Charging System Checks
by Brian McCoy
Well, with the (seemingly) constant issues with the charging system on our VFRs, I thought I’d compile what information I’ve learned through MMI. Perhaps it’ll help you, perhaps not.. but it doesn’t really seem to be information that the average owner knows backwards and forwards.

Tools:

Your handy, dandy multimeter. It should have the ability to check Volts DC (vdc), Volts AC (vac), Amps DC (amps), Resistance (ohms or the omega symbol), and a function for checking diodes.

Some dielectric grease, light sandpaper (cleaning contacts) and the tools needed to get to the bits and pieces might also come in handy.

Parts of the Charging System

There are 5 basic parts to the charging system, they are:

Stator
Rotor
Reg/Rec
Battery and
Wires and connectors

The stator are wire windings (3 ‘loops’) located on the left side of the motor, hidden behind the Rotor. The Rotor is a large metal flywheel with magnets on the inside and attached to the end of the crankshaft.… as the magnetic field passes over of the wire of the stator, AC current is ‘induced’. This AC current travels up some wires to the Regulator/Rectifier, which is under the seat on the inside left frame rail. The Reg/Rec unit is basically a handful of diodes that change the AC current to DC, and regulate how much of that current gets to the battery. You should know what the battery is and does.. it’s on the right side, behind the fairing panel.

Charging System Checks, broken down by component

Stator & Rotor:

There are only 5 basic checks you can do for the stator and rotor. The first one is Insulation Breakdown:

With the bike off, unplug the 3 prong connector on the left side of the bike that’s between the stator and reg/rec unit. (It’s usually tucked in behind the fuel pump.) Then, with your multimeter on Ohms, touch the positive meter lead to one of the stator leads, and the other meter lead to ground. It should read infinite resistance. Check all 3 leads this way (though should all be the same)

The next check is continuity between the stator wires. With your meter still on Ohms, run both of your meter leads to the stator leads, checking resistance between any 2 (3 checks total). Honda says there shouldn’t be any more than 0.2~0.5ohms of resistance between the leads.

Switch your meter to read VAC and start the bike, letting it idle (with the stator still unplugged). You’ll want to perform the same tests (as far as where the meter leads go) as above. When running a meter lead to ground – if you register any VAC, that means that there is an insulation breakdown and part of your charging capacity is leaking off into the bike and never getting to the battery. When you run the meter leads to the stator leads (lead to lead), you should register somewhere between 15~100 VAC (sorry, generic spec sheets on this one).

You’ll want to turn the bike off before doing this final check, but plug the stator back into the reg/rec unit, start the bike and let it idle again. You’ll be checking lead to lead from the stator again, this time showing between 9 and 20 VAC. (generally _ to 1/3rd the unloaded test above)

If you’re not getting any VAC from these readings, you probably have a bad rotor. If you’re getting low VAC readings when checking lead to lead, then you probably have a shorted system. The VAC tests are far more accurate than a resistance test because you’re actually loading the system.. a lot can change in a loaded system.

Regulator/Rectifier:

There’s not a whole lot you can test here (usually, you test around this and if everything else is good, you replace it). You’ll want to disconnect the reg/rec from the rest of the wiring harness so it’s completely isolated. Switch your multimeter to the Diode check (may look similar to an arrow pointing into the middle of a plus sign -->|-- ). You’re going to do 6 forward, and 6 reverse bias checks in sets of 3. For the forward checks, you should get readings between 0.3 and 0.8 VDC. For a forward check, put the red (pos) meter lead on one of the green wires from the reg/rec unit, and the black lead on the yellow leads one at a time. Then put the black meter lead on the red wire from the reg/rec, and the red meter lead on the 3 yellow wires, one at a time. For all the reverse checks, you should get infinate or offline. Place the black meter lead on one of the green wirse coming from the reg/rec and the red lead on each of the yellow wires in turn. Then the red meter lead on the red wire, and the black meter lead to each of the yellow wires.

Battery:

With your meter on VDC, check the battery voltage across the terminals with the key off. It should be above 11vdc (according to Honda). Then, with the leads still on the battery, turn the key on, high beam and brake light – the voltage shouldn’t drop more than 1 VDC in 15 seconds with all those loads.

Wires and Connectors:

With your meter still on VDC, we’re going to check voltage drop between the battery and the reg/rec. You’ll want everything plugged in and ready to go, place one lead on the battery positive terminal and the other on the red wire going to the reg/rec unit, turn the key on. You should see a small number, hopefully smaller than 0.25vdc. Next, we’re going to check between the battery negative terminal and the green wire at the reg/rec unit… again, it should be a small number (below 0.25vdc).

Next, you’ll want to switch your meter to Amps DC (it’s best to have a fused meter, so you don’t melt anything inside the meter.. at least 10amps). The biggest precaution for these readings is to NEVER hook your meter up in parallel when on amps (like, across the battery terminals – you WILL hurt the meter). I like to perform my checks at the main fuse (remove that), and have a little homemade tool to help me. Basically, it’s 2 pieces of wire, with spade ends (like the blades from the fuse) on one end so I can plug it into the main fuse slot, and still connect the relay so the bike will opperate normally. On the other end, I have some connectors that I can easily hook my meter onto (if you have aligator claws for your meter, those work well). Anyway, with your meter plugged into the main fuse, check to see if there’s any ‘draw’ with the key off. If there is, it means you have a ‘leak’ and the battery will drain with the key off. Usually that’s a problem with the reg/rec unit, but could be a ground anywhere. Now, turn the key on (you might want to turn off the fan and put it on low beams).. check the amount of amp draw (max) that you can get… Turn on the loads 1 by one (careful not to go over the fused threshold, if you get close, you can add the loads by turning them on and then off.. seeing the difference). The max loads shouldn’t be much over 10amps. Now, you’ll want to start the bike and see if the amps swing the other direction (from negative, a draw, to positive). Hopefully it’ll do so at or below idle. Also rev the bike a bit (nothing more than 5k) and see what the max charging output is.. should be greater than 1amp to be safe.

With all these checks, you can pretty much isolate any specific component in the charging system, and check that everything’s working as it should. If you need more descritpion of what I’m talking about, just ask the list. Or if you have other questions regarding these checks. Good luck though.

Brian McCoy


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