Need help testing a voltage regulator

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isnowbrd · #1 Unread post by **isnowbrd** » Sat Apr 07, 2007 1:20 pm

I have a Honda VTR that commonly has the voltage regulator fail. I'm trying to follow the instructions in the service manual and needs some serious help. Plus I have no idea how to read the new voltmeter I just bought.

This is what the service manual says to to:

(Is anyone else worried that they can't spell correctly?)

This is the chart for what the resistance should be between the terminals:

This is what the voltmeter showed when I put the BLACK tester on the GREEN terminal and the RED tester on the YELLOW terminal:

But the strange thing is, when I switch the testers around and put the RED tester on the GREEN terminal and the BLACK tester on the YELLOW terminal it shows this:

Shouldn't it show the exact same measurement both ways?? Does this fall into the .5-10 ohms that the manual specifies?

Here are the rest of my results. This one is BLACK tester on the RED/WHITE terminal and RED tester on the YELLOW terminal:

This is with the testers reversed. RED tester on the RED/WHITE terminal and BLACK tester on the YELLOW terminal:

This is RED tester on the RED/WHITE terminal and BLACK tester on the GREEN terminal:

This is with the testers reversed. BLACK tester on the RED/WHITE terminal and RED tester on the GREEN terminal:

Is anyone confused yet?

#2 Unread post by **Sev** » Sat Apr 07, 2007 2:13 pm

A rectifier works by only allowing current to pass through in one direction.

A series of diodes ensure that alternating current turns into DC.

What should happen is the current should be allowed to go one direction, but not the other. Like what happened with your resistance checks using the multimeter.

The issue I'm seeing here is that there is some leakage through the system in the reverse direction - this indicates to me that it's not completely cleaning the AC into DC... basically there is some leakage/lost insulation that needs to be replaced. Probably time for a new rectifier...

These type of tests are easier with a digital multimeter, because it will actually tell you if there is infinite resistance.

Have you checked the rest of the charging system?? How do you know there's a problem with the charging system? There are about.. 18 different checks you can do to find out where the problem is before blaming the regulator... but based on what you have there, there seems to be a problem with the regulator.

isnowbrd · #3 Unread post by **isnowbrd** » Sun Apr 08, 2007 8:45 am

Yeah, I'm going to return my meter and get the digital one that was only $5 more.

I think the VR might be bad because first of all, they are notorious for overheating and failing on this bike. And second of all, when they do go bad they tend to ruin the battery, and I just had to replace the battery which was only two years old. I just want to make sure this new battery doesn't get ruined by a bad VR. And I've also read that when the VR goes bad, it can also ruin the bike's CDI box which is very expensive.

Here are my readings when putting the tester on the brand new battery.
With the bike off = 12.5 volts
While at Idle = 14 volts
Running at 5-6K rpms = 13.5 volts

The service manual says that the regulated voltage should be between 13.5 and 15.5. So I shouldn't have to worry about my VR roasting my battery right? But isn't it a bad sign when the voltage drops when the rpms increase? I want to be able to use my heated jacket with this bike, but am worried about the charging system not being able to handle it.

#4 Unread post by **Sev** » Sun Apr 08, 2007 4:27 pm

Actually, that's normal, I think it's something to do with maximum output of the charging system, plus faster use of the power (because the spark plugs fire more often) don't worry about the voltage dropping. I wouldn't worry about it too much, excess charge should be dumped to ground, if the regulator is working correctly.

You're looking at the rectifier, which turns AC into DC. But the regulator usually gets rolled into the rectifier to make a single unit.

If you really want to know how many accessories you can run then you need to check amperage across the battery, not voltage. However, and here's the issue, you can't do it safely with a multimeter, because it needs to be connected in series - can only be done while the bike is off, and the starting amperage will blow up your meter.

Your bike should be more then fine to run an electric vest though. There's usually some extra current output inherent in the charging system. Plus you could always switch to a couple of LED bulbs like Skier did in his blog, he's got links for everything (this will save a LOT of current).