Topic: CB350F Charging Issue

[mikeswaggs]

I have searched quite a bit on the forums for this topic, but haven't seemed to find much, so I decided to post a question about it.  I have a charging issue, especially at idle.  I purchased an updated voltage regulator (not the factory part, but a modified newer technology part) to try to up the voltage at idle. ( I had read that the old style regulator was inefficient and could be improved upon.)  I still have the issue though of after riding a while, the battery charge diminishes to the point that if I have the brake applied, the power going to the brake light will cut the engine, since there is not enough power to the ignition coils.  If anyone has a solution to this, let me know!  The PO had this same problem, and by charging the bike each time he rode it, he accidentally switched the pos with the neg. and fried the elec. system.  (which by the way was the way it ended up in my garage!)

[TwoTired]

There is quite of bit of information in the electrics FAQ.

What aspect your bike's problem isn't covered there?

Have you done any voltage checks or probing with multimeters?

Have you changed the electrical load from stock?

Cheers,

[supersport_CB400F]

How old is the battery?

[Bodi]

If you're trying to get a 350/4 or a 400F to charge at idle, you're pissing into the wind. They won't do it. Period.
The alternator starts to make more power than the bike draws at around 2500 RPM. That's if everything is perfect.
To get the original performance from the alternator, make sure all the electrical connections between the alternator and the rectifier and regulator are clean and tight. There are bullet connections under the engine cover close by the actual alternator and then there's also the engine plug: these can get corroded pretty badly.
Once those are good, start the bike with a good charged battery and measure the voltage at the black wire to the regulator; compare it with the actual battery "+" voltage. You'll find a surprising difference, I think. Cleaning all the bullet connectors in the harness and the ignition switch connector should help reduce that lost voltage; the regulator power goes through lots of the bullets and the ignition switch. The alternator works on a magnetic field generated by the voltage from the regulator, and any reduction in that voltage means reduced magnetic field and reduced alternator output. If you want to improve charging a bit you can install a relay that feeds full battery voltage to the regulator when the ignition is on, I've done this and it definitely helps.

[schneider419]

hey there, i have a 72 350f, and did you know that the regulator is tuneable? i got my info from this club site. its called adjusting an sohc/4 voltage regulator. its by thomas rupp,/4 # 0009. i hope this helps.
                                                                                                      mike

[TwoTired]

I admire Thomas Rupp for spending the time and effort to write up a proceedure to help others.  It is very unfortunate that he missunderstood the regulator function and got it wrong.  Adjust it his way and you risk overcharging your battery and seriously shortening its life.

The mechanical so-called voltage regulator on the SOHC4 does so in an indirect way.  It's primary function is to keep the alternator from putting more power into the battery when it is fully charged to 14.5 Volts.  It does this by reducing field current in the alternator which reduces its power output.  At all other times it allows the alternator to put out all the power it can, which varies with the RPM of the crankshaft.

However, the regulator can only pass the power it receives on the black wire to the white field wire.  If the bikes wiring reduces the battery voltage delivered to the regulator, then the alternator cannot make full output regardless of RPM.

Rupp's method tries to compensate for the bikes connector and switch contact voltage losses delivered to the black wire on the Regulator, increasing the trip point where the regulator tells the alternator to back off.

Re-adjusting the regulator will not restore full battery voltage to the alternator field, so it will still not reach full output.  Further, if the switch contacts and interconnections in the bike wiring are ever restored, the mal-adjusted regulator will allow the alternator to put power into a fully charged battery during cruise, boiling off electrolyte, and possibly causing heat damage to the battery's plates.  Both these effects will shorten battery life.

I've looked over Rupp's proceedure to see if it could be ammended or corrected into usefullness.  However, since it is based on unsound principles, I feel it is best deleted.  The Honda Shop manual describes the correct way to adjust the mechanical Voltage regulator for proper function.  And, that method is highly preferable.

Regards,

[oldbiker]

If the PO connected the battery the wrong way round, he will have destroyed the rectifier. It cannot have gone completely short circuit as you would then have zero volts to the bike at all as the battery would be shorted. Therefore it must have burnt to open circuit and you will get no charging at any revs. Sort that out as a starting point for your fault finding. If only some of the diodes in the rectifier were burnt out then any charging would be drastically reduced since if one pair of the six diodes is burnt out then output would be reduced by about 66%.

[mikeswaggs]

Thanks for all the posts.  First, I hadn't noticed the electrics FAQ, I somehow missed that one.  Anyway, they do have tons of good information on there, and I am going to try a few ideas.  When I first got the bike, there were electrical pieces missing, and studying the diagram, I found it was the starter solenoid and wires connected to it.  I purchased one online, and installed it.  Also destroyed was the rectifier and wiring harness.  I replaced these two items with used parts found online.  I also replaced the battery, but may not have charged it well initially.  I have since tried to charge it properly with a float charger that I purchased.  After all was replaced, and the bike was running, I found that I had just repaired the problems caused by polarity switching, and not the original problem.  The bike still runs the battery down and has to be charged between each ride.  I can tell though that the alternator does put out good voltage at higher RPMS, since everythng electrical works well while cruising. 

All that said, I am going to follow a few of the suggestions in the electrics FAQ, and then repost.  We'll see what happens.  Another question though, for some reason the elec. start will not work at all, even though the starter appears to be in great shape, and I can hear the starter solenoid click strongly when the starter button is pushed.  Any thoughts?  Thanks!

[Bodi]

The starter circuit is very simple. Try jamming a largeish screwdriver between the 2 large terminal bolts on the solenoid: if the starter motor turns, your solenoid is bad. If it does not turn, you have a bad starter motor or a wiring problem with the fat high-current wires on the starter motor, solenoid, and battery.