Topic: rectifier woes

[crashmaster]

Thanks a lot Bodi! I put the red lead on the red terminal and checked the other terminals with the black lead, and didn’t get any readings. Then I switched and put the black lead on the red terminal, and put the red lead on each of the yellow terminals and get a similar rating from each, with a higher rating from the green terminal. Then I did the same Thing on the green terminal and got similar results, But like opposite as you said. So it seems like everything must be OK. I sure do appreciate your help! I just suck at electricity things.

Is it OK to get some of the rust off and paint this thing inside and out, or should I just stick to the outside case and leave the inside stuff (wires, etc) alone? Wires look kinda dainty. Soak in Evaporust? Seems sketchy on electric stuff.Would like to kind of stop the rust if anyone has advice. Thanks

[bryanj]

Leave the inside allone ,it needs to get rid of heat

[dave500]

using a dump style regulator that runs the field electromagnet full power all the time is bad full stop,that style is designed for and used on permanant magnet type field alternators,use at your own risk.

[crashmaster]

Thanks Bryan - I'll just touch up the paint down the outer case then. The inside really is not bad anyway.

Dave, Are you saying the OEM regulator is not a good choice, or the rectifier?

[bryanj]

I think Dave is talking about a different style of combined reg/rec where the generator is flat out all the time and any extra power is dumped to ground.
The original regulator has only 3 settings
1 zero charge
2 full charge
3 approx half charge

Depending on state of battery charge it fluctuates between 1 and 2 OR 2 and 3

[crashmaster]

Thanks for explaining that Bryan

[dave500]

some people have used that incorrect type thinking theyve fixed it,without really understanding how it all works,it will charge but the magnet is flat out all the time and may burn out.

[Bodi]

With permanent magnet alternators - output always at maximum - a controlled output regulator can be used but the "dump the excess" type is a lot cheaper. So controlled are not used. I remember 60s/70s Triumph and BSA bikes just put a large Zener diode on a heat sink under the headlight. Simple, cheap, and as reliable as most Lucas electrics (boiled batteries were very common).

With an induced field alternator like our SOHC4s use, controlling output is really easy by varying the field coil current. Running the alternator at 100% and dumping excess power works fine for regulation but wastes power and heats the coils.
I think Honda made the coils capable of handling the heat, and there's very little power available over the bike's usage - adding accessories would have it running flat out most of the time anyway. So overheating? Doubtful.
Power loss? Not a concern. The alternator at full load uses maybe 1/3 horsepower. Will cutting that back by a tenth HP have you winning drag races?

In the end, do what you want. Maybe someone will MacGuyver up a PM rotor?

The only thing I caution against is adjusting the OEM electromagnetic regulator. Without the necessary variable power supply it can't be done. And the things are super reliable: charging issues when using one are 99% certain to be harness issues.

[HondaMan]

And the things are super reliable: charging issues when using one are 99% certain to be harness issues.

I agree: except for crash-damaged ones (and one shorted field coil), I have only found that having the three little bullet connectors burned from age and 'hot' headlights or added loads has been the most-common 'low charge' scenario. The bullet connectors are running at their full rating when they are made from steel (OEM wiring) and changing them to modern brass ones always improves the battery charge. I do that to every SOHC4 engine I rebuild.

[willbird]

Taking a quick look it seems as if the automotive regulators that were pretty cheap due to still being used have went up a lot in price now. Also not nearly as readily avail at some random auto zone maybe.



Bill

[rotortiller]

I caution against is adjusting the OEM electromagnetic regulator.

I had mine (750) completely apart, cleaned everything then assembled by the maintenance manual for point cleaning and employed original core gap etc, put it on the bike and adjusted the voltage with a voltmeter and it has been fine for many years. My alternator fully powers the bike at around 2500rpm with the headlight on. I had some voltage/rpm pics in the gallery which is now pooched forever I suspect. That regulator is a tough bit of old tech. Easier to work on that my 6 year old toasted-junky engineered Maytag washing machine.

[newday777]

Is it OK to get some of the rust off and paint this thing inside and out, or should I just stick to the outside case and leave the inside stuff (wires, etc) alone? Wires look kinda dainty. Soak in Evaporust? Seems sketchy on electric stuff.Would like to kind of stop the rust if anyone has advice. Thanks

Sorry for the delayed reply, this morning I went down to the shop and pulled out the NOS rectifier and a used one. On both, it appears that honda dunked them in a bucket of paint. At first I thought maybe the had been sprayed because of the paint on the wires coated at the rectifier end but looking closer they were dunked. Inside and out is painted with the semigloss black.

[kyle750]

Not to hijack the thread but also looking for guidance on an old rectifier

The rectifier in my CB750 is working correctly but is showing its age.  Black metal is rusted, connections are becoming loose (but still holding), and plastic coupler is starting to break.  Perhaps it would be a good idea to buy another in better condition.  Plenty of used for sale on Ebay but I am extremely hesitant to buy old, used, and untested electronics.  Since dismanters offer original rectifiers for less than $20 maybe buy 1 or 2 and hopefully I get one working OK and still in good usable condition. 

Photos of 2 different CB750 voltage rectifiers for sale from well known Honda dismantlers

[bryanj]

Could the paint be electrically insulating type? Also rectifiers rarely fail in my experience unless the battery is fitted backwards

[kyle750]

I sent an offer today on this rectifier which the seller quickly accepted. Untested so a gamble if it is working correctly. IMO  continuing to use my old rectifier is also a gamble as it is clearly long past its useful life. Risk Assessment 

https://www.ebay.com/itm/157629260881

[Deltarider]

[...] Also rectifiers rarely fail in my experience unless the battery is fitted backwards

Also in my experience, so if you choose to install a generic battery, be cautious not to accidently reverse polarity!

[MauiK3]

Those used ones look like the connectors are ok at least