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Discussion Starter · #1 ·
2003 SV650S
Upgraded to MOSFET R/R several years ago. Used Eastern Beaver plugs. Ran new negative wire directly to battery; ran new positive wire to starter relay
Shorai Lithium battery installed ~4yrs ago

Last week, I attempted to start bike after sitting for a couple weeks and a cold front came thru. It did not crank well enough to start. I wasn’t especially surprised. I recharged it with NOCO charger, making it to full within half a day, maybe less. Starts fine now.

I decided to measure voltages and was surprised to see at the battery low 13V up to mid-13V around 5k RPM. I unplugged the R/R output plug to measure there and found almost 15V (maybe slightly over). I checked wire and connector conditions between R/R and battery and see 0 resistance, measuring on the connectors themselves to include their potential contribution.

Shouldn’t it be over 14V at the battery in normal circumstances? Is it possible the battery is going bad and causing this much lower reading? I think my measurement directly at the R/R removes that from the equation as a problem. I think my inspection of the wires between the R/R and battery have removed those as contributors. With the higher output from the R/R, I believe the stator is ruled out.
 

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Have you checked the voltage coming from the stator? Just as a check... I tend to agree with you but I'm going through similar issues with another bike. What type of voltage are you getting at the regulator when you test each yellow wire? I believe you should be in that .2-.9v range.
A 4yo battery may be the problem. It could be worth swapping batteries to see if that fixes it. And yes, my SV stays around 14.7 volts when I'm riding. I can't remember off-hand what it's at idling but I think it's about the same.
Instead of relying on the numbers fumbled by my memory, check here: https://rmstator.com/pub/media/page...stic/pdf/electricals-gremlins-20170223-EN.pdf
 

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... I unplugged the R/R output plug to measure there and found almost 15V (maybe slightly over).
The R/R is not designed to run without a load, so open-circuit voltage (battery disconnected) may give an artificially high reading.
 

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Discussion Starter · #5 ·
Thanks for the help. Did some testing and think I’ve found the problem.

First, stator leads all show a little over 60V at 5k RPM.
Second, I reluctantly poked through the wire insulation at the R/R output and measure over 14V (contrast to low 13V at battery).
Third, I did what I think is a proper voltage drop test by poking the probes into the positive R/R->battery wire. Between my inline fuse and the R/R, it was under 1mV. Between the outbound side of the fuse block and the R/R, it reads almost 400mV. I may have a bad connection in there. It doesn’t account for all the volts I think I’m missing at the battery, but replacing some of that will go a long way.
 

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60V AC stator voltage @5k rpm is good.

The problem may be a failing battery. Vdrop = current x resistance, so if the battery is drawing excessive current the voltage drop will be higher.

The Vdrop might also be directly at the battery terminal; be sure they are clean and tight. If the voltage drops do not add up, try measure voltage from the battery cable lug to the battery post itself - it would be easy to miss that path. Your voltage drop tests should add up exactly, just like measuring a flight of stairs, the total height must equal the sum of the individual steps.

If the R/R mod is wired "direct to battery" that will contribute to larger voltage drop as all the current (charging and full bike currently) is taking a single path. Heavier gauge wire will help.
 

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I had a Shorai in a CBR250 and then put it into a CBR300, it only lasted 3 years for some reason despite normal use.
I do know that lithium batteries dont like overcharging so if your RR is putting out too much voltage it wont have done the battery any good.
 

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Discussion Starter · #8 ·
Guess that wasn’t it, weirdly. With everything connected, I can measure right at the R/R over 14V. Measuring at battery is just over 13V. Resistance in ground between R/R and battery is .1-.2 Ω; positive between R/R and battery is .1-.2 Ω

I cleaned battery posts and faces of all connections as a first step. Wire between the Eastern Beaver pigtail is 12 gauge; pigtail itself may be 14. It’s wired directly to battery with hopefully benefit of fewer connection points and thicker gauge
 

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Have you tried swapping in a different battery as Drewski suggested? That would help narrow down the problem.

14v directly at the R/R output is marginal. That basically guarantees 13.x volts at the battery (not great) even if the wiring/connections are perfect.

Low R/R output voltage can be due to a failing R/R but can also be caused by a failing battery if it is overloading the R/R (too much current draw).
 

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As I am learning more about regulators and the new lithium-ion batteries, I wonder if the shunt-style regulator you are using may be shortening the life of your battery. The newer r/r design is apparently a pretty big upgrade from the shunt on/off setup we have all been running for years; even the mosfet upgrade you installed still operates this way. I assumed the mosfet was still state of the art but I am learning that Shindigen has some newer units out that are superior.
I am about to upgrade my old unit on another bike to a Shindigen SH775. I'm waiting on connectors from Eastern Beaver as well then I will see if this makes everything happy. I figure this will be good practice when the SV decides it's tired of its current charging system. The 775 is supposed to be quite the safeguard to the life of the stator as well which is obviously a bigger pia than a dead battery. I just went through a new stator install on this other bike so I'm replacing everything along the way.
 
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