Charging issue

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Eckhoff

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86 mod Vmax. New regulator, new battery (680), it shows 15 volts when I measure directly on the regulator (when running) with the battery unhooked from the regulator but when I hook on the battery it shows 12, and not charging at all. That’s a new one for me, what in the world could be wrong?

The regulator is directly hooked on both + and -
 

Eckhoff

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Load-test the battery, sounds like it could be defective.
Hm.. I can do that, but I can run the bike on the battery only for hours. I have done that the last few days. I take out the battery in the night and charge it for 5-8 hours and I can run the bike for 7-8 hours including 5-6 starts without any issues. It’s weird that it would take charging from my car battery charger but not from the regulator
 

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Sounds to me like the battery is in good condition.
You show 15 volts from the regulator with no battery but that is a no load condition and really doesn't mean much.
Check the stator for proper AC output but, I'd guess you're new regulator is not doing the job.
 

Eckhoff

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Sounds to me like the battery is in good condition.
You show 15 volts from the regulator with no battery but that is a no load condition and really doesn't mean much.
Check the stator for proper AC output but, I'd guess you're new regulator is not doing the job.
I charged the battery for 10 hours last night and I have just taken a 2 hour ride. It runs good and still has more than enough power to start the bike. But it didn’t charge... I have measured all three wires from the stator, it shows between 30 and 50 volts depending on the rpm. Maybe it’s the new regulator, it’s one of the cheap ones from Ebay
 

02GF74

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It does sound like regulator is bad.

The service manual goes to great detail for testing the charging system, from checking the alternator, rectifier and regulator.

Stupid question but the replacement regulator is a direct like for like replacement and was wired correctly?
 

Pighuntingpuppy

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Solid advice here. One thing I would do is load test wires from regulator to battery. How you do that is place one DVOM lead on the positive terminal of the battery. Place the other DVOM lead on the wire from the regulator. Ideally, you want to see close to 0V. In reality, you will see 0.1V to 0.3V. If you are seeing a 3.0V drop, your wire from the regulator to the battery is bad. You can do this with the ground cables as well to see if one is failing but you do that in reverse. You place one DVOM lead on the negative side of the battery. The other DVOM lead on the ground strap you are testing. Again, ideally, 0V. In reality, 0.1V to 0.3V is what you probably will see.
 

Eckhoff

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Solid advice here. One thing I would do is load test wires from regulator to battery. How you do that is place one DVOM lead on the positive terminal of the battery. Place the other DVOM lead on the wire from the regulator. Ideally, you want to see close to 0V. In reality, you will see 0.1V to 0.3V. If you are seeing a 3.0V drop, your wire from the regulator to the battery is bad. You can do this with the ground cables as well to see if one is failing but you do that in reverse. You place one DVOM lead on the negative side of the battery. The other DVOM lead on the ground strap you are testing. Again, ideally, 0V. In reality, 0.1V to 0.3V is what you probably will see.
I tested it and it showed 3.3 volts between the battery and the red regulator wire. I only understand the basics when it comes to electricity, so where does these 3.3 volts even come from? Does it mean that there is some kind of connection between something where it shouldn’t be a connection?
 
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02GF74

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Is the red regulator wire you mentioned an input to the regulator (most likely connected to the rectifier) or an output, which goes c
to the battery positive?

If this 3.3v is across a wire then that is due to the resistance of the wire and current flowing through it.

Apologies for the lecture but here is a rough analogy of voltage, current and resistance.

Think of current as water flowing through a pipe.

Resistance is like an obstruction in the pipe.

Voltage is like pressure and this with water can be achieved by height differences.

Let's say you have a bucket with a pipe connected on the side near the bottom.

Let's say you fill it a bit with water. You get water flowing out the end of the pipe.

Let's say you fit a plastic flap inside the pipe so it is attached along one edge.

This acts as a valve (resistance) . Water will try to push it down. The amount of water flowing out of the pipe (current) is reduced unless the force of the water is strong enough.

Filling the bucket up to the top will increase the pressure at which it leaves the bucket, equivalent to increasing the voltage.

Now the increased pressure (voltage) is able to push down the flap (resistance) resulting in more water (current) flowing out of the pipe (wire).

So on your situation you have current flowing from the regulator to the battery but the voltage drop you are seeing is due to a resistance between these two points.

This can be due to the wire being too thin (unlikely as I am guessing this is the original loom), badly made crimp connections or corrosion between the connectors. There may be another component in between the two points (for example a fuse)

One thing to try is to temporarily connect a reasonably thick wire directly from the regulator output to the positive battery terminal and measure the voltage again at the battery positive - it should go up if the problem is with the wire.

BTW 3.3volts is a significant drop, I have to question if you are measuring correctly.
To confirm, connect one lead of volt meter to the battery negative, then other lead first to the regulator output, then to the battery positive.

The difference between the 2 voltages should match the 3.3volts you mentioned.
 

02GF74

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Example of the type of valve I'm talking about. Instead of it being hinged, imagine it is glued at one end and made of something that will bend. Water pressure will force it to open.
Screenshot_20210606-000750.jpg
 

DreamV4

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I bought some bike dirt cheap with non-working charging system, it turned out, one wire was grounding (bad insulation, 3 min fix). stator is just 3 coils, get a tester and check resistance and ground of 3 wires.
 

Fire-medic

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VMX12- Service-Manual.pdf (vmoa.net)

Use the service manual electrical section to discover what was wrong with the stator. Increase your troubleshooting knowledge. Post what you find here.

Your post #5 shows output from the stator, but maybe there was some-sort of intermittent short.
 
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