CB450 Electrics

Finally, I am nearly finished (mechanically) with my father and son CB450 project. We got it running pretty well until the new battery died. WTF? Battery is not charging and bike is running off battery. Thought it might be stator, but there is a ground wire on the rectifier which is getting very hot. What could this be?

Given my (not-) awesome record on your other thread, I'm faintly hesitant, but...

I know rectifiers are a common failure, and if we look at a diagram:

... you can see that if one of the lower diodes leaks current (i.e. doesn't act as a one-way valve for current) that the + will run to ground whenever the AC input is placing + on that diode. Putting half (or all, if both have failed) the charging system's output through that ground wire would probably heat it up...

I think this a common problem on older bikes. With any luck, someone will be able to say something definitive soon...

In reply to ransom:

Damn, this is a new rectifier too.

As for my other problem, the T250, I am still stumped, one classic bike shop gave up and another is scratching their collective heads. Don't feel so bad.

Did you get an OEM rectifier for the 450, or one of the aftermarket ones? I have heard that the OEM ones are quite unhappy whether new or 30 years old. The replacement that I used on my CB450 was one of these solid state units (first one on the page, if I remember correctly) and never had an issue.

http://www.oregonmotorcycleparts.com/rectifiers.html

Darn... Sobe stole my answer.

In reply to sobe_death:

It was an OEM rectifier.

Ordered a new one from Oregon. Thx!

In reply to sobe_death:

Had the shop with my bike install the new Oregon rectifier. It made no difference. Battery will not charge, engine will run only when battery is charged, ground wire gets hot.

The fuse boxes suck on old Hondas. There are probably only two or three fuses in there. Splice in a new one that uses modern fuses.

And, of course, clean every ground.

Have a manual? Are you able to verify that the related wiring on the charging system is correct?

I'd rather double-check for correctness than just start throwing out possibilities, but I'm looking at the rectifier diagram and it looks to me like if you have the inputs on the outputs and vice versa, that what should be the ground input would have a path to ground when it's on the + side of its waveform, as well as going back to the positive in (which should be + out), and both outs (which should be AC ins).

Pre-edit: I'd pay attention to Woody's stuff before trying to make sense of my second-paragraph gibberish, but I would have a look at a manual if you're not certain it's correct.

In reply to ransom:

All wiring matches manual. Also I ran a heavy gauge wire from the reg/rect mounting bolt to the batt terminal

Made sure the large wire on the neg. batt terminal is grounded well. Made sure all grounds are clean on the headlight area.

Checked the stator versus the manual and it passes. Batter will hold a charge from the battery charger. Bike is still not charging and dies when the battery runs down. I am at a loss.

Dang.

Does the wiring for your rectifier look significantly different from the diagram above? Two terminals for AC in, and one negative and one positive out? You phrased it "a ground wire on the rectifier which is getting very hot"...

Just trying to figure out how or why that would be. I think that it's either going to be something like Woody's suggestion, or it's going to be a tracing-wires and reaffirming correctness thing...

I mean, it sounds like the charging system is putting out a bunch of current, which is being turned into heat in that ground wire. I don't know how big the wire or how hot, but we've got energy being turned into heat instead of into a charge on your battery.

I'm not even sure what I'd make of it, but what voltage do you get at the battery A) bike completely off and B) running, enough above idle it should be charging?

Check the back side of the fuse box and see if it's melted.

In reply to Woody:

I can check on that tomorrow.

In reply to ransom:

I did not test the voltage myself, but from what I was told, there is basically nil at the battery.

In reply to Moparman:

Nil sitting, or nil running? Nil as in no voltage, or that it's not charging (showing ~12v).

Well, you'd have 12ish if you were just not charging, in either case.

It sounds too simple, but I'm wondering whether the outputs on the rectifier aren't backward.

I'm having fun pondering this stuff to try to logic out an understanding, but Woody's suggestions are all more practical. I feel I should keep pointing that out...

I only suggest that because I had to push a bike home uphill before discovering that the back of the fuse box had melted out and there was no sign of it from the front. Apparently, it was a common problem on Hondas in the 70's.

I know this bike has a main fuse, but do not see a fuse box on the bike or wiring diagram.

Moparman wrote: In reply to sobe_death: Had the shop with my bike install the new Oregon rectifier. It made no difference. Battery will not charge, engine will run only when battery is charged, ground wire gets hot.

Did they read the instructions? I had the same issue on my CB360. you have to combine the yellow and white wires coming out of the stator. The normal way has them going to the headlight switch. With the lights off, you only have 1/2 the charging. turn the lights on and you get it full. if you combine them like what is shown, that gives full charging all the time.

I assume this is the same on your bike - not sure what year it is.

Moparman wrote: ...there is a ground wire on the rectifier which is getting very hot. What could this be?

Typically it's a failed diode that is shunting ac current to ground in a short circuit. Can cause the stator windings to burn out if you let it keep going.

We shall check the stator wire.

thx