225DX Regulator Help Needed

[Frankencelery]

The Yamaha YTM 225DX I purchased last summer came without a battery and both headlight and taillight blown. The previous owner told me that it fries batteries and light bulbs, leading me to expect that the regulator was bad due to overvoltage. Unfortunately, I never actually tested it. I bought a used regulator and decided to install it today.

To get a baseline, I took my digital voltmeter, started up the trike, and measured voltage with the old regulator and again with the new one.

Measuring the output voltage at the battery terminals with the old regulator: about 3vdc at idle, 7vdc revved up. Switching to AC just to see what would happen- 0vac at any speed.

Measuring the output voltage at the battery terminals with the NEW regulator: about 1.5vdc at idle, 3v revved up. Switching to AC just to see what would happen- 10vac at idle, 16v revved up.

Interestingly, the "new" regulator got warm, while the old one stayed cold. This makes me think maybe the new one is actually doing something? Dunno, but it seems odd to be outputing AC. Does anyone know if the regulator is supposed to contain an internal rectifier? If so, my new one is apparently bad too.....

[Sargon2112]

The headlight / taillight circuits on DX's run off of AC only. All the DC circuit does is charge the battery and start the engine. Both the DC and the AC circuits are regulated by the same regulator (which also has a rectifier in it). Sounds like your old regulator was bad for sure... The AC readings on the new one sound about right. I'd still check the harness out good though because those DC readings sound screwy. I'll go out tomorrow and measure mine & report back! Good luck!

[Frankencelery]

Ok, that's helpful. After I posted the question, I decided to install all the replacement bulbs and see what happened. The headlight, taillight, and neutral indicator were all blown, but I had replacements. I replaced all three and they worked fine. I rode it for about 10 minutes last night, and the bulbs didn't blow. I did not get a chance to actually meausre the voltage at one of the bulbs, but knowing it's AC is helpful.

The second thing I thought of is that I'm running it with no battery. It's many years since electronics school, but I remember that some circuits will not work correctly if there's no load, so I wondered if it needed a battery installed to correct the problem. (I didn't want to buy a $90 battery until the regulator issue was resolved...catch-22)

Then I thought: yeah, but what does the regulator do if the battery is full? The battery should look like an (almost) open circuit when it's fully charged, so the regulator should still hang out at about 13.5V, right?

[Sargon2112]

Sounds like your AC circuit is good. As for the DC and the battery thing, installing a battery might just do the trick. The charging circuit is just a current source with a voltage limit (~13 volts or so)... and a current source needs a path (load). Although a charged battery has high resistance, it's far from an open... there's still a path for current to flow through a charged battery since their R is only in the high kOhms.

If you have a Wal-Mart out there in IA, go there for a battery. They carry them and they are cheaper... Auto parts stores carry them too for less than OEM dealers. I have a WalMart battery on mine that is still good after a couple of years. Seems like it was only 40 or 50 bucks. Make sure you charge it like the instructions say, else it won't last long at all.

Good luck man! Let us know how it turns out...

[Frankencelery]

So is AC and DC a different winding on the stator?

[Sargon2112]

Yep, the difference is that the lighting circuit AC is not rectified, but it is regulated. The DC is rectified and regulated. If you remember from electronics school, what a rectified signal looks like... it's called "pulsating DC". When you connect a battery to your trike, that load will flatten out the pulsating DC and should give you your ~13v dc.

[Frankencelery]

I do remember that, and the battery acts like a filter cap to make /l/l/l/l/l/l into more or less steady DC. However, as is being discussed in another similar thread, how do you regulate AC? I have no memory of ever seeing an AC regulator.

[Sargon2112]

Yep, you got it.

There are multiple ways, but the most common way to regulate AC is with a 'clipping' regulator. It uses a zener diode on the input side to determine the output voltage, and a few power transistors and diodes to clean up the clipped signal. It basically chops off the AC signal peaks and troughs.

[crowballs]

Holy crap, these are the exact same issues I'm having. Did you get the new regulator/rectifier from Yamaha? The price I was quoted was rediculous, 140. If you have any suggestions that would be awesome! I need my electrical working before I can enjoy the dunes at night, can't wait!

[Sargon2112]

Crowballs,

Try Ebay or post a wanted ad in the classifieds on this site... get a used one.

[Sargon2112]

Frankencelery,

I have a schematic here somewhere of a clipping regulator I built to put on an old KDX 250 enduro bike... It was six volts AC originally and I built the 12v regulator (14 point something actually) so I could use cheaper 12 volt bulbs in it. I'll dig it up and post it.

What was that other thread you mentioned?

[Frankencelery]

That would be cool Sargon, I'd like to see that. Crowballs, I bought that regulator from a member here on 3WW. I'm still not convinced that it's bad, but I reacted as if it were and bought another one on Ebay on Sunday. We'll see how that works, and if it's ok, I'll sell you my extra one.

My latest thought is to put a big resistor (say 1000 ohm/1w) across the battery terminals to simulate a battery. If the voltage starts to look more like it's supposed to, then I'll know that the battery was supposed to be present, and I'll spring for the battery and put it in. Think that'll work as a test, Sargon?

[crowballs]

Thanks, I'll do that gents.

[Sargon2112]

Hey Frankencelery,

Sounds like a good test... the full voltage drop should develop across your resistor but remember, it will be pulsating DC at a high frequency (frequency = rpms) so when you rev the engine, the voltage might appear to go down depending on your meter... Most meters don't fare too well above a few kHz. Your most accurate reading will be at a "fast idle" if that makes any sense. I'm betting that your new rego is good and the old one was bad... been wrong before though!

Just reading around the forum and man, it's a week for regulator / lighting troubles! Lots of threads about similar problems.

Good luck!

[Sargon2112]

I found the schematic of the AC regulator circuit. I found it online 5 or so years ago. It was for a 6 volt system but changing a couple of components turned it into a 14.4 volter. I built mine on a piece of aluminum (made a good heatsink). I used some tape to make it into a cube then poured it with epoxy. Put it anywhere in parallel with the bike's lighting circuit (on the switched side). It ran on my old (no longer with us) 1980 KDX250 dirt bike for 2 years. It outlasted the bike by a few years, as it is on a friend's bike to this day.