CB350 - Rectifier Output

H

hatchb4ck

Active Member
Running into a bit of a charging issue on the CB350 and thought I'd run it by the forum members.

Initially started out with testing the rectifier, which failed the resistance tests. Inspection of the plastic "cage" around it showed that it had gotten hot enough to melt it where the cooling fins touched the plastic. I swapped it out for a 55v 25A unit from Radio Shack. A bit more testing shows that I have about 35 volts on the red/white wire (output) to the battery, yet still no voltage at the battery. Continuity tests of the red/white wire to the battery are good end to end, not shorts. The new rectifier tests good. The windings in the alternator return good ohm readings.

I plan to test the regulator tomorrow by disconnecting the regulator to see if the voltage at the battery changes. This will only be a momentary test (don't want to fry the battery) if 35V at the red/white wire gets applied to the battery.

My initial thought on this was that as voltage was fed up to the battery, it was routing through the red wire (and inline fuse) to the ignition switch and to a short within the harness but the fuse isn't blowing (which would lend itself to my theory of a short). With the voltage so high, the regulator could be shunting it to ground (bad regulator?)

The red wire normally connected to the positive terminal on the battery had 1-2ohms between it and ground when the key is on and is open when the key is off. I moved on to the black wire from the regulator with the ignition switch disconnected. This test showed less than an ohm and I isolated it down to the right control. Disconnecting the kill switch opened the circuit. I don't think this is a short per se, but rather the resistance reading through the coils.

There are a couple of points where I'm confused. What is the isolation point between the battery and the charging system? The bike runs on battery. Kill switch functions. Starter functions well when the battery is charged. Is there some other test I should be trying to isolate?

Thanks in advance for all the help.

Joe
 
Update -- after continuing to read the different posts concerning testing electrical systems on these honda twins, I headed back to the garage to run through the checks again.

I had checked the continuity of the red/white wire between the rectifier connector and the battery terminal. This checked good, but between the rectifier side of the connector and the rectifier gave intermittent results.

I pulled the stub harness from the bike and as I did so I noticed that when I moved the wire, continuity was present.

Turns out the female spade connector in the plug end had broken away at the narrow portion. This would definitely cause the results I'm seeing with my multimeter during the different testing procedures thus far. Its off to the electronics store to find a replacement female spade to repair the broken one.

I'll post up if this "fixes" the issue.
 
I was going to suggest that perhaps the failure of the rectifier could have fried the regulator. That is still a possibility, so keep that in mind after you fix your faulty connection. Sounds like you are using pretty good methodology for troubleshooting.
 
Thanks AlphaDog...although after a few hours sleep, I realized I was chasing my tail a bit. One of the fundamental rules of voltage in a circuit is that if there is a short, you won't be able to detect any when testing to ground. If there is an open, you will detect max voltage.

The 35V at the output of the rectifier should have been a big red flag.
 
Repaired the broken connector and connected everything back up.

Now, without the bike running, there is battery voltage at the red/white wire connected to the rectifier, which is expected.

I started the bike, but the voltage hung pretty low, just above the battery's 11.4v (I hadn't charged it up before the test). No change with the regulator disconnected.

Tested the output of the alternator directly with the bike running, about 15 volts AC between pink and the other two leads at idle and it climbs to greater than 40 volts AC as the rpms are increased.

Re connected everything and with the light off and the rpms at 5-5500, the best voltage reading at the battery is 12.5v DC.

I'm a little stumped at this point. Technically, the alternator is putting out enough voltage to keep from draining the battery with nothing on (no head light, no brake or tail lights). I'll have to test the voltage with the lights on to see if the output increases due to the other windings coming into play and a larger load on the bike.

I'm charging the battery overnight and will run the tests again tomorrow.
 
Red/white wire often has corrosion at rectifier connection.
It's real common on some Honda's (CB400F1 for one)
The connectors are so close together the pressure from the other 3 holds wire 'mostly' in place
If block connector was corroded the other end may be as well?
The regulator must not be grounded through body, only through the green lead (I forget why)
You can 'see' up to 17 VDC with a low battery before reg 'kicks in'
 
Thanks for the input CrazyPJ. I may have forgot to mention that I replaced the original rectifier with a radioshack unit putting new ends on the connections. I'll work through the grounds on the regulator tomorrow to ensure it is grounding properly.

Maybe I performed the test incorrectly when disconnecting the regulator. I disconnected it completely from the harness (all three wires). I read a post on hondatwins.net indicating that only the black wire should be disconnected.

Does anyone have any thoughts on the proper way to test that?
 
If you disconnect black wire, regulator 'thinks' battery is dead so pushes max voltage to battery
 
Cleaned up the conductors inside the connector between the rectifier and the main harness. Also, charged the battery completely.

The results are better...but still a bit low.

Battery voltage, key off: 12.67v
IDLE voltage: 12.97
3k+ RPM: 13.5+v
Lights on Hi, IDLE: 12.9 but dropped .1 volt over time
Lights on Hi, 3k+ RPM: 13+ climbing and falling slightly with rpm.

With the black wire on the regulator disconnected, there was no significant change in behavior.

Battery voltage, 2hours later, key off: 12.77v

Cleaning the contacts/connectors appears to have improved the voltage reaching the battery. I'm going to continue to go through the connectors cleaning all of them and the grounds.

The voltage variance at IDLE or higher RPM's, although low, seems to be appropriate if corroded connections are the cause. The only question that remains is the behavior with the black regulator wire disconnected. If the resulting voltages were it charging at "max", it would seem that it is attempting to charge at max all the time and the voltage variation is purely rpm induced. Granted, I didn't run the bike much past 5k a couple of times but the voltage climbed to 13.5/13.6v. It didn't hold at any level with rpm change. Say, between 3k and 5k, it didn't reach certain voltage and hold steady.

This leads me to believe that the regulator may not be working AND I have corroded connections.
 
The fact voltage was higher 2 hrs after tests shows it is charging.
Just clean everything up and don't worry about it
You'll probably get 17V DC with black disconnected, could blow all the bulbs so don't rev over 2,000
 
thanks crazypj and AlphaDog...

At this point, I'll clean up the rest of the connections and keep an eye on it.

Sometimes I think winter can't come soon enough for this motorcycle. Gonna strip it down and rebuild it, fresh harness and all.
 
You need a 'spare' to play with and swap parts over when you know it's as you want it It's what I do with 360's ;)
 
I was telling my wife that just the other day..."Honey, I need another motorcycle in the stable."

I'm thinking bobber for the next one and more CC's. Maybe xs650 based. Unless a triumph project falls in my lap.
 
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