To: Dave Maultsby, Ritzo Muntiga
From: Bob Prohaska
Re: VFR800 RR problems.
Here are the observations I was able to make during the short life of my 3rd Electrex RR. I hope they prove of some help. The oscilloscope used was a Tektronix 2234 digital storage oscilloscope with 100 Mhz bandwidth running in glitch detect mode. I didn't time the following events but I think they took about an hour.
The Electrex RR was suspended in free air, leaving the OEM unit bolted in the usual position with a 3.5 inch cooling fan blowing on it. The connections were checked for condition and attached to the Electrex unit. It may be significant that the Electrex RR's that lasted 3k miles had the benefit of the fan; the latest one did not.
I put the scope on the AC input side (using a pair of matched probes and differential mode) across the two parallel connector blades and got initially a reasonable waveform.
It was a nice squarewave, symmetric about ground and about 14 volts in amplitude. No spikes or transients were observed initially, despite the fan switching on and off repeatedly.
I revved the engine a little, up to about 3k rpm, and noticed in a few instances narrow spikes between output pulses. I couldn't get the scope to trigger on them, and they went away in a couple of minutes. The amplitude was not more than thirty volts, I'd guess the duration was some tens of microseconds. The spikes were clearly synchronized with the squarewave and didn't depend on the fan, which switched off and on.
By this time the regulator was too hot to touch comfortably, but not hot enough to cause an immediate burn. The waveform remained reasonable.
I watched a while longer and suddenly the output became unclamped in the "negative" direction. Initially I thought it was a measurement connection problem which I'd seen several times before, but re-connecting the probes didn't help, and measuring another phase pair gave a good waveform. This made me wonder if a rectifier diode had opened. I shut down the bike, took out the RR and ran a cursory check with a multimeter expecting to find an open circuit. Everything looked reasonable but by this time the RR was cool enough to handle comfortably. In my haste I didn't rigorously follow the Electrex fault finding chart, so it's possible I missed something. In any event, the scope said there was a completely open circuit but the multimeter said no! I want to say it wasn't a problem with my test leads, but they were crude enough and had given me enough trouble in the past so that it remains a possibility.
I put the Electrex RR back in the bike, fired it up and got normal waveforms between all phases. The fan cycled on and off, I played with loading the system a bit by altering the heat setting on my heated grips, nothing odd happend.
After watching a bit longer the waveforms started to become non-symmetric, with the "positive" pulses narrower than the "negative" pulses. Eventually, the "positive" pulses vanished and the output voltage sagged a bit at idle but it would still come up if I revved the engine. The waveforms remained normal on the other two phases.
I pulled up the Electrex Fault Finding Chart and ran the diode checks. This time the RR showed a short from one AC input phase to the positive output.
Please note that "positive" and "negative" are in quotes because I neglected to keep the probe polarities consistent between test sessions. The spikes I saw were "positive" and the unclamped voltage was "negative" but I may have switched the test leads between the two events.
Next I put the OEM Honda RR back on the bike and observed many similar features: the waveforms were symmetric with respect to ground until the engine was revved a bit and the regulator started regulating, rather than just rectifying. The regulating action was not smoothly proportional to speed and seemed to oscillate in time, nor was it evenly distributed across phases. The residual voltage was about 2 volts, a bit higher than the 1.5 volt forward drop I expected from an SCR. However, the OEM RR continued to function, giving correct output voltage. I did not observe the 30-odd volt spikes seen with the Electrex RR, but since I couldn't reproduce that event on the Electrex unit either the significance is unknown.
It occurs to me that a reverse leak in an output rectifier diode would let the battery discharge backwards through the regulating thyristor. This could lead to an apparent overcurrent failure, since now the RR would be passing alternator output plus whatever the battery could deliver. It wouldn't show until the regulating action kicked in. Unfortunately it's hard to reconcile this with the apparent intermittent open circuit which I thought I observed.
As an afterthought (the next day, unfortunately) I put an ammeter on the alternator and OEM RR. The short circuit current was about 34 amps, exactly consistent with the 0.47 kW output rating.
A couple of thoughts come to mind: the first is that the phase control looked remarkably imprecise, both on Honda and Electrex regulators. Control should be uniform in time and across phases, not the unbalanced all-or- nothing behavior I observed. Second, the rationale for shunt regulation on a half-kilowatt prime mover seems questionable. I'd be willing to test a series phase controlled regulator. At redline the alternator can muster about 120 volts; that's _not_ high voltage. The connectors and cables can take it easily, and the varnish on the windings is likely good for that much and more unless it's deliberately made very much thinner than usual. Electric-start bikes need considerable excess alternator capacity; continuously shorting it out seems like a difficult way to control an alternator of such high power.
It'll take another volt to get break-even; that's maybe one hundred rpm at idle. Perhaps not a bad trade. I'd be curious to know what your engineering people think of these ideas.
bob prohaska