Author Topic: Voltage drops as Engine speed increases (Read 5371 times)

SubieHo · « **on:** August 13, 2008, 12:05:10 AM »

Hi there,

Newbie here.

I just replaced a 7-year old battery and checked my charging system, and found something pretty curious. At idle, I was getting a DC voltage reading of 13.5. The curious part is that the voltage would drop as engine speed increased -- around 12.8V at 5K rpm. This doesn't seem right, and I was wondering of those on this forum had any ideas?

Generator output is good at around 80-90 AC volts.

I should add that this bike has been rarely ridden and hooked up to a battery tender inside a friend's garage for the past 3 years. I've had it out for about 3 weeks now, except it wouldn't start after a ride of about 60 miles. I pushed started it and it ran fine, but would not crank over even after riding it for another 60 miles.

I searched around and downloaded that handy flow chart but am hoping it was just the old battery.

Bartjan · « **Reply #1 on:** August 13, 2008, 05:29:46 AM »

Voltage seems fine to me.
Remember that when the rev goes up it needs more sparks and thus uses more energy, nothing to worry about

SubieHo · « **Reply #2 on:** August 13, 2008, 10:40:16 AM »

Yes, I'm hoping that it's just the battery, but the the factory manual says that voltage should be between 13.5 & 15.5 volts at 5K rpm. At least I know it's not overcharging.

BTW, this is a '92 B4 with 21K miles (33.6K kms. for everyone else) on the odometer.

Banditmax · « **Reply #3 on:** August 13, 2008, 01:38:27 PM »

It maybe your in need of a new reg rec.

gsxr400 racer · « **Reply #4 on:** August 13, 2008, 07:42:31 PM »

Quote from: Banditmax on August 13, 2008, 01:38:27 PM

It maybe your in need of a new reg rec.

VW_NUT · « **Reply #5 on:** August 14, 2008, 09:47:58 AM »

Where do you guys get your new regulators from?

tomacGTi · « **Reply #6 on:** August 14, 2008, 10:16:36 AM »

Mine is from a GS500: same regulator, plugs et al. Plug and play installation.

Is going to 12.5v at 5k a problem? My new-to-me one does this and is at 13-14.5 at idle. I'd think that it isn't such a big deal considering my old one was at l7v at the same revs.

Bartjan · « **Reply #7 on:** August 14, 2008, 10:21:25 AM »

rgv250 also has the same one, only a bit smaller so it can only be connected with one bolt. but works perfectly.

however I would first test the reg rec before buying another one (I once bought 2 extra ones just to find out I had a loose wire

at least now I have some spares...)

still I think 12,5V is enough.

VW_NUT · « **Reply #8 on:** August 14, 2008, 10:22:02 AM »

I have 2 doing the same thing. One is original bandid the other is a used gs-500 one

How hot do they get during normal operation?

SubieHo · « **Reply #9 on:** August 14, 2008, 11:01:53 AM »

Thanks for all the input, fellas.

Quote from: tomacGTi on August 14, 2008, 10:16:36 AM

Mine is from a GS500: same regulator, plugs et al. Plug and play installation.

Is going to 12.5v at 5k a problem? My new-to-me one does this and is at 13-14.5 at idle. I'd think that it isn't such a big deal considering my old one was at l7v at the same revs.

Yes, I'm inclined to think the same thing, and a bad regulator/rectifier (RR) will usually cause the voltage to overcharge the battery as you experienced.

Quote from: Bartjan

however I would first test the reg rec before buying another one (I once bought 2 extra ones just to find out I had a loose wire banghead at least now I have some spares...)

still I think 12,5V is enough.

Yes, I'm thinking the same thing, but I'll pop everything off and check all my connections today.

Quote from: VW_NUT

I have 2 doing the same thing. One is original bandid the other is a used gs-500 one

How hot do they get during normal operation?

VW_NUT, this is good to hear as this may mean that mine is acting normally. Mine gets hot, but I can still put my fingers on it. It's definitely not overjuicing things.

At this point, I'm inclined to think that the RR is functioning fine because even with the 7-year-old battery, the bike was getting enough juice to run -- it just wasn't charging the old battery enough to run the starter.

The other thing I should add is that when I flick on the high beams, the voltage will increase by .4-.5 v, which indicates that the RR is functioning.

I'll post some more numbers after I pull everything off today and test things.

VW_NUT · « **Reply #10 on:** August 14, 2008, 11:07:52 AM »

ok..

I don't know that mine (hangin_biposto's) is perfect....

I've been chasing down a random hot stall for a while & I am beginning to think its not carb/fuel related. Bike runs 100% no hitches good jetting, good carb synch, etc. but after say 1/2 hour + of riding when I come to a stop and pull in the clutch the bike dies. It will restart with some throttle and after its running perfect. THe bike still rides perfect, it just wants to stall when you pull the clutch in. It seams to be worse if you baby the bike.

I am wondering if this is some sort of electrical issue. I have checked/cleaned the connections at the voltage regulator and the connections to the coils are good.

Battery is less than 1 year old and holds a good charge.

tomacGTi · « **Reply #11 on:** August 14, 2008, 11:33:32 AM »

Do the Electrosport test that Stormi has in her sig and see if that's the case for you RR.

Also, I do find mine gets warm, it's the heat that kills them and running additional things like the headlight, highbeam etc take the load off of the RR which basically turns the excess juice into heat. The heat just goes somewhere else as opposed to the hidden heatsink. I've also added some additional grounds to the RR as well. It was suggested and figured it couldn't hurt.

I know on mine, after really caning it and coming to a stop, sometimes the revs will come down close to dying but it'll come back up and idle normally. When I did the failed exhaust cam mod, the bike would stall doing the same thing. There was something in jetting where I think if the bike's too fat it will dip in rev and come back up but I can't remember at the moment.

Set the idle when the bike is storming hot as opposed to just sitting. I've found it makes a difference when the bike has actually been run versus: crank it over, warm it up and then set idle.

gsxr400 racer · « **Reply #12 on:** August 14, 2008, 11:40:22 AM »

Bartjan

has a good point some times the wires to the reg rec get corroded or fried and you can cut and splice them back together and sometimes the reg rec works fine

VW_NUT · « **Reply #13 on:** August 14, 2008, 11:42:05 AM »

I did set the idle when it was very hot. It is a little high probably 1700 or so. What you describe is exactly what happens. It dips a little then its fine.

I would guess that the jetting is rich, however, the plugs are really clean which suggests its not right?

interfuse · « **Reply #14 on:** August 14, 2008, 12:03:43 PM »

Quote from: VW_NUT on August 14, 2008, 11:07:52 AM

I am wondering if this is some sort of electrical issue. I have checked/cleaned the connections at the voltage regulator and the connections to the coils are good. Battery is less than 1 year old and holds a good charge.

Check you see if your clutch is dragging. Is it hard to find nuetral while stopped?