225DX Regulator Help Needed

[Frankencelery]

Ok, I ran the test. First I used a 1K-ohm 2W resistor from Batt+ to Ground. The scope is set to 5v/cm (I couldn't find my 10x probe) and the DC mode. As you can see in the pic, the voltage is about 50v p-p. The DVM is set on DC, and it shows zero volts.

Then I hooked up the battery from my son's quad, and a strange thing happened...with the key turned off, the lights lit up...very dimly. About 5 seconds later the fuse blew.

So...not sure what to think there. I've been looking at the wiring diagram and trying to figure out how that happened, and the only thing that fits is this regulator is also hosed. I've got another one on the way, so we'll see what happens. If it still doesn't work, then I've got more serious issues. I can easily recognize a machine that's had creative rewiring done, and this isn't like that. Everything looks original.

[Frankencelery]

Oh, and thanks for that clipping regulator schematic, Sargon! Dunno if I'll ever use it, but I can get an idea (pretty rusty on my circuit theory) how it works!

[Sargon2112]

Man, ain't that screwy...? Something to consider here is that there could be something else in the system that's killing regulators... Was the scope hooked up when you attached your son's battery? If it was, try it again (hooking up the battery, new fuse) without the scope hooked to the circuit. I've seen circuits ground out through scopes before.

Also, try hooking up the battery with the regulator unhooked. Just don't fire it up and turn on the lights while the rego is unplugged! You'll be buying bulbs. If you get glowing lights with the regulator and no lights without it, it's either the regulator or the harness going to it.

Could be that the rectifier section of the regulator / rectifier is shorted out. That would explain the 50v p-p triangle wave on your scope.

Just have to keep eliminating things... we'll find it!

[Frankencelery]

Yeah, I have an old Eico scope that's ungrounded and unpolarized. The ground probe is actually connected to one side of the line, so if you happened to try to work on a a piece of equipment that was grounded the same way, and you didn't have the plugs turned the right way, BANG! In this case, I don't think that would happen.

But no, the scope wasn't connected when I hooked up the battery. I turned the ignition off to hook it up, it sparked at the terminal and the lights came on, like I said, dimly, and then blew the fuse. I don't think I'd want to try getting it hooked up and started before the fuse blew again! However, I agree that I should probably try to hook up the battery with the regulator disconnected, and see what happens. From what I see in the wiring diagram, the lights should NOT come on with it disconnected. If they do, we have a short somewhere. Could be wiring harness shorting to ground somewhere, I suppose. My cursory inspection didn't show any sign of that, but I could have missed it. I'll keep you posted.

[Frankencelery]

Ok, I got the second new regulator today. Before installing, I did some more testing.

Measured resistance across the battery terminals. Ignition off- 1ohm. Ignition on- 1ohm. 12V/1ohm=12A. That would explain the fuse blowing!

Put in the new regulator and measured again: Ignition off- infinite ohms. Ignition on- 13ohms. Put it in gear and the resistance went up to thousands of ohms. So the 13ohms is the resistance through the neutral indicator light. Makes sense.

With the new numbers, I decided it was time to start it up. Measured about 2vdc idling, and 5-6vdc revved up. Put the battery in, and measured 13.5v idling, and about 16v revved up. Not quite as regulated as I would hope, but this certainly proves that I've been working with bad regulators!

The only thing I'm not sure of is whether it's safe to put in a battery. 16v seems a little steep for charging voltage, doesn't it? Maybe I need to give up and build my own.....

[Sargon2112]

Well, the service manual says 14 ~ 15 volts should be there at 5000 RPM... so considering that, sounds like you're pretty close. I went out to measure mine just now and guess what? I don't think it's charging! Flat 12.01 volts no matter what the RPM... E-start and the rest of the electrical works though. So I guess I'll be looking into that sometime soon. It could not have been 'not charging' for long though, otherwise the battery would have died from me e-starting it.

You are probably good to go man.

[Frankencelery]

I'm going to call it good, and in the next few days, I'm going to buy a battery. I think I'm going to go with the cheaper generic type that I can get at Wal-Mart for $40 or so. The real Yuasa replacement for this thing is $90, and that's a little steep.

If yours is really not working, that would be a bizarre coincidence, wouldn't it? Remember that DVM's sometimes do a poor job of averaging pulsating DC. Seems to me that my first year electronics instructor disliked DVM's for that very reason. Of course, that was many moons ago!

I can't thank you enough for your help on this. I'm sure everyone else fell asleep days ago, with our discussion of waveforms and clipping regulators. But thank the rest of you who kept reading out of morbid curiousity, I hope you learned something.....I know I did!

[Sargon2112]

No problem man... I'm glad you found the problem. It's also a good thing that we did have this discussion since it did lead me to finding an issue with mine that I would not have found until I had a dead battery! Good luck with it!

I'm thinking of building another one of those regos for my nephew's 70 dirt bike. If I do, I'll post some pics.