Voltage Drop Mystery

[stuarto49]

Background: I bought this bike (2009 with 24K miles, totally stock) last Nov from an independent dealer in SC. Was not able to directly contact the previous owner but after calling a few Yamaha dealers I found the one which had serviced this bike. According to the service dept the bike had several recalls done, specifically the 'ignition and sub-harness'. The battery was replaced just before I bought it, and the dealer mentioned that it was $136, likely from a Yam dealer, so not a cheapie from China.

I have had many bikes (about 29?) from all the countries, mostly sport-touring machines. My work is electrical engineering and have 50 years of hands-on skills. My wiring work on bikes involves soldering, heat-shrink, oversized gauge selection, high-quality components, etc.

I ran 12 ga cables from the battery (thru an in-line fuse) to a power relay and distribution fuse block under the driver seat. Power is then fed to both sets of Denali LED driving lights, horn, heated grips, etc. One of the direct (always on) feeds goes up to the small junction box over the steering head which houses the DATEL voltmeter. A rocker switch turn on the DATEL so there is no draw when not running.

I now have 32K miles on the bike - the battery holds its charge very well and the bike starts instantly even after sitting in cold weather for 1-2 weeks.

I recently did a valve service and inspected the key spiders S4 and S6 and a couple others - absolutely clean, no sign of heat or corrosion. Used ACF-50 anti-corrosion and reassembled.

My DATEL has been synchronized with a FLUKE meter directly on the battery terms - both read exactly the same at all times, key off, engine running at RPMs up to 5000. My DATEL reads 13.5 - 13.6 MAX and I expect closer to 14 volts but cannot determine the problem. Yesterday I pulled the plug from the R-R unit and stripped away just enough insulation from the RED and BLACK wires to be able to connect my meter leads.

RPM ----> 1500 -- 2000 -- 2500 -- 3000+

DATEL - - - 12.8 13.4 13.5 13.6 (max reading)
Fluke at R-R 13.7 14.3 14.3 14.3 (max reading)

So, from the readings I assume that the alternator and R-R are OK and I've got a voltage drop issue. Next I connected the meter between the R-R black wire and the battery NEG term - at 2000 RPM I read 0.48 volts. Between the R-R red wire and the battery POS term I read 0.3 volts. Well, there's my voltage drop! Just to prove this I solder a nice 12 ga wire to the R-R black wire, start the bike, and touch this wire to my NEG power bus under the seat, expecting the DATEL to move up by .5 volt. But, no change! WTF?

I think at this point the 'Car Talk' response might be to cover the DATAL with a piece of black tape and fawgeddaboudit! The bike works fine, all my accessories function perfectly, no wires are smoking - just ride the thing. BUT, I finally thought I had found those lost volts, maybe not?

Confused. Stuart Ostroff, Richmond, VA

 

[PhilJet09]

There's already a long thread here about the exact thing you're talking about by DCarver. You pretty much have it figured out...voltage drop from the RR to the battery tells you there are too many poor connections in between. The simple solution is to run your own wire or buy a pre-made kit for this very issue. I'll see if I can find that thread.

Here it is, lots of reading.

https://www.fjrforum.com/forum//index.php/topic/146331-krzy8-gen2-charging-circuit/

 

[stuarto49]

Thanks very much. I think I had seen (parts of?) that thread while searching for key words.

Gratifying to see that I (also) have found the root of the problem - the harness from the R-R is a bit flimsy plus the ground loops are 'whispering down the lane'. My idea of parallel feeds to the battery are the best solution.

Stuart

 

[dcarver]

Yep. Don't waste time troubleshooting. Simply run new copper from point A to point B. (RR to battery). Mine and several other peeps now have over a year and thousands of miles with 14.3 and better voltage at the battery.

 

[RichDoyle]

I though I'd pipe in here.

I was having some confusion reading this, as my '13 has an identifiable voltage loss and I thought you were describing what I have observed, but apparently not.

In my bike the voltage at the battery when the bike is running above about 2,000 RPMs, is reliably at 14.2-14.3 volts. But measured at the accessory plug, it reads maybe .4 - .5 volts lower, depending on what's turned on: Heated grip level setting, for example. I haven't measured since I've got all-LED brake lights, but hitting the brakes also produced an additional .1 volt drop. All the while the battery voltage is unaffected by these variants. So I conclude that problems that existed in the earlier Gens with the regulator-to-battery connection are not an issue with the GEN III. But voltage at various points of delivery on the bike will vary. It's just a matter of a) is it measurable and (most important) B) does it matter.