. They were black coated. Cleaned the plugs real well and had good spark. At this point, the bike would start but still ran rough with “puffs” in the exhaust pipes and fluctuating voltage at the battery.

    I installed a SH775 a few years ago. So I checked the stator. The AC voltage from the stator’s 3 wires were bad. 3 wires read 40-45V while the third read 5V. When I installed the SH775, I connected the 3 SH775 wires to the old R/R wires and connected the black and red SH775 wires to the battery. When I disconnected the stator wires at the original stator harness wires, the connectors were corroded and the ends of the wires were black and melted. When I checked the stator voltages the wires were disconnected from the harness. I checked the voltage at the battery and the readings were fluctuating still (I don’t understand that at all).

    I installed a new stator from RMSTATOR today and retired the SH775 directly to the stator output wires. I ran the SH775 to a ground on the engine block and connected the red SH775 wire to the original red wire that connects to the harness before the fuse box. Moment of truth, the bike started right up but still had fluctuating voltages at the battery and “puffs” in the exhaust!! The difference before the new stator the fluctuating voltages never jumped above 13.0. After I turned the ignition key off the voltage reading on the battery was 14.4V. I turned the headlight on and the voltage dropped to 12.6.

    Sorry this is so long but wanted to provide as much information as I can. Please share your thoughts and suggestions. Right now I’m thinking that I need to replace the SH775. This has turned into a quest.
    Have not experienced such fluctuating voltage.

    You said fluctuated when running. And talked about voltage with bike off and didnt mention fluctuations.

    Have you tried disconnecting the R/R and then see if fluctuates when bike running??... then will know for sure if is related to the charging system.

    //////////////QUOTE
    I ran the SH775 to a ground on the engine block
    ///////////////EndQUOTE
    Engine block? Try to frame or to the battery negative.

    Have you checked the connection of the thick black wire on back of engine (top of transmission)?

    The stock connection will be to the solenoid mounting bolt with a b/w ground wire from bike harness there too, and is recommemded to also run your own ground wire to there so not relying on that wire in bike harness.
    Last edited by Redman; 01-24-2021 at 08:44 PM.

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    Thank you Redman so much for the reply and fixing my original post format. The multimeter doesnt fluctuate when obtaining readings with the bike off. To disconnect the SH775, would I just disconnect the red output wire from the SH775 only? Or do I disconnect the input stator wires too?

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    //////////QUOTE
    To disconnect the SH775, would I just disconnect the red output wire from the SH775 only?
    //////////EndQuote

    Yes. Could disconnect the stator leads also.

    If I had to make a guess, I would suspect this fluctuation has to do with having the R/R ground to the engine block, so that current has to go thru engine block, and thru engine , thru mounting and/or engine ground ..... and the R/R is trying to regulate its own output voltage, and the connections are kinda far from the battery. (hard to explain) (and just somewhat making theories here).

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    Ill disconnect the SH775 wires this afternoon and start the bike. Ill report the voltage results.

    My previous post indicated that I attached the ground to the engine block (my ignorance of terminology). I grounded the SH775 to the back of the crankcase next to the ground point of the battery.

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    Is the voltmeter in DC mode when checking battery voltage?

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    I grounded the SH775 to the back of the crankcase next to the ground point of the battery.
    why so far? electrically, given the connection was good it shouldn't matter, but the frame is closer. If your starter spins with strength there's unlikely to be any problem with the original cable....and all the bolts attaching engine to frame ensure that the frame itself is also well grounded...

    but for any place you want to ground to, Check the path from that place to the battery negative post....With the bike NOT running, There are two ways to do this...1) with an ohmeter on its lowest setting. The reading should be the same as with the multimeter probes touching each other..say 0 to 2.4 ohms depending on the meter..(this is called "zeroing the meter" many of which do not show "0")
    or 2) get a test light and attach one probe to battery positive, the other to the place you want to attach ground. Use a brake light bulb for this or a turn signal bulb. It should be BRIGHT.
    The meter itself IS a suspect. MOST Usually at the leads. Wiggle them, change them, test them...

    I think you said you had a new stator. So, from that assumption,

    ... you might have AC loose in the system. This might explain the fluctuating voltage seen...a multimeter needs time to settle and fluctuating voltages will confuse it, . It might also explain a jerky ignition as it "confuses" the operation of coils. This might be caused by your R/R, as you are thinking. A blown rectifier will let AC by.

    You might just see this as a flicker in the headlamp or tailight (but it'll be harder to notice there..) when the bike is RUNNING .A test light done the same as "2)" described above may also show it.

    But before settling on an expensive new R/R, repair all the wiring problems you described..burns etc and LOOK for chafe points between the stator and R/R. After that, if you have one, swap a spare R/R in...any working one with 3phase connections should work.
    Last edited by Gorminrider; 01-25-2021 at 12:17 PM.

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