Topic: rectifier again

[davidm]

So I built the rectifier as described by Frank Cooper.  The bike was running great, then suddenly it stopped charging.  I touched the rectifier and found that it wasn't getting hot the way it usually does.  I re-seated all the connections and tested for continuity, as it appeared one had come loose.  Still no charge.  I read somewhere that you could damage the rectifier by not having one of the wires connected, so I assumed that's what had happened.  I picked up a few new bridge rectifiers and built a new one.  Still no heat and still no charging (only 12.5 volts at the battery at 3000 rpms).  I had been trying to correct the improvisational wiring the previous owner had done on this bike and assumed I could have done something to cause it to fail again.

I printed the Three phase charging system inspection procedure from the Electrics FAQ and went through it.  Everything looked good, except the rectifier tests.  The procedure says I should get between 5 and 40 ohms between green and each yellow (forward bias).  With my Ohm meter set to the 200 ohms scale, I got no reliable reading.  I switch to the 2000 ohms scale and I get 409-419 ohms on each yellow lead.  Same is true when I test between yellow/red and each yellow lead.  Infinite resistance on reverse bias.

I'm assuming this means the rectifier is bad, again.  I just wanted to be sure I was reading the meter correctly.  Also, why does this keep failing?  I was thinking of just buying the rectifier made by OREGON motorcycle parts, hoping it will solve my problems, but I'm worried that one will fail also after being on my bike. 

Thoughts anyone?

THankS

[Bodi]

One reasonable way to test the rectifier is to measure the voltage between the yellow wires with the engine running. If the rectifier is all good, you should get equal readings (within about 0.5VDC) on all 3 measurements, all about 13 to 15 volts DC. If one or more readings are higher then the rectifier has a problem.
If these read OK then probably you have a wiring or regulator problem and the alternator is just not making much power. I would trace out the field and stator wires (all the way from rectifier and regulator to the actual coils) and make sure there aren't any bad connections. Then measure the voltage from ground to the F wire on the regulator (should be a white wire to the field coil) it should be at battery voltage or a bit (one volt is OK) less with the engine running and the battery voltage below 13VDC.

[davidm]

Ok, thanks for the tips

So How do I measure the voltage on the yellow wires?  Each wire to ground?

I'm confident the regulator is functioning correctly as I have both the stock electro mechanical one and the KEM electronic one.  Problem exists with both.  And it is a steady 12.5 volts, so I'm thinking this also indicates it is working.

I also tested the yellow wires from the coils (can't get the cover off) and they all seem to test ok, according to the Charging System Inspection procedures.  Wouldn't that rule out the coils?

Thanks again

[Bodi]

measure between the yellow wires, ie 1-2, 1-3, and 2-3.
If you take the side cover off - not the alternator cover - you should be able to trace the yellow stator wires and the 2 field coil wires. You probably have a set of bullet connectors close to the alternator with wires directly from the actual coils connecting to wires going to the engine plug or directly to the rectifier and regulator. These bullets are infamous for causing trouble, they should be clean and tight; if a plastic sleeve is burned black then I think you found a problem. The engine plug is less trouble but should be cleaned.
Regardless of the regulator you have, if there's a fault in the wiring you get low output.
Measure the voltage at the regulator field terminal compared to the battery "+" terminal. It's very common on these bikes for an aged wiring harness to give a much reduced voltage at the regulator, this greatly reduces the alternator output because of the reduced field coil power.

[SohcCBs]

The other way to check the rectifier, with all power and other wires disconnected......with and ohm meter, you'll get an ohm one way and 0 the other.

[davidm]

Thanks again for the help, Bodi.

The only bullet connectors behind that cover were the green and white coil connectors.  THese go to the harness.  From the bullet female to the harness there is 0 resistance.  They looked clean, but I cleaned them off with contact cleaner anyway.

I'm going to test the yellow wires as you've suggested next.   Where should I stick the probes?  Disconnect the rectifier and check there?

Incidentally, I did get the generator cover off.  I'm not sure what it's supposed to look like, but the coils seem wound uniformly.  There was some rusting on the rotor(?) and lots of grease covering the coils.  SHould there be a gasket sealing the cover to the engine?

And what about the 400 ohms as opposed to the 5 - 40 listed in the Inspection procedure?  I have an unopened in the box bridge rectifier and it also gave me 400 ohms on each AC terminal.   Is that normal?

Thanks
D

[Pinhead]

The charging system of these bikes is extremely simple. If you're getting voltage to your regulator when you turn on the key, it'd be really easy to completely re-wire the alternator from that point on. Check out the link in my sig about a cheap R/R.

[davidm]

Thanks for this.  I have built the rectifier from (2) 25a 50v bridge rectifiers and am using the KEM electronic voltage regulator.

Any other suggestions?

Thanks
David

[Pinhead]

50v bridge rectifiers are the absolute minimum. That's probably why you keep burning up rectifiers. The voltage coming out of the stator can be anywhere up to 100 volts (I've seen it personally on my 650 at 6500rpm). Replace those 50v rectifiers with 100v units and I'll bet you'll quit burning them up.

[davidm]

HI everyone,

Thank you all for your input.   Problem solved - for now.

After testing the previous bridge rectifiers that I thought were bad, I realized they were working just fine.  (these are 100V as pinhead suggested).  THe new 50v ones I also tested and they were also fine. 

The problem was one of two possibilities -
The green and white wires from the generator behind the side cover were dirty - though these looked okay when I took them apart, I cleaned them anyway.  Maybe there was just enough dirt in there to break the contact.
OR
I noticed a slightly loose connection on one of the bridge rectifiers and I tightened it up.  It might have been slipping just enough to keep from making constant solid contact.

I reassembled everything to begin to test the yellow leads as suggested by Bodi, and because I coudln't find anything wrong and with some wishful thinking, I checked the voltage at the battery.  Steady 14.5 volts!

YIPEEEEEE!!

Seafoam next to see if I can smooth out the acceleration....

THANKS AGAIN!!!