Topic: rectifier woes

[crashmaster]

1972 CB 750K2. Rectifier wires look bad. Blue wire is the ground under. I assume just replace it all. I can get a used OEM model for $40 locally. I also see new aftermarket styles. Suggestions?

[PeWe]

Bad ground between battery and engine so  the ground cable from rectifier will take all load during use of the starter?
Red has melted that indicate a short somewhere to battery?

A rotten main harness and bad ground to engine can cause that.

Minus cable from battery must have good contact with engine case.  Paint scratched off the frame where it is connected with engine bolt. Paint scratched off on other side of frame against engine case also no paint under where to connect.

I added vaseline where paint was scratched off to avoid corrosion.

[crashmaster]

Thanks PeWe. Is there an advantage to getting a new style rectifier versus OEM style?

[Jerry Rxman Griffin aka MuthaF'er]

If you are serious about repairing your ride then replace that AND the whole wiring harness from the looks of what you have shown us

[crashmaster]

I do plan to replace the rectifier. I am wondering if there is an advantage to buying the new style I see online versus a replacement for the OEM that I have. They look totally different. And I am not on good terms with electrical things So I am looking for advice

[Bodi]

There is no magic in the oem rectifier, it just has packaging that fits and a connector to the harness. Many simple 3 phase rectifier module will work fine, you want compatible voltage and current ratings. You need to mount it and provide a heat sink, then connect it into the harness.
They have 4 terminals - 3 ~ inputs from your stator and a + output to the battery. The case is typically the ground.
You decide whether the inconvenience is worth the cost saving. Some tools you might not have will be needed.
But a melted wire says something is very wrong. Find out what and fix it otherwise a new rectifier might last only a small part of a second.

[crashmaster]

Thanks. I think the problem was resolved by the previous owner at some point. All of the ground wires in that area have been changed. And the bad wires were taped up with electrical tape. So at some point I'm guessing that there was a big time short, and it was fixed but poorly,. Everything worked when I fired up the bike electrically that I could tell. I like the old school look of the original rectifier. I just didn't know if the new models were advantageous. And you lost me at heatsink ha ha ha

[PeWe]

Thanks PeWe. Is there an advantage to getting a new style rectifier versus OEM style?

Use the original  type.
Work fine.

When doing the service of the regulator  according to the CB750 shop manual chapter 8:

Core gap work when adjusted 0.80-0.85mm.
Manual state 0.60-1.0mm

I have adjusted 3 regulators on 2 bikes. Both with voltmeter placed between the tacho and speedo so I see how it charge while riding.

Less than  0.80mm will end up in low charging voltage.  Min value will not charge much over 12.8V, maybe 12.5V

Over 0.85mm will end up in sudden overvoltage.
I suddenly got a crazy charge  counting up over 15V, still going up over 16V. When I had core gap of 0.9mm or a little bit more.

I hade to use all loads I could find to keep it around 15V. Hi, blinkers, brake light. All the way back home.
I did not want to cook the Dyna-S ignition and battery.

I have always charged the battery before the test rides.

I should never adjust according to manual  in the garage. 14.5V at 4000-4500 rpm.
It will continue to increase after 1/2- 1 hour ride.
14V max if adjusting in the garage. Battery is fresh and fully charged before start .

A voltmeter is a good thing.
I'm happy to see 14V with the headlight on.
I have had too many rides where it reached 15V after 1 hour or 2 on constant ride. Now max 14.6V as max. Often a little over 14V.

The voltage level screw another setting to adjust by tests. Hopefully OK. It has red paint on  head to lock it and show no fiddling.

Here my regulator. I have marked the adjuster screw of max voltage with a green pen as a reference for adjustments. So I know where it was.




Clockwise will increase voltage.
1/4 turn is much.

If you measure 14V at 4500 rpm when revving in garage is OK. Do not increase.
If getting 14.5 direct, adjust counterclockwards 1/8 turn.

Run bike with a voltmeter for fine tuning and have constant control
Double check what voltmeter shown when you have multimeter neasure battery. So they match.
If differ 0.3 V good to know when riding if showing 14.5 and it is 14.8V.

Blurry photo. It looked better.

[crashmaster]

Thanks PeWe. Is there an advantage to getting a new style rectifier versus OEM style?

Use the original  type.
Work fine.

Great - thanks!

[Deltarider]

Pewe, in your reply #7, you have used the word 'rectifier' a couple of times where you clearly meant 'regulator'. Could you please correct this?

[PeWe]

Pewe, in your reply #7, you have used the word 'rectifier' a couple of times where you clearly meant 'regulator'. Could you please correct this?

Thanks for the notice.
I have corrected.

[dave500]

thanks pewe,now Delta can sleep!

[PeWe]

thanks pewe,now Delta can sleep!

Yes.
Delta helped me in time to not look like an idiot for others finding out later

I should have modified the post if I had seen it. I have edited some long time after when I see errors.
Better to have it corrected.

[MauiK3]

I love that voltmeter PeWe, I think I need to do that. Can you tell us again what you did, which meter it is, where it's connected? I know you've done that before somewhere. Great setup and very useful in preventing problems from growing. Kind of like my oil pressure gauge :-))

[willbird]

Personally I have not had a need to replace Regulator so far but if it did start acting up I would go solid state in a heartbeat. Nothing says you have to discard the OEM parts, this is not a change that prevents re installing them if you change your mind.

I read years ago anyway that the solid state stuff was far more able to still charge at lower RPM's than the stock setup. If that was TRUE or not I dunno. When I started driving/riding the regulator types we are talking about were still in common use,  and people all knew that things changed when you put the steel cover on, so you adjusted and then just set it on to see how that changed the setpoint. I really never missed external regulators once the internals came into widespread use. You might think that having an external regulator on the firewall made things easier to service and repair but I really never saw that in real life. Swapping a whole junk yard alternator on which I usually had on a shelf as a spare part was simpler really.


Bill

[PeWe]

I love that voltmeter PeWe, I think I need to do that. Can you tell us again what you did, which meter it is, where it's connected? I know you've done that before somewhere. Great setup and very useful in preventing problems from growing. Kind of like my oil pressure gauge :-))

It can be like these. I searched
led digital voltmeter car motorcycle

https://ebay.us/m/eFSDAb
https://ebay.us/m/fKcqnS

https://ebay.us/m/bxesyL

I first connected to first 12V (black) and green wires I found inside headlight bucket.

Later connected to same wires feeding the coils.
0 Volt means no power to coils.. If bike suddenly stop, I'll see why
Or will not start. Maybe kill switch is turned off.


Below my old eBay history when I ordered those to both my bikes. Green match the gauges light and feels OK in the dark which selldom happen.

Seller not visible today.
It is a great gadget, a must have  when used to it.

[Bodi]

"you lost me at heatsink"
The OEM rectifiers case is a heatsink. Adds some thermal mass and also some feeble fins. Since there isn't much current at idle (standing still) but a lot of air movement in there when at riding speed and doing RPMs that do make power, that's enough.
Rectifier modules are usually a shiny metal square with terminals sticking out of the epoxy fill on top.
Every diode has a characteristic forward voltage drop. Some (ie Shottky) diodes have a low forward voltage but usually rectifier diodes will be 0.5V or so.
Good old Ohm's Law says power=volts x amps.
So at 10 amps that 0.5V generates 5 Watts of heat. Not a lot but it has to go somewhere. That shiny metal is really bad at radiating heat. The rectifier is probably OK to above 100C but life goes down with overheating and there is a death limit. So some sort of heat sink is needed. I have used a square of 1/8" aluminum about 2 inches square, has been sufficient.

[PeWe]

I have heard that modern rectifier/regulators gives full power constantly. Regulate by burning via a resistor.

The old CB's have a throttle design.

A friend of mine talked about issues when using low wattage bulbs as LEDs on his bike. More overcharging had to be burned up.

I have tested Shottky diod rectifier. It gave a little more at around 2000-2500 rpm. But started to give 0.4V less  around 4000rpm after 1 hour ride or so. The cooling alu plate it is mounted on was warm, not hot. Same with the Schottky.

Stock rectifier gives 14V at around 3600 rpm with headlight on.

I can swap between schottky and stock by reconnect wires

The alu plate with schottky is fastened  in stock rectifier.

When regulator is properly adjusted and all connectors to-from regulator- alternator windings and rectifier side to battery are tight and free of oxide, stock charging system works fine.

It needs much to get it to stop work.

Most important is to avoid cheap batteries. I got a sudden totally dead battery last summer on my K2.
Charging voltage was over 14V all rhe time. Stopped for gasoline refill.
Ignition on , starter. Totally dead, pilot lamps died too.
Called a friend that live 75km away from that gas station. He brought a working battery.
Swapped batteries and I could ride home.

Battery was  2 years old. Recharged every month, 2 months as minimum.

I had another cheap battery of same kind I could follow with my battery tester. It was bad after 1 year of use. I threw it away after a few months since it became worse despite charging.

Save  $100 US in battery can end up in a higher cost when stranded far away from home.

Bikes have now medium priced AGM batteries for around $150 US.
They behave well, not quick discharge. Need a refill after 2 months of  bike being parked.

The cheap batteries have less lead. The acid level is higher so battery voltage is  around 13.5V.

Expect max life of 2 years. And sudden death.
I had another really cheap since they had reduced price from $50 to 40.
It died after a little bit more than a year.
Quick discharge by just sitting disconnected. Health Cond Cranking Amps not possible to charge over a healthy level

Cheap batteries many years ago  just became weaker on the  starter. Use the kick, start it and ride.

Below schottky rectifier, clamped with an alu plate, thermal paste where it should.

[Deltarider]

Thank you, Pewe. I really appreciate it when people do research themselves and share their experiences. I've also read that modern rectifier/regulators gives full power constantly and shunt the excess, although I don't know if it concerns all or just some. Anyway, it's a warning for all those that assume by buying 'digital', 'electronic', 'LED', they automatically have bought the best.   

[PeWe]

My friend had an Aprilia 1000  Falco  year 2000. Charge full and burn.

Enough that our bikes have a waste spark ignition. Fire a cylinder when it should not. Enough with 1, not 4  and opposite, same with 2,3

The stock charging system is good enough for these old bikes when properly adjusted and serviced.

I'm sure it will survive an EMP if a nuclear device had gone off not far away.
Or future stopping device the law guys might use.

Later bikes with electrical fuel pump, fuel injection and an ECU need more power (Amps).

There are guys that have installed Yamaha R6, R1 charging system on CB750 to get 32A. This to feed heating equipment and other gadgets.

The voltmeter I have installed is now a must have.
It has helped me during several test rides and finding the best setting.
A reason for a ride is always welcome

[Deltarider]

[...]
Enough that our bikes have a waste spark ignition. Fire a cylinder when it should not. Enough with 1, not 4  and opposite, same with 2,3

I wouldn't worry about that, PeWe. Others may correct me, but the way I understand the dual output system is, that there's hardly any energy wasted. I see it as basically the same spark that manifests itself on two spots. It's a circuit; when the current in #1 goes from electrode to ground, it simultaneously goes from ground to electrode in #4. What I'd like to know is the following. I suppose there is a nano short difference in time between the beginning of a spark in #1 and #4. It's a given fact that the spark plug that fires in the exhaust stroke, faces far less resistance (no compression), than the other plug, so could it be that the plug that meets less resistance, more or less triggers the other plug that needs to overcome the resistance of the compression in its cylinder. In other words: is a wasted spark configuration therefore an even more reliable ignition than a conventional one?

The stock charging system is good enough for these old bikes when properly adjusted and serviced.

I agree 100%. I never had to spend a second on the regulator or the rectifier. In 50 years I have not yet had to clean their contacts!
What is a mystery to me, is that the original wiring diagram of many CB500/550 models, including mine, mentions a POINTLESS REGULATOR Really?

The voltmeter I have installed is now a must have.

I like its design: very small and it can be tucked away, so it won't spoil the original look. On the other hand: a must have? Nah, not really.
I quote from my checklist before take off:
Start engine and let it idle. Check
Bring on headlight Check
Situate left hand in front of headlight and increase with right hand RPM to ca 2500 and see if headlight becomes brighter. Check
If it does, the system charges and you're cleared to go.
At the beginning of each season I check a few things. One of them is to monitor the onboard voltage. I then have a voltmeter in my tankbag. After that initial ride, I remove it so I have no further distraction.
An oil pressure meter IMO, is next to useless.
If there's a small thingy like your volt indicator, that indicates the oil temp, I would install it rightaway.
The idea is: blue led = < 80^o working temperature is not yet reached, yellow = 110^o-120^o, approaching limits, red = >120^o, expect hard shifting.
Extinct = working temperature is reached.
This is not the first time I propose this. I wonder why in all those years none of the experts here have developped one. What is needed is: a three LED thingy and a sensor with the right thread. In the developping phase you need an analogue temp meter set up to copy the ohm readings at 80^o, 110^o and 120^oC. How difficult can it be?   

[PeWe]

Hi Delta,
I do not worry about the wasted spark. That's part of the simple design. Waste of energy
RC designed a distributor to fire 1 plug in correct time.
But more moving parts that will wear and can go wrong in the long run.

My car has a coil on top of each sparkplug. They do not live long. Max 100.000km. I have replaced mine 2 times, 210.000km. On the third set since new.
 Audi 1.8T. VW, Seat and Skoda have the same design.

If I should ride my bike on a really long journey. I guess I should add a stock points plate I have adjusted correct before as a spare. Ride with the Dyna-S
I'm sure bike will run fine.

[willbird]

Hi Delta,
I do not worry about the wasted spark. That's part of the simple design. Waste of energy
RC designed a distributor to fire 1 plug in correct time.
But more moving parts that will wear and can go wrong in the long run.

My car has a coil on top of each sparkplug. They do not live long. Max 100.000km. I have replaced mine 2 times, 210.000km. On the third set since new.
 Audi 1.8T. VW, Seat and Skoda have the same design.

If I should ride my bike on a really long journey. I guess I should add a stock points plate I have adjusted correct before as a spare. Ride with the Dyna-S
I'm sure bike will run fine.

I have seen some pushrod V8 dyno work on batch fire vs sequential ignition but I do not recall much on waste spark vs firing individual cylinders. I am sure the work is out there somewhere just not in my normal video lineup. I do know the top fuel dragster guys think there are some HP avail in ignition improvements but rules are in place to prevent an expensive ignition development $$ war maybe.

Bill

[crashmaster]

Thanks everyone. I picked up a used rectifier. I’m looking at the shop manual, but I’m still unclear how to bench test it. I have a red wire a green wire and three yellow wires. I’m supposed to check it for Continuity in both directions, but I don’t get a reading Regardless of which wires I touch with the multi meter. Do I also have to hook it up to a battery? Thinking I’m doing something wrong here

[Bodi]

It's not easy to draw in text.
There are 6 diodes connected together in three pairs, both pointing the same way. Each pair connects to a yellow wire at the point they connect together. The "arrow" on a diode circuit drawing points to where power will flow to positive, the other end flows to negative. So one end of all three pairs are connected together and either go to red (the arrow pointing that way) or green (arrow pointing away).
So:
Starting with one lead on red, a meter on Ohms or "Diode Test" will read no connection (OL or a very high resistance) from there to each yellow, or low resistance on Ohms or about 0.5 on diode test. They all have to be the same. Swap the lead on the red, readings must be opposite and matching (low one way has to be high the other way).
You get 6 readings from red, then repeat from green. Same story essentially but the readings will be reversed compared to from red.
Diodes fail in two ways. Open or short. No reading in either direction means open, low resistance both ways means short. Both are no good and one bad diode in the bridge will reduce output a lot.

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